Agricultural Applications For Pine-based Biochar

Influence of Pyrolysis Conditions on Char Properties Bob Hawkins Managing Research Chemist Eprida Athens, GA

Intro Char’s ability to provide nutrients Char’s ability to facilitate nutrient retention/uptake Low temperature char – temperature range 375-500o

Sample Preparation Batch unit

Sample Preparation Pilot Plant

Volatile Content VM% 28.50% PN

27.50%

no steam 26.50%

pine

25.50%

higher temp no vent

24.50%

vent

23.50% 0

2

4 psig

6

8

Fixed Carbon FC% 70.00% press

69.00%

no steam

68.00%

pine

67.00%

higher temp

66.00%

no vent

65.00%

vent

64.00% 0

2

4 psig

6

8

Charcoal sample ID 9

39 42

2

6

1

9

8

9

8

6

2

1

38

42

40

37

41

39

37

42

40

37

HW 6 38 HW 2 40 HW 0 42 HR 6 38 HR 7 42 8

PB

PB

PB

PC

PC

PC

SD

SD

SD

PN

PN

PN

% C

Total Nutrients Carbon content

80.0

75.0

70.0

65.0

60.0

55.0

37

PN 1 40 PN 2 42 SD 6 37 SD 8 39 SD 9 41 PC 8 37 PC 9 40 PC 1 42 PB 6 38 2 PB 39 9 PB 42 HW 6 38 HW 2 40 HW 0 42 HR 6 38 HR 7 42 8

PN

% N

Total Nutrients Nitrogen content

2.50

2.00

1.50

1.00

0.50

0.00

Charcoal sample ID

Total Nutrients Al

B

Ca

Cu

Fe

K

Mg

Mn

Mo

Na

P

Pb

Zn

Available Nutrients Available Potassium 1400

9000 8000

1200

mg/kg

1000 800 600 400 200 0 360.0

380.0

400.0

420.0

Charring temperature (deg C)

7000 6000

Pine sawdust

5000 4000 3000 2000

Pine bark

1000 0 440.0

Pine chips Oak-sapwood Oak-heartwood Peanut hull pellets

Available Nutrients Available Phosphorous 1000.0 800.0 100.0 600.0 400.0 50.0 200.0 0.0 0.0 360.0 370.0 380.0 390.0 400.0 410.0 420.0 430.0 440.0

m g /k g

150.0

Charring temperature (deg C)

Pine saw dust Pine chips Pine bark Oak-sapw ood Oak-heartw ood Peanut hull pellets

37 1

37 8

42 6

41 8

42 6

40 1

HR

42 8

PB 42 6 H W 38 2 HW 40 0 H W 42 6 H R 38 7

PB 38 2 PB 39 9

PC

PC

PC 37 9

SD

SD 39 9

SD

PN

PN 40 2

PN

% of total P

37 1

PB 42 6 HW 38 2 HW 40 0 H W 42 6 HR 38 7 H R4 28

PC 37 9 PC 40 1 PC 42 6 PB 38 2 PB 39 9

PN 40 2 PN 42 6 SD 37 8 SD 39 9 SD 41 8

PN

% of total K

Available Nutrients Available K as % of total

60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00%

Available P as % of total

50.00%

40.00%

30.00%

20.00%

10.00%

0.00%

Char pH Char pH

12 11

Peanut hull pellet s

10

Pine sawdust

9 pH

Pine chips

8 Pine bark

7 Oak-sapwood

6 Oak-heart wood

5 360.00

370.00

380.00

390.00

400.00 Tem p

410.00

420.00

430.00

440.00

CEC CEC 19.0 18.0 17.0 16.0 15.0 14.0 13.0 12.0 11.0 10.0 9.0 350

PN +250-420 +500-850 PN-pilot No Steam

400

450

500

CEC CEC vs Pressure 14.0 12.0 10.0

PN

8.0

No Steam

6.0

Higher temp

4.0

Pine

2.0 0.0 0

2

4

6

8

Surface Acid Concentration Charcoal surface acids (Titration w ith NaOH)

Total amount of surface acids (meq/g)

3

2.5 pine chips Pine saw dust

2

Pine Bark Hardw ood (red)

1.5

Hardw ood (w hite) Peanut hull pellets

1

No Steam Pilot plant

0.5

0 300

350

400 Charcoal tem perature

450

500

Char Production Need for quick test for QA/QC Use of steam as a sweep gas shows increases in CEC and surface acid formation

PII:SOO16-2361(!Xi)OOO81-6

ELSEVIER

Fuel Vol. 75, No. 9, pp. 1051-1059, 1996 Copyright 0 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0016-2361/96 %15.00+0.00

Influence of temperature on the products from the flash pyrolysis of biomass

Patrick

A. Horne and Paul T. Williams

Department of Fuel and Energy, The University of Leeds, Leeds LS2 9JT, UK (Received 12 May 1995; revised 27 March 1996)

Biomass in the form of mixed wood waste was pyrolysed in a fluidized bed reactor at 400, 450, 500 and 550°C. The char, liquid and gas products were analysed to determine their elemental composition and calorific value. In particular, the liquid products were analysed in detail to determine the concentration of environmentally hazardous polycyclic aromatic hydrocarbons (PAH) and potentially high-value oxygenated aromatic compounds in relation to the process conditions. The gases evolved were COZ,CO and C,-C4 hydrocarbons. The liquids were homogeneous, of low viscosity and highly oxygenated. The molecular weight range of the liquids was 50-1300~. Chemical fractionation of the liquids showed that only low quantities of hydrocarbons were present and the oxygenated and polar fractions were dominant. PAH up to MW 252 were present in the liquids; some of the PAH identified have been shown to be carcinogenic and/or mutagenic. The concentration of PAH in the liquids increased with pyrolysis temperature, but even at the maximum pyrolysis temperature of 550°C the total concentration was < 120ppmw. The liquids contained significant quantities of phenolic compounds and the yield of phenol and its alkylated derivatives was highest at 500 and 550°C. Some of the oxygenated compounds identified are of high value. Copyright 0 1996 Elsevier Science Ltd. (Keywords: biomass; flash pyrolysis; products)

The energy potential of biomass and solid wastes has become increasingly recognized as a means to help meet world energy demand. The use of biomass has a particularly important role as an energy source in developing countries1’2. The utilization of biomass and other alternative fuel sources rather than existing fossil fuels could offer more environmentally acceptable processes for energy production and will aid in conserving the limited supplies of fossil fuels. The recovery of energy from biomass and solid wastes has centred on biochemical and thermochemical processes3. Of the thermochemical processes, pyrolysis has received increased interest, since the process conditions can be optimized to maximize the production of chars, liquids or gasesle3. In particular, the production of pyrolysis liquids has been investigated with the aim of using the liquid product directly in fuel applications or by producing refined fuels and/or chemical ;;t;zEfj . The solid char can be used as a fuel in the form of briquettes or as a char-oil/water slurry, or it can be upgraded to activated carbon and used in purification processes”*. The gases generated have a low to medium heating value but may contain sufficient energy to supply the energy requirements of a pyrolysis plant. The physical conditions of the pyrolysis of biomass, such as temperature, heating rate and residence time, have been shown to have a profound effect on the product ields and composition . High heating rates of up to lc& s-1 at temperatures < 650°C and with rapid quenching, fav&r the formation of liquid products and minimize char and gas formation; these process conditions

are often referred to as ‘flash pyrolysis’. High heating rates to temperatures > 650°C tend to favour the formation of gaseous products at the expense of liquids. Slow heating rates coupled with low maximum temperatures maximize the yield of char. In recent years, various flash pyrolysis processes have been developed to maximize the formation of liquid products for use as fuels or chemical feedstocks. A vortex reactor process has been developed by Diebold”“. This type of pyrolKsk process is an ablative technique. Scott and Piskorz ’ have designed the Waterloo flash pyrolysis process to maximize the liquid product yield. They have used small biomass particles (< 1 mm) as the feed and high heat transfer rates with a hot fluidized bed of sand. Georgia Tech in the USA has used an entrained flow pyrolysis reactor where the biomass particles are rapidly heated by a flow of hot gases13. Vacuum pyrolysis has also been used as a flash pyrolysis technique by Roy et a1.14. The liquid product yields from all the above processes were >50 wt%, with Dieboldgl” and Scott and Piskorz11112reporting yields of >70 wt%. The liquid products from flash pyrolysis processes have been reported as being homogeneous and of low viscosity, and are chemically extremely complex, containing hundreds of different components’5-‘7. The chemical composition of the liquid hydrocarbons and the relation of composition to process conditions has implications for end use as a fuel or chemical feedstock. Many biomass-derived pyrolysis oils are known to contain polycyclic aromatic hydrocarbons (PAH)18-20, some of which have been shown to be carcinogenic and/

Fuel 1996 Volume 75 Number 9

1051

Influence

of temperature

n II

on flash pyrolysis

4-

of biomass: P. A. Horne and P. T. Williams

work the pyrolysis liquids were characterized in detail in relation to process conditions, with particular reference to the contents of PAH and oxygenated aromatic compounds.

S7ktyWVe

EXPERIMENTAL Biomass

The biomass used was a mixture of waste wood shavings obtained from a woodworking company, and therefore represented a mixture of different wood types. Table 2 shows the proximate and ultimate analyses of the biomass pyrolysed. Pyrolysis reactor

Figure 1 Schematic diagram of the fluidized bed pyrolysis reactor

or mutagenic*l’**, which may have consequences for the handling of the fuel. Where the proposed end use of the liquid hydrocarbons is as a chemical feedstock, again the process conditions which optimize the formation of high-value chemicals in the liquid have economic benefits. In this context the oxygenated aromatic hydrocarbons are of particular interest. Biomass-derived oils have been shown to contain phenols’5’23 which have extensive use in the production of resins. In addition, phenolic derivatives have a high value, as they are used as flavourings in the food industry. Syringol and guaiacol are also found in significant concentrations in biomassderived pyrolysis oils and are used in the production of biodegradable polyesters and polyethers. In this work, a semi-continuous fluidized bed reactor was used to flash-pyrolyse a waste wood feed. The pyrolysis temperature range studied was 400-550°C as this is known to give high yields of liquid products whilst minimizing the formation of char and gases. Pyrolytic liquids derived from biomass have been analysed by a number of workers15-17, but there are limited data on the individual yields of PAH and oxygenated aromatic compounds in relation to process conditions, coupled with analyses of the gas phase and char. Therefore in this

The reactor system used was a fluidized bed pyrolysis unit (Figure I). The reactor was 7.5 cm diameter x 50 cm high, constructed from stainless steel. The fluidization gas was nitrogen, preheated before entry into the reactor. The flow-rate of nitrogen was sufficient to provide three times the minimum fluidizing velocity (MFV) to the bed. The bed material was quartz sand with a mean diameter of 250 pm and a static bed depth of 8 cm. The biomass was fed to the reactor via a screw feeder and nitrogen gas stream to the top of the fluidized bed at a rate of 0.2160.228 kg h-l. The residence time of the pyrolytic vapours in the hot reactor was N 2.5 s at a pyrolysis temperature of 500°C. The pyrolysis vapours leaving the reactor were passed through a series of condensers. The initial condensation was provided by two stainless steel condensers which were water-cooled both internally and externally, with the catch pots for each condenser ice-cooled. There followed a series of glass condensers cooled using a mixture of solid carbon dioxide and acetone, which were used to remove any residual vapours from the gas stream. This condensation system was found to be 97% efficient in trapping volatile aromatic hydrocarbons such as toluene and 99% efficient for the condensation of water. The pyrolysis condensate from all the condensers was mixed and stored at -10°C. The water fraction of the pyrolysis liquids was separated from the organic fraction using the standard ASTM D244 and IP 29.1 methods. Gas analysis

The carrier gas stream was sampled after the condensation system to allow for the analysis of any non-condensable gases. Analysis was carried out using gas chromatography. The gases determined were CO and H2 using a molecular sieve SA 60-80 column and CO2 using a silica column, with argon as carrier gas and thermal conductivity detection. For the determination of hydrocarbon gases up to Cs a Porisil C 80-100 column was used, with nitrogen as carrier gas and a flame ionization detector.

Table 1 Proximate and ultimate analyses (wt%) of the wood feed

Elemental analysis

Proximate analysis Volatiles Moisture Ash Ultimate analysis C H 0

91.0 1.5 1.5

The carbon and hydrogen contents of the pyrolysis liquids and char were determined using an elemental analyser. The oxygen content of the liquids and chars was found by difference.

45.9 5.12 46.6

Calor@ic value

1052

Fuel 1996 Volume 75 Number 9

The

calorific

value

of the pyrolysis

liquid

was

Influence

of temperature

on flash pyrolysis of biomass: P. A. Horne and P. J. Williams

determined by bomb calorimetry. The values reported are the gross heat of combustion at constant volume. Oil analysis Molecular weight range. The molecular weight (MW) range of the oils was determined using a mini-column size exclusion chromatography (s.e.c.) system which has been described previouslg4. The system incorporated two 150 mm x 4.6 mm i.d. columns with Polymer Laboratories 5 pm RPSEC 100 A type packing. A third column of the same material was placed in line between the pump and the injection valve, to ensure pre-saturation of the solvent with the column packing material and also to avoid analytical column dissolution and hence loss of performance. The solvent used for the mobile phase was tetrahydrofuran (THF), which has been shown by Johnson and Chum25 to be suitable for the analysis of biomass pyrolysis oils. The calibration system used was based on polystyrene samples of low polydispersity in the MW range from 800 to 860000; also included was benzene for low-MW calibration. Samples were introduced through a 2 ,ul loop injection valve. Two detectors were used: a U.V. detector sensitive to the aromatic compounds, and a refractive index (RI) detector monitoring the elution of all compounds, enabling more information to be obtained regarding the relative contribution to the MW of the difference chemical class fractions24. Ultraviolet scanning of the polystyrene MW fractions in THF indicated that the maximum absorbance was at 262nm. Determination of the maximum efficiency for the system showed that a mobile phase flow rate of 0.26 mL min-’ and a column temperature between 2 and 14°C were optimum24. For practical purposes the column was maintained at 0°C. Column temperature is room26 or elevated maintained at usually temperature27-29. However, the optimum efficiency was obtained at lower than ambient temperatures for the system used in this work. Evaluation of the system has shown that there are systematic variations in the measured MW of n-alkanes, n-alkenes, PAH and alkylated cyclic hydrocarbons compared with the polystyrene standards24. Deviations from polystyrene calibration curves have also been shown previously for other model compounds26>30>31. For biomass pyrolysis oils, Johnson and Chum25 used polystyrene MW fractions and showed that aromatic acids and naphthalenes deviated significantly from the calibration curve. However, in this work the s.e.c. system was used to compare oils derived from different process conditions rather than to determine the absolute MW.

The biomass-derived pyrolysis oils were fractionated using mini-column liquid chromatography. The mini-columns were conditioned by washing with n-pentane. A 250 mg sample of the oil was placed on the column. The samples were added by adsorption on to inert Chromosorb G/AW/DMCS 60-80 support, mixed and then packed above the silica section of the column. This approach is necessary for polar oils, which may produce a solid-phase precipitate with the n-pentane solvent and block the column, and also to improve solvent contact with the oil. The column was then eluted with n-pentane, benzene, ethyl acetate and methanol (polarity relative to Al2O3, 0.00, 0.32, 0.58 and 0.95 respectively), to produce aliphatic, aromatic, oxygenatedaromatic and polar chemical class fractions respectively. Chemicalfractionation.

The fractions were analysed by Fourier transform infrared spectroscopy (FT-i.r.) to determine the efficient separation of the chemical classes. In addition, each fraction was analysed by gas chromatography-mass spectrometry using ion trap detection (g.c.-ITD) to verify the fractionation scheme. The percentage mass in each class fraction was determined by analysis of the total gas chromatogram in relation to known masses of sample and standards analysed by the system. This avoided the necessity to nitrogen-evaporate (blow down) the solvent eluant, which may result in losses of light hydrocarbons. Detailed characterization of the pyrolysis liquids. The concentrations of monocyclic and polycyclic aromatic hydrocarbons (PAH) in the benzene fractions and the oxygenated aromatic species present in the ethyl acetate fraction were determined using gas chromatographymass spectrometry (g.c.-m.s.) The g.c.-m.s. system was a Carlo-Erba Vega HRGC with cold on-column injections, coupled to a Finnigan Mat ion trap detector (ITD). A DB-5 fused silica capillary column 25mx 0.3mm was used and the temperature programme was 60°C for 2min followed by 5 Kmin-’ to 270°C with a dwell time of 25 min at 270°C. The ITD mass range was set at 30-350~ with a scan time of 0.125-2 s. The ITD was linked to a PC with a mass spectral library facility. Identification of the individual constituents in the chemical fractions was carried out using the g.c.m.s. and retention indices23,32Y33. Single-ion monitoring (SIM) was also carried out to confirm the identification of compounds and also to examine the samples for a series of substituted compounds, for example, naphthalene and methyl-, dimethyl- and trimethylnaphthalenes. Quantification was determined by the use of extensive external standards.

RESULTS AND DISCUSSION The yields of the pyrolysis products are shown in Table 2. Several repeat runs were carried out at 550°C under identical conditions to test the repeatability of the process. The differences observed between the yields of the char, liquid and gas for these repeat runs were negligible. The liquid yield for all the runs was >65 wt%, with a maximum yield of 67.8 wt% at 550°C. At pyrolysis temperatures of 500 and 550°C the pyrolysis

Table 2

Product yields (wt%) from the flash pyrolysis of wood

Reactor temperature (“C)

Char

Liquid

Gases

Total

400 450 500 550 550 550

24.1 21.4 18.9 17.3 16.7 17.1

65.5 65.7 66.0 67.0 67.8 66.2

10.2 11.1 14.6 14.9 15.7 15.2

99.8 98.2 99.5 99.2 99.2 98.5

Table 3 Water and organic contents (wt%) of the liquid product from the flash pyrolysis of wood

Reactor temperature (“C) 400 450 500 550

Water

Organic material

28.0 27.6 29.6 26.8

72.0 72.4 70.4 73.2

Fuel 1996 Volume 75 Number 9

1053

Influence

of temperature

on flash pyrolysis

of biomass: P. A. Horne and P. T. Williams

liquid was a homogeneous dark liquid of low viscosity. Similar observations were made by Scott and Piskorz ’ using a fluidized bed process with a pyrolysis temperature of 500°C. The pyrolytic product from the 400 and 450°C fluidized bed pyrolysis temperature experiments was found to be of low viscosity but there were traces of a black tar residue on the base of the storage vial. The pyrolysis liquid product was a mixture of organic material and water. The water content of the liquid was determined using the ASTM D244, IP29.1 method; Table 3 shows the results of this separation. The water content of all the pyrolytic liquids was approximately the same (26.8-29.6wt%). The initial wood feed contained 7.5 wt% moisture, which would be released during pyrolysis and subsequently collected during condensation. This contributed approximately half the water present in the pyrolytic liquid. Therefore water formed by pyrolysis accounts for 14 wt% of the liquid condensate or lOwt% of the initial wood feed. Table 3 also shows that over the temperature range studied, the yield of oil was not significantly affected by a change in temperature. The char yield was reduced as the pyrolysis temperature was increased, from 24.1 wt% at 400°C to 16.7 wt% at 550°C. The char yields reported in this work were higher than those found by other workers1”12. This difference was probably due to the fact that a mixed wood waste was used in this work rather than a single known biomass feedstock as used by Scott et al.11>‘2.The decrease in the char yield with increasing temperature could be due either to greater primary decomposition of the wood at higher temperatures or to secondary decomposition of the char residue. The gaseous product yield increased with pyrolysis temperature. The individual yields of the major gaseous species are shown in Table 4. The increase in gaseous products is thought to be predominantly due to secondary cracking of the pyrolysis vapours at higher Table 4 Yields (wt%) of gases from the flash pyrolysis of wood Reactor teme.

(“(7 400 450 500 550

L

CO COP Hz

CH4

3.75 4.20 6.76 6.71

0.21 0.35 0.58 0.69

6.02 6.32 6.61 6.86

0.018 0.022 0.022 0.023

C2H6

0.05 0.05 0.09 0.16

W4

0.05 0.08 0.26 0.26

C3h

0.03 0.02 0.05 0.04

C3H6

0.05 0.08 0.19 0.45

Table 5 Elemental composition (wt%) of the products from the flash nvrolvsis of wood Reactor temp. (C)

C

H

0

Total liquid product 400 450 500 550

38.6 39.9 37.6 38.1

8.52 8.61 8.42 8.46

51.7 50.4 53.0 52.8

Liquid product after water removal 400 58.1 450 58.0 500 57.2 550 59.6

6.10 6.24 6.12 6.05

34.6 35.0 35.2 33.5

Char 400 450 500 550

3.23 3.16 3.17 2.65

28.2 24.2 22.9 24.4

1054

68.1 71.9 73.0 71.6

Fuel 1996 Volume 75 Number 9

temperatures. However, the secondary decomposition of the char at higher temperatures may also give non-condensable gaseous products. Beaumont and Schwob34 and Samolada et aL3’ investigated the flash pyrolysis of wood and found that as the pyrolysis temperature was raised, the gaseous yield was increased. The yield of CO and CO2 in general increased with increasing pyrolysis temperature. However, the increase in CO was far more pronounced than that of C02. The yield of all the hydrocarbon gases increased with temperature. Similar observations have been made by other workers11’35. Elemental analysis of pyrolysis products

The liquid and char products were analysed to determine their elemental composition. Table 5 shows the elemental compositions of the wet pyrolytic liquid, the oil after removal of water, and the chars. The elemental compositions of the pyrolytic liquids both before and after removal of water were similar for all the pyrolysis temperatures investigated. The similarity was probably due to the particular temperature range studied, the lowest temperature of 400°C being adequate to decompose the wood feed, and the low residence time limiting the amount of secondary reactions. The pyrolysis liquids arising from the reactor before water removal had a carbon content lower than that of the initial wood feed. This indicates that such pyrolytic liquids have a low CV, and the removal of the water is necessary to maximize their CV. The composition of the pyrolytic liquid produced in this work compares well with the finding of Churin36. Characterization of the pyrolysis liquids Molecular weight range. The pyrolytic liquid after water removal was used for determination of the MW range of the oils, because the presence of water caused the RI detector to give inconsistent results. Figure 2 shows MW ranges of the pyrolysis oils for the RI and U.V. detectors. Only the data for the 400 and 550°C pyrolysis oils are shown, for clarity. The oils all showed similar MW ranges from 50 to 1300~ for both the RI and U.V. detectors. The similarity in MW among the oils over the temperature range studied was due to the fact that the lowest temperature, 4OO”C, was sufficient to give almost complete decomposition of the wood feed and the low residence times minimized secondary reactions which might have occurred at higher temperatures. The average MW was -220 and ~275 u for the RI and U.V.detectors respectively. Diebold et a1.37 obtained flash pyrolysis oils from a vortex reactor system at 625°C. They carried out s.e.c. analysis of the oil and found components present in the oil up to and including 2000~. Evans and Milne2’ used molecular beam mass spectrometry (MB-m.s.) to analyse the pyrolysis vapours whilst in the pyrolysis reactor. They found molecular

Table 6

Chemical fractionation of the pyrolysis liquids (wt%)

Reactor temp. (“C) 400 450 so0 550

Pentane eluate

Benzene eluate

Ethyl acetate eluate

Methanol eluate

Total

<0.2 <0.2 <0.2 <0.2

0.42 0.51 0.54 0.54

36.2 37.4 39.3 38.4

56.8 57.6 56.7 55.2

94.6 95.7 96.7 95.3

influence

of temperature

on flash pyrolysis

of biomass: P. A. Horne and P. T. Williams

Table 7 Concentrations (ppmw) of the aromatic compounds present in the pyrolysis oils Reactor temperature (“C)

0 1.6

2.0

1.8

2.2

2.4

2.8

2.6

3.0

3.2

Log Molecular Mass

(b)

oi,4,,,, 16 1.6

2.0

, ,

2.2

2.4

b ‘,

,

2.6

”

,

,

2.8

3.0

),

I

3.2

Log MolecularMass

Figure 2 Molecular mass range of the pyrolysis liquid at 400 and 550°C after removal of water, using refractive index and ultraviolet detection

weights predominantly between 100 and 150 u. The difference between the findings of Evans and Milne and the present results is due to the fact that the condensed pyrolysis liquids were analysed in this work and that of Diebold et al.37. It is thought that some of the smaller species present in the pyrolysis vapours are highly reactive and on condensation can polymerize to form higher-molecular-weight material’. Johnson and Chum25 have suggested that the high apparent MW of biomass pyrolysis oils may be due to solute-solute or solute-solvent association, producing high-molecular-weight complexes. In this work, the samples were prepared with THF immediately prior to analysis, since previous work has shown that storage of the sample in THF for extended periods did result in an increase in apparent MW due to interaction of the sample with the solvent3*. The U.V.detector was used to obtain detail on the MW range of the aromatic fraction of the pyrolysis oils. It showed that there was some high-molecular-weight material present in the oils which was aromatic in nature. This could be formed from the decomposition of the lignin fraction of the wood. Chemical fractionation. The pyrolytic liquids after removal of water were separated into four chemical classes by sequential elution of the column with pentane, benzene, ethyl acetate and methanol to give aliphatics, aromatics including PAH, phenolic and neutral oxygenated compounds, and polar compounds respectively.

Benzene Toluene Dimethylbenzene Ethylbenzene Dimethylbenzene Trimethylbenzene Dihydroindene Indene Benzofuran Methylbenzofuran Tetramethylbenzene Methylindene Naphthalene Methylnaphthalene Biphenyl Acenaphthene Dimethylnaphthalene Trimethylnaphthalene Tetramethylnaphthalene Fluorene Methylfluorene Phenanthrene Anthracene Dimethylfluorene Methylphenanthrene Dimethylphenanthrene Trimethylphenanthrene Tetramethylphenanthrene Pyrene Methylpyrene Dimethylpyrene Chrysene Methylchrysene Benzopyrene

400

450

500

550

7

14 12 1 2 1 5
55 35 2 7 3 7
97 6-l I 24 12 9 4 2 10 13
5

1 2 1 5
The results of the chemical fractionation are shown in Table 6, corrected to account for the removal of water. They show that the liquids are almost exclusively made up of oxygenated compounds. The ethyl acetate fraction, which contains the phenolic and aromatic oxygenated compounds, shows a small but significant increase in concentration from 36.2 to 39.3 wt% of the oil as the pyrolysis temperature increases from 400 to 550°C. The polar material present in the methanol fraction of the liquids shows no significant trend with change in temperature, varying from 55.2 to 57.6 wt%. The hydrocarbons, eluted in the pentane and benzene fractions, account for < 1 wt% of the pyrolytic liquid. The benzene fraction, containing aromatic species, shows a small increase with increasing pyrolysis temperature. The similarity of the results for the chemical fractionation of the oils over the temperature range studied is again due to the fact that the fluidized bed process minimized any secondary reactions and the lowest temperature, 400°C was sufficient to give almost complete decomposition of the wood feed. Characterization of the chemical fractions of the pyrolysis liquids PAH content. The major aromatic hydrocarbon

compounds present in the pyrolysis oils are shown in Table 7, with PAH compounds up to molecular mass 252 identified and quantified. The major aromatic hydrocarbons present in the pyrolysis liquids were the monocyclic compounds such as benzene, toluene and

Fuel 1996

Volume

75 Number

9

1055

influence

of temperature

on flash pyrolysis

of biomass: P. A. Horne and P. T. Williams

dimethyl- and ethylbenzenes. The PAH found were naphthalene and phenanthrene and their alkylated derivatives and in minor concentrations other compounds such as pyrene, chrysene and benzopyrenes. The concentration of PAH increased with increasing temperature. The PAH found have been shown to be carcinogenic and/or mutagenic2113g@. However, even at the highest temperature of 550°C the total concentration of PAH quantified was < 120 ppmw. PAH have been detected by other workers in biomass pyrolysis oils. For example, Pakdel and Roy41 analysed oil from the pyrolysis of Aspen poplar wood chips in a vacuum pyrolysis unit. They found a wide range of PAH including naphthalene, phenanthrene and fluorene and their alkylated substituents, in addition to benzene and its alkylated substituents. In addition, they quantified certain PAH, some of which were biologically active, such as benzo[a]pyrene, chrysene and benzo[k]fluoranthene, but were present in very low concentration, <5ppmw. However, the oil was collected at a biomass pyrolysis temperature of only 263°C. Gasification tars, produced at higher temperatures (XSO’C) than the pyrolysis oils, were found to contain much higher concentrations of PAH. However, the yield of gasification tar was small relative to that of the biomass pyrolysis oils. Elliottlg has also confirmed that PAH are not present in pyrolysis oils produced at temperatures <5OO”C but markedly increase in concentration in gasification tars produced >7OO”C. Desbene et ~21.‘~ analysed pyrolysis oils from the slow pyrolysis of hornbeam biomass. The PAH detected included alkylated naphthalenes, biphenyls, fluorene, anthracene, pyrene and benzofluorene. The composition of the oil depended on whether the pyrolysis was slow or fast. The low concentrations of PAH in the pyrolysis oils in the present work are due to the process conditions used. The relatively low temperatures and residence times restrict the formation of PAH by reducing the amount of possible secondary reactions. For significant quantities of PAH to form during the pyrolysis of biomass, long residence times are needed at temperatures >700”C20. Table 7 shows that as the temperature of pyrolysis was increased, the concentration of PAH in the oils also increased. For each individual PAH there was an increase with increasing pyrolysis temperature. The reactions of the pyrolysis vapours at increased temperatures result in the formation of PAH. The formation of aromatic and polyaromatic hydrocarbons by secondary reactions during pyrolysis has been attributed to at least two mechanisms: a Diels-Alder type reaction, and deoxygenation of oxygenated aromatic compounds42. The calorific values of the pyrolysis liquid after removal of water, the char and the ases from the 550°C run were found to be 22MJ kg- g , 25.9 MJ kg-’ and 15.7 MJ me3 respectively. The original wood feed had a CV of 17.7 MJ kg-‘. Therefore the pyrolysis liquid after removal of water contained -63% of the potential energy in the wood feed. The density of the pyrolytic liquid (1.2 g cme3) was also much greater than that of the initial feed (0.4 gcmp3), giving a much higher energy density. There was a significant amount of water present in the pyrolytic liquid which would significantly reduce its CV. Indeed, the elemental analysis shows that the pyrolysis liquid before removal of water contains significantly less carbon than the original biomass. However, removal of the water may not be beneficial,

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Fuel 1996 Volume 75 Number 9

as the liquid product from the flash pyrolysis of wood has been shown to be unstable at elevated temperatures and polymerizes when exposed to air37. The viscosity of the pyrolytic liquid may also be increased by removing the water, which could affect its use as a fuel. There are conflicting opinions as to the potential uses of pyrolytic liquids derived from biomass. Maggi et aI.43 state that flash pyrolysis bio-oils are corrosive, are not completely volatile, have a high oxygen content and do not mix readily with conventional fuels. They state that bio-oils used in direct combustion processes rarely meet the standards required for fuels. Rapper questions whether pyrolysis liquids meet the requirements of a storable liquid fuel, and states that pyrolysis oils are much lower in quality than even a heavy fuel oil, which itself has a rapidly shrinking market. However, Bridgwater45 has suggested various processes where flash pyrolysis liquids could be used both now and in the future. Many of the processes that he suggests require the pyrolysis liquids to be refined or upgraded before they are suitable for use. Solantausta et a1.46 used flash pyrolysis oils as a fuel in a diesel power plant. They concluded that the preliminary results were positive but that further research was necessary on the storage of the oils and that the oils themselves required more detailed characterization. More detailed characterization of the pyrolysis oils is necessary to optimize their potential. The PAH content of any fuel is of great importance, as these compounds are environmentally hazardous and therefore their concentration in a fuel should be minimized. The process conditions used in this work show that flash pyrolysis gives only low levels of PAH formation from biomass feedstocks. Ethyl acetate fraction. The major compounds present in the ethyl acetate eluates of the pyrolysis liquids were identified and quantified; the results are shown in Table 8. The major constituents of the eluate appear to be light organic oxygenates and phenolic material. The major phenolic compounds present in the ethyl acetate eluate of the pyrolysis liquid were phenols, benzenediols, methoxyphenols and dimethoxyphenols. The concentration of phenol and its alkylated derivatives increased as the pyrolysis temperature was increased, but 500 and 550°C gave similar yields. The formation of methoxypheno1 and its mono- and dimethyl derivatives was greatest at the lower pyrolysis temperatures. This was also true for the overall concentration of dimethoxyphenol and its derivatives. The more severe pyrolysis temperatures of 500 and 550°C would increase the possibility of secondary reactions that could be responsible for the thermal breakdown of the larger phenolic compounds such as methoxy- and dimethoxyphenols to phenol, which would then undergo alkylation, thus giving the increase in alkylated phenols observed at 500 and 550°C. The ethyl acetate fraction also contained large amounts of methylmethoxy-, dimethoxy-, hydroxymethoxy- and dihydroxymethoxyphenylethanones. The concentration of these compounds in the pyrolysis oils varied, depending on the pyrolysis temperature. The other major group of compounds present in this fraction comprised cyclopentanone, cyclopentenone and the methyl and hydroxymethyl derivatives of cyclopentenone. The concentration of these compounds in the pyrolysis oils increased as the pyrolysis temperature was increased. There were large amounts of light organic

Influence

of temperature

on flash pyrolysis

compounds such as glycol aldehyde and the propyl ester of acetic acid, which were greatest in the pyrolysis oil produced at 450°C. Other light organics present in the oils were furanmethanol, furanone and methylfurfural. The concentration of these compounds in general increased with pyrolysis temperature. In the work the biomass pyrolysis liquids have been shown to contain significant quantities of phenolic compounds. These phenolic compounds could be removed from the pyrolysis liquids prior to their combustion, as they have a significant commercial value47148. The use of the pyrolysis liquids for the

Table 8

of biomass: P. A. Horne and P. T. Williams

production of phenolic chemical feedstocks as well as for the production of liquid fuels would increase their potential commercial exploitation. In maximizing the formation of individual phenolic compounds, it must be taken into account that an increase in pyrolysis temperature in this work tended to increase the formation of phenol and its alkylated derivatives whilst reducing the formation of the larger phenolic compounds. Stoikos48 has reviewed the upgrading of biomass oils to high-value chemicals and premium-grade fuels. He reports that oxygenated compounds such as methylphenols (cresols), methyoxyphenol (guaiacol),

Concentrations (ppmw) of the major constituents in the ethyl acetate eluate of the flash pyrolysis oils Reactor temperature (“C) 400

450

500

550

MW 60 (acetic acid methyl ester or glycol aldehyde)

11876

13211

12874

12000

Acetic acid propyl ester

13214

17656

14901

15710

Cyclopentanone

2231

2310

2415

2380

Cyclopentenone

4645

4650

5315

5580

Furanmethanol

2641

2460

2412

2467

Methylcyclopentenone Furanone

610

742

898

845

7178

8141

9542

10024 2308

Methylfuraldehyde

0

0

0

Methylcyclopentenone

0

0

0

681

937

1073

1992

1839

1987

2143

2101

2470

779

1213

2215

2261

3373

3657

2892

2930

Dimethylphenol

116

149

430

436

Methylmethoxyphenol

206

177

143

1412

3432

3771

3730

4028

715

1313

2379

2675

0

0

408

229

Phenol Methylhydroxycyclopentenone Methylphenol Methoxyphenol

Benzenediol Methylbenzenediol Trimethylphenol

0

0

0

0

Dimethylmethoxyphenol

1317

1021

954

750

Hydroxymethylphenylethanone

3003

2974

2854

3097

Dimethoxyphenol

3756

3720

4120

4261

Ethenylbenzenediol

n/a 2711

nla 2881

nla 3214

3542

Tetramethylphenol

Methoxypropenylphenol

1414

MW 168 (unidentified)

4271

3297

3365

3252

Methoxypropenylphenol

6645

6525

4974

4511

Hydroxymethoxyphenylethanone

1316

1723

1721

1775

Dihydroxymethoxyphenylethanone

1190

1303

1021

807

Hydroxymethoxyphenylpropanone

895

1074

876

913

MW 180 (unidentified)

3134

3017

4521

5246

Dimethoxypropenylphenol

2381

2751

2552

2257

597

703

515

465

Hydroxydimethoxybenzaldehyde

1695

1723

2195

1669

Hydroxymethoxypropenylphenol

7660

8305

8778

9203

Dimethoxypropenylphenol

5834

5520

4874

4948

Hydroxydimethoxyphenylethanone

1026

MW 180 (unidentified)

1019

1071

1066

MW210 (unidentified)

641

607

688

906

MW210 (unidentified)

1444

1861

2154

3146

Naphthol Methylnaphthol

33

40

65

54

66

70

99

116

Dimethylnaphthol

0

0

0

0

Trimethylnaphthol

0

0

0

0

Fuel 1996 Volume 75 Number 9

1057

Influence

of temperature

on flash pyrolysis

of biomass: P. A. Horne and P. T. Williams

2-furaldehyde (furfural) and methoxypropenylphenol (isoeugenol), which have been shown to be in high concentration in the oils (Table 8), have a considerable economic potential. Such chemicals have applications in the pharmaceutical, food and paint industries.

8

CONCLUSIONS The formation of pyrolytic liquid products derived from biomass can be maximized using a fluidized bed reactor coupled with moderate temperatures of 400550°C and short residence times. The pyrolysis temperatures of 500 and 550°C gave a pyrolytic liquid product which was homogeneous and of low viscosity. The pyrolytic oil was found to contain material with a molecular mass of up to 1300 u. Chemical fractionation showed that the pyrolytic liquids were composed almost entirely of oxygenated components, with only low quantities of hydrocarbons present. The analysis of the ethyl acetate eluate from the chemical fractionation of the pyrolytic liquids showed that the oils contained significant quantities of oxygenated aromatics, mainly phenol and its derivatives. The concentration of phenol and its alkylated derivatives was greatest at 500 and 550°C whereas the concentration of the larger phenolic compounds was greatest at lower temperatures. Some of the phenolic compounds present have been shown to have a significant commercial value. PAH up to molecular mass 252 were found to be present in the pyrolytic liquids. The concentration of PAH was increased with temperature, but the overall PAH concentration in all the pyrolytic liquids was low. The pyrolytic liquids were found to have a relatively low CV, but they contained -63% of the potential energy in the initial biomass feed and had a much greater density than the original biomass. ACKNOWLEDGEMENTS This work was supported by the UK Science and Engineering Research Council under grant numbers GR/F/06074 and GR/F/87837, whose support the authors gratefully acknowledge.

32(2), 297

14 15

16 17 18

19

20 21 22 23

Strub, A., Chartier, P. and Schleser, G. (Eds), ‘Research in Thermochemical Biomass Conversion’, Elsevier Applied Science, London, 1983 Bridgwater, A. V. and Kuester, J. L. (Eds), ‘Research in Thermochemical Biomass Conversion’, Elsevier Applied Science, London, 1988 Grassi, G., Gosse, G. and dos Santos, G. (Eds), ‘Biomass for Energy and Industry’, Elsevier Applied Science, London, 1990 Diebold, J. and Scahill, J. In ‘Pyrolysis Oils from Biomass: Producing, Analysing and Upgrading’ (Eds J. Soltes and T. A. Milne), Symposium Series 376, American Chemical Society, Washington, DC, 1988 Bridgwater, A. V. In ‘Biomass for Energy and Industry’, (Eds G. Grassi, G. Gosse, and G. dos Santos), Elsevier Applied Science, London, 1990 Esnouf, C., Francois, 0. and Churin, D. In ‘Biomass for Energy and Industry’ (Eds G. Grassi, G. Gosse and G. dos Santos), Elsevier Applied Science, London, 1990 Keirsse, H., Hartoyo, W., Buehens, A., Schoeters, J. and

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Scott, D. S. and Piskorz, J. Can. J. Chem. Eng. 1987,60, 1246 Scott, D., Piskorz, J. and Radlein, D. Znd. Eng. Chem. Process Des. Dev. 198524, 581 Knieht. J.. Gordon. C. W.. Kovac. R. J. and Newman. C. J. In Proceedings of the 1985 Biomass Thermochemical Contractors Meeting, Minnesota, 1985, p. 99 Roy C., de Caumia, B., Plante, P. and Menard, H. In ‘Energy from Biomass and Wastes VII’, 1983, pp. 1147-l 170 Piskorz, J., Scott, D. S. and Radlein, D. In ‘Pyrolysis Oils from Biomass: Producing, Analysing and Upgrading’ (Eds J. Soltes and T. A. Milne), Symposium Series 376, American Chemical Society, Washington, DC, 1988, pp. 167-178 Pouwels, A. D., Tom, A., Eijkel, B. and Boon, J. J. Anal. Appl. Pyrol. 1987, 11,417 Beaumont, 0. Wood Fibre Sci. 1985,17,228 Desbene, P. L., Essayegh, M., Desmazieres, B. and Basselier, J. J. In ‘Biomass Pyrolysis Liquids Upgrading and Utilization’ (Eds A. V. Bridgwater and G. Grassi), Elsevier Applied Science, London, 1991 Elliott, D. C. In Pyrolysis Oils from Biomass: Producing, Analysing and Upgrading’ (Eds J. Soltes and T. A. Milne), Symposium Series 376, American Chemical Society, Washington, DC, 1988 Evans, R. J. and Milne, T. A. Energy Fuels 1987,1, 125 Lee, M. L., Novotny M. and Bartle, K. D. ‘Analytical Chemistry of Polycyclic Aromatic Compounds’, Academic Press, New York, 1981 Williams, P. T. J. Inst. Energy 1990, 63, 22 Williams, P. T. and Home, P. A. J. Anal. Appl. Pyrol. 1995, 31, 15

24 25

26 27 28 29 30 31 32 33

REFERENCES

Janssens, J. In ‘Research in Thermochemical Biomass Conversion’ (Eds A. V. Bridgwater and J. L. Kuester), Elsevier Applied Science, London, 1988 Bridgwater, A. V. In ‘Pyrolysis and Gasification’ (Eds G. L. Ferrero. K. Maniatis. A. Buekens and A. V. Bridawater).,. Elsevier Applied Science, London, 1989 Diebold, J. In ‘Specialists Workshop on Fast Pyrolysis of Biomass’, Copper Mountain, CO, 1980, p. 237 Diebold, J. Am. Chem. Sot. Div. Pet. Chem. Preprints. 1987,

34 35 36 37 38 39 40

Williams, P. T. and Taylor, D. T. J. Anal. Appl. Pyrol. 1994, 29, 111 Johnson, D. K. and Chum, H. L. In ‘Pyrolysis Oils from Biomass: Producing, Analysing and Upgrading’ (Eds J. Soltes and T. A. Milne), Symposium Series 376, American Chemical Society, Washington, DC, 1988, pp. 157-166 Bartle, K. D., Mulligan, M. J., Taylor, N., Martin, T. G. and Snape, C. E. Fuel 1984,63, 1556 Sanchez, V., Murgia, E. and Lubkowitz, J. A. Fuel 1984,63,612 Determann, H. ‘Gel Chromatography’, Springer-Verlag, New York, 1968 Yau, W. W., Kirkland, J. J. and Bly, D. D. ‘Modem Size Exclusion Liauid Chromatoeraohv’. Wilev. New York. 1979 Mulligan, M.. J., Thomas, K. M. and Tytko, A. P. Fuel 1987, 66, 1472 Karlsson, 0. Fuel 1990,69, 608 Lee, M. L., Vassilaros, D. L., White, C. M. and Novotny, M. Anal. Chem. 1982,51,768 Vassilaros, D. L., Kong, R. C., Later, D. W. and Lee, M. L. J. Chromatogr. 1982,252, 1 Beaumont. 0. and Schwab. Y. Znd. End. Chem. Process Des. Dev. 1984,‘23, 637 ’ Samolada, M. C., Stoicos, T. and Vasalos, I. A. J. Anal. Appl. Pyrol. 1990, 18, 127 Churin, E. ‘Catalytic Treatment of Pyrolysis Oils’, Cat. No. CD-NA-12480-EN-C, Commission of the European Communities, 1990 Diebold, J. P., Chum, H. L. Evans, R. L. Milne, T. A. Reed, T. B. and Scahill, J. W. In ‘Energy from Biomass and Wastes’ (Ed. D. Klass), Elsevier Applied Science, London, 1987, pp. 801-829 Williams, P. T. and Taylor, D. T. In ‘Biomass for Energy and Industry’ (Eds G. Grassi, G. Gosse and G. dos Santos), Elsevier Applied Science, London, 1990 Longwell, J. P. In ‘Soot in Combustion Systems and its Toxic Properties’ (Eds J. Lahaye and G. Prado), Plenum Press, New York, 1983 Barfnecht, T. R., Andon, B. M., Thilly, W. G. and Hites, R. A. In ‘Polynuclear Aromatic Hydrocarbons: Chemical Analysis and Biological Fate’ (Eds M. Cooke and A. J. Dennis), Battelle Press, Columbus, OH, 1981

Influence 41 42 43

44 45

of temperature

on flash pyrolysis

Pakdel, H. and Roy. C. Energy Fuels 1991,5,421 Williams P. T. and Home, P. A. Fuel 199574, 1839 Maggi, E., Grange, R. and Delmon, P. In ‘Research in Thermochemical Biomass Conversion’ (Eds A. V. Bridgwater and J. L. Kuester), Elsevier Applied Science, London, 1988, pp. 896-910 Rupp, M. In ‘Biomass Pyrolysis Liquids Upgrading and Utilization’ (Eds A. V. Bridgwater and G. Grassi), Elsevier Applied Science, London, 1991, pp. 219-225 Bridgwater, A. V. In ‘Biomass Pyrolysis Liquids Upgrading and

46 47 48

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Utilisation’ (Eds A. V. Bridgwater and G. Grassi), Elsevier Applied Science, London, 1991, pp. 1l-92 Solantausta, Y., Nylund, N. O., Westerholm, M., Kolijonen, T. and Oasmaa, A. Bioresource Technol. 1993,46, 177 Franck, H. G. and Stadelhofer, J. W. ‘Industrial Aromatic Chemistry’, Springer-Verlag, Berlin, 1988 Stoikos, T. In ‘Biomass Pyrolysis Liquids Upgrading and Utilisation’ (Eds A. V. Bridgwater and G. Grassi), Elsevier Applied Science, London, 1991

Fuel 1996 Volume 75 Number 9

1059

UTILIZATION OF BIOMASS PYROLYSIS FOR ENERGY PRODUCTION, SOIL FERTILITY AND CARBON SEQUESTRATION ROBERT HAWKINS, JON NILSSON AND REBECCA OGLESBY (for authors correspondence, E-mail: [email protected])

Abstract. New pyrolysis technologies have been developed that allow for carbon sequestration through the production of sustainable energy from biomass (bioenergy). These systems produce charcoal (biochar) and energy in the form of heat, steam, electricity, or liquid fuels. Purified hydrogen can also be produced, allowing production of ammonia and future electric systems that utilize hydrogen (such as hydrogen fuel cells). Pyrolysis energy systems produce more power than they consume, and can supply their own power utilizing waste heat from the system. Therefore, this technology could be deployed without the need for existing energy infrastructure. The biochar is a carbon-based co-product that has value as a soil amendment, containing nutrients such as potassium (K), phosphorous (P), magnesium (Mg) and calcium (Ca). When placed in the soil, an increase in soil organic matter (SOM) is observed, along with increases in crop productivity, water retention, and soil biological activity as well as a decreased fertilizer requirement. Pyrolysis technology can be deployed on a large industrial scale, or on small farm or community scales. In these applications it can produce fuel, heat, electricity and fertilizer from crop residues and wastes. The deployment of new biochar and bio-energy systems creates economic opportunities for local communities through the creation of new businesses that develop to support its infrastructure (suppliers of bio-wastes, manufacturer and distribution of co-products, and related agricultural application services etc.). Due to its adaptability to a wide range of feedstocks, over 60 organizations are now involved in biochar research worldwide.

Biomass - manure - organic wastes - crop residues - wood waste

Transport Energy Coproducts Industry

Biofuel bio-oil hydrogen

Pyrolysis

Residual Heat

Optionally, N2, NOX, SOX, CO2 can be added to increase C sink and nutrient content

Returned to soil as bio-char

Figure 1. Concept of low-temperature pyrolysis bio-energy with biochar sequestration. Typically, about 50% of the pyrolyzed biomass is converted into biochar and can be returned to soil. (Adapted from: Lehmann, J. 2007, Bioenergy in the black. Front Ecol Environ 2007; 5(7): 381–387)

Biomass Pyrolysis Technology At the 2007 United Nations Commission on Sustainable Development, a new system of converting biomass to energy was presented which can reduce dependence on oil. This technology is called biomass pyrolysis. In this system, biomass is exposed to high temperatures in the absence of oxygen, producing energy and coproducts. Although pyrolysis biofuel production represents only a small portion of energy production worldwide (UNDP 2004), it has the potential to generate electricity at a cost lower than any other biomass-toelectricity technology available (Bridgewater et. al. 2002). A main advantage to implementing this technology is that a pyrolysis system can supply its own power and heat by utilizing waste heat from the system, so there is no need to supply power or heat from outside sources (Iwasaki, 2003). Therefore, these systems can be deployed without the need for existing energy infrastructure. With these new advances, well over 15 countries are now involved in commercializing biomass pyrolysis systems (http://terrapreta.bioenergylists.org/company). A number of companies are working on making this technolgy more scaleable to agricultural industries with various sizes of pyrolysis units. With these new designs, it is estimated that a 1-ton of biomass per hour unit can produce 1 mw of electricity, 1 megawatt of usable heat and 600 pounds of charcoal per hour. A unit capable of processing 25kg of biomass is estimated to produce 25 kw of heat and electricity and 20 pounds of charcoal per hour.

The EPRIDA pyrolysis plant that operated at the Biomass Conversion Center in Athens, GA. until spring of 2009.

Biomass Pyrolysis vs. Conventional Biomass to Energy Systems In conventional use of biomass for fuel, biomass is harvested and burned, and like fossil fuels, releases compounds back to the atmosphere. This contributes to increased greenhouse gases. In order for the energy cycle to be truly carbon neutral, an amount of biomass equal to that which was harvested must be re-grown so that the plants can absorb an equivalent amount of CO2. To be a steady fuel supply, biomass crops require an increase in agricultural production, which further depletes soil nutrients and minerals. This reduces the ability to grow biomass in the future. Therefore, although biomass crops are a renewable source of energy, they are not necessarily sustainable. With biomass pyrolysis, what was previously considered agricultural waste (crop residues, wood wastes, manures) can create energy and nutrient enhancing soil supplements. The energy created can be converted into several forms including hydrogen and electricity, which can be used to power small farms or fed back onto the energy grid. Examples of feedstocks include: coconut husks, corn stover, bean stubble, tobacco stalks, wastes from agricultural processing, wood wastes from manufacturing and lumber industries, demolition wood wastes,

short-rotation energy crops, municipal solid waste, manure and sewage (Antal 1982). By using agricultural wastes, biomass pyrolysis does not compete with food production.

The Products of Biomass Pyrolysis The main products generated by biomass pyrolysis are pyrolysis vapors, heat and charcoal (biochar). These outputs can be used in a wide range of applications. 1. Pyrolysis vapors can be condensed to form bio-oil Bio-oil is a complex mixture of oxygenated hydrocarbons and water that can be used as low grade heating fuel. Due to its high density, bio-oil is much more economical to transport than either biomass or hydrogen (Czernik et al., 2007). The heating value of bio-oil is about 40% to 50% of that for petroleum-based fuels (Yaman, 2004) and about 60% of ethanol (Raveendran et al., 1996). Bio-oil can be refined to be used as a source of chemical feedstock for gasoline, can be added to petroleum refinery feedstock or combusted in raw form (Samolada et al., 1998). Biomass pyrolysis allows biomass to be processed at dispersed locations where wastes are generated and bio-oil can be transported to a central refinery or power plant. Cost benefits are significant due to the high price of transporting biomass feedstock over large distances (>30 km). Decentralized production of bio-oil also makes sense since biomass is often generated in rural areas where bio-oil can be processed for use in agricultural machinery. 2. Pyrolysis vapors can be used directly for energy In this scenario it is not necessary to condense pyrolysis vapors into bio-oil to extract the energy. Pyrolysis vapors can be burned directly as fuel for integrated heat and power production, or refined to produce fuels and chemicals such as gasoline, diesel, alcohols, olefins, oxychemicals, synthetic natural gas and high purity hydrogen (Magrini-Bair and others, 2007). If the energy is needed for local use, such as on a small farm, it is better to work with the pyrolysis vapors in this form. 3. Pyrolysis vapors can be treated to produce synthetic gas (syngas) Utilizing steam reforming, pyrolysis vapors can produce a syngas consisting of over 50% hydrogen, plus CO, CO2, and small amounts of methane (Czernik et al., 2007). Since these gases are comprised of hydrocarbons, they should not be emitted into the atmosphere in an unaltered state. Instead they can be converted into a clean burning, mid BTU fuel, similar to natural gas. This can be combusted in existing engines, generators, boilers, and turbines to produce heat, steam and electricity. Syngas is also suitable as a cooking fuel and can substitute for propane or natural gas in uses such as home heating. High purity hydrogen from syngas can be suitable for use in hydrogen engines, fuel cells (Czernik et al., 2007) and for production of ammonia fertilizers. The current largest use of hydrogen in the world today is for the production of ammonia. Utilizing pyrolysis to generate hydrogen could replace natural gas as the primary feedstock required to manufacture ammonia based fertilizers. The production of ammonia using natural gas emits carbon dioxide into the atmosphere and fixes the price of fertilizer to the price of natural gas. Production of ammonia from syngas could change this, allowing the price of fertilizer to become influenced by the lower price of biomass wastes. 4. Pyrolysis syngas can create synthetic liquid fuels Pyrolysis of biomass is one of the leading near-term options for renewable production of hydrogen and has the potential to provide a significant fraction of transportation fuel required in the future (Czernik et al., 2007). This can be achieved by use of hydrogen fuel cell vehicles or hydrogen powered combustion engines. Pyrolysis syngas can be used to produce transportation fuels that work with current infrastructures and technologies. Hydrogen and carbon monoxide, main components of the pyrolysis syngas, are the reactants necessary to produce liquid fuels (methanol, ethanol, gasoline, aviation fuel and diesel fuel) via FischerTropsch (F-T) synthesis. F-T synthesis is regarded as the key technological component for converting syngas to transportation fuels and other liquid products (Wilhelm and others, 2001). F-T diesel is not bio-diesel. FT diesel is a clear liquid that gives complete combustion with no particulate emissions and has a higher energy density that petroleum diesel and biodiesel. F-T diesel can be used in all existing diesel engines and can be

mixed without a maximum mixture level with petroleum diesel (Wilhelm and others 2001). For instance Audi won the “24 Hours at LeMans” sports car race with F-T diesel. Currently, F-T fuels are produced from syngas originating from natural gas and coal. Biomass syngas can replace fossil fuels as the primary feedstock. 5. Pyrolysis vapors can produce non-energy products Pyrolysis vapors can also be used to produce a number of co-products such as wood preservative, meat browning, food flavorings, adhesives, or specific chemical compounds (Czernik, 2004). Liquid smoke, the chemical used to add smoke flavor to foods, is currently produced by pyrolysis of mesquite and other hardwoods. In local agricultural applications these vapors can be condensed and used as insecticides, herbicides, and fungicides (Steiner, 2007). The bio-oil by product from these processes can be refined as a source of chemical feedstocks to yield products such as acetic acid (vinegar).

Figure 2. Co-products from Biomass Pyrolysis (Olglesby, Hawkins, 2007)

6. Biomass pyrolysis can create valuable soil amendments One of the most exciting new benefits of biomass pyrolysis is its ability to produce valuable soil amendments in the form of charcoal (biochar). Biochar is currently used in Japan and in other parts of the world by indigenous tribes. Recent archeological exploration has found that indigenous peoples of the Amazon used charcoal to enrich their soil over 1,000 years ago. This was due to the discovery of a black colored soil in the Amazon basin of Brazil termed Terra Preta. It is believed that prior to the arrival of Europeans, the charcoal in these soils was added by native Amazonians to create arable farmland (Lehmann et al., 2006). Phosphorus (P) and calcium (Ca) are normally scarce in the very acidic Oxisols and Utisols that are predominant in this region. In contrast, Terra Preta soils contain higher levels of P and Ca with a higher, almost neutral pH (Glaser et al., 1998). Another distinctive feature of Terra Preta soil is the high stability of its soil organic matter (SOM), and high cation exchange capacity (Sombroek, 2003), all factors that improve soil fertility.

The use of charcoal as a soil amendment is not limited to ancient civilizations such as the ones that created Terra Preta. New research has shown that biochar is more efficient at increasing soil fertility and nutrient retention than un-charred organic matter (Lehmann et al., 2006). Carbon enhanced SOM offers direct value through improved water infiltration, water holding capacity, structural stability, cation exchange capacity, soil biological activity and as a CO2 sink (Lehmann, 2007). Charcoal can also reduce fertilizer runoff and adsorb ammonium ions.

Figure 3: LETS FIND A NEW PHOTO

The use of biochar has recently been authorized for use as a soil amendment in Japan. Of all of the charcoal used in Japan in 1999, the highest percentage of use was in agricultural land as a soil amendment.

The second highest use was in the livestock industry where it used for animal feed and deodorization (Okimori et al.,2003). In the U.S. a system has been developed where biochar can be amended with ammonium bicarbonate producing a valuable carbon based fertilizer called ECOSS (Day and others, 2005). Other benefits of biochar include its ability to: adsorb soil-damaging pesticides and neutralize natural toxins in decomposing organic materials (Yelverton and others, 1996), and increase soil organic content (Blanco-Canqui et al., 2004). On farm trials in the U.S., a 20% increase in corn yield and a 520% in mycorrhizal populations (beneficial soil fungi that plants depend on) was observed where carbon based soil amendments were applied at 7-9 pounds per acre. In two years of trials at the Virginia Polytechnic Institute, a similar product achieved a 10% increase in sweet corn yield, a 30-pound per acre savings in nitrogen for Irish potatoes and a 47% increase in tomato yield (Morse, R and P. Stevens, 2006,-2008). Observations in the field also verified reduced need for irrigation where carbon based amendments were applied ( http://www.carbonchar.com/). Under proper conditions, scientists have also shown that when added to soil, biochar has the potential to increase soil carbon sequestration by as much as 400%. This is due to its beneficial effects on soil microorganisms, which convert soluble organic matter into stable organic compounds (Day, Reicosky, Nichols 2005). 7. Biomass pyrolysis can be used to sequester atmospheric carbon dioxide Charcoal is commonly used for heating and cooking, and in many developing countries is the only available fuel. In traditional methods of charcoal manufacturing all the valuable chemicals (tars, oils and smoke) and heat escape into the atmosphere. While biomass pyrolysis can provide fuel for heating and cooking, it is vastly different than the smoking kilns and barrels that are currently used throughout the world. Pyrolysis systems that produce biochar and energy do not produce pollution, contaminate water supplies, or create waste disposal problems. To ensure that systems producing biochar are clean and do not contribute to green house gas (GHG) pollution, an organization called the International Biochar Initiative has formed and is setting standards for this product (http://www.biochar-international.org/home.html). Biomass pyrolysis can sequester up to 50% of the initial carbon (C) input and return it to the soil. The initial loss of C can be used for energy production and can offset fuel use (Figure 1.). This contrasts greatly with burning of biomass, which sequesters 3% of the initial C as charcoal, with the rest being emitted to the atmosphere, or biological decomposition which retains only 10 – 20% of initial C after 5 – 10 years (Lehmann et al., 2006). Therefore, with its ability to capture and store carbon in the soil, biomass pyrolysis can deliver tradable carbon emission reductions (Lehmann, et.al. 2006). Controlled pyrolysis has recently been approved by the United Nations Framework Convention on Climate Change as a Clean Development Mechanism (CDM) for avoidance of methane production from biomass decay. (http://cdm.unfccc.int/UserManagement/FileStorage/CDMWF_AM_C7UWTIEMRJ05M3D02XWDW80JN989IP).

In a CDM feasibility study on pyrolysis at an industrial tree plantation, it was calculated that annual processing of 368,000 tons of biomass would provide emissions reductions of 230,000 tons of CO2 per year and could provide jobs for approximately 2,600 people (Okimori, 2003). The latest figures published by the World Bank indicate that the carbon market grew in value to an estimated US$30 billion in 2006 (€23 billion), three times greater than the previous year. As of November 2007, over 850 carbon-offset projects have been registered worldwide with about seven percent of them in the area of biomass fuels (UNEP 2008 Yearbook). One of the first machines for offsetting CO2 emission has been in use in Senegal in the Saint-Louis region since the end of 2007 . In partnership with Areva, the technology was transferred to South Africa to the Necsa Company who has a production license for the southern cone of Africa. The calculation evaluating carbon credits generated by this machine result in: 11.6 tons of CO2-equivalent per ton of green charcoal. Air France, through the intermediary Action Carbone of GoodPlanet, is now giving its passengers the option to compensate their CO2 emissions with carbon credits generated primarily by the Pro-Natura green charcoal project in Senegal. (http://www.pronatura.org/index.php?lang=en&page=greenchar#greenchar2) 7. Carbon from biomass pyrolysis can be used in a wide range of non-soil applications In addition to use for soil applications, biomass carbon can also be considered for more traditional applications. The applications for carbon and its compounds are so widespread that it would be impossible to adequately describe them in a single article. Some common examples include: carbon black as a pigment for printing ink, carbon paper, printer toner, a filler in plastics and rubber, graphite as a lubricant and molding material in glass manufacture, in electrodes for dry batteries, in electroplating, in brushes for electrical motors and as a neutron moderator in nuclear reactors. Activated carbon is used in medicine to absorb toxins, poisons or gases from the digestive system and in air and water purification. Due to the fact the fact that carbon can form alloys with iron, it can also be used in steel production, in chemical reduction, case hardening, and in carbides for cutting and grinding tools. One company that has been evaluating biochar for both soil and conventional use has found that it can become a precursor for a wide range of carbon based products (http://c6scientific.com). Another use for biochar that can achieve carbon emission reduction credits under the Kyoto protocol is its use as a replacement for coal in power generation. Biochar can be used as a direct replacement for coal without the need to modify the existing powerplant. All of the CO2 that is released as a result of replacing fossil fuels with biochar counts toward carbon emission reductions and can be traded in the carbon exchange markets. As pyrolysis systems become more readily available, it is important that system managers take advantage of the full range of applications and markets that may be achieved.

Conclusions Biomass fuels such as wood, herbaceous materials and agricultural by-products currently form the world’s third largest primary energy resource, behind coal and oil. At best, conventional biomass to energy is considered to be carbon neutral. Harvesting biomass to produce energy may not be sustainable because it can result in reduced soil productivity by depletion of carbon and nutrients. Biomass pyrolysis addresses this dilemma, because it can utilize waste products and about half of the original carbon can be returned to the soil (Lehmann, 2007). Utilizing biomass pyrolysis for the production of fuels also has significant advantages when compared to coal fuels because it can eliminate the need for post combustion scrubbing and can reduce nitric oxide (NOx) formation (Bisio et al., 1995). In fact such energy is actually CARBON NEGATIVE, because for each carbon molecule recycled back to the atmosphere, one is buried in the soil, so the net effect is to reduce atmospheric CO2! The deployment of biomass pyrolysis systems can create new local businesses, job opportunities and raise the income of people in rural communities (Okimori et al., 2003). Farming communities can benefit most from this system because the biochar co-product can reduce or eliminate purchased fertilizers while sequestering atmospheric CO2 (Glaser and others., 2002). This can create new profit centers for landowners by creating carbon credits and energy, which farmers can use or sell. This can decentralize fertilizer and energy distribution,

making resources more available to farmers. It can reduce agricultural dependence on petroleum and natural gas based products by allowing regional energy production that is cost competitive with fossil fuels. Although biomass pyrolysis represents only a small portion of energy production worldwide it has the potential to generate energy at a lower cost than other energy systems. With its carbon negative footprint, biomass pyrolysis has the ability to do this in a way that can contribute to reduction in greenhouse gas emissions. Given that 1) soil organic carbon is one of the largest reservoirs in interaction with the atmosphere and 2) enhancing natural processes is thought to be the most cost-effective means of reducing atmospheric CO2; biomass pyrolysis provides a way forward toward overcoming the obstacles that are facing biofuels production today. In the words of USDA Soil Scientist, David Laird, we now have “A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality” (Laird, 2008). References (A complete list of the references shown in this paper is available from: http://c6scientific.com). Antal, Michael (1982). Biomass Pyrolysis: A Review of the Literature Part 1- Carbohydrate Pyrolysis. K.W Boer, J.A. Duffie (ed.) Advances in Solar Energy: An annual review of Research and Development Vol 1 American Solar Energy Society, Inc. NY 61-111. Bisio, Attilio and Sharon Boots (1995) Encyclopedia of Energy Technology and the Environment Vol 3 John Wiley & Sons, Inc, New York, NY 2281-2310. Blanco-Canqui, H. and Rattan Lal (2004). Mechanisms of carbon sequestration in soil aggregates. Critical Reviews in Plant Sciences 23(6): 481-504. Czernik, Stefan, Robert Evans, Richard French (2007). Hydrogen from biomass-production by steam reforming of biomass pyrolysis oil. Catalysis Today 129: 265-268. Czernik, Stefan, A.V. Bridgewater (2004). Overview of Application of Biomass Fast Pyrolysis Oil. Energy Fuels 18: 590598 Day, Danny, R.J. Evans, J.W. Lee, D. Reicosky (2005). Economical CO2, SOx, and NOx Capture from Fossil-fuel Utilization with Combined Renewable Hydrogen Production and Large-scale Carbon Sequestration. Energy 30: 25582579. Day D, D Reicosky, K Nichols (2005). Internal report to U.S. Office of Management & Budget. Glaser, Bruno, Ludwig Haumaier, Georg Guggenberger, Wolfgang Zech (1998). Stability of soil organic matter in Terra Preta soils. 16th World Congress of Soil Science, Montpellier, 20-26/08/1998, Proceedings on CD-ROM. Glaser, Bruno, Johannes Lehmann, Christoph Steiner, Thomas Nehls, Muhammad Yousaf, and Wolfgang Zech (2002). Potential of Pyrolyzed Organic Matter in Soil Amelioration. 12th ISCO Conference: 421-427. Iwasaki, W. (2003). A Consideration of the Economic Efficiency of Hydrogen Production from Biomass. International Journal of Hydrogen Energy 28: 939-944. Laird, D.A. (2008) The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality. Agronomy Journal: 100(1) 178-181 Lehmann, Johannes, John Gaunt, Marco Rondon (2006). Bio-Char Sequestration in Terrestrial Ecosystems. Mititagtion and Adaptation Strategies for Global Change 11: 403-427. Lehmann, Johannes (2007). Bio-energy in the black. Frontiers in Ecology and in the Environment 5: 381–387. Magrini-Bair, K., S. Czernik, R. French, Y.O. Parent, E. Chornet, D.C. Dayton, C. Feik, R. Bain (2007). Fluidizable reforming catalyst development for conditioning biomass-derived syngas. Applied Catalysis A: General 318: 199-206.

Okimori, Y, Makoto Ogawa, F. Takahashi (2003). Potential of CO2 Emission Reductions by Carbonizing Biomass Waste from Industrial Tree Plantation in South Sumatra, Indonesia. Mitigation and Adaptation Strategies for Global Change 8: 261-280. Raveendran, K. and Anuradda Ganesh (1996). Heating value of biomass and biomass pyrolysis products. Fuel 75: 17151720. Samolada, M.C., W. Baldauf, and I. A. Vasalos (1998). Production of a bio-gasoline by upgrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking. Fuel 77: 1667 – 1675. Sombroek, W., M L Ruivo, P M Fearnside, B Glaser, and J Lehmann (2003). ‘Amazonian Dark Earths as carbon stores and sinks’, in J. Lehmann, D.C. Kern, B. Glaser and W.I. Woods eds., Amazonian Dark Earths: Origin, Properties, Management, Dordrecht, KluwerAcademic Publishers. 125–139 Steiner, Christoph, K.C. Das, M. Garcia, B Forster, and Wolfgang Zech (2007). Charcoal and smoke extract stimulate the soil microbial community in a highly weathered Xanthic Ferralsol. Pedobiologia In press. UNDP: (2004). World Energy Assessment; ed. J. Goldemberg and T. B. Johansson, New York, NY, UNDP UNEP Website: (United Nations Environment Program) (2008) UNEP Launches Year Book 2008 at its 10th Special Session of the Governing Council/Global Ministerial Environment Forum in Monaco (Monaco, 20 February 2008 ) Wilhelm, D.J., D.R. Simbeck, A.D. Karp, R.L. Dickenson (2001). Syngas production for gas-to-liquids applications: technologies, issues and outlook. Fuel Processing Technology 71: 139-148. Yaman, Serdar (2004). Pyrolysis of biomass to produce fuels and chemical feedstocks. Energy Conversion and Management 45: 651-671.

Yelverton, F.H, Jerome B Weber, G. Peedin, W. D. Smith (1996). Using activated charcoal to inactivate agricultural chemical spills. North Carolina Cooperative Extension Service Pub. AG-442 1-4.

Soil Science and Plant Nutrition (2007) 53, 181–188

doi: 10.1111/j.1747-0765.2007.00123.x

ORIGINAL ARTICLE Blackwell Publishing, Ltd.

Effect of charcoal ORIGINAL ARTICLE on N2O emissions

Effects of charcoal addition on N2O emissions from soil resulting from rewetting air-dried soil in short-term laboratory experiments Yosuke YANAI1, Koki TOYOTA2 and Masanori OKAZAKI2 1

Graduate School of Bio-Applications and Systems Engineering and 2Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan

Abstract Laboratory experiments were conducted to examine the effect of charcoal addition on N2O emissions resulting from rewetting of air-dried soil. Rewetting the soil at 73% and 83% of the water-filled pore space (WFPS) caused a N2O emission peak 6 h after the rewetting, and the cumulative N2O emissions throughout the 120-h incubation period were 11 ± 1 and 13 ± 1 mg N m−2, respectively. However, rewetting at 64% WFPS did not cause detectable N2O emissions (−0.016 ± 0.082 mg N m−2), suggesting a severe sensitivity to soil moisture. When the soils were rewetted at 73% and 78% WFPS, the addition of charcoal to soil at 10 wt% supressed the N2O emissions by 89% . In contrast, the addition of the ash from the charcoal did not suppress the N2O emissions from soil rewetted at 73% WFPS. The addition of charcoal also significantly stimulated the N2O emissions from soil rewetted at 83% WFPS compared with the soil without charcoal addition (P < 0.01). Moreover, the addition of KCl and K2SO4 did not show a clear difference in the N2O 2− emission pattern, although Cl− and SO4 , which were the major anions in the charcoal, had different effects on N2O-reducing activity. These results indicate that the suppression of N2O emissions by the addition of charcoal may not result in stimulation of the N2O-reducing activity in the soil because of changes in soil chemical properties. Key words: denitrification, K fertilization, liming, N2O-reducing activity, rewetting effect.

INTRODUCTION N2O is an important greenhouse gas produced in soil (Bouwman 1990). It has a destructive potential in the stratospheric ozone layer (Crutzen 1981). Nitrification and denitrification are the most important biological processes in the production of N2O in soil. Denitrification is identically the sole process associated with N2O reduction (Zumft 1997). In a previous study, we examined the effects of soil amendments (liming material, inorganic salts and charcoal) on the N2O-reducing activity of denitrifying communities (Yanai et al.). We found that charcoal and its ash, which had a high content of alkali and inorganic salts (Nerome et al. 2005), seemed to promote the growth activity and N2O-reducing activity of denitrifying Correspondence: Y. YANAI, BASE 415, 2-24-16, Nakacho, Koganeishi, Tokyo 184-8588, Japan. Email: yosukey@ yahoo.co.jp Received 31 July 2006. Accepted for publication 15 December 2006. © 2007 Japanese Society of Soil Science and Plant Nutrition

communities and that liming and anions affected these activities more than cations. These results suggest that N2O emissions from soil can be affected by certain soil amendments because of the modifying activity of N2O reduction, assuming that N2O emissions from soil through denitrification depend on the balance of the N2O-producing and N2O-reducing activity of denitrifying communities (Cavigelli and Robertson 2001). In fact, Inubushi et al. (1999) and Azam and Müller (2003) observed stimulation of N2O emissions from soil by the addition of NaCl in a laboratory incubation study, and this result can be explained by the suppression of N2O-reducing activity by Cl− or Na+ (Yanai et al.). In contrast, the effects of liming on N2O emissions from soil are inconsistent in field studies (Borken and Brumme 1997; Butterbach-Bahl et al. 1997; Klemedtsson et al. 1997; Mosier et al. 1998; Tokuda and Hayatsu 2004; Wang et al. 1997) and in laboratory incubation studies (Borken et al. 2000; Clough et al. 2003; Clough et al. 2004; Khalil et al. 2003). Pulses of N2O emission have been observed in field studies following irrigation and precipitation events

182 Y. Yanai et al.

(e.g. Kusa et al. 2006; Ruser et al. 2001) and have been reproduced in laboratory incubation experiments as a rewetting of dry soil (Rudaz et al. 1991). Rudaz et al. (1991) and Ruser et al. (2006) investigated the contribution of nitrification and denitrification to the production of N2O emitted after rewetting using the C2H2 addition method and 15N tracing technique, respectively, and concluded that the N2O was mainly produced through denitrification. In the present study, to examine the relationship between enhancing the N2O-reducing activity of denitrifying communities and N2O emissions from soil, we examined the effects of charcoal and anion species on N2O emissions caused by the rewetting of air-dried soil in the laboratory.

pH (H2O) value was determined in a 1:2.5 air-dried soil (weight) to deionized water (volume) ratio. Total carbon and nitrogen contents of the soils were determined using the dry combustion method using a CN CORDER MT-700 (Yanaco, Kyoto, Japan). Water soluble organic C − and NO3-N contents were determined using a TOC meter (TOC-VCSH, SHIMADZU Co. Ltd., Kyoto, Japan) and an ion chromatograph (LC-20AT, SHIMADZU Co. Ltd., Kyoto, Japan), respectively, in 1:10 extracts (air-dried soil to deionized water w/v) at 240 rpm for 30 min. The population density of denitrifiers in the air-dried soil samples was determined using the most probable number method in five replicates of 10-fold serial dilution (Tiedje 1994). Maximum water-holding capacity (MWHC) was determined using the Hilgard method. Particle density was determined using the pycnometer method (Blake and Hartge 1986). Water-filled pore space (WFPS) was calculated as follows:

MATERIALS AND METHODS Soil samples and charcoal

WFPS = (Gravimetric water content/ρH2O) · (Bulk density/Porosity)

The soil samples examined were the same as those used in our previous study (Yanai et al.). Soil sampling was conducted at the Field Museum Tsukui, the Field Science Center of Tokyo University of Agriculture and Technology, Tokyo, Japan. Soil samples were collected from a grassland field in which one side was planted with Sorghum bicolor (L.) Moench and the other with Sorghum sudanense (Piper) on April 2004 and March 2005, respectively. The soil is classified as Typic Hapludand, and the soil texture is loam to clay loam at a depth of 0–40 cm, with a granular structure (Kurokawa, pers. comm.). After collection, moist soil samples were passed through a 2-mm mesh sieve, and part of the sample was then air-dried. Selected physico-chemical properties of the soil samples are listed in Table 1. Soil

where Porosity = 1 − (Bulk density/Particle density). In the present study, we set the density of water (ρH2O) at 1 g cm−3. The charcoal, which was made from municipal biowaste, was provided by JFE Holdings. The physico-chemical properties of the charcoal are listed in Yanai et al. and its potential usefulness for cultivation was demonstrated by Nerome et al. (2005). Some selected physico-chemical properties of the charcoal and its ash, which was obtained by heating at 700°C for 4 h (as the test of weight loss-onignition; LOI), are listed in Table 2. Charcoal and ash pH (H2O) values were determined in a 1:5 air-dried material to deionized water ratio (w/v). The MWHC and particle density were determined as described above. Anion

Table 1 Selected physico-chemical properties of the air-dried soils examined in this study (oven-dry basis)

Abbreviation of soil name TG2004 TG2005

Total C

−

Total N

C/N Date of pH sampling (H2O) (mg C g−1) (mg N g−1) ratio Apr. 2004 Mar. 2005

6.0 5.4

69.6 70.3

5.62 5.45

12.4 12.9

WSOC NO3 -N −1

−1

(µg g ) 155 74

Denitrifiers (log MPN g )

45.8 6.4

6.5 6.2

Water Bulk Specific content MWHC density gravity −1

−3

(g H2O g ) 0.15 0.13

1.21 1.11

(cm3 cm−3)

(g cm ) 0.58 0.59

Porosity

2.05 2.03

0.72 0.71

MPN, most probable number; MWHC, maximum water-holding capacity; WSOC, water soluble organic carbon.

Table 2 Selected physico-chemical properties of charcoal and its ash examined in this study

Charcoal Ash

pH (H2O)†

LOI (%)

Water content (g H2O g−1)

9.3 11.6

38 –

0.14 0.03

Anion content (µmol g−1)‡

MWHC (g H2O g−1)

Bulk density (g cm−3)

Particle density (g cm−3)

Cl−

NO3

SO4

1.38 –

0.50 0.46

1.64 –

510 1240

0 2

9 80

−

2−

†

1:5 ratio. ‡Air-dried material basis in Yanai et al. LOI, weight loss-on-ignition; MWHC, maximum water-holding capacity; –, not determined.

© 2007 Japanese Society of Soil Science and Plant Nutrition

Effect of charcoal on N2O emissions

−

contents (Cl−, NO3 and SO4 ) in these materials were determined using an ion chromatograph (LC-20AT, SHIMADZU Co. Ltd. Kyoto, Japan) in 1:20 extracts (air-dried material to deionized water w/v) at 240 rpm for 30 min. 2−

Measurement of N2O emissions from soil after rewetting To simulate the thin surface layer in arable fields, where the soil could be subjected to air-drying following continuous clear weather, 30 g of sieved air-dried soil was placed in a Petri dish (1.3 cm height and 8.5 cm diameter) without compaction. As a result, the thickness of the soil was approximately 0.8 cm. To simulate the condition of the soil during or immediately after precipitation, distilled water was added into the soil samples in the Petri dishes to more than 70% of their MWHC (equivalent to 64% of the water-filled pore space [WFPS]). Immediately after rewetting the soil sample, N2O emissions were periodically measured using the closedchamber method (Hutchinson and Mosier 1981). A clear glass bell-jar (14 cm width, 26 cm height, 2.32 L) was used as a gas-tight chamber to monitor the concentration change in the headspace gas. The inlet and outlet of the bell-jar were sealed with a rubber stopper and a rubber septum, respectively, and the bottom part of the bell-jar was tightly attached with a ground glass-plate using a high vacuum-sealing compound (HIVAC-G, Shin-Etsu Chemical Co. Ltd., Tokyo, Japan). A pressurecontrolling bent (Hutchinson and Mosier 1981) was installed at the rubber stopper in the inlet and gas samples were collected through the rubber septum installed at the outlet. After placing the chamber onto the soil sample, headspace gas was withdrawn five times at 2 or 8 min intervals, depending on the rate of concentration change. N2O concentration in the collected gas sample was analyzed using a gas chromatograph (GC-14A, SHIMADZU, Kyoto, Japan) equipped with an electron capture detector and a stainless steel column packed with Porapak-Q (80/ 100 mesh, 3 mm diameter, 2 m length). The column and detector temperatures were kept at 90°C and 330°C, respectively. Argon containing 5% CH4 was used as a carrier gas at a flow rate of 23 mL min−1. The N2O emission rate was calculated using the linear regression method (Hutchinson and Mosier 1981). After measurement of the N2O emission rate, the chamber was removed and the soil sample was left at room temperature (approximately 20–28°C) without a lid on the Petri dish. The water content was maintained during the incubation period by adding distilled water. N2O emissions were monitored until the first peak of N2O emissions disappeared. As a preliminary experiment, we examined the effect of moisture content after rewetting on the N2O emissions from soil (TG2005). Distilled water was added into the © 2007 Japanese Society of Soil Science and Plant Nutrition

183

soil samples at 17.0, 19.9 and 23.1 mL to adjust the rewetted condition to 70, 80 and 91% MWHC, equivalent to 64, 73 and 83% WFPS, respectively. This experiment was conducted in triplicate.

Effect of soil amendments on N2O emissions from soil resulting from rewetting Based on the result of the preliminary experiment (Fig. 1), the moisture content after rewetting was adjusted to more than 73% WFPS in this study. First, to simulate precipitation in grassland amended with charcoal in the surface layer, 2 mm-sieved charcoal was mixed with soil (TG2004) in three of six Petri dishes at 10 wt% (equivalent to 13 vol%) before rewetting, and the N2O emissions were compared with the remaining three Petri dishes as the non-added control. The soil samples were added with distilled water to moisten the soil of the non-added control at 78% WFPS. Second, to test whether the effect of the charcoal addition on the N2O emission results from the stimulation of N2O-reducing activity by pH increase, the charcoal or its ash was mixed with soil (TG2005) in three of nine Petri dishes before rewetting, and three Petri dishes as the non-added control. The amounts of added charcoal and its ash were determined in order to set soil pH (H2O) at 6.0, and the rate of addition was 8.2 and 1.6 wt%, equivalent to 9.7 and 2.0 vol%, respectively. The soil samples were rewetted by adding distilled water, which was necessary to

Figure 1 Effect of rewetting on N2O emissions from soil (TG2005). An air-dried soil sample was rewetted using distilled water at 64 (×), 73 (
) and 83% () of the water-filled pore space (WFPS) and incubated at room temperature. The values shown are the mean ± standard deviation of three replicates. The cumulative N2O emissions during the 120-h incubation period at a rewetting level of 64, 73 and 83% WFPS were −0.016 ± 0.082, 11 ± 1 and 13 ± 1 mg N m−2 (equivalent to −0.003 ± 0.03, 2.3 ± 0.3 and 2.8 ± 0.4 µg N g−1soil), respectively.

184 Y. Yanai et al.

moisten the soil of the non-added control at 73% WFPS. Third, to estimate the interaction between the rate of charcoal addition and the moisture content after rewetting, N2O emissions were compared with three levels of charcoal additions (0, 2 and 8.2 wt%, equivalent to 0, 2.4 and 9.7 vol%, respectively) in triplicate. Distilled water was added to the soil samples to moisten the soil of the non-added control (0% charcoal) at 83% WFPS. were not only the major anion Finally, as Cl− and SO2− 4 species of the charcoal (Table 2), but also were applied into arable fields through fertilization, we examined the effect of anion species of K solution on N2O emissions after rewetting. Of the nine Petri dishes containing the soil samples (TG2005), distilled water, 10 mmol L−1 KCl and 5 mmol L−1 K2SO4 solution were each added to three dishes to adjust to 73% WFPS of the soil, and the N2O emissions were compared. The concentration of K solution was decided based on the concentration of K in a commercial liquid fertilizer (Otsuka Chemical Co. Ltd., Osaka, 2− Japan), and the estimated load of Cl− and SO4 added with the charcoal, ash and K solution is listed in Table 3.

83% WFPS, and the cumulative N2O emissions throughout the 120-h incubation period at room temperature were −0.016 ± 0.082, 11 ± 1 and 13 ± 1 mg N2O-N m−2 (−0.003 ± 0.03, 2.3 ± 0.3 and 2.8 ± 0.4 µg N2O-N g−1soil), respectively (Fig. 1). Rewetting over 73% WFPS triggered N2O emissions, but there were no significant differences in the cumulative N2O emissions between soils rewetted at 73% and 83% WFPS (P = 0.180).

Effects of charcoal addition on N2O emissions after rewetting at 73% WFPS for TG2004 The highest N2O emission rate was observed 30 h after rewetting, and the values were 2620 ± 460 and 383 ± 74 µg N m−2 h−1 in the treatments without and with charcoal addition, respectively (Fig. 2). The addition of

Calculation of the cumulative N2O emission and statistical analysis The cumulative N2O emissions were estimated using the linear trapezoidal method, and the value was expressed as an arithmetic mean and standard deviation (SD). The level of significance of the treatments was examined using an unpaired t-test for TG2004 and by anova followed by Tukey’s multiple comparison tests for TG2005 (P < 0.05). If one of the mean values of the triplicates appeared to lose normality (mean − 2SD < 0), the original data were log-transformed before comparison (Bland and Peacock 2002).

RESULTS N2O emissions from soil after rewetting N2O emissions were not detected after rewetting at 64% WFPS, but were detected after rewetting at 73% and

Figure 2 Effect of charcoal addition on N2O emissions from soil (TG2004) rewetted at 78% of the water-filled pore space of the soil. The values shown are the mean ± standard deviation of three replicates. The cumulative N 2O emissions during the 168-h incubation period for the non-added control and the 10 wt% charcoal addition were 105 ± 14 and 11.1 ± 2.4 mg N m−2 (equivalent to 19.9 ± 2.7 and 2.1 ± 0.5 µg N g−1 soil), respectively.

Table 3 Estimation of Cl− and SO4 load onto soil (TG2005) by the addition of charcoal, ash and K solution 2−

Application rate or concentration Charcoal Charcoal Ash KCl K2SO4

Concentration in soil solution (mmol L−1) at

Added into soil (µmol g−1 soil) Cl 2 wt% 8.2 wt% 1.6 wt% 10 mmol L−1 5 mmol L−1

–

10 42 20 7.5 0

SO

73% WFPS 2− 4

0.2 0.7 1.3 0 3.7

Cl

−

NA 46 23 8.5 0

SO

83% WFPS 2− 4

NA 0.8 1.5 0 4.3

2−

−

SO4

10 40 NA NA NA

0.2 0.7 NA NA NA

Cl

NA, not applicable with respect to the objectives of this study; WFPS, water-filled pore space. © 2007 Japanese Society of Soil Science and Plant Nutrition

Effect of charcoal on N2O emissions

185

charcoal decreased the N2O emission peak by 85% of that of the control without charcoal. The cumulative N2O emissions were 105 ± 14 and 11.1 ± 2.4 mg N m−2 (19.9 ± 2.7 and 2.1 ± 0.5 µg N g−1 soil) in the treatments without and with charcoal addition, respectively. The charcoal addition significantly decreased N2O emissions by 89% of the control value without charcoal (P < 0.01).

Effects of liming (pH 6.0) with charcoal and its ash on N2O emissions after rewetting at 73% WFPS for TG2005 The highest N2O emission rate was observed at 12 h after rewetting in the non-added control and the ashadded soil (Fig. 3), but N2O emissions were kept at a low level in the charcoal-added soil throughout the observation period (72 h). The cumulative N2O emissions throughout the 72-h incubation period in the non-added control, ash-added and charcoal-added soils were 4.1 ± 1.9, 4.3 ± 1.2 and 0.8 ± 0.7 mg N m−2 (0.9 ± 0.4, 1.0 ± 0.3 and 0.2 ± 0.2 µg N g−1 soil), respectively. Charcoal addition decreased N2O emissions by 80% of the value of the non-added control (P < 0.05), whereas ash addition did not.

Effects of charcoal addition on N2O emissions after rewetting at 83% WFPS for TG2005 The N2O emission rate at 6 h after rewetting was lower in the 2 and 8.2 wt% charcoal added-soils than in the

Figure 4 Effect of charcoal addition on N2O emissions from soil (TG2005) rewetted at 83% of its water-filled pore space. The values shown are the mean ± standard deviation of three replicates. The cumulative N 2O emissions during the 72-h incubation period for the non-added control and the 2 and 8.2 wt% charcoal additions were 6.8 ± 0.9, 10.0 ± 0.8 and 10.3 ± 0.6 mg N m−2 (equivalent to 1.5 ± 0.2, 2.2 ± 0.2 and 2.4 ± 0.1 µg N g−1soil), respectively.

non-added control, while the N2O emission rate more than 12 h after the rewetting was higher in the 2 and 8.2 wt% charcoal added-soil than in the non-added control (Fig. 4). The cumulative N2O emissions throughout the 72-h incubation period in the non-added control, and in the 2 and 8.2 wt% charcoal-added soil were 6.8 ± 0.9, 10.0 ± 0.8 and 10.3 ± 0.6 mg N m−2 (1.5 ± 0.2, 2.2 ± 0.2 and 2.4 ± 0.1 µg N g−1soil), respectively. The addition of charcoal at 2 and 8.2 wt% significantly increased N2O emissions by 47% and 51% of the values of the non-added control, respectively (P < 0.01).

Effects of KCl and K2SO4 on N2O emissions after rewetting at 73% WFPS for TG2005

Figure 3 Effect of liming by using charcoal and its ash on N 2O emissions from soil (TG2005) rewetted at 73% of its waterfilled pore space. The values shown are the mean ± standard deviation of three replicates. The cumulative N 2O emissions during the 72-h incubation period for the non-added control, ash-amended soil and charcoal-amended soil were 4.1 ± 1.9, 4.3 ± 1.2 and 0.8 ± 0.7 mg N m−2 (equivalent to 0.9 ± 0.4, 1.0 ± 0.3 and 0.2 ± 0.2 µg N g−1soil), respectively. © 2007 Japanese Society of Soil Science and Plant Nutrition

The highest N2O emission rate was observed 12 h after rewetting (Fig. 5). The mean N2O emission rate was higher in 10 mmol L−1 KCl than in 5 mmol L−1 K2SO4 and the non-added control, but considerable variability was observed in the KCl-added soil. The cumulative N2O emissions throughout the 72 h incubation in the non-added control, 10 mmol L−1 KCl and 5 mmol L−1 K2SO4 were 2.9 ± 0.6, 5.3 ± 6.1 and 4.4 ± 1.5 mg N m−2 (0.6 ± 0.1, 1.2 ± 1.3, 1.0 ± 0.3 µg N g−1 soil) with CV values of 21, 115 and 34% (17, 108 and 30%), respectively. There were no significant differences between the control and the 10 mmol L−1 KCl (P = 0.9986) or 5 mmol L−1 K2SO4 additions (P = 0.8559), or between the 10 mmol L−1 KCl and 5 mmol L−1 K2SO4 additions (P = 0.8794).

186 Y. Yanai et al.

Figure 5 Effect of Cl− and SO4 of K salts on N2O emissions from soil (TG2005) rewetted at 73% of its water-filled pore space. An air-dried soil sample was rewetted using distilled water (control) or a K solution and incubated at room temperature. The values shown are the mean ± standard deviation of three replicates. The cumulative N 2O emissions during the 72-h incubation period for the non-added control, the 10 mmol L−1 KCl-added soil and the 5 mmol L−1 K2SO4 added soil were 2.9 ± 0.6, 5.3 ± 6.1 and 4.4 ± 1.5 mg N m−2 (equivalent to 0.6 ± 0.1, 1.2 ± 1.3 and 1.0 ± 0.3 µg N g−1 soil), respectively. 2−

DISCUSSION The present study demonstrated that rewetting of air-dried soil at 73% WFPS caused significant N2O emissions (Fig. 1), and the N2O emissions were suppressed by the addition of charcoal (Figs 2,3). This suppression of the N2O emissions was first considered to be a liming effect because charcoal has alkali (Table 2) and it had the potential to increase the N2O-reducing activity of denitrifying communities (Cavigelli and Robertson 2000), which might cause a decrease in N2O emissions (Cavigelli and Robertson 2001). Therefore, liming resulting from the ash was expected to have a similar potential for promoting N2O-reducing activity to the charcoal itself. We checked the soil pH (1:2.5 ratio) after the observation of N2O emission from soils to which charcoal and its ash had been added and there were no significant differences between these amendments (5.7 ± 0.03 and 5.6 ± 0.01, respectively, P = 0.08), but these treatments were significantly different from the non-added control (4.9 ± 0.2, P < 0.01, n = 3). However, the addition of ash did not suppress N2O emissions (Fig. 4). Moreover, the suppressive effects of charcoal addition on N2O emissions were not observed when the soils were rewetted at 83% WFPS (Fig. 4). These results indicate that soil pH amendments, which are intended

to stimulate the N2O-reducing activity, may not explain the suppression of the N2O emissions from soil rewetted at 73% WFPS (Figs 2,3). In addition, irrespective of the inhibitory effects of Cl− and the stimulatory effects 2− of SO4 on N2O-reducing activity of denitrifying communities (Yanai et al.), there were no clear differences in the N2O emissions when KCl and K2SO4 were added to the soils (Fig. 5). This finding could result from the use of concentrations (5 and 10 mmol L−1) that were too low to affect the denitrifying communities (Table 3) because the effects of Cl− and were detected at more than 40 mmol L−1 in the liquid medium in our previous study (Yanai et al.). Nevertheless, these results suggested that amelioration of the chemical properties of soil in order to stimulate the N2O-reducing activity may not be related to the suppression of the N2O emissions from soil rewetted at 73% WFPS (Figs 2,3). Increases in N2O emission rates with increasing soil water contents have been reported from laboratory and field studies and have been attributed to increasing denitrifying activity induced by decreased O2 diffusion into the soil (Ruser et al. 2006 and references therein). In the present study, we observed a similar trend, namely, that N2O emissions increased with increases in the water content of soil by rewetting at 73% and 83% WFPS, whereas significant N2O emissions were not detected by rewetting at 64% WFPS (Fig. 1). This result suggests that a decrease in the moisture conditions from 83% to 73% WFPS did not affect the denitrifying communities, while a decrease from 73% to 64% WFPS may result in a significant decrease in the anoxic microsites, which results in the suppression of denitrification. Thus, undetectable N2O emissions from soil rewetted at 64% WFPS may not be the result of complete denitrification, including N2O reduction to N2, but, rather, to insufficient development of anoxic microsites in the soil to trigger denitrification. Possibly, this was caused by the soil sample TG2005, which had less denitrification activity because of a lower population density of denitrifiers, soil pH, and the amount of substrate compared with the soil sample TG2004 (Table 1). In addition, the decay of the N2O emission rate in the later incubation period after rewetting may be the completion of N2O production (stepwise reductions of − − NO3, NO2, and NO) rather than the kinetic equilibration of N2O production and reduction followed by N2 production. Ruser et al. (2006) observed few N2 emissions after rewetting, indicating a low or undetectable contribution of N2O-reducing activity in the later incubation period after rewetting. Therefore, the N2O-reducing activity of denitrifying communities may not significantly affect N2O emissions after rewetting of air-dried soil, suggesting that the suppressive effect of the charcoal addition on N2O emissions (Figs 2,3) might result from inhibition of N2O-producing activity of denitrifying communities. © 2007 Japanese Society of Soil Science and Plant Nutrition

Effect of charcoal on N2O emissions

Although there was no direct evidence to show a linkage between the addition of charcoal and the suppression of N2O emissions from soil (Figs 2,3), the added charcoal itself probably absorbed water and improved the aeration of the soil, leading to a suppression − − of N2O production (stepwise reduction of NO3 , NO2 and NO) similar to the soil rewetted at 64% WFPS (Fig. 1). In fact, the charcoal examined was made up of porous particles, whereas the ash was nearly pulverized. Such differences in the size and structure possibly affect the water absorption capacity of these materials, and may consequently cause differences in the soil aeration, the denitrification process, and N2O emissions from soil, although the charcoal addition did not significantly affect the MWHC or the particle density (data not shown). Hence, the significant increases in N2O emissions by the addition of charcoal to soil rewetted at 83% WFPS (Fig. 4) can be interpreted as an interaction between the insignificant improvement of the aeration of the soil and the stimulation of the N2O-producing activity resulting from neutralization (e.g. Cavigelli and Robertson 2000). Charcoal was examined in this study because of its potential use for soil amendments in temperate regions (Nerome et al. 2005) and in the tropics (Glaser et al. 2002; Yamato et al. 2006). Although any extrapolation of the findings from this short-term laboratory study to a longterm field scale should be conducted with caution, field applications of charcoal possibly suppress N2O emissions from arable soil, depending on the moisture or aeration conditions of the soil. In contrast, our understanding of the process of suppressing N2O emissions from soil by charcoal is still preliminary. Therefore, further studies are necessary to understand both the mechanisms and possible side-effects of charcoal addition to soil on the suppression of N2O − emissions from soil, such as the activity of NO3 assimila− tion, NO2 accumulation in soil or NOx emissions from soil.

ACKNOWLEDGMENTS The authors thank Dr Yuzo Kurokawa (Tokyo University of Agriculture and Technology) for providing soil samples and Mr Sumio Yamada (JFE Holdings) for providing the charcoal samples. The work described in this report was financially supported by a Sasakawa Scientific Research Grant from The Japan Science Society (16-315), the TUA&T 21 Century COE program (Evolution and Survival of Technology-based Civilization: Professor Masayuki Horio) and by the Japan Society for the Promotion of Science Research Fellowships for Young Scientists (17-6518).

REFERENCES Azam F, Müller C 2003: Effect of sodium chloride on denitrification in glucose amended soil treated with ammo© 2007 Japanese Society of Soil Science and Plant Nutrition

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nium and nitrate nitrogen. J. Plant Nutr. Soil Sci., 166, 594 –600. Blake GR, Hartge KH 1986: Particle density. In Physical and Mineralogical Methods. Ed. A Klute, pp. 377–382, Soil Science Society of America, Madison. Bland M, Peacock J 2002: Normal distribution. In Statistical Questions in Evidence-based Medicine. Ed. K Adachi, pp. 79–85, Shinoharashinsha Press, Tokyo (in Japanese). Borken W, Brumme R 1997: Liming practice in temperate forest ecosystems and the effects on CO 2, N2O and CH4 fluxes. Soil Use Manage., 13, 251–257. Borken W, Grundel S, Beese F 2000: Potential contribution of Lumbricus terrestris L. to carbon dioxide, methane and nitrous oxide fluxes from a forest soil. Biol. Fertil. Soils, 32, 142–148. Bouwman AF 1990: Exchange of greenhouse gases between terrestrial ecosystems and the atmosphere. In Soils and the Greenhouse Effect. Ed. AF Bouwman, pp. 61–127. John Wiley, New York. Butterbach-Bahl K, Gasche R, Breuer L, Papen H 1997: Fluxes of NO and N2O from temperate forest soils: Impact of forest type, N deposition and of liming on the NO and N2O emissions. Nutr. Cycl. Agroecosys., 48, 79–90. Cavigelli MA, Robertson GP 2000: The functional significance of denitrifier community composition in a terrestrial ecosystem. Ecology, 81, 1402–1414. Cavigelli MA, Robertson GP 2001: Role of denitrifier diversity in rates of nitrous oxide consumption in a terrestrial ecosystem. Soil Biol. Biochem., 33, 297–310. Clough TJ, Kelliher FM, Sherlock RR, Ford CD 2004: Lime and soil moisture effects on nitrous oxide emissions from a urine patch. Soil Sci. Soc. Am. J., 68, 1600–1609. Clough TJ, Sherlock RR, Kelliher FM 2003: Can liming mitigate N2O fluxes from a urine-amended soil? Aust. J. Soil Res., 41, 439–457. Crutzen PJ 1981: Atmospheric chemical processes of the oxides of nitrogen, including nitrous oxide. In Denitrification, Nitrification and Atmospheric Nitrous Oxide. Ed. CC Delwiche, pp. 17– 44. John Wiley, New York. Glaser B, Lehmann J, Zech W 2002: Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – A review. Biol. Fertil. Soils, 35, 219–230. Hutchinson GL, Mosier AR 1981: Improved soil cover method for field measurement of nitrous oxide fluxes. Soil Sci. Soc. Am. J., 45, 311–316. Inubushi K, Barahona MA, Yamakawa K 1999: Effects of salts and moisture content on nitrous oxide emission and nitrogen dynamics in Yellow soil and Andosol in model experiments. Biol. Fertil. Soils, 29, 401– 407. Khalil MI, Van Cleemput O, Rosenani AB, Fauziah CI, Shamshuddin J 2003: Nitrous oxide formation potential of various humid tropic soils of Malaysia: A laboratory study. Nutr. Cycl. Agroecosys., 66, 13–21. Klemedtsson L, Klemedtsson AK, Moldan F, Weslien P 1997: Nitrous oxide emission from Swedish forest soils in relation to liming and simulated increased N-deposition. Biol. Fertil. Soils, 25, 290–295. Kusa K, Hu R, Sawamoto T, Hatano R 2006: Three years of

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nitrous oxide and nitric oxide emissions from silandic andosols cultivated with maize in Hokkaido, Japan. Soil Sci. Plant Nutr., 52, 103 –113. Mosier AR, Delgado JA, Keller M 1998: Methane and nitrous oxide fluxes in an acid Oxisol in western Puerto Rico: Effects of tillage, liming and fertilization. Soil Biol. Biochem., 30, 2087–2098. Nerome M, Toyota K, Islam T-MD et al. 2005: Suppression of bacterial wilt of tomato by incorporation of municipal biowaste charcoal into soil. Soil Microorganisms, 59, 9–14 (in Japanese with English summary). Rudaz AO, Davidson EA, Firestone MK 1991: Sources of nitrous oxide production following wetting of dry soil. FEMS Microbiol. Ecol., 85, 117–124. Ruser R, Flessa H, Russow R, Schmidt G, Buegger F, Munch JC 2006: Emission of N2O, N2 and CO2 from soil fertilized with nitrate: Effect of compaction, soil moisture and rewetting. Soil Biol. Biochem., 38, 263–274. Ruser R, Flessa H, Schilling R, Beese F, Munch JC 2001: Effect of crop type-specific soil management and N fertilization on N2O emissions from a fine-loamy soil. Nutr. Cycl. Agroecosys., 59, 177–191. Tiedje JM 1994: Denitrifiers. In Microbiological and

Biochemical Properties. Eds RD Weaver, JS Angle and PS Bottomley, pp. 245–267, Soil Science Society of America, Madison. Tokuda S, Hayatsu M 2004: Nitrous oxide flux from a tea field amended with a large amount of nitrogen fertilizer and soil environmental factors controlling the flux. Soil Sci. Plant Nutr., 50, 365–374. Wang YP, Meyer CP, Galbally IE, Smith CJ 1997: Comparisons of field measurements of carbon dioxide and nitrous oxide fluxes with model simulations for a legume pasture in southeast Australia. J. Geophys. Res., 102, 28 013–28 024. Yamato M, Okimori Y, Wibowo IF, Anshori S, Ogawa M 2006: Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Sci. Plant Nutr., 52, 489– 495. Yanai Y, Hatano R, Okazaki M, Toyota K. Chemical factors affecting the N2O-reducing activity of denitrifying communities – Analysis of the C2H2 inhibition-based N2O production curve of soil. Zumft WG 1997: Cell biology and molecular basis of denitrification. Microbiol. Mol. Biol. Rev., 61, 533–616.

© 2007 Japanese Society of Soil Science and Plant Nutrition

US Offset Market •  Trends – Fossil fuels will likely be capped – Favor domestic projects over international projects

•  Destroying methane emissions •  Sequestration –  Forestry –  Soil Management –  Biochar?

Sequestration Projects •  Clean Development Mechanism –  Reforestation/afforestation only –  Temporary credits Expected CERs Until 2012 (%) in each category

Demand-side EE 1%

Fuel switch 7%

Afforestation & Reforestation 0.4%

Transport 0.2% HFCs, PFCs & N2O reduction 27%

Supply-side EE 10%

CH4 reduction & Cement & Coal mine/bed 20% Renewables 35%

Outline •  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

$ = CO2 Sequestered x Price • Low Quality US Projects •  Chicago Climate Exchange: $2-$4/mt CO2 •  High Quality US Projects •  Voluntary Carbon Standard: $4-$9/mt CO2 •  California Climate Action Registry: $5-$11/mt CO2 •  Mature International Markets •  EU Emissions Trading Scheme: $10-$40/mt CO2 •  Projections for Early US Market •  Markey-Waxman Bill : $10-$15/mt CO2

Biochar GHG Reductions GHG Reduction

Reduction Size

Qualify for Carbon Finance?

Sequestration

Large

Yes

Fuel switch

Medium

Likely to be capped

Less fertilizer  fewer Medium/Large soil emissions (N2O and CH4)

Hard to measure

Less fertilizer  less fertilizer production

Indirect, hard to measure, likely to be capped

Small/Medium

Currently Methodologies Avoidance of methane production from biomass decay through controlled pyrolysis •  Small scale •  No credit for carbon sequestration, but… •  Char must be “biologically inert” •  Volatile C/Fixed C ratio lower than 50%

Next Step: Sequestered Carbon

Carbon Gold methodology for proposed to the Voluntary Carbon Standard

Outline •  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

Unresolved Methodology Issues •  Recalcitrance •  Guarantee 100 years of permanent sequestration •  Carbon Gold: Volatile C/Fixed C ratio lower than 50% •  Soil monitoring •  What happens to char that erodes out of the soils?

Unresolved Methodology Issues •  Ownership – Three entities, same reduction 1.  Feedstock owner 2.  Pyrolysis plant 3.  Land owner •  Carbon Gold: Credits pyrolysis plant •  Sequestered carbon can only be claimed once

Unresolved Methodology Issues •  Environmental impact –  Heavy metals –  Criteria air pollutants –  Microbe health –  Carbon already in soil

Resolved Issue: Waste Feedstocks •  Leakage –  Changes in emissions outside the project itself •  Direct: Biomass fuel unavailable •  Indirect: displace current farm land for biochar feedstock plantations  land use change •  Carbon Gold: “biomass that would otherwise have been left to decay or been burned in an uncontrolled manner”

Carbon Markets and Biochar: An Offset Buyers Perspective North American Biochar Conference August 10th, 2009

Peter Weisberg Offset Project Analyst [email protected] 503-238-1915

Outline •  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

Source: The McKinsey Quarterly. 2007. “A cost curve for greenhouse gas reductions.”

US Offset Market •  Trends – Fossil fuels will likely be capped – Favor domestic projects over international projects

•  Destroying methane emissions •  Sequestration –  Forestry –  Soil Management –  Biochar?

Sequestration Projects •  Clean Development Mechanism –  Reforestation/afforestation only –  Temporary credits Expected CERs Until 2012 (%) in each category

Demand-side EE 1%

Fuel switch 7%

Afforestation & Reforestation 0.4%

Transport 0.2% HFCs, PFCs & N2O reduction 27%

Supply-side EE 10%

CH4 reduction & Cement & Coal mine/bed 20% Renewables 35%

Outline •  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

$ = CO2 Sequestered x Price • Low Quality US Projects •  Chicago Climate Exchange: $2-$4/mt CO2 •  High Quality US Projects •  Voluntary Carbon Standard: $4-$9/mt CO2 •  California Climate Action Registry: $5-$11/mt CO2 •  Mature International Markets •  EU Emissions Trading Scheme: $10-$40/mt CO2 •  Projections for Early US Market •  Markey-Waxman Bill : $10-$15/mt CO2

Biochar GHG Reductions GHG Reduction

Reduction Size

Qualify for Carbon Finance?

Sequestration

Large

Yes

Fuel switch

Medium

Likely to be capped

Less fertilizer  fewer Medium/Large soil emissions (N2O and CH4)

Hard to measure

Less fertilizer  less fertilizer production

Indirect, hard to measure, likely to be capped

Small/Medium

Currently Methodologies Avoidance of methane production from biomass decay through controlled pyrolysis •  Small scale •  No credit for carbon sequestration, but… •  Char must be “biologically inert” •  Volatile C/Fixed C ratio lower than 50%

Next Step: Sequestered Carbon

Carbon Gold methodology for proposed to the Voluntary Carbon Standard

Outline •  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

Unresolved Methodology Issues •  Recalcitrance •  Guarantee 100 years of permanent sequestration •  Carbon Gold: Volatile C/Fixed C ratio lower than 50% •  Soil monitoring •  What happens to char that erodes out of the soils?

Unresolved Methodology Issues •  Ownership – Three entities, same reduction 1.  Feedstock owner 2.  Pyrolysis plant 3.  Land owner •  Carbon Gold: Credits pyrolysis plant •  Sequestered carbon can only be claimed once

Unresolved Methodology Issues •  Environmental impact –  Heavy metals –  Criteria air pollutants –  Microbe health –  Carbon already in soil

Resolved Issue: Waste Feedstocks •  Leakage –  Changes in emissions outside the project itself •  Direct: Biomass fuel unavailable •  Indirect: displace current farm land for biochar feedstock plantations  land use change •  Carbon Gold: “biomass that would otherwise have been left to decay or been burned in an uncontrolled manner”

Outline •  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

•  3 Programs •  Oregon Program •  Smart Energy •  Colorado Carbon Fund •  16 projects, $8.8 million in funding, 2.6 million tons of CO2 offset •  Non-profit - Laboratory for innovative offset projects

Project Development Timeline Upfront Payment

Proposal

Due Diligence

Contract Negotiation

Commercial Operation

Annual Monitoring

Annual payment “upon delivery”

Peter Weisberg Offset Project Analyst [email protected] 503-238-1915 x 207

Chemosphere 67 (2007) 1033–1042 www.elsevier.com/locate/chemosphere

Differential sorption behaviour of aromatic hydrocarbons on charcoals prepared at different temperatures from grass and wood Ludger C. Bornemann b

a,b,*,1

, Rai S. Kookana a, Gerhard Welp

b

a CSIRO Land and Water, Adelaide Laboratory, Waite Road, Urrbrae SA, Australia Institute of Crop Science and Resource Conservation of the University of Bonn, Division of Soil Science, Nussallee 13, 53115 Bonn, Germany

Received 27 June 2006; received in revised form 13 October 2006; accepted 19 October 2006 Available online 8 December 2006 In memory of the 100th anniversary of the birth of Prof. Dr. H.C. Eduard Mu¨ckenhausen (February 17th 1907)

Abstract Naturally occurring charcoals are increasingly being recognized as effective sorbents for organic compounds. In this study we investigated the sorption of benzene and toluene in single-sorbate and bi-sorbate systems on different types of charcoals produced in laboratory, employing the batch sorption technique. Air dried plant materials from Phalaris grass (Phalaris tuberosa) and Red Gum wood (Eucalyptus camadulensis) were combusted under limited oxygen supply at 250 C, 450 C, and 850 C. The resulting charcoals were characterized for their specific surface areas, total cation content, and pore size distributions (pore size distribution only for wood combusted at 450 C and 850 C). For the materials treated at 850 C not only the surface area, microporosity, and total amount of sorbed sorbate increased markedly, but also the non-linearity of the sorption isotherm. The pore size distributions and surface areas as well as an indifferent sorption behaviour and competition effects for both sorbates indicated that pore filling mechanisms were the dominating processes governing the sorption on these microporous, high temperature treated materials. For the materials treated at lower temperatures the affinity of toluene was higher compared to that of benzene. In the bi-sorbate system the overall uptake of benzene increased. These phenomena might be due to the stronger hydrophobicity of toluene, and to a varying potential for swelling of the matrix and pore deformation by the two sorbates. The significantly lower sorption capacity of the Phalaris-derived material compared to the Red Gum charcoal correlated with its smaller surface area and higher cation content.  2006 Elsevier Ltd. All rights reserved. Keywords: Charcoal; Aromatic hydrocarbons; Pore filling; Hydrophobic partitioning

1. Introduction Charcoal, the solid residue of partially combusted biomass, is a major constituent of the non-living organic matter of many soils and sediments (Schmidt and Noack, 2000). Together with other species of pyrolytic carbon it comprises a ubiquitous group of materials in our environment, commonly named black carbon (BC) (Goldberg, 1985). Currently, little is known about formation, move*

1

Corresponding author. Tel.: +49 228 73 9368; fax: +49 228 73 2782. E-mail address: [email protected] (L.C. Bornemann). PMB 2, Glen Osmond, SA 5064, Australia.

0045-6535/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.10.052

ment, and oxidation of charcoal, but there are indications that frequent vegetation fires and alluvial transport are playing a major role (Skjemstad et al., 1997). Charcoal withstands biological and chemical degradation to a considerable degree (Goldberg, 1985) and plays an important role in the global carbon cycle and carbon sequestration due to accumulation processes (Jenkinson, 1990). Several studies revealed the potential of charcoal to serve as a strong sorbent for environmental pollutants, thereby playing a crucial role in governing their environmental fate and risks to human and ecosystem health. Polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), and polychlorinated dibenzo-dioxins

1034

L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

(PCDD) have been detected on carbonaceous geosorbents and are contaminants of environmental concern (e.g. Accardi-Dey and Gschwend, 2003; Abelmann et al., 2005; Lohmann et al., 2005). However, the majority of studies dealing with sorption on activated carbon, soot, coal, charcoal, graphite, opaque particles and other forms of BC has been conducted utilizing rather simple aromatic compounds as model substances like benzene, toluene, or phenanthrene (e.g. Gustafsson et al., 1997; Kleineidam et al., 2002; Zhu and Pignatello, 2005). The sorption of these model substances on BC species has been shown to be strong and highly non-linear (e.g. Accardi-Dey and Gschwend, 2003; Braida et al., 2003; Nguyen et al., 2004; James et al., 2005). Several attempts to explain the sorption behaviour of organic materials with varying physicochemical properties have been made during the last decade. Chiou et al. (2000) introduced the term of ‘‘high surface area carbonaceous material’’ (HSACM). Small amounts of charred material like soot or charcoal are considered to be responsible for the non-linear sorption of polar and apolar components. The involved mechanisms are assumed to be hydrophobic partitioning and pore filling, according to the Polanyi–Manes (PM) model (Manes, 1998). The theory postulates the existence of a nonpolar, microporous adsorption site with a characteristic adsorption potential, which is influenced by the nature of the sorbent, and the distance of the sorption site from the sorbent surface. Also interactions of water and adsorbent surface are taken into account. The fundamental idea is a condensation of the adsorbate in (micro-) pores while exhibiting the same physical properties as the unconfined bulk organic liquid or solid. The sorption capacity is believed to be restricted by the pore volume occupied by the mixed phase of condensed liquids or solids. Consequently, the sorption of hydrophobic organic contaminants (HOC) on BC materials would be mainly governed by its microporosity and its hydrophobic character. The physical properties of charcoals from burned biomass are strongly dependent on the conditions during the combustion process (Shafizadeh, 1984). According to Schmidt and Noack (2000), charcoals produced by vegetation wildfires consist mainly of several randomly orientated stacks of graphitic sheets. Still, the structure is influenced crucially by a number of combustion parameters. The main factors are the fuel type, fuel load, fuel condition, weather condition, substrate heterogeneity, fire intensity, and duration (Patterson et al., 1987). Karapanagioti et al. (2004) stated that ‘‘. . .the charcoal particle subgroup of organic matter is heterogeneous in nature’’, and therefore concluded that different subgroups of charcoal have to be distinguished in order to optimize the predictions for the bulk sorption behaviour. So far, little attention has been directed to the heterogeneity within the subgroup of charcoals. From work of Raison (1979) and Scott (1989) we know that elevated ground temperatures during most wildfires may vary between 200 C and 500 C, with highest temperatures for scrub-

land wildfires ranging up to levels between 700 C and 1000 C. Despite these extreme temperature ranges, artificial charcoals as used in most sorption studies consisted either of charcoals produced from one fixed, or only a small range of temperatures (Sander and Pignatello, 2005; Zhu and Pignatello, 2005; Zhu et al., 2005). A study by James et al. (2005), however, employed a range of different combustion temperatures for three species of softwood. Still, the sorptive behaviour of the range of natural charcoals remains poorly understood and data is lacking for charcoals produced from different parent materials at various temperatures. The objectives of this study were (i) investigate the sorptive properties of charcoals produced from hardwood and herbaceous material at various temperatures representative of wildfires, and (ii) compare the sorption behaviour of two simple aromatic model compounds on the range of charcoals in single and bi-sorbate systems. 2. Experimental section 2.1. Wood and grass charcoal production Red Gum (Eucalyptus camadulensis) chips, as used for gardening purposes, were purchased from a landscape supplier, and a pure stand of Phalaris pasture grass (Phalaris tuberosa) was cut from a meadow. Both materials were air dried at 40 C. Thin pieces of Red Gum wood were hand picked, the Phalaris grass was milled into coarse segments and the dust was separated by sieving (2 mm grid). To allow a uniform combustion process, the materials were stacked uncongested in porcelain crucibles with lids. The filled crucibles were weighed and subsequently placed in a muffle furnace. For the charcoals combusted at 250 C and 450 C, the furnace was ramped from room temperature to the final temperature in 1 h. As a second stage, the final temperature was held for 2 h for the Red Gum wood. Due to the more combustible nature of the Phalaris grass, the final temperature was held only for 1 h in this case. The furnace was then switched off to allow the crucibles to cool down to room temperature. The Red Gum wood treated at 850 C was combusted for only 1 h after reaching the final temperature, for the Phalaris grass the time was reduced to half an hour. The charred material was weighed and grinded to powder on a N.V. THEMA disc-rotating mill for 3 min. In the following, the abbreviations R250, R450, and R850 are used for the Red Gum charcoals, P250, P450 and P850 for the Phalaris charcoals. 2.2. Determination of charcoal properties The continuous flow method at 77 K was employed for quantification of adsorbed and desorbed N2, using a QUANTACHROME QUANTASORB QS-13 SurfaceArea Particle-Size Analyzer and ultra high purity gaseous nitrogen (99.999%, from BOC Gases). Surface areas for all six utilized charcoals were calculated from three-point

4 20 371 – – – – – – 1.9 1.8 1.6 2.7 4.4 5.8 27 400 44 070 58 200 17 640 29 240 36 080

e

c

d

a

b

Sum of combusted matter (Charcoal). Sum of dry matter (precursor material). Micropore-volume (<2 nm). Total pore volume. Specific surface area after Brunauer et al. (1938).

5 380 7 660 12 660 2 020 3 490 4 740 Red Gum 250 C Red Gum 450 C Red Gum 850 C

2 360 3 680 4 720

8 34 605 – 0.02219 0.2757 – 0.00375 0.2469 0.4 0.4 0.3 0.6 0.9 1.3 6 110 8 690 13 150 840 1 280 2 580 140 320 660 4 850 6 700 9 400 Red Gum 250 C Red Gum 450 C Red Gum 850 C

280 390 510

Vtotald (mlliq g 1) Vmicroc (mlliq g 1) Sum DMb (%) Sum CMa (%) Sum (mg kg 1) K (mg kg 1) Na (mg kg 1) Mg (mg kg 1) Ca (mg kg 1)

All experiments were conducted in 32 ml KIMAX glass culture-tubes (Kimble Glass Inc. USA) with PTFElined screw lids to minimize sorption effects on the container. Aliquots of 32 mg of charcoal were weighed in the reaction vials and hydrated with 20 ml Milli-Q water for 42 h in an end-over-end shaker. A pre-hydrating period of at least 20–24 h is required due to the hydrophobic nature of the charcoal (Zhu and Pignatello, 2005; Zhu et al., 2005). After hydrating, the test sorbate was added as a stock solution in a methanol-carrier. Benzene, toluene, pro-

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Sample name

2.3. Batch sorption

Table 1 Selected char properties and composition details

regression, based on the BET equation after Brunauer et al. (1938). Additionally, the pore size distribution of R450 and R850 was evaluated using BET nitrogen adsorption technique at 77 K. The details of the method and uncertainties associated with the measurement have been published elsewhere (Badalyan and Pendleton, 2003). Outgassing of the charcoal was carried out at 300 C for 8 h at a background vacuum of 1 · 10 4 Pa, similar to that used for charcoal samples by Braida et al. (2003). For the pore volume evaluation, we employed aS-plot analysis, where the adsorption properties of a porous solid are compared with those of a non-porous standard material exhibiting surface chemistry similar to the test sample (Badalyan and Pendleton, 2003). Moisture content was determined by comparison of sample mass before and after evacuation at 300 C. We classified pore width (dp), according to IUPAC recommendations as follows: micropores: dp < 2 nm, mesopores: 2 < dp < 50 nm, and macropores: dp > 50 nm. Pores, which were smaller than 2 nm were analyzed using the Horvath– Kawazoe (H–K) method (Horvath and Kawazoe, 1983). This method calculates the effective micropore size distribution of slit-shape pores using the data from adsorption isotherms. Using the H–K equation we calculated effective mean width of slit pores (dp), and correlated it with the ads value of DV , where DVads is the incremental amount of Drslit nitrogen adsorbed (converted to condensed liquid volume of nitrogen) and Drslit is the corresponding incremental width of slit pores. The individual and cumulative frequencies were calculated for a range of dp data. Further information on the characteristics of these materials has recently been published by Smernik et al. (2006) and Yu et al. (2006). For the measurement of the total cation contents by atomic absorption spectroscopy (AAS), 0.2 g of the charred material was weighed into microwave vessels and 2 ml H2O2 (35%) and 5 ml HNO3 (70%) were added. The samples were then digested, using a MILESTONE mls 1200 Digestion Unit (300 W, 5 min, 600 W, 5 min, 500 W, 3 min). The samples were converted into 50 ml volumetric flasks and made up to volume in Milli-Q water. The liquid was filtered through 0.45 lm filters and 0.5 ml of the sample was diluted 20 times prior to AAS analysis. Charcoal properties and composition details are presented in Table 1.

N2 BET-SSAe (m2 g 1)

L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

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pyl-benzene, methanol, and dichloromethane with HPLCgrade purity (>99.9%) were used in the experiments. For practical reasons the sorbate concentrations were prepared as ll l 1and converted into lg l 1 in the calculations. In the single-sorbate system, for the materials treated at 250 C and 450 C, the initial sorbate concentrations were covering 2.20–87.90 lg ml 1 for benzene, and 2.17–86.6 lg ml 1 for toluene. Due to the considerably higher sorption capacity of the 850 C materials the concentration range was expanded to 351.6 lg ml 1 for benzene and 346.4 lg ml 1 for toluene. In the bi-sorbate systems both sorbates were added in equal amounts, the total sorbate concentration therefore being doubled, compared to the single-sorbate systems. In order to prevent varying solvent effects, methanol was always kept at 1% by volume throughout all experiments. Specifications regarding the maximum concentration of carrier-solvent avoiding interference with the sorption process are inconsistent (e.g. Kleineidam et al., 2002; Karapanagioti et al., 2004; Sander and Pignatello, 2005). However, we found in preliminary experiments that keeping the solvent concentration constant at 1% provided reproducible results. To avoid headspace (in order to minimize volatilization losses), the vials were filled up to their capacity with Milli-Q water. As charcoal in such small concentrations suspended in water would hardly settle down during centrifugation, 0.32 ml of 1 M CaCl2-solution was added in order to support the flocculation. A final concentration of 0.01 M CaCl2 was also chosen by other authors (Ahmad et al., 2001; Sander and Pignatello, 2005). The vials were placed in the end-over-end shaker again to equilibrate for 24 h. According to Braida et al. (2003), at low initial concentrations (8 lg ml 1), benzene sorption reached an equilibrium after eight days, but the vast majority of benzene (>95%) was already sorbed within 24 h. For higher initial benzene concentrations (1600 lg ml 1) the apparent equilibrium was shown to be reached after 24 h. Kwon and Pignatello (2005) reported that maximum sorption of benzene on the charcoal also utilized by Braida et al. (2003) was achieved within 20 h. From these findings, together with observations that diesel soot uptake of PAHs occurs within hours to one or two days (Bucheli and Gustafsson, 2000) we concluded that equilibration times of 24 h would be appropriate for our purposes. The samples were then centrifuged at 650 g for a duration of 10 min. Subsequently, 5 ml of the supernatant were transferred to PTFE-lined extraction vials with 15 ml capacity and extracted with 2 ml dichloromethane. Prior to extraction, propyl-benzene was added as an internal standard. The extraction tubes were then shaken by hand vigorously and an aliquot of the solvent was transferred into PTFE-lined GC-vials. Analysis of the extracts was performed on a PERKIN ELMER Auto System Gas Chromatograph equipped with a flame ionization detector (FID). The column was a DB-5 column with a length of 30 m, an internal diameter of 0.25 mm and a film thickness of 0.25 lm. The injection temperature was 200 C with 1 ll of sample injected. Helium was used as the carrier gas with

a constant pressure of 22 psi. The detector was heated to 250 C. The initial temperature of the oven was set to 35 C, held for 3 min, and then ramped to 80 C with a rate of 5 C min 1.

3. Results 3.1. Charcoal properties Charcoals combusted at 250 C and 450 C exhibited relatively low surface areas as revealed by N2-BET surface area measurement, whereas the surface areas of the high temperature treated charcoals (850 C) were very high (Table 1). The Red Gum charcoals exhibited a much bigger surface area than the Phalaris charcoals at corresponding temperatures. The ratio of the surface areas of the Red Gum charcoals to the ones from Phalaris drops from 2 at 250 C to 1.7 and 1.6 at the higher combustion temperatures. For both materials the outstanding increase of the surface areas (by almost 20 times) occurred between 450 C and 850 C. This critical change was also documented by the pore size distribution of R450 and R850. The total pore volume of the 850 C material was higher by more than an order of magnitude than that for the 450 C material (Table 1). Furthermore, the fraction of the micropores (pores <2 nm), vmicro [mlliq g 1], revealed a microporosity of 90% for the 850 C material, whereas the 450 C material did not exceed a microporosity of about 17%. The diagram displaying the integral pore size distribution indicated a relatively wide range of pore widths, i.e. 0.5–300 nm, the steep slope at about about 1.2 nm pore diameter indicating the large contribution of this pore size for the 450 C material (Fig. 1). On the contrary, the range of pore size distribution for the 850 C material was very narrow (Yu et al., 2006). Here, the overall dominating pore sizes ranged from only 0.4–1 nm, with insignificant participation of pores with a diameter >10 nm (Fig. 1). Corresponding to the observed N2-BET surface areas, the pore size distribution illustrates the extraordinary increase of the inner surface area with decreasing diameter of the pores. The total cation content of the Phalaris charcoals exceeds the one of the Red Gum charcoals by a factor greater than four (Table 1). Differences in the cation contents of grass and wood are also documented in literature. Harmand et al. (2004) found a value of about 0.4% for the sum of calcium, magnesium and potassium in Red Gum wood (Eucalyptus camadulensis) from Cameroon. Considering the low proportion of sodium contributing to the total cation content of our Red Gum charcoal (2–5%), the findings of Harmand et al. (2004) are in line with our data (Table 1). For a Phalaris species harvested between July and October in Sweden, the sum of the four cations also determined in our study was reported to be about 1.8% of the dry matter (Burval, 1997), and thus again in good agreement with our data set (Table 1).

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0.03

0.20

0.02

0.10

0.01

-1

0.30

Vtotal [mlliq g ] R450

Vtotal [mlliq g-1] R850

L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

R850 R450 0.00 0.1

1.0

10.0 d p [nm]

100.0

0.00 1000.0

Fig. 1. Integral pore size distribution of the charred material. Total pore volumes (vtotal) of R850 (ordinate on the left) and R450 (ordinate on the right), plotted against the diameter of the pores (dp).

3.2. Influence of the combustion temperature on the sorption process Fundamental differences in the sorptive behaviour of benzene and toluene were found for the Red Gum materials treated at different temperatures. In Fig. 2, we plotted the sorbed concentration of sorbate q [mg g 1] against the final concentration in aqueous solution Cf [mg ml 1]

1000

a: Benzene

100

R250 R450 R850

-1

q [mg g ]

10

1 1000

b: Toluene

100 R250 R450 R850

10 1 0.00

0.02

0.04

0.06 0.08 -1 C f [mg ml ]

0.10

0.12

0.14

Fig. 2. Sorbed amount of sorbate q plotted against the final sorbate concentration Cf. Single-sorbate sorption isotherms for (a) benzene and (b) toluene on R250, R450, and R850. Error bars represent standard deviation of duplicate samples (n = 2). Symbols may cover error bars.

and found Langmuir-type sorption isotherms for R850, after the classification by Giles et al. (1960). Both, benzene and toluene were sorbed by R850 to a much higher degree than by the other materials. Comparing the respective coefficients of determination (R2) and especially the standard errors of estimate (SEE), the isotherms from single and bi-sorbate experiments on R850 showed considerably better fits to the Langmuir than to the Freundlich equation (Table 2). The calculated maximum uptake (Smax) of each sorbate in the bi-sorbate system was about half of the maximum uptake in the single-sorbate systems, where benzene and toluene were sorbed in comparable amounts (Table 2). Sorption isotherms of R250 and R450 could successfully be described with the model after Freundlich. For benzene, R250 and R450 exhibited a comparable sorption, whereas toluene expressed a slightly higher affinity to R450 compared to R250 (Fig. 2 a and b). In contrast to R850, the sorption of toluene on R450 and R250 was significantly higher than that of benzene (Fig. 3 a and b; Table 2). Whereas toluene was hardly affected by competition from benzene, the benzene uptake even increased in combination with toluene on both materials. 3.3. Influence of the precursor material on the sorption process The apparent difference between the Phalaris- and Red Gum-derived materials was the lower sorption capacity of P850 as compared to R850 (Table 2). For P850, the calculated maximum uptake after the Langmuir equation resulted in a value of Smax = 153 mg g 1, whereas the corresponding value for the Red Gum charcoal was as large as

1038

Table 2 Results of model fits to single and bi-sorbate isotherms Temperature (C)

Single-/bi-solute

Sorbate

Smaxa (mg g 1)

KLb (ml mg 1)

R2c (–)

SEE

Phalaris Redgum Redgum Redgum Redgum Redgum Redgum Redgum Redgum Phalaris Redgum Redgum Redgum Redgum

850 850 850 850 850 450 450 450 450 250 250 250 250 250

Single Single Single Bi Bi Single Single Bi Bi Single Single Single Bi Bi

Benzene Benzene Toluene Benzene Toluene Benzene Toluene Benzene Toluene Benzene Benzene Toluene Benzene Toluene

153 ± 5.6 222 ± 3.0 236 ± 13.4 114 ± 8.3 113 ± 1.2 – – – – – – – – –

245 ± 91 491 ± 99 326 ± 121 1367 ± 373 8872 ± 2895 – – – – – – – – –

0.99 1.00 0.97 0.96 1.00 – – – – – – – – –

0.05 0.05 0.03 0.01 0.01

d

(–)

ne (–)

KFf (mln mg1

0.41 ± 0.05 0.45 ± 0.06 0.39 ± 0.10 0.44 ± 0.07 0.50 ± 0.18 0.51 ± 0.4 0.50 ± 0.01 0.48 ± 0.04 0.47 ± 0.01 0.56 ± 0.03 0.55 ± 0.04 0.58 ± 0.03 0.56 ± 0.06 0.52 ± 0.04

452.5 ± 1.5 981.7 ± 1.7 689.6 ± 2.2 979.0 ± 1.8 7206.1 ± 7.7 60.9 ± 1.2 150.4 ± 1.1 69.2 ± 1.2 126.7 ± 1.1 56.6 ± 1.1 63.1 ± 1.2 126.3 ± 1.1 83.5 ± 1.3 110.3 ± 1.2

Number of observations is 22 for benzene and toluene on materials treated at 850 C in single sorbate systems, 18 for all other systems. a Maximum sorbate uptake (Langmuir model). b Langmuir affinity coefficient. c Coefficient of determination (Langmuir model). d Standard error of estimate (Langmuir model). e Freundlich exponent. f Freundlich affinity coefficient. g Coefficient of determination (Freundlich model). h Standard error of estimate (Freundlich model).

n

g 1)

R2g (–)

SEE

0.86 0.83 0.60 0.87 0.51 0.96 1.00 0.96 0.99 0.98 0.96 0.98 0.92 0.95

0.24 0.29 0.38 0.22 0.37 0.07 0.03 0.07 0.04 0.05 0.07 0.05 0.10 0.08

h

(–) L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

Char type

L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

100 a: R250

q [mg g-1]

10

1 100 b: R450

10

1 0.0001

0.001 0.01 C f [mg ml-1] Benzene single Benzene bi

0.1

Toluene single Toluene bi

Fig. 3. Sorbed amount of sorbate q plotted against the final sorbate concentration Cf. Sorption isotherms for (a) single- and bi-sorbate systems of benzene and toluene on R250, and (b) single- and bi-sorbate systems of benzene and toluene on R450. Error bars represent standard deviation of duplicate samples (n = 2). Symbols may cover error bars (Freundlichlinearization).

Smax = 222 mg g 1. Similar observations were made for the 250 C materials. The Freundlich sorption coefficient (KF) for P250 showed reduced uptake of benzene compared to R250 (Table 2), however, the slopes indicated by the Freundlich exponent (n) were similar for both materials. 4. Discussion 4.1. Effect of the combustion temperature on sorption properties of charcoal Except for R850, surface areas of laboratory-produced charcoals in published studies are generally comparable with our data. The surface area of 600 m2 g 1and a microporosity of 90% as observed for R850 exceeds the maximum values found in the literature. According to Sander and Pignatello (2005), N2-BET surface areas for typical charcoals ranged from 200–500 m2 g 1. However, literature data (Nguyen et al., 2004; James et al., 2005) and our own results suggest that surface areas of charcoals may change considerably with varying combustion temperatures and precursor materials. Surface areas and the pore volumes appear to escalate, and the pore size distribution shifts to a mostly microporous pattern above a critical temperature. According to Hellwig (1985), combustion temperatures of 250 C are only sufficient to cause the evolution of volatiles, whereas at temperatures as high as 450 C the softening of the woody material is already initiated. Results of Haghseresht et al. (1999), who examined carbonaceous

1039

adsorbents using 13C NMR, indicated that increased heat treatment results in enhanced contribution of aromatic structures and an increase of amorphous carbon and molecular disorder, thereby having impact on amount and size of micropores. Although the amount of micropores is still low, the maximum peak for the pore widths of about 1.1 nm for the material combusted at 450 C (Fig. 1) is displaying the beginning of micropore formation. It is noteworthy that despite a significantly higher hydrophobicity of toluene (benzene: KOW = 134.9; toluene: KOW = 498.8), the calculated maximum uptake (Smax) on R850 was in about the same order of magnitude for both sorbates in the single-sorbate systems, as well as in the bisorbate system. Especially the results of the bi-sorbate experiments are consistent with the theory of Chiou et al. (2000) and indicate the pore filling mechanism. According to the assumption of an universal adsorbate for the pore filling process, the amount of adsorbed benzene and toluene should be about the same when identical volumes of the sorbates are added. Furthermore, the suppression of the sorbed amount of benzene and toluene from the respective competitor in the bi-sorbate system compared to the singlesorbate system should be about 50% and almost identical for both sorbates, since the densities of benzene and toluene are differing only slightly (benzene: 0.879 g ml 1; toluene: 0.866 g ml 1). As seen in Table 2, the calculated maximum uptake for benzene and toluene in the bi-sorbate experiment was indeed identical for each sorbate and about the half of the calculated capacities in the single-sorbate experiments. Considering that in the bi-sorbate system the two sorbates were added in identical amounts, condensation of the sorbates in the pores of this highly microporous material (Table 1) could explain the observed phenomenon. This is also supported by studies of Zhu and Pignatello (2005), addressing pore filling as the most likely dominant process for the sorption of aromatic compounds on such materials. In their study, the sorptive abilities of a charcoal from maple wood shavings were compared with that of (non-porous) graphite as a model. The experiments displayed size exclusion effects on the charcoal for compounds exceeding a certain molecular size, and enhanced sorption on the charcoal compared to the graphite, despite a charcoal graphite partition coefficient >1. By investigating the effect on pore blocking by lipids on the same material as used by Zhu and Pignatello (2005), Kwon and Pignatello (2005) showed that benzene sorption is largely located in the interior pore work. Still, essential differences are apparent between the material used by Zhu and Pignatello (2005) and the charcoals used in our study. The surface area of the maple wood charcoal (400 m2 g 1) examined by Zhu and Pignatello (2005) was considerably lower than the one of our R850 material (605 m2 g 1). Also the microporosity of our material (90%, Table 1) exceeds the one of the char from maple wood shavings (80%). The degree of non-linearity of the sorption process increases with increasing microporosity (after the Polanyi–Manes model), and might thus explain that the isotherms for our R850 could be described by the

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Langmuir model, whereas the isotherms for the maple wood char showed better fit to a Freundlich sorption isotherm. The sorption on charcoals produced at lower temperature in our study also fitted better to Freundlich model. Kleineidam et al. (2002) investigated the sorption of different low-polarity organic compounds on a series of carbonaceous adsorbents, covering humic soil organic matter, thermally altered carbon materials, and purely engineered microporous sorbents. Employing the PM-model combined with linear partitioning for sorbents containing humic material, they were able to predict unique sorption isotherms by employment of solubility normalized aqueous concentrations. Their results suggest that the PM-model is the most appropriate model for sorption processes on highly porous materials. However, some concerns about potential artefacts resulting from enhanced water adsorption to functional groups of sorbents with varying hydrophilicity have been expressed (Li et al., 2005). Also recent results by Yang et al. (2006) showed that gaps in the understanding of the PM-model still exist. Their study revealed, that the molar volume alone (as employed e.g. by Sander and Pignatello, 2005) in some cases may fail to be an appropriate scaling factor in order to obtain matching isotherms of hydrophobic compounds with varying molecular sizes. Although the PM-model is increasingly used for modelling of sorption processes, our results among with those of other researchers (e.g. Xia and Ball, 2000) show that the classical approaches like the Freundlich model and the Langmuir model may still be adequate in some cases. These models are appropriate here, as the aim of our investigations was to detect general differences in the sorptive properties of various charcoals, rather than seeking a specific mechanism or an improvement in modelling of sorption isotherms. The higher sorption of toluene in comparison with benzene on R250 and R450 (Fig. 3a and b; Table 2) is possibly due to its higher hydrophobicity. However, toluene sorption in single and bi-sorbate system was the same, showing no competitive effect. Sander and Pignatello (2005) examined the competitive sorption of benzene, toluene, and nitrobenzene on the charcoal mentioned above, which was also utilized by Zhu and Pignatello (2005). In their bi-sorbate experiments, the amount of competitive sorbate was kept constant while the concentration of the test sorbate changed. From their resulting competitive sorption isotherms it can be seen that competition effects were most pronounced when the competitor solutes were added at high concentrations together with a low concentration of test sorbate. Competition effects diminished as the concentrations of the two competing sorbates converged. This explains the lack of significant competition effect from either sorbate in our bi-sorbate systems, as in our experiments both sorbates were always added in equal concentrations. In our bi-sorbate experiments, the sorption of benzene on R250 and R450 was even enhanced compared to the singlesorbate system (Fig. 3a and b; Table 2). The reasons for this are unclear, but may be related to the ability of aromatic compounds like benzene and toluene to cause the swelling

of charcoal particles. Jonker and Koelmans (2002) found in their experiments that different solvents exhibited varying abilities to extract PAHs from soot and sediments and proposed a two-step mechanism. According to them, the PAHs are being extracted by an initial swelling of the sorbent matrix with a subsequent displacement of sorbates by solvent molecules. Among a selection of seven popular solvents, also comprising two mixtures of benzene and other solvents, toluene was proven to be the best suited solvent for the extraction of PAHs from charcoal. Therefore, the enhanced sorption of benzene in the bi-sorbate systems may result from a toluene-induced swelling of the matrix, thereby opening up additional sorption sites for the smaller benzene molecules and toluene itself being sterically hindered to penetrate by its larger molecular size. Braida et al. (2003) proved that certain benzene concentrations were able to induce the swelling of charcoal matrices, thereby increasing the sorption capacity and inducing sorption hysteresis by pore deformation and solvent entrapment. 4.2. Influence of the precursor material on the sorption process The lower (33%) sorption capacity of P850 compared to R850 (Table 2) is ascribed to the physicochemical differences between the respective materials. Although the exposure time to the heat treatment was already reduced due to the more combustible nature of the grass, the charred grass appeared to be much more disaggregated compared to the wood charcoal. A more extensive combustion, resulting in the loss of sorption active constituents may have resulted in the reduced sorption capacity. James et al. (2005) found that surface area, pore volume, and microporosity are not increasing endlessly with increasing combustion temperatures, and that softening temperatures are also dependent on the precursor material. In their study, a heating temperature of 820 C resulted in drastically reduced surface areas and microporosity for a charcoal from Betula pendula, compared to charcoal produced at a temperature of 700 C. For Auraucaria araucana, the softening temperature was already reached at 450 C. Another explanation for the reduced sorption capacities could be the overall higher cation content in Phalaris grass compared to Red Gum wood (Table 1). As the charcoal was weighed in as bulk, and was not corrected for its content of mineral constituents, a higher cation content reduces not only the proportion of highly sorptive BC in the bulk, but also increases the hydrophilic character of the whole sample. The latter is true as these cations are present as salts, their hydrophilic character hindering the sorption of hydrophobic components. Haghseresht et al. (1999) found that the content of aromatic carbon in the precursor correlated with the contribution of amorphous carbon in the corresponding charcoal. A high amount of amorphous carbon results in an increased abundance of sorption-active edge sites as well as in an increased disorder, thereby supporting the formation of micropores and increasing the sorption capacity

L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

(Haghseresht et al., 1999). The content of aromatic carbon in plant tissue is mainly governed by its lignin content. The lignin content of hardwood (35%) (Anderson and Tillmann, 1977) is considerably higher than the one for grasses, with values ranking between 3% and 10% (Butler and Bailey, 1973). We suggest that also the slightly lower sorption capacity of Phalaris charcoals is likely to be the combined effect of their smaller surface area, stronger hydrophilic effects from mineral salts, and lower lignin content.

Appendix A Table of symbols Cf Kd KF KL n q Smax

5. Conclusions The results from the present studies demonstrated that charcoals prepared under different combustion temperatures exhibit substantially different physicochemical and thus also sorptive properties, especially if a critical ‘‘softening temperature’’ is exceeded during combustion. For the observed precursor materials, this critical temperature was within the scope of temperatures observed for wildfires (200–1000 C) (Raison, 1979; Scott, 1989). The charcoals derived from herbaceous material expressed basically comparable sorptive patterns to wood charcoals. However, their mineral contents were higher, whereas the N2-surface areas and sorption capacities were lower than for the wood charcoals. The observed highly non-linear sorption behaviour of R850 and P850 showed better fits to Langmuir isotherms than to Freundlich isotherms and was most likely indicative of pore filling processes on the highly microporous charcoal studied here. The surface area varied orderly with increasing combustion temperature among the observed charcoals and gave a good indication for the sorptive abilities of the charcoals. Also other parameters such as hydrophobicity and swelling of the sorbing matrix seemed to be important for sorption of aromatic hydrocarbons, as indicated by the enhanced sorption of benzene on R250, R450, and P250 in the presence of toluene. More work is needed to establish the effect of combustion conditions on the nature of charcoals and their subsequent impact on sorption and desorption behaviour of organic contaminants.

Acknowledgements The measurement of pore size distributions was conducted by Dr. Alexander Badalyan (University of South Australia), N2 BET-SSA and total cation contents were determined by Mr Lester Smith (CSIRO Australia). Ms Natasha Waller (CSIRO) provided valuable technical assistance during these studies. The authors would like to thank Dr. Sonja Brodowski (University of Bonn) and Dr. G.-G. Ying (CSIRO) for their comments on the manuscript. Ludger Bornemann was partially funded by the ‘‘Studienstiftung des deutschen Volkes’’ while working on this project at CSIRO laboratories in Adelaide.

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SW V vmicro VP vtotal dp DVads Drslit

final sorbate concentration (mg ml 1) soil water partition coefficient (l kg 1) Freundlich affinity coefficient (mln mg1 n g 1) Langmuir affinity coefficient Freundlich exponent sorbed amount of sorbate per mass of sorbent (mg g 1) maximum sorbate uptake (mg kg 1) (Langmuir model) water solubility (mg l 1) total volume (ml) volume of micropores (mlliq g 1) vapour pressure (mm HG at 20 C) total pore volume (mlliq g 1) pore diameter (nm) incremental amount of nitrogen absorbed (mlliq g 1) incremental width of slit pores (nm)

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Boston and New York harbour sediments. Environ. Sci. Technol. 39, 141–148. Manes, M., 1998. Activated carbon adsorption fundamentals. In: Meyers, R.A. (Ed.), Encyclopedia of Environmental Analysis and Remediation. John Wiley, New York, pp. 6–68. Nguyen, T.H., Brown, R.A., Ball, W.P., 2004. An evaluation of thermal resistance as a measure of black carbon content in diesel soot, wood char, and sediment. Org. Geochem. 35, 217–234. Patterson, W.A., Edwards, K.J., Maguire, D.J., 1987. Microscopic charcoal as a fossil indicator of fire. Quat. Sci. Rev. 6, 3–23. Raison, R.J., 1979. Modifications of the soil environment by vegetation fires: a review. Plant Soil 51, 73–108. Sander, M., Pignatello, J.J., 2005. Characterization of charcoal adsorption sites for aromatic compounds: insights drawn from single-solute and bi-solute competitive experiments. Environ. Sci. Technol. 39, 1606– 1615. Schmidt, M.W.I., Noack, A.G., 2000. Black carbon in soils and sediments: analysis, distribution, implications and current challenges. Global Biogeochem. Cycles 14, 777–793. Scott, A.C., 1989. Observations on nature and origin of fusain. Int. J. Coal Geol. 12, 443–475. Shafizadeh, F., 1984. The chemistry of pyrolysis and combustion. In: Rowell, R.M. (Ed.), The Chemistry of Solid Wood. Am. Chem. Soc., Washington, DC, pp. 481–529. Skjemstad, J.O., Clarke, P., Golchin, A., Oades, J.M., 1997. Characterization of soil organic matter by solid-state 13C NMR Spectroscopy. In: Cadish, G., Giller, K.E. (Eds.), Driven by Nature: Plant Litter Quality and Decomposition. CAB International, Wallingford, UK, pp. 53–271. Smernik, R.J., Kookana, R.S., Skjemstad, J.O., 2006. NMR characterization of 13C-benzene sorbed to natural and prepared charcoals. Environ. Sci. Technol. 40, 1764–1769. Xia, G., Ball, W., 2000. Polanyi-based models for the sorption of lowpolarity organic contaminants on a natural sorbent. Environ. Sci. Technol. 34, 1246–1253. Yang, K., Zhu, L., Xing, B., 2006. Adsorption of polycyclic aromatic hydrocarbons by carbon nanomaterials. Environ. Sci. Technol. 40, 1855–1861. Yu, X.Y., Ying, G.G., Kookana, R.S., 2006. Sorption and desorption behaviour of diuron in soil amended with charcoal. J. Agric. Food Chem. 54, 8545–8550. Zhu, D., Pignatello, J.J., 2005. Characterization of aromatic compound sorptive interactions with black carbon (charcoal) assisted by graphite as a model. Environ. Sci. Technol. 39, 2033–2041. Zhu, D., Kwon, S., Pignatello, J.J., 2005. Adsorption of single ring organic compounds to wood charcoals prepared under different thermochemical conditions. Environ. Sci. Technol. 39, 3990–3998.

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Sorption and Desorption Behaviors of Diuron in Soils Amended with Charcoal XIANG-YANG YU,†,‡ GUANG-GUO YING,†,§

AND

RAI S. KOOKANA*,†

Downloaded by UNIV OF GEORGIA on August 4, 2009 Published on October 11, 2006 on http://pubs.acs.org | doi: 10.1021/jf061354y

CSIRO Land and Water, Adelaide Laboratory, PMB 2, Glen Osmond 5064, South Australia, Australia; Food Safety Research Institute, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; and Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

Charcoal derived from the partial combustion of vegetation is ubiquitous in soils and sediments and can potentially sequester organic contaminants. To examine the role of charcoal in the sorption and desorption behaviors of diuron pesticide in soil, synthetic charcoals were produced through carbonization of red gum (Eucalyptus spp.) wood chips at 450 and 850 °C (referred to as charcoals BC450 and BC850, respectively, in this paper). Pore size distribution analyses revealed that BC850 contained mainly micropores (pores ≈ 0.49 nm mean width), whereas BC450 was essentially not a microporous material. Short-term equilibration (<24 h) tests were conducted to measure sorption and desorption of diuron in a soil amended with various amounts of charcoals of both types. The sorption coefficients, isotherm nonlinearity, and apparent sorption-desorption hysteresis markedly increased with increasing content of charcoal in the soil, more prominently in the case of BC850, presumably due to the presence of micropores and its relatively higher specific surface area. The degree of apparent sorption-desorption hystersis (hysteresis index) showed a good correlation with the micropore volume of the charcoal-amended soils. This study indicates that the presence of small amounts of charcoal produced at high temperatures (e.g., interior of wood logs during a fire) in soil can have a marked effect on the release behavior of organic compounds. Mechanisms of this apparent hysteretic behavior need to be further investigated. KEYWORDS: Diuron; sorption; desorption; soil; charcoal; carbonization; hysteresis

INTRODUCTION

Black carbon (e.g., soot and charcoal) produced from the incomplete combustion of vegetation and fossil fuel is ubiquitous in terrestrial and aquatic environments (1, 2). In addition to dispersal through biomass and fossil fuel combustion in the environment, some agricultural practices may also contribute to the increasing amount of black carbon in agricultural soils. For example, it is an old practice in the eastern and southern parts of China to mix firewood ashes with soils and livestock dung followed by heating and aging for several months, before the mixture is added directly into the field as a fertilizer. Direct burning of plant residues in the field after harvest for land clearing is common all over the world. Such agricultural practices will also provide direct input of black carbon into agricultural soil (3-6). Terrestrial black carbon, being erosionprone, is readily transported by wind and water and is often deposited into aquatic ecosystems. Black carbon has been found to make a significant proportion of soils and sediments: 15* Corresponding author (e-mail [email protected]; fax +61 8 83038565). † CSIRO Land and Water. ‡ Jiangsu Academy of Agricultural Sciences. § Chinese Academy of Sciences.

30% of total organic matter in marine sediments (7) and 1231% of deep-sea sediments (8), 18-41% of the soils and sediments collected from the suburban area of Guangzhou, China (9), up to 30% of soils collected around Australia (4, 10), and up to 45% of total organic carbon (TOC) in soils collected from Germany (11). It has been well recognized that the presence of charcoal in soil could not only enhance the sorption of organic contaminants such as pesticides (12) but also influence the nature of the sorption mechanism (13). Research in recent years (14) has shown that the residues produced from burning wheat and rice were 400-2500 times more effective than soil in sorbing diuron over the concentration range of 0-6 mg/L in water. However, the effect of these amendments on the desorption behavior of diuron was not investigated in that study. The nature and properties of black carbon are strongly affected by the nature of parent materials (wood, grass) and the temperature experienced during combustion (2, 15). Charcoals formed from lignocellulosic materials under conditions of pyrolysis become increasingly carbonized as temperatures rise above 500 °C and are completely carbonized as temperatures approach 1000 °C (15). Under relatively high pyrolysis temperatures (500-700 °C), the charcoal derived from wheat was

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found to be well carbonized and had a relatively high surface area and low oxygen content (16). Such chars have been reported to show high affinity for organic compounds (16, 17), especially for polar solutes (16). Despite the fact that the environmental fate and impact of contaminants (bioaccessibility, bioavailability, and toxicological impact) are strongly influenced by their desorption behavior (18-21), the effect of black carbon on the desorption behavior of compounds has so far received limited attention. Braida et al. (22) observed pronounced hysteresis in the sorption of benzene in water to pure-form maple-wood charcoal prepared by oxygen-limited pyrolysis. Here they found that the sorption of wood charcoal was highly irreversible and proposed that hysteresis was due to pore deformation of charcoal during desorption of the sorbate, leading to entrapment of molecules as the polyaromatic scaffolding collapsed during desorption. The objective of this study was to assess the effect of the presence of small amounts of charcoal materials (prepared from eucalyptus wood at two different temperatures of 450 and 850 °C) in soil on the sorption-desorption behaviors of pesticides in soil. Sorption and desorption behaviors were investigated to assess the role of the types and amounts of charcoal as sorbent for pesticides (represented by diuron as a model nonionic pesticide) in soils amended with various amounts of charcoals. EXPERIMENTAL PROCEDURES Chemicals. Diuron [N-(3,4-dichlorophenyl)-N,N-dimethyl urea, with purity >99%] was obtained from Sigma-Aldrich (Sydney, Australia). Diuron is a nonionic urea herbicide with a very wide use globally. The herbicide is nonvolatile (vapor pressure is 1.1 × 10-3 mPa at 25 °C), has a water solubility of 36.4 mg/L, and is stable in neutral media. Its reported average soil half-life is in the range of 90-180 days (23). Sodium azide was obtained from Fluka (Sydney, Australia). Calcium chloride of analytical grade and all solvents of HPLC grade were obtained from Merck Pty. Ltd. (Victoria, Australia). A stock solution of 100 mg/L of diuron was prepared in methanol. Charcoal, Soil, and Sorbent. Charcoals were prepared from red gum wood (Eucalyptus spp.), at two different temperatures, namely, 450 and 850 °C (BC450 and BC850, respectively). Red gum woodchips were air-dried at 40 °C, and pieces of <5 mm were hand picked for the carbonization process. The woodchips were placed in porcelain crucibles with lids in a temperature-programmable muffle furnace (S.E.M., Australia). The temperature of the furnace was ramped to the defined temperature (450 or 850 °C) and held for 2 h for BC450 and for only 1 h for BC850. The prepared black carbon materials were ground to a fine powder on a disk-rotating mill for 3 min. The specific surface areas (SSA) of the two charcoals were evaluated using the Brunauer, Emmett, and Teller (BET) nitrogen adsorption technique (24) at 77 K, using an automated manometric gas adsorption apparatus (25) and ultrahigh-purity gaseous nitrogen (99.999%, from BOC Gases). The details of the method and uncertainties associated with the measurement have been published elsewhere (25). Outgassing of the charcoal was carried out at 300 °C for 8 h at a background vacuum of 1 × 10-4 Pa, similar to that used for charcoal samples by Braida et al. (22). For the pore volume evaluation, we employed RSplot analysis, where the adsorption properties of a porous solid are compared with those of a nonporous standard material exhibiting surface chemistry similar to that of the test sample (25). Moisture content was determined by comparison of sample mass before and after evacuation at 300 °C. We classified pore width (dp) according to the International Union of Pure and Applied Chemistry (IUPAC) recommendations as follows: micropores, dp < 2 nm; mesopores, 2 < dp < 50 nm; and macropores, dp > 50 nm. Pores smaller than 2 nm were analyzed using the Horvath-Kawazoe (H-K) method (26). This method calculates the effective micropore size distribution of slit-shape pores using the data from adsorption isotherms. Using the H-K equation we calculated the effective mean width of slit pores (dp) and correlated it with the

Yu et al. value of ∆Vads/∆rslit, where ∆Vads is the incremental amount of nitrogen adsorbed (converted to condensed liquid volume of nitrogen) and ∆rslit is the corresponding incremental width of slit pores. The individual and cumulative frequencies were calculated for a range of dp data. Other properties of these chars as characterized using NMR techniques have been published elsewhere (27). The soil used in this experiment was collected from the Roseworthy Campus, University of Adelaide, and was amended with charcoal. After air-drying, the soil was passed through a 2 mm sieve. This soil contained 87.8% sand, 1.3% silt, 8.3% clay, and 1.4% organic matter and is of sandy loam texture. The soil pH value was 6.8 in a 1:5 (soil/water) soil suspension and had a maximum water-holding capacity of 34.2% (v/v) and a cation exchange capacity of 9.3 cmol(+)/kg. The soil was sterilized by autoclaving at 120 °C under 300 kPa chamber pressure for 30 min three times within 3 days. Charcoal-amended soils used in the experiment were prepared by mixing the above soil and the two types of charcoal at different ratios. The percentages of charcoal materials in the amended soils were 0, 0.1, 0.5, 1.0, 2.0, and 5.0% (w/w) for BC450 and 0, 0.1, 0.2, 0.5, 0.8, and 1.0% (w/w) for BC850. The charcoal-amended soils were thoroughly mixed on a rotary shaker for 7 days before their use as sorbents for sorption and desorption experiments. Sorption and Desorption Isotherms. Diuron sorption by the sorbents was measured by the batch equilibration technique. Preliminary kinetic experiments showed sorption and desorption of diuron in charcoal-amended soils reached an apparent equilibrium within 24 h. Although sorption is known to continue for days at a very slow rate, for the comparative assessment between different chars under similar conditions, the 24 h shaking time was deemed to be adequate for the purposes of this study. The sorbents were suspended in 10 mL of 0.01 M CaCl2 solutions (containing 0.5% NaN3 to inhibit microbial activity) spiked at concentrations from 1 to 27 mg/L of diuron. The amounts of charcoal-amended soil used in the experiments were adjusted to allow for 30-80% of the added chemical to be sorbed at equilibrium. On the basis of our preliminary experiments, for BC450-amended soil an aliquot of 1.0 g of soil was used for 0, 0.1, 0.5, 1.0, and 2.0% and only 0.2 g of soil for 5.0%. For BC850-amended soils, an aliquot of 0.5 g of soil was used for 0.1 and 0.2% and only 0.2 g for 0.5, 0.8, and 1.0% amendment. The suspensions were shaken on a rotary shaker at room temperature (22 ( 2 °C) at 120 rpm for 24 h and then centrifuged at 4000 rpm for 60 min. After centrifugation, an aliquot of the supernatant in each tube was taken out and analyzed directly by highperformance liquid chromatography (HPLC). Each sorption test was carried out in triplicate. Losses during the test were monitored by including two blank controls in each test: one tube that had only a chemical solution without any sorbent and the other control tube that had only the sorbent and CaCl2 solution without chemical. Tests showed losses due to adsorption to glassware and degradation were negligible, and no interferences were found during the analysis of solutions. This is consistent with previous studies and the nature of the chemical (persistent and nonvolatile). Desorption experiments were conducted for those samples with the highest sorption loading. After 24 h of equilibration, the tubes were centrifuged and 5 mL of the supernatant in each tube was taken out for analysis. Another 5 mL of 0.01 M CaCl2 (including 0.5% NaN3) was added into each tube, and the tubes were shaken for 24 h again. The desorption process was repeated three more times for each tube. All tests were performed in triplicate. Pesticide Analysis. Analysis of diuron in the supernatant fraction from sorption and desorption experiments was carried out on an Agilent 1100 series high-performance liquid chromatograph (HPLC) fitted with a diode array detector and an SGE C18 RS column (250 × 4.6 mm, 5 µm). Acetonitrile (ACN) and water were used as the mobile phase, which was programmed from 36% ACN at 0 min to 80% ACN at 6 min at a flow rate of 1 mL/min. The UV wavelength for detection of diuron was 248 nm. The detection limit for diuron was 0.03 mg/L. Data Analysis. The sorption and desorption isotherms were fitted with the linear form of the Freundlich equation

log Cs ) log Kf + N log Cw

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where Cw is the concentration of the chemical in solution, Cs is the concentration of the chemical in the sorbent, Kf is the Freundlich sorption coefficient, and N is the exponent indicative of sorption mechanism. The sorption-desorption apparent hysteresis index (H) was determined by the equation (28)

H ) N/Nd where N and Nd are the Freundlich exponents calculated from the sorption and desorption isotherms, respectively.

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RESULTS AND DISCUSSION

Characteristics of Charcoals. Upon carbonization at 450 and 850 °C, 100 g of red gum chips produced about 36.1 and 28.8 g of charred materials, respectively. These are relatively higher yields of charcoal than those derived from burning crop residues (29). The color was gray to black for the BC850, whereas for BC450 it was a little brown to black. The relatively lower mass that remained under higher burning temperature indicates that BC850 is carbonized to a greater degree than BC450. The higher mass recovery of red gum chip-derived charcoal is believed to be due to the more condensed structure of wood chips than that of crop residues. For the charcoal BC450, the shape of the nitrogen adsorption isotherm was similar to that for nonporous materials (Figure 1A), suggesting a negligibly small micropore volume (30). In contrast, the BC850 is a microporous material with a high specific surface area. The initial steep portion of the adsorption isotherm for BC850 is indicative of the presence of micropores in the charcoal material (30). The SSA for BC850 was much higher than that of charcoal BC450 (Table 1) and also higher than wheat-residue-derived chars, the highest SSA of which was reported to be 438 m2/g (charred at 600 °C) (16). Chun et al. (16) also found char surface area to increase with increasing charring temperatures (300600 °C); however, SSA measurement of char produced at 700 °C was lower than that of char produced at 600 °C, which they speculated to be due to microporous structures which were destroyed at 700 °C. Charcoal BC450 has a very low level of microporosity (peak maxima occurred at a pore width of about 1.1 nm) (Figure 2). This may indicate the beginning of micropore formation at 450 °C. Increasing the preparation temperature, as in the case of charcoal BC850, clearly promoted the formation of micropores with the maximum peak occurring for pore widths of about 0.49 nm and essentially all pores <1 nm in pore width. From the pore volume values listed in Table 1, we regard charcoal BC450 as a non-microporous material. Therefore, the lower temperature (450 °C) used for the preparation of charcoal materials did not lead to the formation of microporous structure. In contrast, charcoal BC850 is predominantly a microporous material with about 89.6% of volume from micropores (in terms of specific micropore volume). It is customary to express the total specific pore volume (V pore total) of an adsorbent as the liquid volume adsorbed at a certain value of relative pressure (P/P0 ) 0.95) (31). The gaseous nitrogen volume adsorbed at this value of relative pressure was converted into a liquid volume of nitrogen. For mixed-pore materials, the mesopore volume is determined as the difference between the total specific pore volume and total specific micropore volume. Sorption-Desorption Isotherms and Their Nonlinearity. The presence of charcoal in the soil caused the sorption isotherms to change progressively into highly nonlinear, concavedownward-shaped isotherms (Figures 3 and 4). Most of the data on sorption and desorption isotherms fitted well to the Freund-

Figure 1. Nitrogen adsorption/desorption isotherm for (A) BC450 and (B) BC850. Table 1. Characteristics of Black Carbon Materialsa BC burning temp (°C) abbrev 450 850

SSA (m2/g)

BC450 27.330.035 BC850 566.390.31

moisture content (%) 11.7 9.9

micro V total [mL (liq)/g]

pore V total [mL (liq)/g]

0.00374 ± 0.00004 0.02219 ± 0.00004 0.2469 ± 0.0039 0.2757 ± 0.0015

a V micro ) volume of total specific microspore; V pore ) volume of specific total total microspore and total specific pore.

lich equation (Table 2); however, at the highest level of charcoal amendment, the fit was noted to be relatively poor in both types of chars. Instead, the data showed a much better fit to the Langmuir model in these cases. The increasing Freundlich sorption coefficient Kf values and decreasing N values with charcoal content in soil (Table 2) show that the sorption capacity of diuron on charcoal-amended soils gradually increased with increasing content of charcoal in soil. The N values decreased from 0.83 to 0.25 and 0.16, respectively, for BC450 and BC850,

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Figure 3. Influence of BC450 on sorption and desorption of diuron in soil. (Inset) Sorption−desorption on unamended soil and on 0.1% BC450.

Figure 4. Influence of BC850 on sorption and desorption of diuron in soil. (Inset) Sorption−desorption on unamended soil and on 0.1% BC850. Table 2. Freundlich Constants for the Sorption (Kf, N) and Desorption (Kfd, Nd) of Diuron on Soil Amended with Charcoal and the Calculated Hysteresis Index (H)

Figure 2. Pore size distribution for (A) BC450 and (B) BC850. Using the Horvath−Kawazoe (H−K) method (26), we calculated the effective mean width of slit pores, dp, and plotted against the value of ∆Vads/∆rslit, where ∆Vads is the incremental amount of nitrogen adsorbed (converted to condensed liquid volume) and ∆rslit is the corresponding incremental width of slit pores.

as the amount of charcoal in soil increased from 0.1 to 5.0% of BC450 and to 1.0% of BC850 (Table 2). Highly nonlinear sorption isotherms and high sorption capacity for organic compounds on sorbents (e.g., soils and sediments) containing black carbon have been observed in a number of studies (e.g., refs 32-35). Soil organic carbon has commonly been hypothesized to consist of an amorphous phase and a condensed phase of organic carbon (36, 37), which are considered to be responsible for partitioning and sorption, respectively. Depending upon the relative contents of the two phases of organic carbon, sorption by soils and sediments could range from linear partitioning to highly nonlinear sorption (34, 38, 39). Due to the highly nonlinear nature of isotherms, a comparison of sorption affinities among the charcoal-amended soils needs to be calculated for a specific solution concentration [e.g., Cw

content of charcoal in charcoal soil (%)

Kf

original soil

4.08 0.83 0.9974

N

R2

Kfd

Nd

R2

5.40 0.73 0.9975

H 1.14

BC450

0.1 0.5 1.0 2.0 5.0

4.47 28.0 514 109 314

0.82 0.45 0.37 0.34 0.25

0.9994 11.1 0.9983 47.5 0.9979 78.6 0.9958 168 0.9980 427

0.48 0.23 0.21 0.12 0.10

0.9944 0.9990 0.9977 0.9772 0.8784

BC850

0.1 0.2 0.5 0.8 1.0

25.3 72.8 224 350 500

0.37 0.32 0.22 0.21 0.16

0.9979 0.9911 0.9875 0.9928 0.9249

0.28 0.09 0.04 0.02 0.01

0.9958 1.32 0.9926 3.54 0.9990 5.14 0.9004 9.75 0.8194 14.92

39.5 138 371 576 727

1.69 1.93 1.79 2.87 2.37

of 1 mg/L, where Kf ) Kd(Cs/Cw)]. On this basis the sorption capacities of the charcoal amended soil were 7-80 times for BC450 and 5-125 times for BC850 in comparison to that of charcoal-free soil (Table 2). The sorption contribution of even small additions of charcoals to the soil (0.5% of BC450 and 0.1% of BC850) was very high indeed (>85%), assuming no change in inherent sorption capacity of soil. This shows that the presence of even small amounts of highly carbonaceous black carbon (charcoal, soot, or other carbonaceous materials) can dominate sorption of an organic compound in soils and sediments. Desorption Behavior and the Role of Microporosity. Sorption and desorption isotherms were compared to assess the

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Sorption/Desorption of Diuron in Charcoal-Amended Soils degree of reversibility of sorption reaction. Due to the short equilibration time (24 h) employed here, it is not appropriate to refer to the discrepancy between the sorption and desorption flanks of the isotherms as true hysteresis. This is because the sorption kinetics may have been slow and the sorption reaction may have continued beyond the point in time when the desorption part of experiment was initiated. Nevertheless, a comparison of these isotherms does provide an assessment of the impact of the nature of sorbate on the desorption behavior of diuron or lack of it. For the purposes of this study, by hysteresis we mean “apparent hysteresis”. The highly nonlinear sorption isotherm and relatively flat desorption isotherm in Figures 3 and 4 provide visual evidence of apparent sorption-desorption hysteresis on the charcoalamended soils. We calculated the hysteresis index (H), defined as the N/Nd ratio (28), to quantify the degree of apparent hysteresis. The H values for all of the sorbents are listed in Table 2. For the original soil sample the H value was 1.14, indicating minimal desorption hysteresis. As the content of charcoal in the soil increased, the value of H also increased. For the soils amended with charcoal BC850, the H values increased rapidly from 1.32 for the soil with 0.1% of charcoal to 14.92 for 1.0% of charcoal. For the soils amended with charcoal BC450 the H value also progressively increased but at a slower rate. The results showed that besides the high sorption capacity, charcoal produced under higher temperature either had stronger sorption or provided domains for diffusion of sorbate into micropores. In this way the more microporous structure may lead to effective sequestration of a compound. This is consistent with the studies reporting poor bioavailability and bioaccessibility of organic compounds sorbed on black carbon materials (40, 41). Comparison of the results for the two types of charcoal materials also revealed that although the sorption capacity of a soil could be enhanced to the same level by adding differential amounts of chars (0.8% BC850 vs 5% BC450), the degree of reversibility was quite different between the two charcoals. In the present study, the discrepancy between sorption and desorption isotherms at comparable levels of sorption (e.g., 0.8% BC850 vs 5% BC450, Table 2) was clearly much more prominent in the case of charcoal BC850. To assess if a link between the microporosity and apparent desorption hysteresis exists, we plotted the values of the total pore volume for each sorbent calculated from the V pore total value and the content of charcoal material in the soil against the apparent hysteresis index (H) in Figure 5. Here, we assumed that the soil free of charcoal is a nonporous material and that the pore volume of the charcoal-amended soils was mainly provided by the added charcoal. Figure 5 shows a good relationship between these two parameters; the H index increased exponentially (y ) 1.582 e0.008x, R2 ) 0.8982) as the total pore volume of the sorbent increased. A smaller increase in H value at lower pore volume is essentially associated with the presence of charcoal BC450 and only small amounts of BC850. This is because charcoal BC450 had a negligible proportion of micropores, whereas in BC850 essentially all pores existed as micropores of <1 nm width. These micropores either entrapoed the sorbed molecules of diuron or caused a slow and prolonged sorption phase, which may have led to the apparent hysteresis due to nonequilibrium processes. Braida et al. (22) noted swelling of a sorbent during benzene sorption and suggested pore deformation during desorption causing desorption hysteresis. It has also been suggested in other studies that surface-specific adsorption, entrapment into micropores, and partitioning into

8549

Figure 5. Relationship between total pore volume and apparent hysteresis

index (H).

condensed structures of soil organic matter are among the main causes of chemical sequestration (35-37, 42-45). Conclusions. This study showed that the presence of small amounts of black carbon in the form of charcoals in soil, especially those produced at high temperatures (e.g., interior of wood logs during a fire), can have a major effect on the sorption and desorption behaviors of organic compounds such as the diuron pesticide. The marked effect on the desorption of highly carbonaceous materials such as charcoal produced at high temperatures is expected to have strong implications for the bioavailability of such compounds in terrestrial and aquatic ecosystems. The role of such carbonaceous materials on sorption-desorption kinetics and bioavailability needs to be further investigated. ACKNOWLEDGMENT

We acknowledge the contributions by Drs. Phillip Pendleton and Alexander Badalyan (University of South Australia) in measuring pore size distribution; Jan Skjemstad and Evelyn Krull (CSIRO) for advice and comments on synthetic char production; Tasha Waller and Sonia Grocke (CSIRO) for technical support; and Dr. Ron Smernik (University of Adelaide) for helpful comments on the manuscript. LITERATURE CITED (1) Goldberg, E. D. Black Carbon in the EnVironment; Wiley: New York, 1985. (2) Schmidt, M. W. I.; Noack, A. G. Black carbon in soils and sediments: analysis, distribution, implication, and challenges. Global Biogeochem. Cycles 2000, 14, 777-793. (3) Schmidt, M. W. I.; Knicker, H.; Hatcher, P. G.; Ko¨gel-Knabner, I. Impact of brown coal dust on the organic matter in particlesize fractions of a Mollisol. Org. Geochem. 1996, 25, 29-39. (4) Skjemstad, J. O.; Clarke, P.; Taylor, J. A.; Oades, J. M.; McClure; S. G. The chemistry and nature of protected carbon in soil. Aust. J. Soil Res. 1996, 34, 251-271.

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(5) Guo, L. P.; Erda, L. Carbon sink in cropland soils and the emission of greenhouse gases from paddy soils: a review of work in China. Chemosphere: Global Change Sci. 2001, 3, 413-418. (6) Young, R.; Wilson, B. R.; Mcleod, M.; Alston, C. Carbon storage in the soils and vegetation of contrasting land uses in northern New South Wales, Australia. Aust. J. Soil Res. 2005, 43, 2131. (7) Middelburg, J. J.; Nieuwenhuize, J.; Breugel, P. V. Black carbon in Marine sediment. Mar. Chem. 1999, 65, 245-252. (8) Masiello, C. A.; Druffel, E. R. M. Black carbon in deep-sea sediments. Science 1998, 280, 1911-1913. (9) Song, J. Z.; Peng, P. A.; Huang, W. L. Black carbon and kerogen in soils and sediments: 1. Quantification and characterization. EnViron. Sci. Technol. 2002, 36, 3960-3967. (10) Schmidt, M. W. I.; Skjemstad, J. O.; Czimczik, C. I.; Glaser, B.; Prentice, K. M.; Gelinas, Y.; Kuhlbusch, T. A. J. Comparative analysis of black carbon in soils. Global Biogeochem. Cycles 2001, 15, 163-167. (11) Schmidt, M. W. I.; Skjemstad, J. O.; Gehrt, E.; Ko¨gel-Knabner, I. Charred organic carbon in German chernozemic soils. Eur. J. Soil Sci. 1999, 50, 351-365. (12) Hilton, H. W.; Yuen, Q. H. Adsorption of several pre-emergence herbicides by Hawaiian sugar cane soils. J. Agric. Food Chem. 1963, 11, 230-234. (13) Yamane, V. K.; Green, R. E. Adsorption of ametryn and atrazine on an oxisol, montmorillonite and charcoal in relation to pH and solubility effects. Soil Sci. Soc. Am. Proc. 1972, 36, 58-64. (14) Yang, Y. N.; Sheng, G. Y. Enhanced pesticide sorption by soils containing particulate matter from crop residue burns. EnViron. Sci. Technol. 2003, 37, 3635-3639. (15) Allen-King, R. M.; Grathwohl, P.; Ball, W. P. New modeling paradigms for the sorption of hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments and rocks. AdV. Water Resour. 2002, 25, 985-1016. (16) Chun, Y.; Sheng, G. Y.; Chiou, C. T.; Xing, B. S. Compositions and sorptive properties of crop residue-derived chars. EnViron. Sci. Technol. 2004, 38, 4649-4655. (17) Sheng, G. Y.; Yang, Y. N.; Huang, M. S.; Yang, K. Influence of pH on pesticide sorption by soil containing wheat residuederived char. EnViron. Pollut. 2005, 134, 457-463. (18) Alexander, M. How toxic are toxic chemicals in soil? EnViron. Sci. Technol. 1995, 29, 2713-2717. (19) Nam, K.; Alexander, M. Role of nanoporosity and hydrophobicity in sequestration and bioavailability: tests with model solids. EnViron. Sci. Technol. 1998, 32, 71-74. (20) Huang, W. L.; Yu, H.; Weber, Jr., W. J. Hysteresis in the sorption and desorption of hydrophobic organic contaminants by soils and sediments. 1. A comparative analysis of experimental protocols. J. Contam. Hydrol. 1998, 31, 129-148. (21) Kan, A. T.; Fu, G.; Hunter, M.; Chen, W.; Ward, C. H.; Tomson, M. B. Irreversible sorption of neutral hydrocarbons to sediments: experimental observations and model predictions. EnViron. Sci. Technol. 1998, 32, 892-902. (22) Braida, W. J.; Pignatello, J. J.; Lu, Y.; Ravikovitch, P. I., Naimark, A. V.; Xing, B. Sorption hysteresis of benezene in charcoal particles. EnViron. Sci. Technol. 2003, 37, 409417. (23) Tomlin, C. D. S. The Pesticide Manual, 12th ed.; British Crop Protection Council: Surrey, U.K., 2000. (24) Brunauer, S.; Emmett, P. H.; Teller, J. Adsorption of gases in multimolecular layers, J. Am. Chem. Soc. 1938, 60, 309-319. (25) Badalyan, A.; Pendleton, P. Analysis of uncertainties in manometric gas-adsorption measurements. I: Propagation of uncertainties in BETAnalyses. Langmuir 2003, 19, 7919-7928. (26) Horvath, G.; Kawazoe, K. Method for the calculation of effective pore size distribution in molecular sieve carbon. J. Chem. Eng. Jpn. 1983, 16, 470-475. (27) Smernik, R. J.; Kookana, R. S.; Skjemstad, J. O. NMR characterization of 13C-benzene sorbed to natural and prepared charcoals. EnViron. Sci. Technol. 2006, 40, 1764-1769.

Yu et al. (28) Sanchez-Camazano, M.; Sanchez-Martin, M. J.; Rodriguez-Cruz, M. S. Sodium dodecyl sulphate-enhanced desorption of atrazine: effect of surfactant concentration and of organic matter content of soils. Chemosphere 2000, 41, 1301-1305. (29) Yang, Y. N.; Sheng, G. Y. Pesticide adsorptivity of aged particulate matter arising from crop residue burns. J. Agric. Food Chem. 2003, 51, 5047-5051. (30) Gregg, S. J.; Sing, K. S. W. Adsorption, Surface Area and Porosity; Academic Press: London, U.K., 1982. (31) Rouquerol, F.; Rouquerol, J.; Sing, K. Adsorption by Powders and Porous Solids; Academic Press: San Diego, CA, 1999. (32) Kleineidam, S.; Schu¨th, C.; Ligouis, B.; Grathwohl, P. Organic matter facies and equilibrium sorption of phenanthrene. EnViron. Sci. Technol. 1999, 33, 1637-1644. (33) Accardi-Dey, A.; Gschwend, P. M. Reinterpreting literature sorption data considering both absorption into organic carbon and adsorption onto black carbon. EnViron. Sci. Technol. 2003, 37, 99-106. (34) Cornelissen, G.; Gustafson, O. Sorption of phenanthrene to environmental black carbon in sediment with and without organic matter and native sorbates. EnViron. Sci. Technol. 2004, 38, 148155. (35) Huang, W. L.; Peng, P. A.; Yu, Z. Q.; Fu, J. M. Effects of organic matter heterogeneity on sorption and desorption of organic contaminants by soils and sediments. Appl. Geochem. 2003, 18,955-972. (36) Xing, B. S.; Pignatello, J. J. Dual-mode sorption of low-polarity compounds in glassy poly (vinyl chloride) and soil organic matter. EnViron. Sci. Technol. 1997, 31, 792-799. (37) Weber, W. J., Jr.; Mcglnley, P. M.; Katz, L. E. A distributed reactivity model for sorption by soils and sediments. 1. Conceptual basis and equilibrium assessment. EnViron. Sci. Technol. 1992, 26, 1955-1962. (38) Huang, W. L.; Weber, W. J., Jr. A distributed reactivity model for sorption by soil and sediments. 10. Relationships between desorption, hysteresis, and the chemical characteristics of organic domains. EnViron. Sci. Technol. 1997, 31, 2562-2569. (39) Chiou, C. T.; Kile, D. E.; Rutherford, D. W. Sorption of selected organic compounds from water to a peat soil and its humic-acid and humin fractions: potential sources of the sorption nonlinearity. EnViron. Sci. Technol. 2000, 34, 1254-1258. (40) Yang, Y. N.; Sheng, G. Y.; Huang, M. Bioavailability of diuron in soil containing wheat-straw-derived char. Sci. Total EnViron. 2006, 354, 170-178. (41) Zhang, P.; Sheng, G. G.; Feng, Y.; Miller, D. M. Role of wheatresidue-derived char in the biodegradation of benzonitrile in soil: nutritional stimulation versus adsorptive inhibition. EnViron. Sci. Technol. 2005, 39, 5442-5448. (42) Ghosh, U.; Gillette, J. S.; Luthy, R. G.; Zare, R. N. Microscale location, characterization, and association of polycyclic aromatic hydrocarbons on harbor sediment particles. EnViron. Sci. Technol. 2000, 34, 1729-1736. (43) Ahmad, R.; Kookana, R. S.; Alston, A. M.; Skjemstad, J. O. The nature of soil organic matter affects the sorption of pesticides. 1. Relationship with carbon chemistry as determined by 13C CPMAS NMR spectroscopy. EnViron. Sci. Technol. 2001, 35, 878-884. (44) Abelmann, K.; Kleineidam, S.; Knicker, H.; Grathwohl, P.; Ko¨gel-Knabner, I. Sorption of HOC in soils with carbonaceous contamination: Influence of organic-matter composition. J. Plant Nutr. Soil Sci. 2005, 168, 1-14. (45) Lu, Y. F.; Pignatello, J. J. Demonstration of the “conditioning effect” in soil organic matter in support of a pore deformation mechanism for sorption hysteresis. EnViron. Sci. Technol. 2002, 36, 4553-4561. Received for review May 12, 2006. Revised manuscript received August 31, 2006. Accepted September 4, 2006.

JF061354Y

Science of the Total Environment 354 (2006) 170 – 178 www.elsevier.com/locate/scitotenv

Bioavailability of diuron in soil containing wheat-straw-derived char Yaning Yanga,c, Guangyao Shenga,T, Minsheng Huangb a Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701, U.S.A. Department of Environmental Science and Technology, East China Normal University, Shanghai 200062, P.R. China c Department of Civil and Environmental Engineering, University of Illinois, Urbana, IL 61801, U.S.A.

b

Received 19 October 2004; accepted 26 January 2005 Available online 23 March 2005

Abstract This study evaluated the bioavailability of diuron in soil as influenced by char arising from the burning of wheat straw. The wheat char was a highly effective sorbent for diuron. The presence of 1% wheat char in soil resulted in a 7–80 times higher diuron sorption. A 10-week incubation resulted in b40% of 0.5 mg/kg diuron in 0.5% char-amended soil microbially degraded, as compared to 50% in char-free soil under the same conditions. Over the experimental range of diuron application rates from 0 to 12 mg/kg and of char contents from 0% to 1.0%, a 4-week bioassay indicated that both the barnyardgrass survival rating and the fresh weight of aboveground biomass decreased with increasing diuron application at given char contents but increased with increasing char content at potentially damaging diuron application rates. Residual analyses of bioassayed soils showed that the soils with char contents of 0.5% and higher and diuron application rates of 3.0 mg/kg and higher, as compared to those with no or low (0.05%) char and a diuron application rate of 1.5 mg/kg, had higher residual diuron levels but higher barnyardgrass survival ratings and fresh weights. These results suggest that enhanced sorption of diuron in soil in the presence of wheat char reduced the bioavailability of diuron, as manifested by reduced microbial degradation of diuron and its herbicidal efficacy to barnyardgrass. This study may have greater implication than for burning of wheat straw that field burning of vegetations may reduce bioavailability of pesticides. D 2005 Elsevier B.V. All rights reserved. Keywords: Bioavailability; Diuron; Microorganism; Barnyardgrass; Sorption; Wheat char

1. Introduction Many studies have suggested that soil-bound organic contaminants are unavailable for microbial T Corresponding author. Tel.: +1 479 575 6752; fax: +1 479 575 3975. E-mail address: [email protected] (G. Sheng). 0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2005.01.026

degradation (Ogram et al., 1985; Shimp and Young, 1988; Steen et al., 1980). Although recent research suggested that limited biodegradation of soil-sorbed pesticides may occur (Feng et al., 2000; Park et al., 2001, 2002, 2003), liquid-phase contaminants are much more bioaccessible to soil microorganisms (Ogram et al., 1985; Guerin and Boyd, 1992; Lahlou and Ortega-Calvo, 1999). Other studies have estab-

Y. Yang et al. / Science of the Total Environment 354 (2006) 170–178

lished that phytotoxicity of herbicides is directly related to their concentrations in the soil solution (e.g., Lambert, 1966; Pillay and Tchan, 1971). It is generally true that only dissolved nutrients and organic chemicals in the soil interstitial bulk-like water (i.e., plant-available water above the wilting point) are available for plant-root uptake. Sorption largely controls concentrations of organic contaminants in the soil solution and thus is the major determinant of the bioavailability of pesticides to both microorganisms and plants. Enhancing sorption by increasing soil organic matter content leading to a reduction in the solution-phase concentrations results in a decreased microbial degradation of organic contaminants (e.g., Guerin and Boyd, 1993). Charcoal dipping or banding effectively protects many plants from herbicidal injury (Arle et al., 1948; Burr et al., 1972; Chandler et al., 1978; Jordan and Smith, 1971; William and Romanowski, 1972). Sorptive properties of agricultural soils, and thus bioavailability of pesticides, are often influenced by agricultural practices. Field burning of crop residues worldwide incorporates the resulting chars into soils. Hilton and Yuen (1963) postulated that the retained sorptivity of many Hawaiian soils for ureas and striazines after oxidative removal of soil organic matter by hydrogen peroxide was a result of the peroxideresistant soil chars arising from burning of sugarcane trash. Toth et al. (1999) observed a reduction in the phytotoxicity of diuron applied over the ash of recently burned kangaroo grass, due primarily to the diuron sorption by the ash. We confirmed their postulation by measuring the sorption of pesticides on soil-free chars from burning of crop residues. Sorption of diuron by the chars from burning of wheat straw and rice residue was 400–2500 times higher than that by a soil with 2.1% organic matter (Yang and Sheng, 2003a). Amendment of the soil with the wheat char up to 1% (by weight) enhanced the sorptivity of the soil for diuron in proportion to the char content. The char aged in the soil for one month remained highly effective for diuron sorption and dominated the sorption, although a small reduction (b30%) in sorptivity was observed (Yang and Sheng, 2003b). Further aging of the char for up to 12 months did not result in a further sorptivity reduction, indicating that the char was resistant to degradation. One direct consequence of the high sorptivity of crop-residue-

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derived chars may be the reduced bioavailability of pesticides in soils to both microbes and plants. The reduction in microbial degradation of benzonitrile in a soil in the presence of wheat char has been reported (Zhang et al., 2004). Reduced microbial degradation increases the persistence of pesticides and thus the environmental risk associated with pesticide use. The high sorptivity of crop-residue-derived chars may also reduce herbicidal efficacy to weeds. Poor herbicidal efficacy is a concern both economically and environmentally due to additional application of herbicides for weed control. In this study, we determined the bioavailability of diuron to soil microorganisms and to barnyardgrass (Echinochloa crus-galli (L.) Beauv.) in soil in the presence of wheat-straw-derived char. Use of barnyardgrass, a common rice weed, has both agronomic and environmental significance. Our objectives were to determine the microbial degradation of diuron and its efficacy to barnyardgrass in relation to soil sorption in the presence of wheat char and to evaluate the impact of crop-residue-derived chars on the bioavailability of pesticides in soil. Results from laboratory measurements and greenhouse bioassays indicated that wheat char was a highly effective sorbent for diuron and its presence in soil resulted in enhanced diuron sorption and subsequently diminished bioavailability.

2. Materials and methods 2.1. Materials Wheat char used in this study was from our previous studies (Yang and Sheng, 2003a,b). Airdried wheat (Triticum aestivum L.) straw (10 kg) was collected from the Arkansas Agricultural Research and Extension Center in Fayetteville, Arkansas. Wheat char was obtained by burning the straw on a stainless steel plate (1 m  1 m) in an open field under natural conditions in a July afternoon. The BET surface area of the char was determined to be 10.1 m2/ g in a commercial service laboratory. Chemical analysis showed that the char contained 13% elemental carbon and 42% silica. Soil, classified as Stuttgart silt loam, was collected at the Rice Research and Extension Center, Stuttgart,

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Arkansas. The soil had a mechanical composition of 17.1% sand, 60.4% silt, and 22.5% clay. The soil contained 2.1% organic matter and had a cationexchange capacity of 8.5 cmolc/kg. The soil, without records of crop residue burns, was presumed to contain minimal levels of chars. The soil was air-dried, ground, and passed through a 1-mm sieve. Char-amended soils were prepared by thoroughly mixing soil with accurately weighed char in exact char contents of 0.05%, 0.1%, 0.5%, and 1.0% (by weight). Diuron with a purity of 99% was purchased from ChemService (West Chester, PA) and used as received. Diuron is an electroneutral molecule. The pesticide has a water solubility of ~42 mg/l and a log K ow of 2.68 at room temperature (Howard and Meylan, 1997). The Henry’s Law constant of 2.710 6 atm m3/mol indicates that the pesticide is non-volatile and therefore suitable for prolonged laboratory and greenhouse studies. Diuron is a urea compound primarily used as a preemergence herbicide in soils to control germinating grasses and broad-leaved weeds. As a photosynthesis inhibitor, diuron injures weeds with symptoms of foliar chlorosis concentrated around veins (sometimes interveinal) followed by necrosis. A mixed diuron-degrading culture was isolated from soil collected in a cotton field where diuron has been applied annually for over 15 years. One gram of the soil was inoculated into 100 ml of medium containing mineral salts (Stanier et al., 1966), 0.1 ml of vitamin solution (Wolin et al., 1963), and saturated diuron. The mixture was incubated for 1 week at 28 8C on a platform shaker at 150 rpm. After two serial transfers to fresh medium, the culture enrichment was obtained. Preliminary tests showed that the isolated culture readily degraded diuron in solution. Barnyardgrass seeds, collected from the plant grown in a rice field in Stuttgart, AR in 1983, were acid-scarified in 1 N nitric acid for 1 h at room temperature. The seeds were washed with deionized water, spread evenly on filter paper in petri dishes, covered with another filter paper, watered with 3 ml of deionized water, and incubated in the dark at room temperature for 72 h for germination. 2.2. Sorption isotherms for diuron Sorption of diuron by soil, wheat char, and 1% char-amended soil was measured by the batch

equilibration technique. Various quantities of diuron in 0.005 M CaCl2 solution were added into 25-ml Corex glass centrifuge tubes containing sorbents with a constant mass between 0.01 and 3.5 g. The mass of sorbents was adjusted to allow for N40% of added diuron to be adsorbed. Additional 0.005 M CaCl2 solution was added to bring the total liquid volume to 10 ml. Initial concentrations of diuron ranged from 1.25 to 12.5 mg/l. The tubes were closed with Teflonlined screw caps and rotated (40 rpm) at room temperature (~25 8C) for 48 h. Other measurements have shown that sorption of diuron by both the soil and the char reached apparent equilibria within 24 h; the sorption by char-amended soil was thus assumed to also reach equilibrium within the same duration. After the establishment of sorption equilibria, sorbents and aqueous phases were separated by centrifugation at 6000 rpm (RCF=5210 g) for 30 min. The diuron concentrations in supernatants were analyzed by high-performance liquid chromatography (HPLC). The amount of diuron sorbed was calculated from the difference between the amount initially added and that remaining in equilibrium solution. All measurements were in duplicate with a variation generally b5%, and the calculated average data were reported. The measurements with blanks not containing sorbents found that glass tubes did not adsorb diuron and no processes other than sorption contributed to the loss of solution-phase diuron. 2.3. Microbial degradation of diuron Sterilized soil and 0.5% char-amended soil (200 g each) were placed in 1000-ml glass beakers, spiked with 2 ml of 50 mg/l diuron stock solution in acetone, thoroughly mixed, and allowed for acetone to evaporate for 2 days. The soils were then watered to near the field capacity and aged for another 2 days to allow the diuron sorption to complete. Three 5-g samples from each of the soils were extracted with 5 ml of H2O and 5 ml of water-saturated ethyl acetate for 72 h. Following the phase separation, 2 ml of ethyl acetate were dried under N2 gas and redissolved in 1 ml of methanol. The diuron concentrations in methanol were analyzed by HPLC. The recoveries were 95.2% and 85.2% for soil and char-amended soil, respectively. Each soil was inoculated with 5 ml of the isolated culture enrichment. Preliminary tests

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found that 5 ml of the enrichment in 200 g of soil gave an appreciable degree of diuron degradation in one week. The soils were thoroughly mixed again. The beakers were then covered with aluminum foil and placed in the dark at room temperature. Three 5-g soil samples from each beaker were taken weekly for 10 weeks for diuron analysis. The soils were extracted following the same extraction procedures as those for the recoveries, except that extracting water contained 0.5% Ag2SO4 to immediately terminate biodegradation. The diuron concentrations were adjusted for the recoveries. The soils, watered when necessary, were maintained moist throughout the degradation experiment. 2.4. Barnyardgrass bioassay for diuron A series of 4 diuron solutions with concentrations of 60, 120, 240, and 480 mg/l in acetone were prepared. Five milliliters of each of the solutions, along with acetone only, were added to 200 g of charfree soil or char-amended soils in plastic bags, resulting in the diuron levels of 0, 1.5, 3.0, 6.0, and 12 mg/kg in the soils, respectively. The five diuron levels were referred to as 0X, 1X, 2X, 4X, and 8X, where X=1.5 mg/kg and is within the range of recommended field application rates. The five char contents were 0%, 0.05%, 0.1%, 0.5%, and 1%. The combination of the 5 diuron rates and the 5 char contents resulted in a total of 25 treatments. Each treatment was in triplicate. The soils were thoroughly mixed in the bags, and transferred to plastic cups following the evaporation of acetone from the opened bags. A small quantity of soil (~20 g) was first removed from each cup. Ten pregerminated barnyardgrass seeds with extended radicles and hypocotyls were placed evenly on the soil surface in each cup and then covered with the previously removed soil. Following planting, the cups were placed in a completely randomized block design in a greenhouse, watered with 40 ml of deionized water, and maintained moist throughout the experiment. The greenhouse was maintained at 34/20 8C day/night temperatures with a 14-h lighting cycle. Barnyardgrass seedling survival was visually rated two weeks after planting as percent of survival between 0 and 100, with 0% representing no survival and 100% complete survival (no injury).

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The survival rating was performed independently by three individuals. Average survival ratings were calculated using the data from the replicated samples from all the individuals. Four weeks after planting, plants were cut at the soil level and immediately weighed to obtain the fresh weights of the aboveground biomass. All the visual survival rating and fresh weight data were statistically analyzed using the SAS program. Following the bioassay, the soil samples of selected treatments were analyzed for residual diuron by HPLC using the extraction procedures described earlier. The average diuron concentration of the replicate soils of the same treatment was reported. The soils from the following 6 treatments were selected based on the char contents, diuron rates, and barnyardgrass aboveground fresh weights: S0-0, S0-1.5, S0.05-1.5, S0.5-3.0, S1-3.0, and S1-6.0, where the suffix C-D to S represents the char content (C)-applied soil concentration of diuron (D). 2.5. Analysis of diuron Diuron in the supernatants from sorption experiments and in the extracts from microbial degradation and greenhouse bioassay tests was analyzed on a Hitachi reversed-phase high-performance liquid chromatograph (Hitachi High-Technologies Tokyo, Japan) fitted with a UV-visible detector set at the maximum absorption wavelength for diuron (252 nm). A Phenomenex Prodigy C18 column was used (Alltech Assoc., Deerfield, IL). The mobile phase was a mixture of acetonitrile and water (50:50, v/v) at a flow rate of 1.0 ml/min. The injection volume was 20 Al.

3. Results and discussion Isotherms for the sorption of diuron by soil, wheat char and 1% char-amended soil are presented in Fig. 1, in which the amount of diuron sorbed (mg/kg) is plotted against the equilibrium concentration (mg/l) in water. No single mathematical models provided adequate fits for the sorption data. The curves were drawn to assist in visualization and comparison of the data. Soil effectively sorbed diuron, rather consistent with the prediction from the log K ow value of diuron

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100 Soil 1% Wheat Char in Soil

80 9000

60

6000 Wheat Char

3000

40

0 0

2

4

6

20 0 0

2

4

6

8

10

Equilibrium Concentration (mg/L) Fig. 1. Isotherms for sorption of diuron from water by soil, wheat char, and char-amended soil.

and the soil organic matter content. Wheat char had a much higher sorptivity than soil for diuron (see the inset in Fig. 1). From the curves, we estimated that the char was 700–37,000 times more effective than the soil in sorbing diuron over the experimental concentration range (0–6 mg/l). These results are similar to those obtained in our previous study (Yang and Sheng, 2003a). It has also been reported in the literature that chars (the term ash was used) derived from burning of vegetation are effective adsorbents for pesticides (Yang and Sheng, 2003b; Toth and Milham, 1975). Much higher sorptivity of wheat char than of soil resulted in enhanced sorption of diuron by the soil in the presence of the char, as indicated in Fig. 1. Calculations show that 1% char-amended soil sorbed about 7–80 times more diuron than char-free soil over the experimental concentration range. Assuming that the amendment of soil with 1% char did not change the sorptivity of the soil for diuron, 1% char contributed N86% to the total sorption of diuron, indicating the predominance of the char for diuron sorption. Normalization of the sorption to char content resulted in a diuron isotherm slightly lower than that for soil-free char, which may have resulted from the competitive sorption of dissolved soil organic matter on the char. While the diuron sorption by charamended soil was evaluated with only one char content, enhanced sorption at other char contents is expected. At recommended field application rates, enhanced diuron sorption in the presence of wheat

char may decrease the concentration of diuron in the soil solution, leading to reduced biodegradation and loss of herbicidal efficacy. An evaluation of the bioavailability of diuron to soil microorganisms in the presence and absence of wheat char in soil was made by comparing the degradation of diuron in char-free soil and 0.5% char-amended soil, both inoculated with the same size of an isolated diuron-degrading culture. The initial diuron concentration in both soils was 0.5 mg/kg. We simply measured the dissipation of diuron over incubation time and did not identify the degradation products, thus offering no mechanistical information on the diuron transformation reaction. In Fig. 2, the degradation is expressed as the percent of total diuron degraded at given time. Although diuron is a rather persistent pesticide in field soils, it slowly degraded in field soils (Hill et al., 1955). It has been reported that mixed cultures from pond water and sediment aerobically degraded diuron to several identified products and carbon dioxide (Ellis and Camper, 1982). While we did not know the species and the population of the isolated cultures, diuron in both soils was degraded with time. The degradation was slower in charamended soil than in char-free soil. Over a 10-week incubation, b40% of diuron in 0.5% char-amended soil was degraded, in comparison to about 55% in char-free soil. While direct degradation of soil-sorbed organic compounds by bacteria may occur, we did not know whether such a process was involved in diuron degradation. However, our results clearly show that 60

Diuron Degraded (%)

Amount of Diuron Sorbed (mg/kg)

174

50 40 30 20 Soil 0.5% Wheat Char in Soil

10 0 0

20

40

60

80

Incubation Time (days) Fig. 2. Microbial degradation of diuron over time in sterilized soil and char-amended soil inoculated with a mixed enrichment culture.

Y. Yang et al. / Science of the Total Environment 354 (2006) 170–178

rate at a given char content and decreased with increasing char content at a given diuron application rate. The observation is consistent with the earlier sorption measurements that the presence of wheat char enhanced the diuron sorption by soil. By four weeks after planting (prior to cutting), uninjured barnyardgrass showed continued growth, whereas injured ones did not recover (Fig. 3). More quantitative barnyardgrass bioassay to evaluate the impact of wheat char on the bioavailability of diuron was obtained by visually rating barnyardgrass survival two weeks after planting and by weighing aboveground fresh biomass four weeks after planting (Fig. 4). Without application of diuron, barnyardgrass was somehow injured in char-free soil. In the presence of wheat char (z0.05%), the injury was eliminated. This suggests that unknown herbicides likely phytotoxic to barnyardgrass may be present in char-free soil but deactivated by the char. A full rate of diuron (1.5 mg/kg) in char-free soil showed almost complete injury to barnyardgrass. However, both the barnyardgrass survival rating and fresh weight increased with increasing char content. A char content of 0.5% or higher was sufficiently high that diuron completely lost its efficacy to barnyardgrass. The application rates of 3 mg/kg and higher resulted in complete-to-partial losses of diuron efficacy to barnyardgrass. Similar to the observations with the full rate of diuron, the

1.0 0.5 0.1 0.05 0.0

0.0

1.5

3.0

6.0

Wheat Char in Soil (%)

enhanced sorption in the presence of wheat char reduced the bioavailability of diuron to soil microorganisms. Reduced biodegradation of benzonitrile by a bacterium in soil in the presence of wheat char was also due to enhanced sorption (Zhang et al., 2004). In addition to elemental carbon and silica, wheat char contained 21% potassium, 1.5% phosphorous, 0.64% nitrogen, and other microelements (Yang and Sheng, 2003b). When in their available forms in soil, some of these nutrients may stimulate microbial activity. We have found that when benzonitrile was not limiting, 1% wheat char provided nutritional stimulation on benzonitrile degradation (data not shown). Such a stimulation on diuron degradation in 0.5% charamended soil was not obvious. Fig. 3 is the photograph comparing the barnyardgrass growth among the soil samples subjected to diuron applications in the absence and presence of wheat char just prior to cutting the plants for their fresh weights. The samples consisted of 25 cups, each representing one of the three replicates for each of all the treatments, and were placed de-randomized to aid visualization. In the absence of diuron application, barnyardgrass showed a normal growth without observable growth stimulation by wheat char nutrients. One week after planting, the barnyardgrass injury was obvious (photograph not shown). The injury increased with increasing diuron application

175

12

Application Rate of Diuron (mg/kg) Fig. 3. Photograph showing barnyardgrass growth in soils as a function of diuron application rate and wheat char content four weeks after planting.

176

Y. Yang et al. / Science of the Total Environment 354 (2006) 170–178

(b)

100

0.05

) ) Fresh Weight (g

0.04

80

0.03

ron (m

12

g/kg)

nt

0

Rate

1.5 3.0

of Diu

6.0

ron (m

0 12

ar

6.0

0

Ch

of Diu

0.00

nte

nt

(%

Rate

1.5 3.0

Co

0

ar

0

)

1.0 0.5 0.1 0.05

0.01

(%

1.0 0.5 0.1 0.05

20

0.02

n te

40

Co

60

Ch

Survival Rating

(%)

(a)

g/kg)

Fig. 4. Growth of barnyardgrass in soils as a function of diuron application rate and wheat char content showing (a) survival rating of barnyardgrass two weeks after planting, and (b) fresh weight of barnyardgrass four weeks after planting.

survival rating and fresh weight at higher application rates increased with increasing char content over the tested range of char contents in soil. The Student’s t test at the 95% level of confidence (a=0.05) was used to compare the individual survival ratings and fresh biomass weights at various char contents and diuron application rates. Survival ratings and fresh weights were statistically different (a=0.05) for V0.05% char with no diuron application, for V0.5% char with 1.5 mg diuron/kg, for z0.1% char with 3.0 mg or 6.0 mg diuron/kg (fresh weights were significantly different forz0.5% char with 6.0 mg diuron/kg), and for z0.5% char with 12 mg diuron/kg. These results suggest the decreased bioavailability of diuron to barnyardgrass with increasing char content in soil, due presumably to enhanced sorption of diuron in the presence of the char. The sorptive role of wheat char in reducing diuron bioavailability (efficacy) to barnyardgrass is confirmed by measuring residual concentrations of diuron in soils after cutting barnyardgrass. Soils from 6 selected treatments, where barnyardgrass fresh weights differed significantly, were analyzed for residual diuron. The concentrations in the three replicate soils of each treatment were highly invariant, with the difference b4.3%. The average concentrations were calculated and presented in Table 1. Charfree soil (S0-0) did not contain a measurable level of diuron. All other soils that had received diuron

contained residual diuron with levels of about 40– 49% of their respective application rates. The soils S01.5 and S0.05-1.5 containing no or low char (0% and 0.05%, respectively) had residual diuron concentrations of ~0.7 mg/kg and produced much lower barnyardgrass fresh weights than the soil S0-0, indicating the availability of diuron to barnyardgrass in these soils. Although the soils S0.5-3.0 and S1-3.0 containing 0.5% and 1% char, respectively, had residual diuron concentrations almost twice those in the soils S0-1.5 and S0.05-1.5, the barnyardgrass fresh weights associated with the former two soils were much higher than those with the latter two. In fact, the barnyardgrass fresh weights with the soils Table 1 Relationship between measured residual concentrations of diuron and barnyardgrass fresh weights in selected soil and char-amended soil samples subjected to various treatments four weeks after planting as influenced by percent char content and application rate of diuron Soil

Rate of Barnyardgrass Residual Char content diuron fresh fresh weight (g) concentration weight (g) (mg/kg) (%)

S0-0 S0-1.5 S0.05-1.5 S0.5-3.0 S1-3.0 S1-6.0

0 0 0.05 0.5 1 1

0 1.5 1.5 3.0 3.0 6.0

0.0242 0.0007 0.0030 0.0224 0.0308 0.0378

0.00 0.73 0.69 1.28 1.20 2.42

Y. Yang et al. / Science of the Total Environment 354 (2006) 170–178

S0.5-3.0 and S1-3.0 were similar to that with char-free soil without receiving diuron application (i.e. the soil S0-0). The barnyardgrass fresh weight with the soil S1-6.0 containing an even higher level of residual diuron remained high. These results indicate that diuron in soils with high contents of wheat char was largely unavailable to barnyardgrass. Our measurements indicate that at typical application rates of diuron, a char content of as low as 0.1% may appreciably reduce the bioavailability of diuron in soil. We reported that burning of wheat straw produced wheat char at ~6% of the straw weight (Yang and Sheng, 2003a). Using the average production of wheat straw of ca. 6000 kg/ha, its burning would generate ~360 kg/ha wheat char. If this wheat char were mixed in soil with a density of 1.4 g/cm3 to the depth of furrow slice (~0.15 m), a single burning would result in a wheat char content of~0.02%. Cropresidue-derived chars are expected to accumulate in soils, as crop residues are repeatedly burned, and the resulting chars are expected to remain to be highly effective sorbents for pesticides (Yang and Sheng, 2003b). As such, field burning of crop residues may effectively reduce the bioavailability of pesticides.

4. Conclusions Wheat char is a highly effective sorbent for diuron. Field burning of wheat straw incorporates the resulting wheat char into soil and enhances the sorption of diuron by the soil. A direct consequence of this agricultural practice is the reduced bioavailability of diuron in soil. We found that diuron was less biodegradable in soil in the presence of wheat char. Its herbicidal efficacy to barnyardgrass decreased with increasing char content in soil and, at recommended field application rates, could be completely lost when the soil char content was 0.5% or higher. Reduced bioavailability of diuron appeared to result from the enhanced sorption in soil in the presence of wheat char. Although only wheat char and diuron were tested in this study, it is expected that chars arising from field burning of other crop residues and vegetations also effectively sorb other pesticides and reduce their bioavailability. The presence of crop-residue-derived chars in soil may increase the environmental risk of pesticides and reduce their efficacy to pests.

177

Acknowledgments This research was supported by USDA National Research Initiative Competitive Grants Program (Grant No. 2002-35107-12350).

References Arle HF, Leonard OA, Harris VC. Inactivation of 2,4-D on sweetpotato slips with activated carbon. Science 1948;107:247 – 8. Burr RJ, Lee WO, Appleby AP. Factors affecting use of activated carbon to improve herbicide selectivity. Weed Sci 1972; 20:180 – 3. Chandler JM, Wooten OB, Fulgham FE. Influence of placement of charcoal on protection of cotton (Gossypium hirsutum) from diuron. Weed Sci 1978;26:239 – 44. Ellis PA, Camper ND. Aerobic degradation of diuron by aquatic microorganisms. J Environ Sci Health 1982;B17:277 – 89. Feng Y, Park J-H, Voice TC, Boyd SA. Bioavailability of soilsorbed biphenyl to bacteria. Environ Sci Technol 2000;34: 1977 – 84. Guerin WF, Boyd SA. Differential bioavailability of soil-sorbed naphthalene to two bacterial species. Appl Environ Microbiol 1992;58:1142 – 52. Guerin, WF, Boyd, SA Bioavailability of sorbed naphthalene to bacteria: influence of contaminant aging and soil organic carbon content. Sorption and degradation of pesticides and organic chemicals in soil. SSSA Special Publ No 32. Soil Sci Soc Am and Am Soc Agron, Madison, WI; 1993. p. 197–208. Hill GD, McGahen JW, Baker HM, Finnerty DW, Bingeman CW. The fate of substituted urea herbicides in agricultural soils. Agron J 1955;47:93 – 104. Hilton HW, Yuen QH. Adsorption of several pre-emergence herbicides by Hawaiian sugar cane soils. J Agric Food Chem 1963;11:230 – 4. Howard PH, Meylan WM. Handbook of Physical Properties of Organic Chemicals. Boca Raton, FL7 Lewis Publ.; 1997. 1585 pp. Jordan PD, Smith LW. Adsorption and deactivation of atrazine and diuron by charcoals. Weed Sci 1971;19:541 – 4. Lahlou M, Ortega-Calvo JJ. Bioavailability of labile and desorptionresistant phenanthrene sorbed to montmorillonite clay containing humic fractions. Environ Toxicol Chem 1999;18:2729 – 35. Lambert SM. The influence of soil-moisture content on herbicidal response. Weeds 1966;14:273 – 5. Ogram AV, Jessup RE, Ou LT, Rao PSC. Effects of sorption on biological degradation rates of (2,4-dichlorophenoxy) acetic acid in soil. Appl Environ Microbiol 1985;49:582 – 7. Park J-H, Zhao X, Voice TC. Biodegradation of non-desorbable naphthalene in soils. Environ Sci Technol 2001;35:2734 – 40. Park J-H, Zhao X, Voice TC. Development of a kinetic basis for bioavailability of sorbed naphthalene in soil slurries. Water Res 2002;36:1620 – 8. Park J-H, Feng Y, Ji P, Voice TC, Boyd SA. Assessment of bioavailability of soil-sorbed atrazine. Appl Environ Microbiol 2003;69:3288 – 98.

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Pillay AR, Tchan YT. Phytotoxicity of diuron in some Australian soils. Proc Weed Soc NSW 1971;IV:21 – 4. Shimp RJ, Young RL. Availability of organic chemicals for biodegradation in settled bottom sediments. Ecotoxicol Environ Saf 1988;15:31 – 45. Stanier RY, Palleroni NJ, Doudoroff M. The aerobic pseudomonads: a taxonomic study. J Gen Microbiol 1966;43:159 – 271. Steen WC, Paris OF, Baughman GL. Effects of sediment sorption on microbial degradation of toxic substance. In: Baker RA, editor. Contam Sediments, vol. 1. Ann Arbor, MI7 Ann Arbor Science Publ.; 1980. p. 477 – 82. Toth J, Milham PJ. Activated-carbon and ash-carbon effects on the adsorption and phytotoxicity of diuron. Weed Res 1975; 15:171 – 6. Toth J, Milham PJ, Kaldor CJ. Decreased phytotoxicity of diuron applied over ash of recently burned kangaroo grass (Themeda australis (RBr) Stapf). Plant Prot Q 1999;14:151 – 4.

William RD, Romanowski RR. Vermiculite and activated carbon adsorbents protect direct-seeded tomatoes from partially selective herbicides. J Am Soc Hortic Sci 1972;97:245 – 9. Wolin EA, Wolin MJ, Wolfe RS. Formation of methane by bacterial extracts. J Biol Chem 1963;238:2882 – 6. Yang Y, Sheng G. Enhanced pesticide sorption by soils containing particulate matter from crop residue burns. Environ Sci Technol 2003a;37:3635 – 9. Yang Y, Sheng G. Pesticide adsorptivity of aged particulate matter arising from crop residue burns. J Agric Food Chem 2003b;51:5047 – 51. Zhang P, Sheng G, Wolf DC, Feng Y. Reduced biodegradation of benzonitrile in soil containing wheat-residue-derived ash. J Environ Qual 2004;33:868 – 72.

J. Pestic. Sci., 33(3), 266–270 (2008) DOI: 10.1584/jpestics.G08-08

Note

Simultaneous biodegradation of chloroand methylthio-s-triazines using charcoal enriched with a newly developed bacterial consortium Ken-ichi YAMAZAKI,† Kazuhiro TAKAGI*,†,†† Kunihiko FUJII,††† Akio IWASAKI,††† Naoki HARADA†††† and Tai UCHIMURA† †

Department of Applied Biology and Chemistry, Tokyo University of Agriculture, Setagaya-ku, Tokyo 156–8502, Japan †† Organochemicals Division, National Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki 305–8604, Japan ††† Kowa Research Institute, Kowa Co., Ltd., Tsukuba, Ibaraki 305–0856, Japan †††† Faculty of Agriculture, Niigata University, Nishi-ku, Niigata 950–2181, Japan (Received February 18, 2008; Accepted April 10, 2008)

A special type of charcoal, Charcoal A100, was enriched with a newly developed bacterial consortium using a perfusion method. The bacterial consortium consisted of a methylthio-s-triazine-degrading bacterium (Rhodococcus sp. FJ1117YT) and the chloros-triazine-degrading bacterial consortium CD7 (containing Bradyrhizobium japonicam CSB1, Arthrobacter sp. CD7w and b -Proteobacteria CDB21). Enriched charcoal was capable of degrading chloro-s-triazines (simazine and atrazine) and methylthio-s-triazines (simetryn and dimethametryn) simultaneously in sulfur-free medium. Almost complete degradation was observed after 4-day cultivation of chloro-s-triazines and 9-day cultivation of methylthio-s-triazines. These triazines were mineralized via their 2-hydroxy analogues.

Keywords: biodegradation, methylthio-s-triazines, chloro-s-triazines, bacterial consortium, Charcoal A100.

Introduction The s-triazines are recognized as a major class of herbicides and are widely used in agriculture for controlling various weeds, and they have been detected in ground and surface water.1–3) Among the removal technologies for such residual pesticides, bioremediation is considered to be the most cost-effective and safe technology; therefore, many studies concerning s-triazine-degrading

bacteria have been reported. In our study, bacterial consortium CD74) was obtained which can mineralize simazine, and a degrading bacterium b -Proteobacteria CDB21 was isolated from CD7 by Iwasaki et al.5) It was considered that CD7 was more effective for bioremediation than strain CDB21 because strain CDB21 could not utilize simazine for its growth in mineral salt medium without cyanocobalamin, but CD7 could utilize simazine as sole carbon and nitrogen sources in mineral salt medium.4,5) In addition, a special type of charcoal, Charcoal A100, enriched with CD7 was developed, and was placed under the subsoil of a golf course to degrade simazine. The simazine-degrading capability of the enriched charcoal was maintained for nearly 2 years.4) Thus, Charcoal A100 enriched with CD7 is considered to be an effective material for bioremediation; however, CD7 and strain CDB21 could not degrade methylthio-s-triazines detected in river water,3,6) a lake basin,7) and river sediments,8) while Rhodococcus sp. FJ1117YT9) can transform methylthio-s-triazines to their hydroxyl analogues via sulfur oxidation, and accumulate hydroxy-striazines. It is considered that simultaneous degradation of chloro- and methylthio-s-triazines using a mixture of these bacteria is meaningful because river water3,10) and river sediment3) contamination with both triazines has been reported. To take advantage of these useful properties of CD7 and Charcoal A100, this study describes the development of Charcoal A100 enriched with strain FJ1117YT and CD7, and demonstration of the simultaneous degradation of chloro- and methylthio-striazines using this novel material.

Materials and Methods 1.

2. * To whom correspondence should be addressed. E-mail: [email protected] Published online July 14, 2008 © Pesticide Science Society of Japan

Materials

Simazine, atrazine, simetryn, and dimethametryn were purchased from Kanto Kagaku. Cyanuric acid and simazine-2-hydroxy were purchased from Dr. Ehrenstorfer GmbH. The sulfur-free mineral salt medium (MM) used in this study contained Na2HPO4 · 12H2O 1.2 g/l and KH2PO4 0.5 g/l. Prior to autoclaving, the medium was supplemented with 10 ml/l of a sulfur-free solution of trace elements, which contained MgCl2 · 6H2O 2000 mg/l, FeCl2 · H2O 200 mg/l, ZnCl2 10 mg/l, MnCl2 5 mg/l, CoCl2 24 mg/l, CuCl2 5 mg/l, NiCl2 · 6H2O 5 mg/l, Na2MoO4 5 mg/l, H3BO4 30 mg/l, Ca(OH)2 50 mg/l, and EDTA 500 mg/l. Mineral salt medium containing sulfate (MM
S) was also used. MM
S contained MgSO4 20 mg/l and a solution of trace elements described by YanzeKontchou and Gschwind.11) MM and MM
S were supplemented with s-triazines before autoclaving. Vitamin mixture was used as described by Fujii et al.9)

Analytical methods

The concentration of s-triazines in the medium was determined using HPLC (Tosoh) using the following method. Separation of s-triazines was achieved at 40°C on an ODS column (Capcell Pak C18 UG120 3250 mm, 5 m m particle size; Shiseido) with a mo-

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bile phase containing a gradient mixture of acetonitrile and water (20%/80% 0 min–20%/80% 5 min, linear gradient–40%/60% 11 min, and linear gradient–20%/80% 15 min–20%/80% 20 min). The injection volume was 50 m l and the eluted compounds were detected by UV at 220 nm. Metabolites of s-triazines were determined using LC-ESI-MS. Separation was achieved using LC Alliance 2695 (Waters) system equipped with the same ODS column as above (40°C). A mixture of acetonitrile/0.2% acetic acid was used as the eluent (5%/95% 0 min, linear gradient–50%/50% 10 min–80%/20%10.1 min–80%/20% 15 min, and linear gradient–5%/95% 20 min). The injection volume was 10 m l. The ESIMS system was Quattro micro API (Waters) with the flow rate of nebulization set at 100 l/h and the flow rate for desolvation gas (N2) set at 500 l/h. The respective temperatures of source and desolvation were set at 100 and 350°C; and capillary voltage was 3.5 kV. Detection was performed by scanning between m/z 100 and m/z 300 under cone voltage of 35 V in positive ion mode. Cyanuric acid was detected at m/z 128 [MH] under cone voltage of 23 V in negative ion mode, and simazine-2-hydroxy was m/z 184 [M
H]
under cone voltage of 35 V in positive ion mode.

3.

Enrichment of Charcoal A100 with strain FJ1117YT and CD7

Charcoal A100 (Toyo Denka Kogyo) was used as the enrichment material. Enrichment of charcoal with a bacterial consortium was performed using a charcoal perfusion method, which was modified from the soil perfusion method described by Audus.12) First, washed Charcoal A100 (7.5 g, dry weight) was packed in perfusion apparatus equipped with glass sintered filter, and then autoclaved. Subsequently, three pieces of stab cultures of CD7 on a MM agar plate containing 40 mg/l simazine were placed on the charcoal, and the charcoal layer was covered with glass fiber filter paper. Enrichment was performed in the dark at 25°C. MM (300 ml) containing 5 mg/l simazine was perfused with air lift using an air pump for 14 days. The concentration of simazine in the perfusion fluid was determined by HPLC, and the perfusion fluid was replaced twice. After 14 days, the glass fiber filter paper was replaced. A phosphate buffer suspension of strain FJ1117YT was placed on the filter paper. MM (300 ml) containing 5 mg/l simazine, 5 mg/l simetryn was perfused under similar conditions for 21 days, and the perfusion fluid was replaced once during the perfusion process. Lastly, MM (300 ml) containing 5 mg/l simetryn was used as perfusion fluid for 38 days, and was replaced once. The vitamin mixture was added twice. Total enrichment time was 73 days, and this material was used thereafter. Non-enriched Charcoal A100 was also perfused as a control under the same conditions.

4.

Preparation of DNA and analysis of 16S rRNA gene

Adherent bacteria on the surface of Charcoal A100 enriched with strain FJ1117YT and CD7 were removed by sonication in phosphate buffer for 2 min. Charcoal A100 inhabited with strain FJ1117YT and CD7 was pulverized, and total DNA was extracted with Fast DNA Kit for soil (Q-Bio gene). Total DNA of

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267

strain FJ1117YT and each member of CD7 were extracted from suspensions of bacterial colonies grown on R2A agar (Difco) plates by a protocol for gram-positive bacteria of DNeasy Blood & Tissue Kit (QIAGEN). Nucleotide sequences of 16S rRNA genes of isolated bacteria were analyzed by direct sequencing of the PCR products described previously.5)

5.

Denaturing gradient gel electrophoresis (DGGE) analysis

Touchdown PCR was performed with a TP600 thermal cycler (Takara BIO) using GoTaq Green Master Mix (Promega). GM5Fgc-clamp and R534,13) primers designed from a sequence of the variable V3 region of 16S rRNA, were used for PCR. DGGE analysis was performed using 6% polyacrylamide gel (ratio of acrylamide to bisacrylamide 37.5 : 1) in 1TAE (40 mM Tris base, 20 mM acetic acid, and 1 mM EDTA) with a 30% to 60% denaturant gradient (100% denaturant containing 7 M urea and 40% formamide). Electrophoresis was performed at a constant voltage of 150 V and at a temperature of 60°C for 3.5 h by using the DcodeTM universal mutation detection system (Bio-Rad). After electrophoresis was completed, the gel was stained with SYBR gold (Invitrogen) for 20 min, rinsed, and the bands were visualized with a Molecular Imager Pharos FX plus system (BioRad).

6.

Simultaneous degradation of chloro- and methylthio-s-triazines using Charcoal A100 enriched with strain FJ1117YT and CD7

Charcoal A100 enriched with strain FJ1117YT and CD7 (0.4 g dry weight) was inoculated in MM (30 ml) containing 5 mg/l each of simazine, atrazine, simetryn, and dimethametryn or in MM
S containing 5 mg/l of each herbicide in 50 ml flasks. The flasks were shaken at 120 rpm at 25°C for 15 days. As controls, sterile Charcoal A100 and/or Charcoal A100 enriched with only CD7 were inoculated and shaken under the same conditions. The concentration of s-triazines in the medium was determined periodically by HPLC. Cyanuric acid, simazine-2-hydroxy, and hydroxy analogues of atrazine and dimethametryn in the medium after 15 days were measured by LC-ESI-MS.

Results and Discussion 1.

Enrichment of Charcoal A100 with a bacterial consortium

The extent of enrichment of Charcoal A100 with strain FJ1117YT and CD7 was determined from the change in the concentration of simazine and simetryn in the perfusion fluid. In the first step of enrichment, CD7 was enriched in Charcoal A100. Concentration of simazine in the CD7-inoculated charcoal decreased faster than the control, and the degradation rate of simazine increased with every replacement of the perfusion fluid (data not shown). The charcoal was subsequently further enriched with strain FJ1117YT and perfused with MM containing simazine and simetryn. Simazine was degraded almost immediately (Fig. 1-A until Day21), in contrast to the slow degradation of simetryn (Fig. 1-B until Day21). The disappearance rate of

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Fig. 1. Enrichment of strain FJ1117YT and CD7 in Charcoal A100 using a charcoal perfusion method. Changes in the concentrations of simazine (A) and simetryn (B) during enrichment are illustrated (both figures overlapped until 21 days). Charcoal A100 without enrichment was used as a control. In order to enrich CD7, MM containing 5 mg/l simazine was perfused for 14 days before these data. The arrows indicate as follows: replacement with MM containing simazine and simetryn (black), replacement with MM containing simetryn (white), and addition of vitamin mixture (striped).

simetryn was initialing almost the same as that of control, but increased after the second perfusion (Fig. 1-B on Day8). The decrease of pesticides in sterile Charcoal A100 was considered to occur because pesticides were adsorbed on Charcoal A100. In order to aid the growth of strain FJ1117YT,9) vitamin mixture was added but had little effect on the enrichment of FJ1117YT. However, because the enrichment of CD7 was sufficient, MM containing simetryn without simazine was further perfused (Fig. 1-B after Day21), and the degradation rate of simetryn was further increased. This result indicates the enrichment of strain FJ1117YT in Charcoal A100.

2.

less than 0.1 mg/l and hydroxy analogues of atrazine and dimethametryn were not detected (data not shown). This result suggests that hydroxyl analogues of methylthio-s-triazines, which can not be metabolized by strain FJ1117YT, were mineralized by CD7 via N-ammelide analogue and cyanuric acid. These results also indicate that methylthio-s-triazines could be mineralized by the bacterial consortium that included strain FJ1117YT and CD7. In conclusion, the respective degradation abilities of CD7 and strain FJ1117YT were successfully maintained in Charcoal

Detection of bacterial community in Charcoal A100 enriched with strain FJ1117YT and CD7

Colony isolation from the bacterial consortium CD7 and subsequent analyses of 16S rRNA genes revealed that CD7 consisted of Bradyrhizobium japonicam CSB1, Arthrobacter sp. CD7w and strain CDB21. The presence of all members of CD7 and strain FJ1117YT enriched in Charcoal A100 were confirmed by PCRDGGE analyses (Fig. 2).

3.

Simultaneous degradation of chloro- and methylthio-s-triazines, and detection of their metabolites

Charcoal A100 enriched with strain FJ1117YT and CD7 was applied to simultaneous degradation of chloro- and methylthio-s-triazines. Simazine and atrazine were degraded to by 80–100% with Charcoal A100 enriched with both strain FJ1117YT and CD7 or CD7 alone after 9 days, and were completely degraded after 15 days (Fig. 3-A, B). On the other hand, simetryn and dimethametryn were degraded by over 80% with strain FJ1117YT and CD7 enriched charcoal in sulfur-free medium, but they were not degraded in the presence of sulfate (in MM
S) (Fig 3-C, D). In the sulfur-free medium with strain FJ1117YT and CD7 after 15 days, the concentrations of simazine-2-hydroxy and cyanuric acid were

Fig. 2. PCR-DGGE band profiles of bacterial strains inhabiting Charcoal A100. Each lane represents DNA samples extracted from the following specimens: Charcoal A-100 enriched with FJ1117YT and CD7 (A); FJ1117YT (B); CDB21 (C); CSB1 (D); and CD7w (E).

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Simultaneous biodegradation of chloro- and methylthio-s-triazines

269

Fig. 3. Time course of simultaneous degradation of chloro- and methylthio-s-triazines with Charcoal A100 enriched with strain FJ1117YT and CD7. Degradation of simazine (A), atrazine (B), simetryn (C), and dimethametryn (D) by strain FJ1117YT and CD7 with (
) or without () sulfate, with CD7 alone (), and using non-enriched Charcoal A100 as a control () are shown.

A100. Chloro- and methylthio-s-triazines were degraded simultaneously and their metabolites were hardly detected. The expected metabolic pathways of chloro- and methylthio-s-triazines in the mixed culture are shown in Fig. 4. Degradation of methylthio-striazines by the bacterial consortium, strain FJ1117YT and CD7, was suppressed by the presence of sulfate (Fig. 3) as well as the culture of strain FJ1117YT reported previously.9) However, Char-

coal A100 enriched with strain FJ1117YT and CD7 could be a promising model to construct a multifunctional material enriched with bacterial consortium for in situ bioremediation. On the basis of this study, we will attempt to construct another charcoal material, which will include methylthio-s-triazines-degrading bacteria that are not suppressed by external sulfur sources.

Fig. 4. The expected metabolic pathways of chloro- and methylthio-s-triazines degraded by CD7 (strain CDB21) and strain FJ1117YT. Simazine (R1, R2C2H5) and atrazine [R1C2H5, R2CH(CH3)2] were selected as chloro-s-triazines, and simetryn (R1, R2C2H5) and dimethametryn [R1C2H5, R2CH(CH3)CH(CH3)2] were used as methylthio-s-triazines in this study.

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Journal of Pesticide Science

Acknowledgments This work was supported in part by a Grant-in-aid (Hazardous Chemicals) from the Ministry of Agriculture, Forestry, and Fisheries of Japan (HC-05-2441-1). References 1) D. A. Belluck, S. L. Benjamin and T. Dawson: ACS Symp. Scr. 459, 254–273 (1991). 2) F. E. Pick, L. P. van Dyk and E. Botha: Chemosphere 25, 335–341 (1992). 3) C. J. Miles and R. J. Pfeuffer: Arch. Environ. Contam. Toxicol. 32, 337–345 (1997). 4) K. Takagi, A. Iwasaki and Y. Yoshioka: Proceedings of the 2nd international conference on soil pollution and remediation, Nanjing 228–230 (2004).

5) A. Iwasaki, K. Takagi, Y. Yoshioka, K. Fujii, Y. Kojima and N. Harada: Pest. Manag. Sci. 63, 261–268 (2007). 6) A. Tanabe, H. Mitobe, K. Kawata and M. Sakai: J. Chromatogr. A 754, 159–168 (1996). 7) M. Sudo, T. Kunimatsu and T. Okubo: Wat. Res. 36, 315–329 (2002). 8) T. Kawakami, H. Eun, T. Arao, S. Endo, M. Ueji, K. Tamura and T. Higashi: J. Pestic. Sci. 31, 6–13 (2006). 9) K. Fujii, K. Takagi, S. Hiradate, A. Iwasaki and N. Harada: Pest. Manag. Sci. 63, 254–260 (2007). 10) http://web.nies.go.jp/edc/edrep/report/1-1-2-1.htm (in Japanese) 11) C. Yanze-Kontchou and N. Gschwind: Appl. Environ. Microbiol. 60, 4297–4302 (1994). 12) L. J. Audus: Nature 158, 419–419 (1946). 13) G. Muyzer, E. de Waal and A. Uitterlinden: Appl. Environ. Microbiol. 59, 695–700 (1993).

EFFECT OF LOW‐TEMPERATURE PYROLYSIS CONDITIONS ON BIOCHAR FOR AGRICULTURAL USE J. W. Gaskin, C. Steiner, K. Harris, K. C. Das, B. Bibens

ABSTRACT. The removal of crop residues for bio‐energy production reduces the formation of soil organic carbon (SOC) and therefore can have negative impacts on soil fertility. Pyrolysis (thermoconversion of biomass under anaerobic conditions) generates liquid or gaseous fuels and a char (biochar) recalcitrant against decomposition. Biochar can be used to increase SOC and cycle nutrients back into agricultural fields. In this case, crop residues can be used as a potential energy source as well as to sequester carbon (C) and improve soil quality. To evaluate the agronomic potential of biochar, we analyzed biochar produced from poultry litter, peanut hulls, and pine chips produced at 400°C and 500°C with or without steam activation. The C content of the biochar ranged from 40% in the poultry litter (PL) biochar to 78% in the pine chip (PC) biochar. The total and Mehlich I extractable nutrient concentrations in the biochar were strongly influenced by feedstock. Feedstock nutrients (P, K, Ca, Mg) were concentrated in the biochar and were significantly higher in the biochars produced at 500°C. A large proportion of N was conserved in the biochar, ranging from 27.4% in the PL biochar to 89.6% in the PC biochar. The amount of N conserved was inversely proportional to the feedstock N concentration. The cation exchange capacity was significantly higher in biochar produced at lower temperature. The results indicate that, depending on feedstock, some biochars have potential to serve as nutrient sources as well as sequester C. Keywords. Agricultural residues, Biochar, Bioenergy, Black carbon, Carbon sequestration, Charcoal, Plant nutrition, Pyrolysis, Soil fertility, Soil organic carbon.

P

yrolysis of crop residues to produce renewable ener‐ gy is one option to reduce the use of fossil fuels. Py‐ rolysis generates biochar, oil, and gas products that can all be used as fuels (Ioannidou and Zabaniotou, 2007). Pyrolytic biochar can also potentially be used as a low‐ cost sorbent (Ioannidou and Zabaniotou, 2007) or as a soil amendment to improve soil fertility and sequester carbon (Lehmann et al., 2006; Steiner, 2007). Removal of crop resi‐ dues for energy production can have deleterious effects on soil organic carbon (SOC) and consequently on soil fertility (Lal, 2004). Pyrolysis of crop residues with C returned to the soil in the form of biochar may help maintain or increase stable SOC pools and cycle nutrients back into agricultural fields. Pyrolysis with biochar C sequestration may offer an option to reduce the conflict between cultivating crops for different purposes, e.g., energy vs. C sequestration or food. There are several lines of evidence that charcoal plays an important role in soil fertility. Charcoal has been identified as an important soil constituent in fertile Chernozems (Schmitdt et al., 1999) and in anthropogenic enriched dark

Submitted for review in August 2008 as manuscript number SW 7634; approved for publication by the Soil & Water Division of ASABE in November 2008. The authors are Julia W. Gaskin, Sustainable Agriculture Coordinator, Christoph Steiner, Post‐Doctoral Associate, Keith Harris, Technician, K. C. Das, Associate Professor, and Brian Bibens, Research Engineer, Department of Biological and Agricultural Engineering, Driftmier Engineering Center, University of Georgia, Athens, Georgia. Corresponding author: Julia W. Gaskin, Department of Biological and Agricultural Engineering, Driftmier Engineering Center, University of Georgia, Athens, GA 30602; phone: 706‐542‐1401; fax: 706‐542‐1886; e‐mail: [email protected].

soil (Terra Preta) found throughout the lowland portion of the Amazon Basin (Glaser et al., 2000). Research on tropical soils indicates that charcoal amendments can increase and sustain soil fertility (Steiner et al., 2007). The beneficial ef‐ fects appear to be related to alterations in soil physical, chem‐ ical, and biological properties, such as reduced acidity (Topoliantz et al., 2005), increased cation exchange capacity (CEC) (Cheng et al., 2008; Liang et al., 2006), enhanced ni‐ trogen (N) retention (Lehmann et al., 2003; Steiner et al., 2008b), increased microbiological activity (Steiner et al., 2008a), and increased mycorrhizal associations (Warnock et al., 2007). Research on the effect of wildfire charcoal in for‐ est ecosystems indicates that it stimulates microbial activity (Pietikäinen et al., 2000) and influences nitrogen cycling (Berglund et al., 2004; DeLuca et al., 2006; Wardle et al., 1998). Research also indicates that charcoal is recalcitrant (Seiler and Crutzen, 1980), and it may persist for hundreds or thousands of years. Charcoals produced from wildfire or traditional charcoal production may have different chemical and physical charac‐ teristics from pyrolytic biochars created under specific con‐ ditions for energy production. Both feedstock and pyrolysis conditions such as temperature and carrier gas affect the chemical and physical characteristics of biochar (Antal and Grønli, 2003; Bansal et al., 1988; Benaddi et al., 2000; Guo and Rockstraw, 2007a; Strelko et al., 2002). Most of the liter‐ ature discusses high‐temperature biochars that are produced at greater than 500°C or activated carbon typically produced at 800°C. As pyrolysis temperatures increase, volatile com‐ pounds in the biochar matrix are lost, surface area and ash in‐ crease, but surface functional groups that can provide exchange capacity decrease (Guo and Rockstraw, 2007a).

Transactions of the ASABE Vol. 51(6): 2061-2069

E 2008 American Society of Agricultural and Biological Engineers ISSN 0001-2351

2061

Pyrolysis of nutrient‐rich feedstock is likely to produce nutrient‐rich biochar, but nutrient conservation and availabil‐ ity in biochars is not well understood. Nutrients susceptible to volatilization such as N are almost completely lost after a burn (Giardina et al., 2000). Whether elements are retained during pyrolysis, the availability of nutrients for plants, and the effect of pyrolysis conditions on these characteristics are unclear. For biochar to be used in agriculture, a better under‐ standing of its properties and how it affects soil fertility is needed. Therefore, our objectives were to determine the ef‐ fect of feedstock, temperature, and carrier gas on key charac‐ teristics of biochar for agricultural use. Specifically, we wished to compare characteristics critical for agricultural use including pH, CEC, total nutrient concentrations, and poten‐ tially available nutrient concentrations in biochars from three feedstocks under two temperature regimes using two carrier gases with and without secondary steam activation.

MATERIALS AND METHODS BIOCHAR PRODUCTION We selected three common feedstocks to represent a range of physical properties and mineral content: raw poultry litter from broiler houses (Gallus domesticus, PL), pelletized pea‐ nut hulls (Arachis hypogaea, PN), and raw pine chips (Pinus taeda, PC). Biochars were produced in a batch pyrolysis unit at two peak temperatures (400°C and 500°C) with either steam or nitrogen (N2) as a carrier gas. The biochars produced with N2 as a carrier gas were produced with or without steam activation at the original pyrolysis temperatures (400°C and 500°C). Each of the production combinations (three feed‐ stocks, three pyrolysis types, two temperatures = 18) was rep‐ licated three times. The conversion efficiency was calculated as the percentage of the feedstock input (dry weight, DW) and biochar output (biochar DW / feedstock DW). CHEMICAL ANALYSES Biochars were ground in a ball mill to pass a 300 mm sieve before nutrient analysis. Feedstock and the biochars were analyzed for total C, N, and sulfur (S) by dry combustion (CNS‐2000, Leco Corp., St. Joseph, Mich.). Total minerals were extracted using a closed‐vessel microwave digestion with HNO3 (USEPA method 3050; USEPA, 1994). A Meh‐ lich I extraction (0.05 M HCl + 0.0125 M H2SO4) (Mehlich, 1953) was also used on biochar samples as an index of poten‐ tially plant‐available nutrients. Aluminum, Cu, Ca, Fe, Mg, Mn, P, K, Na, and Zn were measured by inductively coupled plasma spectrometry (ICP, Thermo Jarrell‐Ash model 61E, Thermo Fisher Scientific, Waltham, Mass.). Biochar pH was measured in deionized water using a 1 to 5 wt/wt ratio. Samples were thoroughly mixed and allowed to equilibrate for 1 h. The pH was measured with a digital pH meter (AR15, Thermo Fisher Scientific, Waltham, Mass.). Cation exchange capacity of the biochar was measured by a modified ammonium‐acetate compulsory displacement

(Sumner and Miller, 1996). Samples were leached with de‐ ionized water five times before starting the CEC extraction to reduce interference from soluble salts. Twenty mL of de‐ ionized water was added to a 1 g sample of biochar in a dis‐ posable nalgene 0.45 mm cellulose nitrile filter flask. The flask was placed on an orbital shaker and shaken at 180 rpm for 5 minutes. The sample was vacuum filtered, and the lea‐ chate was saved for further analysis. After the fifth wash, 10mL of Na‐acetate (pH 7) was added to the sample, and the mixture shaken for 10 min. This process was repeated three times to ensure that exchange sites were saturated with Na ions. Biochar samples were then washed three times with ethanol to remove excess Na. Sodium ions were displaced with NH4‐acetate (pH 7) three times and measured by atomic adsorption (PE 4100ZL, Perkin Elmer, Waltham, Mass.). The reserved leachate from the five washings (CEC proce‐ dure above) was composited and analyzed for dissolved car‐ bon (DC), dissolved inorganic carbon (DIC), ammonium‐ nitrogen (NH4-N), and nitrate‐nitrogen (NO3-N). Dissolved carbon and DIC was measured by combustion (Shimadzu TOC‐5050A, Shimadzu, Columbia, Md.). Dissolved organic C (DOC) was calculated by difference (DOC = DC - DIC). Nitrate‐nitrogen and NH4-N were analyzed on an autoanalyzer using cadmium reduction and phenate colorimetric methods (EnviroFlow 3000, Perstorp, Toledo, Ohio). STATISTICAL ANALYSES Treatment effects were analyzed by general linear model (GLM) univariate analysis of variance (ANOVA). The detection limit was used for results below the detection limit, if other results were above the limit. This allowed a conservative estimate of the elemental concentration of the biochar. If all results were below the detection limit, then no statistical analysis was performed. Significant differences (p< 0.05) between the feedstock and treatments were separated by the Tukey test. Statistical analyses and plots were performed using SPSS 12.0 and SigmaPlot 8.02 (SPSS, Inc., Chicago, Ill.).

RESULTS AND DISCUSSION Steam pyrolysis of the peanut hull pellets in the batch reactor presented difficulties due to excessive swelling by the peanut hull feedstock that clogged the reactor. Low‐temperature steam pyrolysis in a batch reactor may not be appropriate for this feedstock. Analysis of PC and PL biochars revealed no difference in total nutrients, Mehlich I extractable nutrients, CEC, or pH between steam and N2 as carrier gas; consequently, we report on the results from pyrolysis with the N2 carrier gas with or without subsequent steam activation. INFLUENCE OF FEEDSTOCK The total element concentrations in the feedstock had the strongest influence on the chemical composition of the

Table 1. Total element concentrations in the three agricultural feedstocks used for pyrolysis at 400°C and 500°C. Values in g kg‐1 Values in mg kg‐1 Feedstock Poultry litter (PL) Peanut hulls (PN) Pine chips (PC)

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C 326 552 571

N

P

45.1 19.5 13.6 0.61 0.9 0.08

K

S

Ca

Mg

Al

Fe

Na

Cd

Cr

Cu

29.5 5.06 0.59

5.8 0.9 0

28.0 1.84 0.75

5.66 0.79 0.21

6.32 0.92 0.03

3.91 0.42 0.13

9.27 0.04 0.04

1.4 <1 <1

7.3 2.0 2.1

381 377.0 49.9 3.5 36.5 44.0 15.2 15.6 1.7 13.8 2.1 <1.0

Mn

B

Mo

Ni

Zn

8.0 1.5 <2.0

414 20.2 47.8

TRANSACTIONS OF THE ASABE

Table 2a. Means and standard errors for pH, CEC, and total macronutrient concentrations in poultry litter, peanut hull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a] Poultry Litter (PL) Peanut Hulls (PN) Pine Chips (PC) 400°C

500°C

400°C

500°C

400°C

500°C

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

pH (S.U.)

10.1 ±0.04

10.1 ±0.07

9.74 ±0.05

9.88 ±0.09

10.5 ±0.05

10.5 ±0.10

10.1 ±0.02

9.96 ±0.01

7.55 ±0.09

7.99 ±0.09

8.30 ±0.15

Feedstock 8.10 ±0.60 PC
Temp.

CEC (cmol kg‐1)

61.1 ±0.73

57.4 ±1.4

38.3 ±1.7

37.0 ±1.6

14.2 ±0.46

11.7 ±2.04

4.63 ±0.10

4.46 ±0.13

7.27 ±0.54

6.00 ±0.11

5.03 ±0.85

6.02 ±3.12 PC
500<400

C (g kg‐1)

392 ±3.8

399 ±7.4

392 ±8.6

421 ±23

732 ±14

762 ±3.4

804 ±1.7

806 ±5.8

739 ±17

761 ±3.6

817 ±1.9

PL
400<500

N (g kg‐1)

34.7 ±0.79

34.7 ±0.77

30.9 ±0.89

32.3 ±1.6

24.3 ±0.18

24.0 ±0.37

24.8 ±0.89

24.8 ±0.34

2.55 ±0.40

1.95 ±0.06

2.23 ±0.09

2.20 ±0.12 PC
500<400

P (g kg‐1)

30.1 ±0.16

32.2 ±2.3

35.9 ±1.6

34.8 ±2.6

1.83 ±0.11

1.70 ±0.12

1.97 ±0.03

2.06 ±0.11

0.15 0.14 ±0.004 ±0.004

0.14 ±0.02

0.20 ±0.02 PC
400<500

K (g kg‐1)

51.1 ±1.3

52.6 ±4.9

58.6 ±2.9

54.7 ±1.5

15.2 ±0.58

14.40 ±1.40

16.4 ±0.19

16.5 ±0.79

1.45 ±0.06

1.51 ±0.07

1.45 ±0.18

2.25 ±0.25 PC
400<500

Ca (g kg‐1)

42.7 ±0.30

45.7 ±3.0

50.4 ±2.2

49.1 ±3.7

4.62 ±0.06

4.46 ±0.29

5.12 ±0.12

5.21 ±0.20

1.71 ±0.11

1.69 ±0.02

1.85 ±0.14

2.17 ±0.04 PC
400<500

Mg (g kg‐1)

10.7 ±0.23

11.4 ±0.91

12.9 ±0.50

12.4 ±1.0

2.19 ±0.06

2.17 ±0.16

2.50 ±0.05

2.59 ±0.11

0.60 ±0.04

0.58 ±0.03

0.59 ±0.06

0.76 ±0.01 PC
400<500

S (g kg‐1)

13.67 ±0.39

12.3 ±0.09

13.93 ±1.1

13.9 ±0.37

0.56 ±0.02

0.51 ±0.03

0.55 ±0.09

0.37 ±0.09

0.01 ±0.04

0.16 ±0.05

0.06 ±0.01

0.08 ±0.04 PC, PN
[a]

SA

820 ±17

SA = steam activation. Table 2b. Means and standard errors for total micronutrient and selected element concentrations in poultry litter, peanut hull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a] Poultry Litter (PL) Peanut Hulls (PN) Pine Chips (PC) Feedstock 400°C

500°C

400°C

500°C

400°C

Temp.

500°C

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Al (g kg‐1)

9.87 ±1.36

8.12 ±1.59

13.02 ±0.36

14.25 ±1.97

2.40 ±0.07

2.33 ±0.16

2.73 ±0.05

2.81 ±0.13

0.07 ±0.01

0.05 ±0.005

0.07 0.06 ±0.01 ±0.008 PC, PN
400<500

Fe (g kg‐1)

6.06 ±0.52

5.55 ±0.42

8.03 ±0.55

8.89 ±1.27

1.00 ±0.02

0.97 ±0.07

1.15 ±0.02

1.20 ±0.06

0.15 ±0.11

0.04 ±0.007

0.05 ±0.01

400<500

Na (g kg‐1)

15.1 ±0.31

15.8 ±1.37

17.2 ±1.02

16.6 ±1.12

0.026 0.028 ±0.001 ±0.006

0.035 0.044 ±0.004 ±0.005

<0.014 0.053 ±0.004 ±0.032

0.013 0.075 ±0.002 ±0.054 PN, PC
B (mg kg‐1)

91.5 ±3.16

96.0 ±8.25

100 ±0.31

93.0 ±3.98

32.5 ±1.57

29.9 ±2.87

33.7 ±0.27

34.1 ±1.15

5.69 ±0.30

4.21 ±0.62

Cd (mg kg‐1)

2.75 ±0.73

<2.65 ±0.83

<1

<1.10 ±0.10

<1.35 ±0.35

<1.35 ±0.35

<1

<1

<1

<1

<1

<1

Cr (mg kg‐1)

28.0 ±4.1

28.8 ±5.2

59.4 ±3.3

56.1 ±4.5

3.95 ±0.31

3.00 ±0.57

3.63 ±0.31

3.94 ±0.16

<1

1.23 ±0.09

3.43 ±0.88

17.7 ±5.9

PN, PC
400<500

Cu (mg kg‐1)

805 ±23

880 ±49

1034 ±68

943 ±81

16 ±0.60

13 ±1.27

19 ±0.50

19 ±1.84

25 ±7.03

10 ±6.18

9 ±2.34

13 ±5.57

PC, PN
400<500

Mn (mg kg‐1)

596 ±5.6

637 ±37

725 ±29

697 ±46

116 ±2.3

116 ±8.0

131 ±2.3

136 ±5.7

274 ±9.3

269 ±7.8

258 ±30

350 ±4.0

PN
400<500

Mo (mg kg‐1)

17.1 ±5.3

12.1 ±0.41

14.2 ±1.1

13.8 ±1.2

4.78 ±3.6

<1

<1

<1

<1

<1

<1

<4.11 ±3.11

PC, PN
Ni (mg kg‐1)

13.6 ±0.00

19.5 ±3.7

20.3 ±1.1

29.1 ±8.4

<2.29 ±0.29

<2 ±0

<2 ±0

<10.4 ±8.0

<2 ±0

<2 ±0

<2.91 ±0.55

17.5 ±14.7

PC, PN
Zn (mg kg‐1)

628 ±12

680 ±41

752 ±28

728 ±50

35 ±2.2

31 ±2.9

37 ±2.1

36 ±0.00

15 ±1.1

16 ±0.7

18 ±0.6

20 ±2.4

PC, PN
[a]

6.69 ±0.21

Biochar

SA

0.20 ±0.07

6.94 ±1.33

PC, PN
PC
400<500

SA = steam activation; < indicates mean contains results below the detection limit; ±0.00 indicates all results were near instrument detection limit.

biochar. Concentrations of plant nutrients in the feedstocks generally followed the pattern of PC < PN < PL. Feedstock carbon concentrations had the opposite pattern, with PL < PN < PC (table 1). There were significant differences in C concentrations in the biochar, with PL containing less C than the PN or PC biochar (table 2a). The nutrient‐rich poultry litter contains relatively more minerals than the other feedstocks, which

Vol. 51(6): 2061-2069

decreases the C content. Nitrogen, P, K, Ca, and Mg concentrations in the biochar were significantly different, with PC < PN < PL (table2a). The concentration of the micronutrients B, Cu, Fe, Mn, Na, and Zn were significantly higher in PL biochar (p < 0.05), but there were no differences detected between the PN and PC biochars except for Mn (table 2b). Concentrations of metals such as Al, Cr, Ni, and Mo were low. The PL biochar contained the highest

2063

Figure 1. Percentages with standard errors of feedstock nutrients conserved in the biochar and percentages of total nutrients that were Mehlich I extractable at two pyrolysis temperatures and in three biochars. Letters above the columns indicate significant difference of nutrients conserved between biochar types (p < 0.05, n = 3). Letters within columns indicate significant difference in the percentage of total nutrients that were MehlichI extractable (p < 0.05, n = 3).

concentrations of these metals, as would be expected from the higher feedstock concentrations. Cadmium was below the detection limit in PC biochars and near or at the detection limits in PL and PN biochars (table 2b). The amount of N conserved ranged from 27.4% in the PL biochar to 89.6% in the PC biochar and was inversely proportional to the feedstock N concentration (fig. 1b and table 1). The higher N losses seen from the PL were likely due to the volatilization of the poultry manure NH4-N and easily decomposable N-containing organic compounds in the manure, such as uric acid. In contrast, the low concentration of N in the PC feedstock is likely to be incorporated into complex structures that are not easily volatilized. About 60% of the P in the PL and PC feedstock was retained in the PL and PC biochar, while nearly 100% of the P in the PN feedstock was retained in the PN biochar (fig. 1c).

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In general, the PL biochar had a lower proportion of nutrients retained than the PN or the PC biochar (figs. 1c through 1f). This may be due to a higher proportion of some of these elements retained in the aqueous/bio‐oil fraction in PL biochar (K. C. Das, 2007, unpublished data, University of Georgia, Athens, Ga.). The pattern of Mehlich I extractable concentrations was similar to that of the total nutrient concentrations (tables 3a and 3b). There were significant differences in Mehlich I extractable P, K, Ca, and Mg concentrations, with PC < PN < PL. There were differences by feedstock in the percentage of the total nutrients that were Mehlich I extractable (figs. 1a through 1f). Only 19% of the PL biochar P was Mehlich I extractable compared to over 40% in the PN biochar (400°C, fig. 1c). About 90% of the PL biochar K was Mehlich I extractable compared to only 45% in the PN biochar (400°C,

TRANSACTIONS OF THE ASABE

Table 3a. Means and standard errors of the Mehlich I macronutrient concentrations in poultry litter, peanut hull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a] Poultry Litter (PL) Peanut Hulls (PN) Pine Chips (PC) Feedstock 400°C

500°C

400°C

500°C

400°C

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

P (g kg‐1)

5.58 ±0.31

4.09 ±1.22

5.33 ±0.18

4.66 ±0.20

0.76 ±0.02

0.67 ±0.06

0.57 ±0.04

0.59 ±0.03

0.03 0.034 ±0.002 ±0.004

0.04 0.06 ±0.008 ±0.03 PC
K (g kg‐1)

46.2 ±0.96

34.1 ±8.40

38.1 ±2.68

40.0 ±2.81

6.84 ±0.16

6.28 ±0.67

5.91 ±0.28

6.76 ±0.30

0.30 ±0.009

0.38 ±0.02

0.41 ±0.06

0.97 ±0.32 PC
Ca (g kg‐1)

3.34 ±0.84

1.95 ±0.82

2.21 ±0.36

1.63 ±0.13

1.68 ±0.02

1.48 ±0.15

1.19 ±0.06

1.22 ±0.06

0.30 ±0.04

0.31 ±0.05

0.43 ±0.10

0.39 ±0.16 PC
Mg (g kg‐1)

3.09 ±0.28

2.19 ±0.68

3.03 ±0.13

2.92 ±0.05

0.80 ±0.03

0.62 ±0.09

0.37 ±0.02

0.39 ±0.01

0.05 0.06 ±0.008 ±0.009

0.06 ±0.01

0.08 ±0.04 PC
[a]

Biochar

Temp.

500°C

SA

Biochar

SA

SA = steam activation. Table 3b. Means and standard errors of the Mehlich I micronutrient and selected element concentrations in poultry litter, peanut hull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a] Poultry Litter (PL) Peanut Hulls (PN) Pine Hips (PC) Feedstock 400°C

500°C

400°C

500°C

400°C

Temp.

500°C

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Al (g kg‐1)

0.47 ±0.11

11.3 ±2.24

1.43 ±0.31

1.52 ±0.24

330 ±24

585 ±213

1129 ±32

1360 ±51

6.17 ±0.59

6.35 ±0.53

7.53 ±1.12

12.12 ±4.76

PL, PC
400<500

Fe (g kg‐1)

0.66 ±0.21

3.16 ±0.08

0.06 ±0.007

0.19 n=1

140 ±2.2

142 ±18

197 ±3.8

221 ±11

3.72 ±0.26

4.58 ±0.19

14.6 ±2.89

33.3 ±8.39

PL, PC
400<500

Na (g kg‐1)

9.57 ±0.19

7.08 ±1.61

6.98 ±0.43

7.24 ±0.07

0.02 0.02 ±0.001 ±0.002

0.02 0.03 ±0.58 ±0.002

0.03 0.03 ±0.002 ±0.002

0.03 0.08 ±0.005 ±0.037 PN, PC
B (mg kg‐1)

16.7 ±1.59

18.8 ±2.05

18.67 ±0.85

20.4 ±0.59

4.20 ±0.12

4.96 ±1.08

3.97 ±0.22

5.84 ±0.66

0.45 ±0.04

0.41 ±0.07

0.52 ±0.07

1.15 ±0.49 PC
Cr (mg kg‐1)

0.19 ±0.03

0.19 ±0.02

0.14 ±0.01

0.11 ±0.01

<0.04

<0.04

0.41 ±0.04

0.52 ±0.03

<0.06

<0.06

<0.06

<0.06

Cu (mg kg‐1)

0.40 ±0.06

0.29 ±0.08

<0.08 ±0.02

<0.05 ±0.005

0.67 ±0.04

<0.59 ±0.32

<0.04 ±0.001 <0.04

6.55 ±2.18

2.48 ±0.68

2.70 ±0.89

3.82 ±3.34

Mn (mg kg‐1)

7.69 ±1.23

8.64 ±1.28

6.75 ±1.03

5.17 ±0.43

24.7 ±0.70

21.2 ±2.33

14.4 ±0.45

16.3 ±0.71

22.6 ±2.61

25.2 ±3.79

24.1 ±6.67

36.2 ±12.5 PL
Mo (mg kg‐1)

0.87 ±0.19

1.11 ±0.22

1.42 ±0.14

1.94 ±0.19

<0.04

<0.04

<0.04

<0.04

0.15 ±0.002

0.25 ±0.06

0.11 ±0.03

0.65 ±0.35

Ni (mg kg‐1)

<0.08

<0.08

<0.08

<0.08

<0.08

<0.08

<0.08

<0.08

<0.2

<0.2

<0.2

<0.2

Zn (mg kg‐1)

0.06 ±0.01

0.30 ±0.02

0.05 ±0.07

<0.04

10.51 ±1.22

7.36 ±0.59

5.58 ±0.26

6.30 ±0.45

2.20 ±0.17

2.31 ±0.21

1.36 ±0.26

3.66 ±1.17 PL
[a]

PL, PN
SA = steam activation; < indicates mean contains results below the detection limit.

fig. 1d). Manganese and Zn concentrations were significantly lower in the PL biochar than the PC or PN biochars. Copper, Al, and Fe was also lower in the PL biochar compared to the PN biochar. These patterns are the reverse of that seen in the feedstock or the total element concentrations in the biochars. If pyrolysis can reduce P and other metal availability in poultry litter, it may reduce some of the environmental concerns associated with land application of poultry litter. These results should be interpreted with caution. The Mehlich I extraction, which is a weak double acid extraction, may not have been strong enough to remove these acid‐ soluble cations under the high pH conditions found in the PL biochar. The Mehlich I extraction was developed for acidic soils in the southeastern U.S. with low CEC or base saturation (Kuo, 1996), and it is the standard extraction used for plant‐ available nutrients and fertilizer recommendations in Alabama, Georgia, Florida, South Carolina, Tennessee, and Virginia. In this study, Mehlich I extractable element concentrations were used as an index to compare the

Vol. 51(6): 2061-2069

potential for different biomass sources and production techniques to supply plant‐available nutrients. The extraction has not been calibrated for biochar and may not reflect actual plant‐available nutrient concentrations. However, data from a greenhouse trial using pine chip and peanut hull biochar amendment of three different Ultisols (Speir, 2008) and from a field trial with the same biochars (Gaskin et al., 2007) indicate an increase in Mehlich I K and Mg in soils amended with peanut hull biochar. The increased Mehlich I K in the soil was reflected in an increase of these nutrients in corn tissue (Zea mays) in the field trial. The pH and CEC of the biochars were also significantly influenced by feedstock (table 2a). All the biochars were basic, with the highest pH seen in the PN biochar. Tryon (1948) reported increased soil pH with the addition of pine and hardwood charcoal. He attributed the greater pH increase seen in the hardwood charcoal treatment to the higher ash content, in particular to the hydrolysis of salts of Ca, K, and Mg in the presence of water. In this study, PC biochar had both the lowest total concentrations of these cations and the

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Table 4. Means and standard errors of dissolved carbon (DC), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), ammonium‐nitrogen (NH4-N), and nitrate‐nitrogen (NO3-N) in leachate from poultry litter, peanut hull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a] Poultry Litter (PL) Peanut Hulls (PN) Pine Chips (PC) Feedstock Temp. 400°C

500°C

400°C

500°C

400°C

500°C

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

SA

Biochar

DC (g kg‐1)

2.20 ±0.31

1.85 ±0.25

0.85 ±0.01

0.75 ±0.02

0.51 ±0.09

0.40 ±0.02

0.52 ±0.02

0.41 ±0.10

0.13 ±0.10

0.13 ±0.10

0.12 ±0.05

DIC (g kg‐1)

0.39 ±0.04

0.44 ±0.04

0.57 ±0.03

0.54 ±0.03

0.32 ±0.03

0.31 ±0.03

0.38 ±0.03

0.37 ±0.04

DOC (g kg‐1)

1.81 ±0.34

1.46 ±0.29

0.28 ±0.04

0.21 ±0.04

0.20 ±0.06

0.10 ±0.03

0.14 ±0.03

NH4‐N (mg kg‐1)

8.5 ±0.39

6.69 ±0.69

11.3 ±6.41

3.49 ±0.15

2.86 ±0.27

1.94 ±0.01

NO3‐N (mg kg‐1)

<0.4

<0.4

<0.4

<0.4

1.02 ±0.01

1.07 ±0.02

[a]

SA 0.19 ±0.07 PC
500<400

0.014 0.025 ±0.003 ±0.003

0.034 0.055 ±0.005 ±0.012 PC
400<500

0.10 ±0.03

0.12 ±0.01

0.10 ±0.01

0.09 0.10 ±0.003 ±0.01

500<400

2.12 ±0.12

2.28 ±0.44

1.75 ±0.29

7.93 ±6.16

2.41 ±0.16

2.37 ±0.08

1.27 ±0.06

1.11 ±0.02

<0.4

<0.4

<0.4

<0.4

PC, PN
SA = steam activation; < indicates mean contains results below the detection limit.

lowest pH, which would support Tyron's hypothesis; however, the pH of PL biochar was similar to the PN biochar although it contained higher concentrations of total Ca, K, and Mg than PN biochar (table 2). Higher CEC was associated with higher concentrations of minerals in the feedstock. Mészáros et al. (2007) hypothesized that K, Mg, Na, and P in the biomass may catalyze the formation of oxygen groups on the biochar surface at low pyrolysis temperatures. Oxygen groups such as carboxyls, lactones, and phenols could contribute to the presence of negative surface charges (Boehm, 1994). Dissolved C concentrations were very low (table 4). Feedstock had a significant effect on DC in the biochar leachate, with PC < PN < PL. Dissolved inorganic C was also affected by feedstock, with PC < PN < PL. The PL biochar had a higher proportion of DOC than PC or PN biochars. The PL feedstock is a combination of wood chip (typically pine) bedding and poultry manure. The manure may contribute to higher DOC leached from the PL biochar. DOC plays an important role in many soil processes, including serving as an energy source for the microbial community and reacting with other soil solution components (Sposito, 1989). Biochars are known to contain condensed volatile compounds. These compounds are either lost to the gaseous or liquid phase or undergo further reactions to form secondary char at high temperatures (Antal and Grønli, 2003). Garcia‐Perez et al. (2007) identified water‐soluble compounds from pyrolysis of lignin materials to contain mono‐ and oligo‐sugars, formic and aecetic acids, as well as methanol, hydroxyl‐acetaaldehyde, and 1‐hydroxyl‐2‐ propanone. Schnitzer et al. (2007) identified numerous organic compounds in the light and heavy fractions of poultry litter pyrolyzed at 330°C, including N-heterocyclics, substituted furans, phenol and substituted phenols, benzenes and substituted benzenes, as well as aliphatic C chains. It is likely that some of these compounds remain trapped in the biochar pore structure, but few of these compounds appear to be immediately water soluble. Ammonium‐nitrogen in the biochar leachate was also found in very low concentrations (table 4). No NO3-N was detected in any of the leachates. The NH4-N concentrations were highest in the leachate from the PL biochar. Fresh poultry litter typically contains about 2.8 g NH4-N kg-1 (University of Georgia Agricultural and Environmental

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Services Laboratory, unpublished data). Small amounts of this NH4-N may remain trapped, or microbes may have mineralized nitrogen‐containing organic compounds in the biochar. Das et al. (2008) found that the liquid products obtained from poultry litter pyrolysis enhanced microbial growth in well water and concluded that N-heterocyclic compounds derived from proteins were responsible for that increase. A small fraction of these compounds may be present in the biochars. INFLUENCE OF PYROLYSIS TEMPERATURE The average conversion ratio (biochar weight / feedstock weight) was 33.2%. Biochar yield decreased with increased pyrolysis temperature, and except for N, nutrient concentrations were higher in the biochar produced at 500°C (tables 2a andb). Due to the wide range of initial nutrient concentrations in the feedstock, there were significant interactions between feedstock and temperature for total N, P, Mg, Mn, Cu, Fe, Zn, and Al (p < 0.05). As noted earlier, N was conserved in the biochar (fig. 1b). After forest fires, on average, only 3% of the N in the biomass is found in ash, which contains black carbon or biochar (Giardina et al., 2000). Almendros et al. (2003) found C and N enrichment in charred residues during thermal transformation of peat organic matter. Nitrogen was incorporated into structures resistant to heating at moderate thermal oxidation by aromatization and formation of heterocyclic N (Almendros et al., 2003). Studies of wildfire effects on biomass composition indicate that N begins to volatilize at 200°C, and above 500°C half of the N in organic matter is lost to the atmosphere. Our study indicated that a relatively high proportion of the feedstock N was conserved at low pyrolysis temperatures, and as expected more N was retained in the biochar at 400°C compared to 500°C (fig. 1b). Knicker et al. (2005) has shown that fire and carbonization can increase the N content of SOC, but the alterations in chemical structure have long‐term consequences for N availability (Knicker and Skjemstad, 2000). Field trials of PN and PC biochar as a soil amendment with corn (Zea mays) indicate that PN biochar N is not plant available (Gaskin et al., 2007). However, Tagoe et al. (2008) studied N recovery of 15N‐labeled chicken manure and did not find differences in N availability between carbonized and dried chicken manure.

TRANSACTIONS OF THE ASABE

The CEC of biochar produced at 500°C was significantly less than that produced at 400°C (table 2a, p < 0.01). There was a significant interaction between feedstock and temperature. In general, the literature indicates the loss of surface functional groups with the increase in pyrolysis temperature. Guo and Rockstraw (2007b) showed that the number of acidic functional groups decreased with increasing temperature. The highest decrease occurred between 300°C and 400°C, and the loss of these acidic groups slowed after 400°C. This process may have contributed to the lower CEC seen at higher temperatures. Iyobe et al. (2004) indicated that lignin and cellulose undergo thermolysis at 400°C to 500°C, which creates acidic functional groups such as carboxyls and phenolic hydroxyls. Chun et al. (2004) found decreasing acidity and increasing basicity with increasing pyrolysis temperature. Temperature influenced DC (table 4). The higher temperature reduced the concentration of organic C but increased inorganic C significantly. INFLUENCE OF STEAM ACTIVATION Steam activation had little effect on the studied parameters (tables 2a, 2b, 3a, 3b, and 4). Production technology is known to influence physical parameters, and steam can improve the yield and surface characteristics at elevated pressures and temperatures (Antal and Grønli, 2003). At the relatively low pyrolysis temperatures used in this study, we only found significantly higher C and Mehlich I extractable B concentrations in steam‐activated biochar (p< 0.05).

CONCLUSIONS

Figure 2. Representative relationship of the ratio of nutrient (K) in the biochar to feedstock and conversion efficiency for pine chip, peanut hull, and poultry litter biochars. Solid circles represent means, and bars indicate standard errors.

The total concentration of other elements (P, K, Ca, and Mg) significantly increased with increasing volatization losses of C, H, O, and N (tables 2a and 2b). Potassium is representative of the nutrient concentration seen (fig. 2). Potassium and P vaporize at temperatures above 760°C, S and Na need temperatures above 800°C, and Mg and Ca are lost only at temperatures above 1107°C and 1240°C, respectively (Lide, 2004, reviewed by Knicker, 2007). There was a significant interaction between temperature and feedstock for Mehlich I extractable concentrations of these elements (p = 0.05). At the low nutrient concentrations seen in the PC biochar, temperature appeared to have little effect. In the PN and PL biochars, Mehlich I extractable nutrients tended to decrease with increasing temperature. Mehlich I extractable Al and Fe were significantly increased in the 500°C biochar (table 3b).

Vol. 51(6): 2061-2069

Pyrolytic biochar has the potential to be used in agricultural production to sequester carbon and serve as a fertilizer. Although pyrolysis conditions are known to affect the chemical and physical characteristics of biochar, at the relatively low pyrolysis temperatures used in this study, feedstock characteristics had the greatest influence on key agricultural characteristics. Carbon concentrations in the biochars decreased with increasing mineral content of the feedstock. Little DC was leachable from the fresh biochar. A high proportion of the feedstock N was conserved in the biochar; however, the N may not be plant available. Nutrients such as P, K, and Ca are extractable with a weak double acid extractant and may be plant available. The higher pyrolysis temperature increased nutrient concentrations, except for N, but decreased CEC. Recent literature has shown that natural long‐term oxidation of biochar in the soil increases the amount of negative charges on the biochar surface (Cheng et al., 2008). Development and optimization of pyrolysis and post‐production treatments to increase CEC or available nutrients is important in order to increase the immediate benefits of biochar applications in agriculture. ACKNOWLEDGEMENTS This work was conducted with funding from the State of Georgia and the U.S. Department of Energy. We wish to thank Dr. Jim Kastner for his helpful comments on various ideas in the manuscript, and Mr. Roger Hilten for assistance with this project.

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Knicker, H., F. J. Conzález‐Vila, O. Polvillo, J. A. González, and G. Almendros. 2005. Fire‐induced transformation of C- and Nforms in different organic soil fractions from a dystric cambisol under a Mediterranean pine forest (Pinus pinaster). Soil Biol. Biochem. 37(4): 701‐718. Kuo, S. 1996. Phosphorus: Part 3. Chemical methods. In Methods of Soil Analysis, 869‐919. Madison, Wisc.: SSSA and ASA. Lal, R. 2004. Soil carbon sequestration impacts on global climate change and food security. Science 304(5677): 1623‐1627. Lehmann, J., J. P. da Silva Jr., C. Steiner, T. Nehls, W. Zech, and B. Glaser. 2003. Nutrient availability and leaching in an archaeological anthrosol and a ferralsol of the central Amazon basin: Fertilizer, manure and charcoal amendments. Plant Soil 249(2): 343‐357. Lehmann, J., J. Gaunt, and M. Rondon. 2006. Bio‐char sequestration in terrestrial ecosystems: A review. Mit. Adapt. Strat. Global Change 11(2): 403‐427. Liang, B., J. Lehmann, D. Solomon, J. Kinyangi, J. Grossman, B. O'Neill, J. O. Skjemstad, J. Thies, F. J. Luizão, J. Petersen, and E. G. Neves. 2006. Black carbon increases cation exchange capacity in soils. SSSA J. 70(5): 1719‐1730. Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na, and NH4. Mimeo 1953. Raleigh, N.C.: North Carolina Department of Agriculture, North Carolina Soil Test Division. Mészáros, E., E. Jakab, G. Varhegyi, J. Bourke, M. Manly‐Harris, T. Nunoura, and M. J. Antal. 2007. Do all carbonized charcoals have the same chemical structure? 1. Implications of thermogravimetry: Mass spectrometry measurements. Ind. Eng. Chem. Res. 46(18): 5943‐5953. Pietikäinen, J., O. Kiikkilä, and H. Fritze. 2000. Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus. Oikos 89(2): 231‐242. Schmitdt, M. W. I., J. O. Skjemstad, E. Gehrt, and I. Kögel‐Knabner. 1999. Charred organic carbon in German chernozemic soils. European J. Soil Sci. 50(2): 351‐365. Schnitzer, M. I., C. Monreal, G. Jandl, P. Leinweber, and P. B. Fransham. 2007. The conversion of chicken manure to biooil by fast pyrolysis: II. Analysis of chicken manure, biooils, and char by curie‐point pyrolysis‐gas chromatography/mass spectrometry. J. Environ. Sci. Health B 42(1): 79‐95. Seiler, W., and P. J. Crutzen. 1980. Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere from biomass burning. Climatic Change 2(3): 207‐247. Speir, R. A. 2008. Use of pyrolysis char in southeastern soils. MS thesis. Athens, Ga.: University of Georgia, Warnell School of Forestry and Natural Resources. Sposito, G. 1989. The Chemistry of Soils. New York, N.Y.: Oxford University Press. Steiner, C. 2007. Slash and char as alternative to slash and burn: Soil charcoal amendments maintain soil fertility and establish a carbon sink. PhD diss. Bayreuth, Germany, University of Bayreuth, Faculty of Biology, Chemistry and Geosciences. Steiner, C., W. G. Teixeira, J. Lehmann, T. Nehls, J. L. V. d. Macêdo, W. E. H. Blum, and W. Zech. 2007. Long‐term effects of manure, charcoal, and mineral fertilization on crop production and fertility on a highly weathered central Amazonian upland soil. Plant Soil 291(1‐2): 275‐290. Steiner, C., K. C. Das, M. Garcia, B. Förster, and W. Zech. 2008a. Charcoal and smoke extract stimulate the soil microbial community in a highly weathered xanthic ferralsol. Pedobiologia 51(5‐6): 359‐366. Steiner, C., B. Glaser, W. G. Teixeira, J. Lehmann, W. E. H. Blum, and W. Zech. 2008b. Nitrogen retention and plant uptake on a highly weathered central Amazonian ferralsol amended with compost and charcoal. J. Plant Nutrition Soil Sci. (in press). Strelko, V., D. J. Malik, and M. Streat. 2002. Characterisation of the surface of oxidized carbon adsorbents. Carbon 40(1): 95‐104. Sumner, M. E., and W. P. Miller. 1996. Cation exchange capacity and exchange coefficients. In Methods of Soil Analysis, 1201‐1230. Madison, Wisc.: SSSA and ASA.

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Tagoe, S. O., T. Horiuchi, and T. Matsui. 2008. Effects of carbonized and dried chicken manures on the growth, yield, and N content of soybean. Plant Soil 306: 211‐220. Topoliantz, S., J.‐F. Ponge, and S. Ballof. 2005. Manioc peel and charcoal: A potential organic amendment for sustainable soil fertility in the tropics. Biol. Fert. Soils 41(1): 15‐21. Tryon, E. H. 1948. Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecol. Mono. 18(1): 81‐115.

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USEPA. 1994. Methods for the determination of metals in environmental samples. Supplement I EPA‐600/R‐94/111/May 1994. Cincinnati, Ohio: U.S. EPA, Environmental Monitoring Systems Laboratory. Wardle, D. A., O. Zackrisson, and M. C. Nilsson. 1998. The charcoal effect in boreal forests: Mechanisms and ecological consequences. Oecologia 115(3): 419‐426. Warnock, D. D., J. Lehmann, T. W. Kuyper, and M. C. Rillig. 2007. Mycorrhizal responses to biochar in soil: Concepts and mechanisms. Plant Soil 300: 9‐20.

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Chapter _ CHARACTERIZATION OF CHAR FOR AGRICULTURAL USE IN THE SOILS OF THE SOUTHEASTERN UNITED STATES J. GASKIN, K. DAS, A. TASISTRO, L. SONON, K. HARRIS, B. HAWKINS Dept. of Biological and Agricultural Engineering and Soil, Plant and Water Laboratory, University of Georgia, and EPRIDA., Athens, Georgia, US Abstract:

Char produced from the pyrolysis of biomass has potential as an agricultural amendment for increasing agricultural productivity in the infertile, low C soils of the southeastern United States, but it is unclear if the chars produced by pyrolysis plants will function in soils similar to the charcoal in Terra Preta. Recent work in characterizing pyrolysis char indicates that the feedstock, temperature, and carrier gas has a strong influence on important characteristics for agricultural production, such as available nutrients, cation exchange capacity, and mineralization rates. Preliminary data indicate pyrolysis char may increase CEC, sorbs P, and serves as a source of plant available K. Nitrogen mineralization data and first growing season field trials with corn (Zea mays) indicate although some mineralization may occur, N in high N char (2%) is not readily available. A better understanding of char effects on soil processes is needed.

Keywords:

char, Ultisols, agricultural amendment, nutrients, nitrogen, mineralization, cation exchange capacity, phosphorus sorption

1. INTRODUCTION Char produced from the pyrolysis of biomass has potential as an agricultural amendment in low fertility soils. Much of the interest in its potential use as an agricultural amendment has been stimulated by research discussed in this book and the previous volumes on the role of charcoal in Terra Preta soils. Results from studies conducted in South American and African tropics on acidic, highly-weathered Oxisols with low organic carbon, cation exchange capacity, and base saturation indicates that addition of charcoal has significantly influenced nutrient cycling, soil biology, and crop productivity (Glaser et al. 2002; Lehmann and Rondon 2006; Oguntunde et al. 2004). Increased yields and biomass have been reported for various legumes (Iswaran et al. 1980; Lehman et al. 2003; Topoliantz et al. 2005) and for corn (Lehmann and Rondon 2006; Oguntunde et al. 2004). Increased productivity may be related to available nutrients (Glaser et al. 2002; Lehman et al. 2003; Steiner et al. 2007), or increases in pH (Topoliantz et al. 2005; Steiner et al. 2007), and cation exchange capacity (CEC)(Steiner et al. 2007, Liang et al. 2006), as well as changes in water relations and soil biology (Glaser et al. 2002; Steiner et al. 2004). Although most studies report increased plant productivity with charcoal addition, plant biomass decreases have been observed, particularly at high application rates (Glaser et al. 2002). These responses could be related to nitrogen immobilization through high C:N ratios and sorption of NH4-N and NO3N(Lehmann and Rondon 2006). The southeastern United States is an important agricultural area. The state of Georgia alone has approximately 4.3 million hectares of corn (Zea mays), soybean (Glycine max), cotton (Gossypium hirsutum), and peanuts (Arachis hypogaea) in production and 9.6 million hectares of forestland largely in loblolly pine (Pinus taeda) production (USDA 2002; Georgia Forestry Association 2007). The growing interest in biofuels is increasing demands on row crop production and may also increase demand on forestlands. The Ultisols of the southeastern United States are similar to tropical Oxisols with low organic carbon contents of less than 1%, low cation exchange capacities of approximately 5 cmol kg-1, and low base saturation of usually less than 30% (Perkins 1987). Char produced as a byproduct of energy production through pyrolysis may provide an opportunity to increase the productivity of southeastern soils, similar to the way charcoal functions in Terra Preta. However, because char characteristics vary with feedstock and pyrolysis conditions (Harris et al. 2006; Antal and Gronli 2003), a better understanding of the influence of these factors on char characterisitics and the effect of different chars on soil processes in the southeastern United States is needed.

2. PYROLYSIS CONDITIONS AND CHAR CHARACTERISTICS Char or charcoal corresponds to black carbons that result from the incomplete combustion of biomass. Black carbon consists of graphite-like planes (graphene layers) that show varying degrees of disorientation. The resulting spaces between these planes constitute porosity. The capacity of char to remove impurities from solutions and gases has been known for many centuries. This is due to the porous nature of the material (Barkauskas 2002) and to the surface chemical properties including the type and number of functional groups (Stoeckli et al. 2004). Charcoal has chemical reactivity due to the existence of unsaturated valence (active sites) at the edges of the aromatic planes. The ratio of these active sites in relation to the inert carbon atoms within

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the graphene layers increases as the surface area increases. Heteroatoms, such as oxygen, hydrogen or nitrogen also have a strong influence on the mechanisms of the adsorption process. Oxygen is the most important heteroatom and is part of chemical groups that have both Lewis base properties such as chromene and pyrone or acidic properties such as anhydrides, lactones, lactols, phenols, carbonyls, and carboxyls. The presence and quantity of these groups affect the capacity of char to add to the cation or anion exchange capacity of the soil and other soil productivity properties. Charcoals are known to sorb cations (Lima and Marshall 2005a) and also anions when basic surface oxides are present due to exposure to the atmosphere (Boehm, 1994). These sorption capacities may create the potential for char to retain needed nutrients in the low exchange capacity soils of the southeastern United States.

2.1 Feedstocks The mineral content of the char depends upon the nature of the feedstock and can influence the surface chemistry of charcoal by interaction with electrons of the aromatic rings and through electron paramagnetism. (Benaddi et al. 2000). Ash complicates interpretation of surface phenomena of carbon. Ash solubility in water is variable, making the analysis of surface groups difficult at higher ash concentrations. Insoluble metal oxides involved in the charge development on the carbon surface become charged in aqueous suspension, and are considered part of the active surface sites. Feedstock particle size also affects char yield from pyrolysis. At low pyrolysis temperature, larger particle sizes favor longer inter-pore residence time for volatiles increasing yield (Antal and Gronli, 2003).

2.2 Pyrolysis Conditions Important parameters that determine quality and yield of the carbonized product are the rate of heating, final temperature, and the gas environment (Bansal et al., 1988). A low heating rate during pyrolysis leads to lower volatilization and higher char yields. This creates char with higher carbon contents but does not affect char microporosity. In addition, chars developed at low heating rates are heavier and denser than those from high heating rates. This may be an advantage for agricultural use in terms of handling properties. The final temperature during pyrolysis typically ranges between 400 and 600 oC, and does not exceed 800 oC. Guo and Rockstraw (2007) observed that surface area and porosity did not develop at temperatures < 300 oC and that from 300 oC onwards, the concentration of acidic surface groups decreased with increasing temperature. The decrease occurred more quickly between 300 and 400 oC, and slowed after 400 oC, probably due to an equilibrium between decomposition and formation of strong acidic surface groups, or because most of the temperature-sensitive strong acidic groups had disappeared. Iyobe, et al. (2004) reported that thermolysis of cellulose or lignin occurred actively at 400 to 500 oC, with the formation of acidic functional groups, such as carboxyls and phenolic hydroxyls. The amount of acidic functional groups continue to decrease with pyrolysis temperatures > 600 oC. Hydroxide (C-OH), C=O, and C-H groups are largely lost at temperatures > 650°C, and most of the aromatic and C-H groups are decomposed above 750°C (Antal and Gronli, 2003). Above 950°C chars are almost like graphite with little active chemistry on its surfaces. The effect is decreasing ability to sorb cations. Asada et al. (2002) reported that char obtained by carbonizing bamboo at 500 oC had the highest removal effect for NH3 compared to carbonizing at 700 or 1000oC. In general, these data indicates chars produced at lower temperatures (<500 oC) may hold the greatest promise for agricultural use in terms of nutrient holding capacity. The gas environment during pyrolysis also exerts considerable influence on char properties. Lower carrier gas flow rates result in longer residence time of vapors in the char matrix, which allows for char-catalyzed secondary reactions to occur. Steam may increase the presence of oxygen in surface functional groups. Carbon-oxygen surface compounds are by far the most important in influencing surface reactions, surface behavior, hydrophilicity, and electrical and catalytic properties of carbons. Substantial quantities of oxygen can be introduced in the course of charcoal production by an oxidating gas such as steam (Strelko et al. 2002).

2.3 Comparison between traditional two-step pyrolysis and activation with 1-step steam pyrolysis Typically chars produced at temperatures around 400 to 600 oC do not have the well developed surface areas or adsorbent properties of activated carbons because of tars deposited on the solid surface that restrict pore structures. Steam activation at temperatures between 800 and 1,100 oC physically removes these residues and opens pores. After activation, chars have higher surface area, adsorption capacity and pore size distribution (Gregova et al. 1994; Alaya et al. 2000). The combination of this two-step process into a single step, which involves pyrolyzing under steam conditions, may increase surface area and increase adsorbent properties, and requires less energy and less time. Steam pyrolysis at low temperatures (600 oC) has been shown to increase micropores with the ratio of micropore volume to total pore volume approaching 95% (Alaya et al. 2000). These authors suggest that steam enhances the evolution of volatile molecules at

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lower temperatures and prevents the cracking of volatiles. In addition, gasification (conversion of solids to gases) is induced much earlier (600 oC compared to 800 to 900 oC in non-steam environments) and results a more porous carbon skeleton. Chars produced at lower temperatures with steam may have a more active surface chemistry; however, the literature is not clear about the impacts of one-step processing on nutrient properties and surface chemistry. Based on available literature on char and activated carbons, it appears that chars produced at low pyrolysis temperatures with steam may hold the greatest promise for agricultural use due to lower production cost, higher surface functional groups for sorption, and a more dense char product.

3. AGRICULTURAL CHARACTERISTICS OF PYROLYSIS CHAR 3.1 Feedstock and Pyrolysis Condition Effects on Nutrient Status Analyses of char from common feedstocks in the Southeastern US confirm the effect of feedstock and temperature on char composition. Total nutrients were analyzed in chars produced from peanut hull (PN), pine chip (PC), and hardwood (HW) feedstocks pyrolyzed at low temperatures (380, 400, and 420 oC) with steam in a small furnace, and poultry litter (PL) at 400 oC in a batch reactor in a steam flow environment (Table 1). At these lower pyrolysis temperatures, the initial nutrient content of the feedstock had a larger effect on char nutrient concentration than pyrolysis temperature (Table 1, Figure 1). Small increases in pyrolysis temperature increased the total nutrient concentration in the char of most nutrients (e.g. K, Figure 1). Table 1. Total carbon and nutrient concentrations for feedstocks and chars (on an as is basis) produced from those feedstocks at 400 oC with steam. Constituent

Peanut hull Poultry Litter Pine chips Hardwood Feedstock Char Feedstock* Char Feedstock Char Feedstock Char C (%) 47.7 65.5 N/A 41.7 46.5 67.0 44.7 70.3 N (%) 1.44 2.00 3.80 3.70 0.05 0.14 0.20 0.30 C:N 33 33 N/A 11 949 543 224 234 S (%) 0.13 0.13 0.42 1.18 0.02 0.02 0.02 0.02 P mg kg -1 732 1,620 11,930 33,580 30.0 235 92.9 278 -1 K mg kg 6,340 15,372 19,339 45,593 436 1,973 937 2,409 Ca mg kg -1 1,880 4,420 17,900 46,760 418 1,686 794 2,709 * Average Georgia poultry litter concentrations analyzed by the University of Georgia Agricultural and Environmental Services Laboratory N/A – not available

9000 8000 7000

K mg kg-1

6000 5000

PC

4000

HW

3000

PN

2000 1000 0 380

400

420

Tem perature

Figure 1. Total nutrients in char produced from pine chips (PC), hardwoods (HW), and peanut hulls (PN) pyrolized with steam at three different temperatures.

At these low pyrolysis temperatures, the total N concentration in the char was similar to that of the initial feedstock (Table 1). Total N concentration in the PL and PN char was high at 3.7% and 2%, respectively. The PL char concentration was higher than that reported for active carbon produced from turkey litter (1.12%) although the N concentration of the turkey litter feedstock was similar at 3.84%(Lima and Marshall 2005b). The turkey litter active carbon was produced at 700 oC and activated with steam at 800 oC, which may have volatilized more N. The N concentrations in PC and HW char were similar to those reported for pinewood (0.11%) and oak board (0.18%) char by Antal and Gronli (2003).

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Although the N concnetration of the PN char is potentially high enough to offer a substantial nitrogen input and the C:N ratio is relatively low (33, Table 1), the N does not appear to be readily available. Nitrogen mineralization was very low in incubations (24-days at 25 o C, 55% water filled pore space) of infertile, low C Tifton soils (fine-loamy, siliceous, thermic Plinthic Kandiudults) amended with PN and PC chars at 11 and 22 Mg ha-1 equivalent rate (Table 2). These PN and PC chars were produced in a pilot scale pyrolysis unit at 400 oC with steam. Peanut hull char C and N concentrations were 72.85and 1.90%, respectively, and PC char C and N were 76.99 and 0.17%, respectively. There was no statistical difference in NH4-N concentrations between the control and char amended soils (p=0.05). There was a trend for higher NO3-N concentrations in the PN amended soils, but only the PN 11 Mg ha-1 rate was statistically different from the control. Table 2. Mean change (final –initial) in ammonium- and nitrate-nitrogen concentrations with standard deviations in Tifton soils amended with peanut hull (PN) and pine chip (PC) char at 11 and 22 Mg ha –1 and incubated for 24 days. Analysis of variance with mean separation by Tukey-Kramer Multiple Comparison test. Letters within the same column indicate statistical difference at the p=0.05 level.

Feedstock

PN 11 PN 22 PC 11 PC 22 Control

n

Δ NH4-N

Δ NO3-N

---------------mg kg-1-------------1.49 +/- 0.24 5.53 +/- 0.65b 0.94 +/- 0.78 5.08 +/- 0.62a 1.19 +/- 0.36 3.62 +/- 0.51a 1.44 +/- 0.26 4.41 +/- 0.16a 1.37 +/- 0.38 3.26 +/- 1.66

4 4 4 4 4

We saw similar indications that N in the high N char was not plant available in the first year of field trials on similar Tifton soils with irrigated corn (Zea mays, Gaskin et al. 2006). Peanut hull char was incorporated to a depth of 15 cm in microplots (1.8 x 2.2 m) at rates of 0, 11 and 22 Mg ha-1 in a factorial combination with two rates of nitrogen fertilizer (0 and 213 kg N ha-1) surface applied as ammonium nitrate. Tissue samples at the earleaf stage during the first growing season only showed a significant effect (p=<0.0001) due to N fertilizer. The mean N tissue concentration in the PN char/no N fertilizer treatments were similar to the control (1.40%) and had average N concentrations averaging 1.13% for the PN 11 and 1.52% for the PN 22 treatment. Nitrogen tissue concentrations in the N fertilized treatments averaged 2.91%. At the p=0.05 level, there was a significant effect due to N fertilizer for both grain yield and stover (p= <0.0001; Figure 2), but no significant effect due to char rate for grain (p=0.7197). There was a significant effect of char rate for stover (p=0.0241). The interaction between char and fertilizer was only significant for the stover (p=0.0145). These preliminary data indicate, although some N may be mineralizing, the N in the PN char is not readily available to microorganisms in the short–term (24-days) and is not highly plant available over a growing season (approximately 4 months). Stover

PN 11 Co nt ro l

PN 22

PN 22 PN 11 Co nt ro l Fe rti liz er PN 22 + PN F 11 + F

Fe rti liz er PN 22 + PN F 11 + F

Mg ha-1

Grain 18 16 14 12 10 8 6 4 2 0

Treatm ent

Figure 2. Corn grain yield and stover (dry wt basis) from Tifton soil plots amended with peanut hull (PN) biochar. Fertilizer – N fertilizer check, PN22+F- PN char at 22 Mg ha-1 + N fertilizer, PN11+F- PN char at 11 Mg ha-1 + N fertilizer, PN22- PN char at 22 Mg ha-1, PN11 char at 11 Mg ha-1, Control- no amendment or N fertilizer.

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Although N in the char does not appear to be readily available, the char may serve as a source for other nutrients, particularly K. Mehlich I K at the end of the first growing season was higher in the PN char amended plots than the control (Table 3). Table 3. Mehlich I K in Tifton soil amended with peanut hull (PN) char at 11 and 22 Mg ha-1. Analysis of variance with mean separation by TukeyKramer Mulitple Comparision Test. Letters within rows indicate statistical difference at p=0.05 level. Depth cm 0-15 15-30

Fertilizer Control PN 11 PN 11 + F PN 22 PN 22 + F --------------------------------------------------- mg kg-1 --------------------------------------------------------28.3 +/- 8.7a 21.3 +/- 4.4a

33.2 +/- 12.6a 24.0 +/- 8.4a

53.2 +/- 6.8b 43.2 +/- 4.1b

49.2 +/- 9.9b 38.4 +/- 7.4b

74.1 +/- 11.0c 68.2 +/- 11.3c

65.9 +/- 14.3c 51.0 +/- 7.0c

3.2 Feedstock and Pyrolysis Condition Effects on Cation Exchange Capacity The PN, PC, and HW chars (Table 1) were analyzed for cation exchange capacity (CEC) using a modified Na-acetate /ethanol/NH4-acetate compulsory replacement method (Sumner and Miller 1996) with sodium analyzed by atomic absorption spectrophometry. Due to interference of the char ash, chars were leached with deionized water before analysis to remove soluble salts. In this preliminary study, there was a trend for higher CEC at 400 oC (Table 4). The PN char had the highest CEC perhaps due to its higher initial mineral concentrations. Table 4. Mean cation exchange capacity and standard deviation in peanut hull(PN), pine chip (PC) and hardwood (HW) chars produced at three pyrolysis temperatures with steam.

Feedstock PN PC HW

380° C

Temperature 400° C

420° C

---------------------------------cmol kg-1-----------------------------------36.7+/-0.76 (n=4) 44.0+/-0.35 (n=2) 28.0+/-5.26 (n=4) 18.6+/-1.34 (n=3) 27.0+/-0.60 (n=2) 16.5+/-2.42 (n=4) 22.6+/-0.04 (n=2) 22.9+/-3.21 (n=2) 14.1+/-0.34 (n=2)

3.3 Feedstock and Pyrolysis Condition Effects on Sorption Properties

Subsamples of the PC and PN chars (Table 1) pyrolyzed at 420oC were ground to <420 µm and washed with deionized water to remove soluble salts and air-dried. Chars were then added to Tifton soils at the rate of 0.05 g char g-1 soil and phosphorus sorption isotherms were determined using batch techniques. Soil-char mixtures were equilibrated with five concentrations of P (0, 5, 20, 50, and 100 mg P L-1) in 0.01M CaCl2 matrix. The capacity and intensity of sorption by soil varied with the type of char added to soil. The amount of P sorbed was highest in soil amended with PN char, while the lowest P sorption occurred in unamended soil (Figure 3). All systems showed a sharp increase in adsorption at low equilibrium P concentrations but sorption eventually reached a plateau. This is a characteristic of an L-curve isotherm where the adsorbate (P) has high affinity for the sorption sites but sorption diminishes regardless of the amount of adsorbate as surface area decreases (Sposito 1989). Such a relationship suggests a strong interaction between the P and the exchange surfaces and that the overall sorption was dependent on the properties of both components (Giles et al. 1960; McBride 1994).

5

160

P adsorbed (mg kg-1)

140 120 100 80 60

Soil + PC

40

Soil + PN

20

Soil alone

0 0

20

40

60

80

100

120

P concentration at equilibrium (mg L-1) Figure 3. Phosphorus adsorption isotherm form a Tifton soil amended with pine chips (PC), and peanut hull (PN) chars pyrolyzed at 420 oC with steam at 0.05 g char g-1 soil .

4. SUMMARY Soils in the southeastern United States are typically have low C, CEC, and base saturation. Studies of Terra Preta soils show charcoal has an important influence on these soils productivity and reviews of the activated carbon literature illuminate some of the physical and chemical mechanisms that could influence soil productivity with char addition. Pyrolysis chars may have the potential to supply nutrients, sorb cations and anions. The literature and our data indicate pyrolysis conditions and the feedstock have considerable effects on char characteristics. Our studies on feedstocks commonly available in the southeastern United States indicate had CECs that potentially increase the ability of low C loamy sands to retain nutrients. Some chars also have the potential to increase P sorption. It is unknown at this point if there would be subsequent desorption of P by char and what affect this may have on crops. Preliminary studies indicate that N from chars with a relatively high N content such as peanut hulls was not readily bioavailable during the first year of cropping, but some chars contain mineral nutrients such as K that are available to crops. Our preliminary work indicates char addition may have potential agricultural benefits, but a better understanding of how char from various feedstocks and produced under different pyrolysis conditions changes soil processes and crop response is needed.

5. REFERENCES Alaya, M.N., B.S. Girgi, and W.E. Mourad. (2000). Activated carbon from some agricultural wastes under action of onestep steam pyrolysis. Journal of Porous Materials 7: 509-517. Antal, M.J. and M. Gronli. (2003). The art, science, and technology of charcoal production. Industrial and Engineering Chemistry Research 42:1619-1640. Asada, T., Ishihara, S., Yamame, T., Toba, A., Yamada, A., and Oikawa, K. 2002. Science of bamboo charcoal: study on carbonizing temperature of bamboo charcoal and removal capability of harmful gases. Journal of Health Science 48[6], 473-479. Bansal, R.C., J. Donnet, F. Stoeckli. 1988. Active Carbon. Marcel Dekker, Inc. New York. 482 pp. Barkauskas, J. (2002). Functional groups on the surface of activated carbons. Part A. Investigation by means of proton affinity distribution. Chemine Technologia, 24 (3). Benaddi, H., T. J. Bandosz, J. Jagiello, J. A. Schwarz, J. N. Rouzaud, D. Legras, and F. Beguin. 2000. Surface functionality and porosity of activated carbons obtained from chemical activation of wood. Carbon 38(5):669-674. Boehm, H.P. (1994). Some aspects of the surface chemistry of carbon balcks and other carbons. Carbon, 32 (5), pp. 759769. Gaskin, J., L. Morris, D. Lee, R. Adolphson, K. Harris, and K.C. Das. (2006). Effect of pyrolysis char on corn growth and loamy sand soil characteristics. Abstracts of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meetings. Nov. 12-16, 2006. Indianapolis, IN.

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Georgia Forestry Commission. (2007). Georgia Facts. http://www.gfagrow.org/facts.asp

Giles, C.H., MacEwan, T.H., Nakhwa, S.N., and Smith, D. 1960. Studies in adsorption. isotherms and its use in diagnosis of adsorption mechanisms and in measurements of specific surface areas of solids. J. Chem. Soc., London, 3973-3993. Glaser, B., J. Lehmann, and W. Zech. (2002). Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review. Biology and Fertility of Soils 35:219-230 Gregova, K., N. Petrov, and S. Eser. (1994). Adsorption properties and microstructure of activate carbons produced from agricultural by-products by steam pyrolysis. Carbon 32(4):693-702. Guo, Y. and D. A. Rockstraw. 2007. Physicochemical properties of carbons prepared from pecan shell by phosphoric acid activation. Bioresource Technology, 98 (8), 1513-1521 Harris, K., J.W. Gaskin, L.S. Sonon, and K.C. Das. (2006). Characterization of pyrolysis char for use as an agricultural soil amendment. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meetings. Nov. 12-16, 2006. Indianapolis, IN. Iswaran, V., K.S. Jauhri, and A. Sen. (1980). Effect of charcoal, coal and peat on the yield of moong, soybean and pea. Soil Biol. Biochem. 12:191-192. Iyobe, T., T. Asada, K. Kawata, and K. Oikawa. (2004). Comparison of removal efficiencies for ammonia and amine gases between woody charcoal and activated carbon. Journal of Health Science 50[2], 148-153. Liang, B., J. Lehman, D. Solomon, J. Kinyangi, J. Grossman, B. O’Neill, J.O. Skjemstad, J. Thies, F.J. Luizao, J. Peterson, and E.G. Neves. (2006). Balck carbon increases cation exchange capacity on soils. Soil Sci. Soc. Am. J. 70:1719-1730. Lehman, J. and M. Rondon. (2006). Bio-char soil management on highly weathered soils in the humid tropics. In: Uphoff, N., A.S. Ball, E. Fernandes, H. Herren, O.Husson, M.Lang, C. Palm, J. Pretty, P. Sanchez, N. Sanginga, and J. Theis (eds). Biological Approaches to Sustainable Soil Systems. CRC Taylor and Francis, Boca Raton, FL. Lehman, J. J. Pereira da Silva, Jr., C. Steiner, T. Nehls, W. Zech, and B Glaser. (2003). Nutrient availability and leachng in an archealogical Ahtrosol and a Ferrasol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant and Soil 249:343-357. Lima, I. and W.E. Marshall. 2005a. Adsorption of selected environmentally important metals by poultry manure-based granular activated carbons. Journal of Chem Technol Biotechnol 80:1054-1061. Lima, I and W.E. Marshall. 2005. Utilization of turkey manure as granular activated carbon: physical, chemical and adsorptive properties. Waste Management 25:726-732. McBride, M.B. 1994. Environmental Chemistry of Soils. Oxford University Press, 406 pp. Oguntunde, P.G., M. Fosu, A.E. Ajayi, N. van de Giesen. (2004) Effects of charcoal production on maize yields, chemical properties and texture of soil. Biol. Fertil. Soils 39:295-299. Perkins, H.,F. (1987). Characterization Data for Selected Georgia Soils. The Georgia Agricultural Experiments Stations, College of Agriculture, The University of Georgia. Athens, GA. Special Publication 43. Sonon, L. K. Harris, J. Gaskin, and K Das. (2006). Phosphorus sorption characteristics of Tifton soil amended with pyrolysis-derived chars. Abstracts of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meetings. Nov. 12-16, 2006. Indianapolis, IN. Sposito, G. (1989). The Chemistry of Soils. Oxford University Press. NY, USA. Stoeckli, F., A. Guillot, and A.M. Slasli. (2004). Specific and non-specific interactions between ammonia and activated carbons. Carbon 42 (8-9): 1619-1624. Strelko, V., D.J. Malik, and M. Streat. (2002). Characterisation of the surface of oxidized carbon adsorbents. Carbon 40(1):95-104. Steiner, C., W.G. Teixeira, J. Lehman, T. Nehls, J.L. Vasconcelos de Macedo, W. E. H. Blum, W. Zech. (2007). Lang term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant Soil 291(1-2):275-290. Steiner, C. W.G. Teixeira, J. Lehman, and W. Zech. (2004). Microbial response to charcoal amendments of highly weathered soils and Amazonian dark earths in Central Amazonia – Preliminary results. In: B. Glaser and W.I. Woods (eds). Amazonian Dark Earths: Explorations in Space and Time. Springer-Verlag, New York, NY. pp. 195212. Sumner, M.E. and W.P. Miller. (1996). Cation exchange capacity and exchange coefficients. In: Methods of Soil Analysis. Part 3. Chemical Methods. Soil Sci. Soc. Am. and Am. Soc. Agron. SSSA Book Series No. 5. Topoliantz, S., J-F. Ponge, and S. Ballof. (2005). Manioc peel and charcoal: a potential organic amendment for sustainable soil fertility in the tropics. Biol. Fertil. Soils 41:15-21. USDA. (2002). Census of Agriculture. 29 May 2007.

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Distributed Hydrogen Production with Profitable Carbon Sequestration: A Novel Integrated Sustainable System for Clean Fossil Fuel Emissions and a Bridge to the New Hydrogen Economy and Global Socio-Economic Stability

Danny M. Day, Eprida, Inc., 6300 Powers Ferry, Suite 307, Atlanta, Georgia danny.day AT eprida.com, 404-228-8687 Robert J. Evans, National Renewable Energy Laboratory, Golden, Co James W. Lee, Oak Ridge National Laboratory, Oak Ridge, TN Introduction and Abstract Carbon dioxide (CO2) emissions from fossil fuel combustion directly contribute to ris ing atmospheric CO2 levels, which in turn are likely linked to global climate change. The need for efficient and economical technologies to rapidly sequester point source production of carbon dioxide has become both an urgent and widespread technical need. The significant adoption of any mitigation technology requires a measurable return to end-users. An example is coupling enhanced oil recovery (EOR) with deep well injection of CO2, though to be economically viable, the carbon dioxide source must be co-located with the oil fields. We propose an integrated sequestration approach in which agricultural waste products are used to produce hydrogen, a renewable fuel, and a carbon sequestering soil amendment (char) as a valuable co-product. The dual function char, derivitized with ammonium bicarbonate (2NH4 HCO3 ) (“ABC”) obtained from treating power plant CO2 emissions, acts both as an enriched carbon, organic slow release fertilizer and a long-lived carbon storage medium in soils or ECOSS™.

This project had the following objectives:

?To verify a hydrogen co-product could be produced that would offer sufficient value for high volume application ?Test a simply production process that would allow the co-product to be produced from the exhaust of fossil fuel combustion, ?Analyze the material for characteristics needed of a large volume co-product.

The ammonium bicarbonate technology, developed through the collaboration of Oak Ridge National Laboratory (ORNL), the National Renewable Energy Laboratory (NREL) and Eprida Scientific Carbons, Inc. (E-SCI), operates at ambient temperature and pressure and does not require carbon dioxide separation or energy intensive compression. Chars generated from agricultural waste pyrolysis have been derivitized with the ammonium bicarbonate. This research provides results that point toward the utilization as a time-release fertilizer while concurrently sequestering stable charcoal in soils and producing an excess of hydrogen. This hydrogen manufacturing and sequestration strategy utilizes the largest existing market for hydrogen (i.e. the production of fertilizer) and leverages the existing farm fertilizer infrastructure to restore soil carbon lost by erosion and extensive tillage. An ancillary benefit of this process is the accrual of carbon credits from capturing power plant emissions, producing a long-lived carbon soil amendment, and enhancing plant growth. If this integrated strategy ultimately proves successful, then the agricultural sector can play an inte gral role in developing the hydrogen economy and restore soil carbon, sequestering vast amounts of carbon, while increasing available nitrogen and sustained natural sequestration will occur through enhanced plant growth. Implementation could allow hydrogen production to work synergistically with fossil fuel emission reductions. A global economic stimulus is possible through profitable sequestration, increased farm productivity, local energy production, rural income opportunities, small business development and offer hope for a positive and sustainable future.

1

Step 1. Hydrogen Production Leveraging Photosynthesis Extract Hydrogen From Organic Matter

Catalytic Steam Reforming 60% H2 20% CO2 7% CO 3% CH4

100-Hour Field Demonstration of Hydrogen From Biomass Catalytic Steam Reforming (August 2002)

Plus 20% (by weight) Charcoal

But why produce charcoal? 2

Step 2: Evaluation of Charcoal as a Sequestration Media and Carrier for Plant Nutrients A Valuable Co-Product? We began to investigate the use of the material as a soil amendment and nutrient carrier after employees mentioned that a mound of char, used to supply char for start-up operations was covered in vegetation and more specifically turnips. Someone had tossed some turnip seeds, on the two year old, chest high, char pile. It was comprised only of char with no soil, yet on plants completely covered the mound. The plants appeared healthy with roots that enveloped each char particle. The turnips, unfortunately could not be inspected as they already had been eaten, but it was reported they were “Good!”.

The missing turnips

Charcoal Background ? Forest fires have been sequestering carbon in the soil in as charcoal for billions of years ? The half-life of charcoal in the soil is measured in 1000’s of years (Skjemstad) ? Charcoal even in weathering environments can be found as old as 11,000 years old (Gavin) Charcoal is a natural part of all soil carbon content

Carbon in the Soil ?Char is a pyrogenic carbon, often lumped under the classification of black carbon ? Black carbon is a term widely used for soot, an amorphous residue of combustion and a contributor to global warming. Char is not soot. ? Char found in soils from forest and range fires has a carbon framework remaining after the pyrolysis of volatile organics. ? Charcoal has proven itself with over 2000 years of testing as a soil amendment in terra preta soils.

The Terra Preta Soil Experiment, 2000 Years Old Terra Preta refers to black high carbon (9%) earth-like anthropogenic soil with enhanced fertility due to high levels of soil organic matter (SOM) and nutrients such as nitrogen, phosphorus, potassium, and calcium. Terra Preta soils occur in small patches averaging 20 ha. These man-made soils are found in the Brazilian Amazon basin, also in Western Africa and in the savannas of South Africa. C14 dating the sites back to between 800 BC and 500 AD. Terra Preta soils are very popular with the local farmers and are used especially to produce cash crops such as papaya and mango, which grow about three times as rapid as on surrounding infertile soils. (Map reprinted by permission: Steiner, 2002)

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Current Research

The images above were provided for this poster by Christoph Steiner, who has been recreating Terra Preta soils in Brazil since 1999. •Amount of applied organic matter (25% increase of Corg in 0-10 cm • Increased the soil C content ~ 0.75% •Applied Charcoal 11 t / ha •Mineral fertilizer: N (30), P (35), K (50), lime (2100 kg/ha) International Workshop on Anthropogenic Terra Preta Soils, (July 2002 Brazil)

Pyrogenic Carbon Benefits •

Terra Preta soils contain 15-60 Mg/ha C in 0-0.3m but 1-3Mg/ha may be sufficient to enhance plant growth (GLASER et al.)

•

Surface oxidation increased cation exchange capacity (GLASER)

•

Char decreased leaching significantly (LEHMANN)

•

Char traps nutrients and supports microbial growth (Pietikainen)

•

Char increased available water capacity by more than 18% than surrounding soils (GLASER)

•

Char experiments have shown up to 266% more biomass growth (STEINER) and 324% (Kishimoto and Sugiura)

Characteristics of an Optimized Pyrogenic Fertilizer

Good cation exchange

600 C 450 C 400 C

Int ita il pH

12

4.

900 C

10

Internal pore structure for deposition

8

3.

10 9.5 9 8.5 8 7.5 7 6

Low leaching rates

4

2.

Leaching Examination of Different Chars

2

A source for microbial energy

pH

1.

100ml Rinse - Char Sample 20.0g

Intra-particle volatile fatty acids deposits (Runkle et al.) occurring inside exothermic zone of pyrolysis are an excellent microbial energy source (Westjohn et al.) for processing nitrogen compounds. We speculated that near the dew point temperature a suitable material might require no outside fuel. Leaching experiments were conducted of materials from different temperatures. Crushed and sieved (US #30 mesh), 20g samples was soaked for 5 minutes in 48% NH 4 NO 3 solution and allowed to dry for 24 hours. Samples were leached with 100 ml rinses ( 8.0 pH). The 400C sample displayed very low leaching rates and was chosen as a starting material.

4

Step Process Step 3: 3: Process MapMap An additional benefit of the process is its ability to combine with SOx and NOx from fossil fuel exhaust. Both of the molecules are scrubbed from the exhaust to form value added nutrients.

Process Flow : H2 Production w/ECOSS (Patent Pending) Forest Residue / Energy Crops

CO2

H2 + CO2

Pressure Swing Adsorption

Pyrolysis Reactor #1

Char

Pyrolysis Reactor #2 (Opt)

Char

Steam Reformer

Steam

Pyrolysis Reactor #3 (Opt)

Char

Pyrolysis Off-Gas

(or alternate H2 System)

H2 (73%) Use/Sell

Water

H2 (27%)

Purifier/Dryer

Compressor

Heat Exchanger

Recycling Pump

Metering

Catalytic Converter

Condenser

Clean Exhaust

Nutrient Mix/PK Ammonia

Char

N2

(Opt. Ammonia Purchased)

Blending Fluidized Cyclone

Fossil Fuel Gases w/ CO 2/SO x/NOx

5

Multistage Release ECOSS Fertilizer

Step 4: 4: Bench Bench Step Scale Reactor 50 kg of char was prepared at 400C. After initial heat up, no additional heat was added and the pyrolysis unit ran exothermically. The high temperature rotary value discharged the char into a closed container where it cooled. The granular material was ground and sieved to a uniform particle range. (2030 US Mesh)

The reactor was fed powdered char, ammonia (saturated with water), and CO2. A variable speed rotor suspended the particles and as the ammonia and CO2 derivitized ammonium bicarbonate, they would gain mass and move down the cyclone until reaching the discharge cyclone. The speed of the rotor controlled average residency time. The sand like material formed within 5-15 minutes and the larger granules (Nitrogen >10%) between 15-30 minutes.

Step 5: Analysis Exterior

The exterior images show the visible build up on the outside of the particles. After crushing a particle, the formation of the ammonium bicarbonate inside the fractures and interior cavities can be clearly identified.

Formation of ABC in Fractures

Char

Sand like

Granular

Slow Release Mechanisms

Volcano like Structures around pores

Exterior Buildup as Expected

Sizable Interior Cavities

Interior View 422x 6

The SEM to the left is of the sand like material and was taken of the crushed interior. The charred carbon framework of the plant cell structure is visible, appearing like plastic. The volatile organics inside this char provide the needed energy source for microbial action. The ammonium bicarbonate appears as cotton-like fibers.

Interior Image (Sand Like - 2000X)

Charred Plant Framework

The image below shows ammonium bicarbonate has filled the interior of the large granular particles.

ABC Deposits

Granular Interior – 1000X

Step 6: Potential Impacts Evaluation Carbon Dioxide per Million BTU

Bituminous Diesel

Fuel

Gasoline Propane

CO2 kg/MBTU

Liquified Petroleum Gases (LPG) Natural Gas (Pipeline) H2 & ECOSS

-100

-50

0

50

100

Current energy use ~400Ej/yr (Lysen) and CO2 is increasing by 6.1 Gt/yr (IPCC). Each 1.0 MBTU H2/ECOSS represents 91kg (as measured, not calculated) of sequestered CO2, then 6.1Gt/91kg equals 0.07Ej or 0.01.8% of the current world consumption of energy. 7

Conclusions Material Balance and Production Limits (Energy is not the limiting factor) At theoretical maximum H2 –CO2 conversion there would only be enough CO2 to convert 61% of H2 to ABC and since our target nitrogen content for the pyrogenic carbon is 10%, (requiring 45% carbon by weight), our limit becomes the 20% carbon char (wt. 12) vs the 56% of ABC (mol.wt. 79). The limit is therefore the carbon char as a carrier utilizing only 27% of available hydrogen but sequestering 91kg of carbon dioxide (as measured experimentally) per million BTU of hydrogen utilized for energy. In addition, there is more than 91kg when the carbon sequestered in the form of additional plant growth and CO2 equivalents from reduced greenhouse gas emissions from lower power plant and fertilizer NOx release. ?

Hydrogen and carbon sequestration can be economically combined.

?

Production of a valuable sequestering co-product during hydrogen production has a

potentially large volume application ?

The material displays characteristics which will reduce nutrient leaching and loss

?

Production of a nutrient inside carbon pores for physical slow release mechanism possi-

bly enhancing plant uptake and reducing fertilizer GHG emissions. ?

Physical micro pore structure offers safe haven for enhanced microbial activity and in-

creased soil fertility ?

Intra-particle deposition of volatile fatty acids offer microbial energy source and enhance-

ment of nitrogen compound processing. ?

Increased cation exchange and water holding capacity provide better plant-soil efficien-

cies. ?

Provides a stable sequestration method where existing fertilizer business infrastructure

can profit ?

Offers forestry and agriculture a method to enhance carbon sequestration and fiber/crop

yields danny.day AT eprida.com 404-228-8687 http://www.eprida.com

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Danny Day Eprida 6300 Powers Ferry Rd, Suite 307 Atlanta, GA 30339

The Potential for Biofertilisers The growth in agricultural production during the last three decades has been accompanied by a sharp increase in the use of chemical fertilisers, causing serious concern (Marothia, 1997). Foremost among these concerns is the effect of excessive fertiliser (especially nitrogenous fertilisers) on the quality of soil and ground water.8 Biofertilisers are considered to be an important alternative source of plant nutrition. They are biologically active products, including bacteria, algae or fungi, with the ability to provide plants with nutrients. Most biofertilisers belong to one of two categories: nitrogen fixing and phosphate solubilising. Nitrogen fixing biofertilisers fix atmospheric nitrogen into forms which are readily useable by plants. These include rhizobium, azatobacter, azospirillum, blue green algae (BGA) and azolla. While rhizobium requires symbiotic association with the root nodules of legumes to fix nitrogen, others can fix nitrogen independently. Phosphate solubilising micro-organisms (PSM) secrete organic acids which enhance the uptake of phosphorus by plants by dissolving rock phosphate and tricalcium phosphates. PSMs are particularly valuable as they are not crop specific and can benefit all crops (Table 2). Table 2. Major biofertilisers and target crops Biofertiliser Rhizobium A zatobacter A zospirillum Blue green algae (BG A) A zolla Phosphate solubilising microorganisms (PSMs)

Target Crop Leguminous crops (Pulses, oilseeds, fodder) W heat, rice, vegetables rice, sugarcane rice rice all

Production of biofertilisers in India The idea of using micro-organisms to improve land productivity has been around in India for at least 70 years, but it was only in the 1990s that large scale production of various biofertilisers commenced. Presently, a number of agricultural universities, state agricultural departments and commercial enterprises produce various biofertilisers. The promotion of biofertilisers is mainly carried out by the National Biofertiliser Development Centre (Ghaziabad), which was set up in 1987. The main objectives of the National Centre are to: 8 Water containing excess of nitrates can affect the blood’s ability to transport oxygen, with serious health implications (WHO, 1963).

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• produce and market biofertilisers of required quality; • isolate and maintain biofertiliser strains suitable to various agro-climatic regions; • train agricultural extension workers; • promote biofertilisers through field demonstrations; • prepare quality parameters; • test samples of biofertilisers produced by others; • provide technical and financial assistance to units producing biofertilisers. The National Centre has the capacity to produce 375 tons of biofertilisers per year. In addition to this, 58 commercial production units have been set up with government support. India’s total production in 1998-99 was reported to be 16,000 tons.9 Rhizobium accounts for the largest proportion (40%) of the total production in India. This is followed by azatobacter. With the increase in the price of phosphate fertilisers, the potential for the use of PSM has also increased.

Effectiveness of biofertilisers A considerable amount of research has been done to establish the effectiveness of biofertilisers on various crops, in different agro-climatic regions. Most agricultural universities, the ICAR and the National Biofertiliser Development Centre have carried out a number of field trials to document the effectiveness of these micro-organisms. These programmes show that the use of biofertilisers can have a significant effect on the yield of most crops. However, their effectiveness is found to vary greatly, depending largely on soil condition, temperature and farming practices. As an example, Table 3 shows the effect of azatobacter on yield. Table 3. Effect of azatobacter on crop yield Crop

Increase in yield over yields obtained with chemical fertilisers (%)

Food grains W heat Rice M aize Sorghum

8-10 5 15-20 15-20

Crop

Increase in yield over yields obtained with chemical fertilisers (%)

O ther Potato Carrot Cauliflo w er Tomato Cotton Sugarcane

13 16 40 2-24 7-27 9-24

Source: Das, 1991

9 Dr. T. Singh, pers. comm., Director, National Biofertiliser Development Centre.

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The Case Study: Karnal and Bhiw ani Districts, Haryana A field study was initiated in two districts in Haryana to try to understand why biofertilisers and biopesticides were not being adopted on a wide scale. The study focused on two districts: Karnal and Bhiwani. While Karnal represents intensive agriculture with a high degree of irrigation, Bhiwani represents dryland farming, with low level irrigation. The potential for biofertilisers and pesticides is described below, followed by the results of our interviews with farmers to establish why biofertilisers and biopesticdes have not been taken up more widely.

The Potential for Biopesticides and Biofertilisers in Haryana The problems caused by excessive pesticide use are particularly serious in rice and cotton in Haryana, both important crops in our study districts. The American bollworm, jassid and white fly in cotton; and stem borer in rice; have developed resistance to chemicals in many parts of Haryana, including parts of the districts studied. In this situation there is great potential for biopesticides. The potential of biofertilisers is evidenced by the fact that about 90% of Haryana’s soil is deficient in nitrogen, indicating severe nutrient deficiency (Dahiya et al., 1993). The dryland districts such as Bhiwani, Mohindergarh, Sirsa and Faridabad are particularly low in nitrogen, and soils are short of organic matter due to poor vegetative cover, high temperatures and the light texture of soil. Biofertilisers could play a role in providing the much needed nutrients and improving soil conditions in these dryland areas, which account for about 28% of the state’s total cultivable area. Biofertilisers can also reduce the intensity of chemical fertiliser consumption, especially in irrigated areas. With the increase in cropping intensity (see below), the use of chemical fertilisers has increased significantly in these areas. The use of organic manure, on the other hand, has not increased. As a result, many parts of Haryana face deteriorating soil conditions and increasing ground water contamination. The suitability of biofertilisers for various crops grown in Haryana has been shown through demonstrations conducted by the Hissar Centre of the National Biofertiliser Development Centre (NBDC). Azatobacter and azospirillum, which can be used for a wide range of crops, are estimated to have particularly large potential. For example, NBDC experiments showed an increase in yield between 3 and 25% with the application of azotobacter in cotton. Similarly, in the case of wheat, use of azotobacter resulted in yield increases between 2 and 20%.10

10 National project on use and development of biofertilisers. Biofertiliser News, 1(2), December 1993.

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The potential for the use of rhizobium is largely confined to the dryland areas of Haryana, where pulses are commonly grown, and where the soils show poor to moderate nodulation.11

Karnal District In Karnal the main nutrient and pest problems relate to the district’s high cropping intensity. Wheat-rice rotation has been common for some time now, and cropping intensity has recently increased further with the introduction of short duration rice varieties such as Govinda (90 days). Planting these varieties allows farmers to take two rice crops between April and October. The first paddy crop is planted in April-May, as soon as wheat has been harvested. This rice crop is ready for harvest by mid July. This is followed immediately by the transplanting of fresh paddy seedlings. The second rice crop is harvested by the end of October, to be followed by wheat, which is sown by early November. This very high intensity of cropping has worsened both the soil quality and pest problem in parts of Karnal. It is extremely damaging to the soil condition, as large amounts of nutrients are used continuously without replenishment. As a new crop is planted as soon as the older crop is harvested (sometimes both activities are done simultaneously), there is no time for proper land preparation and for using organic manure. As the use of chemical fertilisers has increased to provide the required nutrients, soil and water conditions have deteriorated. The problem of pests and pesticide use in Karnal is largely confined to rice. Growing two rice crops without a break is one factor. The continuation of rice plants in the same field, and the high degree of moisture, enable pests to multiply without a break, leading to particularly intense pest attacks in the second crop. Another reason is the popularity of certain basmati varieties which are highly susceptible to pests and diseases. This is particularly serious in one of the most popular of these varieties, called duplicate basmati. This variety was introduced about five years ago from West UP, and became very popular because of its high yields,12 and totally replaced the desi (traditional) basmati variety in many areas. After performing well for three years, the variety began to be affected by pests (stem borer, leaf folder and white back plant hopper) and diseases (sheath blight, blast and bacterial leaf blight) two years ago. The attack was particularly severe last year, forcing many farmers to stop planting basmati in general, and duplicate basmati in particular. In one of the villages we studied, Kuuchhpura, farmers made up to 15 pesticide applications last year but could not save the crop. This year, very few farmers have planted basmati in the village.

11 The assimilation of atmospheric nitrogen by the roots of pulse (and other leguminous) crops is carried out by the nodules formed in the roots of these plants. The low degree of nodulation suggests that their ability to assimilate atmospheric nitrogen is low and that they could benefit from the use of rhizobium. 12 Compared to the average yield of 10 quintal/acre from desi basmati, the yields of duplicate basmati were about 20 quintal/acre.

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The problem of pesticide resistance in stem borer is now common in Karnal, largely caused by the indiscriminate and excessive use of pesticides. Another important reason relates to the fact that farmers in Karnal do not spray their fields themselves. This is done by professional workers who are sent by the shops selling pesticides. As these workers are paid by the area covered, they do a rushed job. The spraying is not uniform: while some parts of the fields get very little, others get excessive pesticides. Secondly, in order to save time they use about one third of the water prescribed to make the pesticide solution. The non-uniform spray of highly concentrated pesticide solution is reported to be a major reason for the development of resistance in rice pests in many parts of the district.13

Bhiw ani District In Bhiwani, the focus of the study is on cotton and gram, which, along with wheat and mustard are the main crops in the area. The use of chemical fertilisers is comparatively low in Bhiwani, being used only on wheat and cotton, and not at all on gram and mustard. But, as in Karnal, use of organic manure is not common and the condition of the soil is poor. Three biofertilisers have potential for Bhiwani: rhizobium for gram and azatobacter and PSM for wheat. The potential of rhizobium is reported to be particularly high in Bhiwani because the level of nodulation is very low. The District Agriculture Department is responsible for the sale of rhizobium in Bhiwani. Being a major gram growing district, it was allocated the largest amount of rhizobium last year and its sale to farmers is subsidised at the rate of 50%. The main pest problem in Bhiwani concerns cotton, which is attacked by American, pink and spotted bollworm, white fly and jassid. These pests have become resistant to most pesticides. According to a study of pesticide use in Bhiwani in 1998, about 70% of farmers reported that they were unable to control pests with pesticides (Saini and Jaglan, 1998). Some of these farmers had used up to 11 pesticide applications. The pest problem in Bhiwani is closely linked with the spread of irrigation facilities. Large parts of Bhiwani district are irrigated by the Indira Gandhi Canal, which suffers from large scale seepage. This has led to a rise in the groundwater level from 50-60 feet below the surface in the past to 5-10 feet at present in many areas. As a result, water logging and high humidity are serious problems in many areas of the district. Apart from causing direct damage, this has also created favourable conditions for the growth of pests. Consequently, the problem of pests has become extremely serious in the district during the last five years. The pest problem caused the area under cotton to decline in the second half of the 1990s from 57, 000 hectares in 1996-97 to 51,000 hectares in 1999-2000.14 As in rice 13 Information from the District Agricultural Officers. 14 Information provided by the State Agricultural Department, Bhiwani.

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in Karnal, the pest problem in cotton in Bhiwani is closely related to the susceptibility of the varieties being planted. The cultivation of cotton in this area is comparatively new: it was introduced in the 1970s. Most of the varieties introduced since then are long staple, American types. Although they fetch high prices, they are highly susceptible to various cotton pests. The problem of pests and the excessive use of pesticides in Bhiwani is mostly confined to the American varieties. Desi varieties, which are comparatively resistant to pests and diseases, require less use of pesticides. We observed a shift back in favour of desi cotton in one of the divisions of Bhiwani following severe losses to pests to the American varieties. Whilst many more farmers would prefer to shift to desi cotton varieties, as they provide stable yields, their wholesale prices are too low. In addition it appears that the state agriculture department prefers to promote long staple American varieties, as they have large domestic and export markets.

Farmers’ Perspectives We selected 11 villages from the two districts, six villages from Karnal and five from Bhiwani, in which to interview farmers to establish their awareness and use of biofertilisers and biopesticides. A total of 74 farmers from these villages were interviewed, and were mainly selected because they had attended one of the demonstration programmes carried out by government agencies to promote IPM, biopesticides and biofertilisers (58 of the farmers, or about 80% of the sample). However, some farmers who had not been to the programmes were also interviewed (16 farmers). All the farmers were men; only men had participated in the demonstration programmes, and we were told that men take the decisions about the types of fertilisers and pesticides to be used. The farmers included in the study represent the range of small, medium and large farmers. While 29% of the farmers have less than 5 acres of land, 46% have between 5 and 20 acres. 25% of the farmers have landholdings larger than 20 acres. In terms of education, about one third of the farmers have studied up to class 10 or more. A semi-structured questionnaire was used for interviews, which were conducted in farmers’ homes.

Findings: Biopesticides Although biopesticides and bio-control agents are important components of IPM, the IPM programmes being conducted by various agencies put very little emphasis on these agents. None of the farmers we interviewed had ever used biopesticides, and few were even aware they existed. We found that none of the farmers had even used neem, widely believed to be commonly used by Indian farmers. In fact, we found that IPM itself was not being practised by most farmers. While some of the farmers were aware of IPM practices, such as the need for monitoring and

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augmenting natural enemies of pests, very few farmers have adopted these practices. None of the farmers practised IPM fully, but about 15% practised partial IPM. In most cases this meant delaying the first spray of pesticides until damage by pests becomes evident. The situation is particularly bad in Bhiwani, where 85% of farmers reported not using IPM at all and only 9% reported using some aspects of IPM. Compared to this, 20% of farmers reported using limited IPM in Karnal. This is despite the fact that most of the farmers included in the study participated in the IPM demonstration programmes conducted by the Central IPM.

W hy is IPM not practised? We found four important reasons for the low acceptance of IPM: 1. Lack of awareness. This reason was found to be particularly important in Bhiwani, where 77% of farmers were unaware of the concepts of IPM. Compared to this, fewer than 3% of farmers in Karnal were unaware of IPM. Clearly, there is a big districtwise difference in the success of IPM demonstration programmes and state agricultural extension workers in familiarising farmers with IPM. In Karnal these agencies have been successful in at least making farmers aware of the need to practise IPM. 2. Lack of skills. Almost all the farmers, including all of those who were aware of IPM, reported that they lacked the skills necessary to practise IPM. Their ability to practise IPM was, for example, severely constrained by the fact that most of them could not differentiate between harmful and beneficial insects. In fact, many farmers thought that all insects were a potential threat to their crop and had to be destroyed. They were also not able to work out economic thresholds15 to determine the timings of pesticide application. 3. Lack of faith in IPM. This factor was found to be very important amongst 60% of farmers in Karnal. Although almost all of them were aware of IPM, they felt that they did not have sufficient faith in it to reduce the use of chemical pesticides. Many of them felt that the support from the agricultural department was not adequate for them to try IPM practices, which were considered risky. As the CIPM personnel do not keep in touch with the farmers after IPM demonstrations, they felt that they would not get adequate advice and support if things went wrong. Similarly, the local extension workers (ADOs) are not sufficiently trained in IPM to instil confidence in the farmers. The issue of skills and confidence is obviously linked to the intensity of training provided by the IPM agencies to farmers and extension workers. We found that the training is very basic and superficial, being conducted for three to four days in a village, during which 30 villagers and five extension workers are trained. The farmers felt that the training was not intensive and did not impart sufficient skills for them to feel competent and confident in following IPM practices. 15 The economic threshold is the level of pest population at which the damage to crop justifies the use of pest control methods.

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4. IPM practices are difficult and cumbersome. About 70% of the farmers in both districts who were aware of IPM, felt that the IPM practices were too cumbersome and time consuming to be used regularly. Both the monitoring of pest populations and the calculation of economic thresholds were considered by farmers to be impractical. In Karnal, where cropping intensity is high, the farmers felt that they did not have time to keep a close watch on their fields to monitor pests and calculate economic thresholds.

W hose advice is taken? An important reason for the failure of the IPM programme, and the lack of biopesticide use, is related to the fact that most farmers depend on shopkeepers for advice on pesticide application. More than 80% of the farmers reported that shopkeepers, dealers and representatives of pesticide manufacturers were their most important sources of information about pest control methods (Table 4). Table 4. Importance of source of advice for pesticide application O ther Farmers Karnal Bhiw ani Total

12 (30) 10 (30) 22 (30)

Extension w orkers and agricultural university 18 (45) 9 (26) 27 (36)

Shops/manufacturers/ dealers 33 (83) 27 (80) 60 (81)

Number of responses=74. Note that some farmers listed more than one source of advice as being equally important Note: Figures in parenthesis indicate percentages.

Compared to the manufacturers and sellers of pesticides, agricultural extension workers play a small role, especially in Bhiwani, where only 26% of farmers reported them to be important. The role of shopkeepers and dealers is particularly important because many farmers (58%) purchase their pesticides on credit. This gives the shopkeepers strong control over the amount and choice of pesticides used. It also makes it easier for the shopkeepers to sell spurious pesticides. Finally, we found that the knowledge of the State Agricultural Department about biopesticides was extremely limited. This was particularly true of the village level workers (ADOs), but also the case even in the Central IPM office in Faridabad. Considering the importance given to the use of biopesticides by national government agencies, the neglect of biopesticides at the state and district level is difficult to understand. The main emphasis is on the monitoring of pest populations and the use of economic thresholds, which farmers find too difficult and time consuming. Further, the Haryana

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Agricultural University recommends the use of only two biopesticides (Bt and neem) on only one vegetable crop. On all other crops, including cotton and rice, the recommendations include only chemical pesticides.

Findings: Biofertilisers Few (19%) farmers have ever used biofertilisers in the two districts. Their number was especially small in Karnal, where only three out of 40 farmers had used them. In Bhiwani about 75% of farmers were not even aware of biofertilisers; the proportion of such farmers was even higher in Karnal (85%). The most important reason for this lack of awareness is the fact that agriculture extension workers do not promote biofertilisers. On the whole, only 15% of farmers had been told about biofertilisers by the extension workers. The emphasis on biofertilisers was particularly low in Karnal, where only one farmer out of 40 had heard about them from extension workers. The District Agricultural Departments do not have a positive attitude towards biofertilisers. They feel that their quality is poor, and their performance totally unreliable. Therefore, they are not prepared to risk their reputation and good will with the farmers by recommending them. The extension services run by the Haryana Agriculture University (krishi vigyan kendra) feel that in areas of wheat/paddy rotation, such as Karnal, the potential of biofertilisers is low. The farmers in these areas can get the same yield by using the recommended dose of chemical fertilisers. As these fertilisers are easy to use, the farmers prefer them. Biofertilisers have to be stored and applied in conditions which are suitable for the multipication of micro-organisms. This requires special facilities and care, which farmers are often unable to provide. Chemical fertilisers, on the other hand, can be stored and applied without special care. In fact, the KVK in Karnal does not recommend the use of biofertilisers at all. Nevertheless, the extension workers in Bhiwani are required to sell a fixed number of rhizobium packets. This explains the larger number of farmers who are aware of biofertilisers, and have used them in this district. But we found that a large proportion of the rhizobium allotted to the district is not sold to the farmers, and is allowed to go to waste. The ADOs say that the quality and performance is so poor that the farmers are not interested in buying it. The quota is shown as sold in official records, and the payment is made by the ADOs from their salary.16 The fact that the rhizobium meant for sale in various pulse growing districts is not being used by farmers is widely known to both the State Agricultural Department and the National Biofertiliser Development 16 For example, one of the ADOs in Bhiwani was given a quota of 2000 packets of rhizobium this year. He could manage to sell only about 200 packets, mostly to his contact farmers. But these have not actually been used by the farmers. He feels that the contact farmers accept biofertilisers because they want to stay in the good books of the ADOs, from whom they receive subsidised or free goods, such as seed kits. He will have to pay to the Agricultural Department Rs. 8,000/- (@Rs. 4.00 a packet).

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Centre. However, every year the practice of fixing quotas and reporting of sale is carried out, as if rhizobium is actually being used. Out of 19 farmers who were aware of biofertilisers, 14 had used them, showing that farmers are prepared to try biofertilisers. However, most of these farmers stopped using them after one crop - only three were still using them. Two reasons were reported to be important for the discontinuation of use: lack of availability and poor performance.

Availability Many farmers who stopped using biofertilisers reported that this was partly because the supply was extremely unreliable. This was largely because biofertilisers were not being sold by most shops. While none of the shops stock biofertilisers in Karnal, two shops in Bhiwani do. The shopkeepers, in turn, say that they do not stock biofertilisers because sales are poor. One of the Bhiwani shops, for example, has been stocking biofertilisers from National Fertilisers Ltd. for the last four years but has sold only 30 packets.

Q uality It is clear that the poor quality and performance of biofertilisers present serious problems. Most studies suggest that the biofertilisers being sold in the market are contaminated and have a low count of micro-organisms. It is therefore not surprising that their performance is poor and uneven. For example, in a survey of rhizobium carried out by ICRISAT, 90% of samples from India were found to have a rhizobia count lower than that required for effective performance (Singleton et al., 1996). Incidentally, this problem exists in most developing countries. For example, in a survey of 12 developing countries, only 19% of the samples met the standards prevalent in developed countries (Singleton et al., 1996). The poor performance of biofertilisers in India is primarily linked to inappropriate strains and inefficient production technology. Essentially, the production of bacterial biofertilisers requires the selection of strains appropriate for a particular crop in a given agro-climate. These strains are mass multiplied by adding bacterial culture to a suitable sterilised broth, either using the shake flask method (for small scale production) or the fermenter method (for large scale production). When an adequate growth of bacteria is achieved, the solution is mixed with a carrier such as lignite or charcoal and is packaged. As agro-climatic conditions and soil characteristics vary widely, a large range of strains of each biofertiliser needs to be isolated for each area. The problem of identifying suitable strains is particularly serious in north India, as many of the strains do not survive the very hot temperatures prevalent in these areas. Until strains which can tolerate wide variations in temperature can be identified, the performance of biofertilisers will remain uneven. The Haryana Agriculture University is reported to be working in this direction and has developed improved strains for pearl millet, wheat, mustard, potatoes, and flowering plants. These are, however, yet to be used in large scale production.

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Furthermore, the production of biofertilisers is prone to contamination, which reduces the effectiveness of micro-organisms. It is, therefore, vitally important that throughout the process extreme care is taken to maintain sterile conditions. It is also important that precautions are taken to avoid contamination during the packaging, storage and application of biofertilisers. The production technology employed in India is inefficient and is responsible for most of the contamination common in Indian biofertilisers. Generally, production is undertaken by the flask method, which is unsuitable for large scale production. Although some firms use fermenters, they lack the sophisticated controls and monitoring facilities necessary to regulate factors such as pH, temperature and aeration. As a result the quality of the bacterial broth is often poor and uneven. Another problem relates to the fact that Indian producers do not sterilise the carriers used for mixing the bacterial solution. For example, both the producers in Haryana, the Hissar Biofertiliser Centre and the HAU, use non-sterilised charcoal, as they do not have facilities to sterilise large amounts of charcoal in a short time. This is an important cause of the poor quality and short shelf life of these biofertilisers (Singh et al., 1999). Although India has ISI (Indian Standards Institution) standards for some of the biopesticides (rhizobium and azatobacter), they are not enforced. This is reportedly because the ISI lacks facilities to test biofertilisers.

Conclusions Biopesticides The problem of pests, the development of pesticide resistance and the excessive use of pesticides need to be seen in the totality of the agricultural system. Our study shows that in Karnal and Bhiwani the problem is linked to the increase in cropping intensity (three crops in Karnal), the expansion of irrigation facilities (Bhiwani), the release and adoption of susceptible varieties (govinda and basmati rice in Karnal, and American cotton varieties in Bhiwani), purchase of pesticides on credit (in both the districts) and inappropriate agricultural practices (the use of contract labour for pesticide application, using power spraying machines in Karnal). In the circumstances, mere reliance on pest control, without correcting the basic problem in the system, will not produce sustainable results. The efforts of various government agencies to popularise integrated pest management (IPM), and the use of biopesticides have had little impact. IPM departments have very little knowledge and experience of biopesticides, and most state agricultural universities, on whose recommendations pest control methods are promoted, do not include the use of biopesticides in their recommendations. In the absence of active promotion by the agriculture department, the demand for these products has not developed. It is for this reason that most private shops and dealers do not stock and sell biopesticides.

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Gatekeeper Series no. 93

A Study of Biopesticides and Biofertilisers in Haryana, India

Ghayur Alam 2000

Submitting papers to the Gatekeeper Series We welcome contributions to the Gatekeeper Series from researchers and practitioners alike. The Series addresses issues of interest to policy makers relating to the broad area of sustainable agriculture and resource management. Gatekeepers aim to provide an informed briefing on key policy issues in a readable, digestible form for an institutional and individual readership largely comprising policy and decision-makers within aid agencies, national governments, NGOs and research institutes throughout the world. In addition to this primary audience, Gatekeepers are increasingly requested by educators in tertiary education institutions, particularly in the South, for use as course or seminar discussion material. Submitted material must be of interest to a wide audience and may combine an examination of broad policy questions with the presentation of specific case studies. The paper should conclude with a discussion of the policy implications of the work presented.

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Use short sentences and paragraphs. Keep language simple. Use the active voice. Use a variety of presentation approaches (text, tables, boxes, figures/ illustrations, bullet points). Length: maximum 5,000 words

Abstract Authors should also include a brief summary of their paper – no longer than 450 words.

Editorial process Please send two hard copies of your paper. Papers are reviewed by the editorial committee and comments sent back to authors. Authors may be requested to make changes to papers accepted for publication. Any subsequent editorial amendments will be undertaken in consultation with the author. Assistance with editing and language can be provided where appropriate. Papers or correspondence should be addressed to: Gatekeeper Editor Sustainable Agriculture and Rural Livelihoods Programme IIED, 3 Endsleigh Street, London WC1H ODD, UK Tel:(+44 020) 7388 2117; Fax: (+44 020) 7388 2826; e-mail: [email protected]

The Gatekeeper Series produced by IIED’s Sustainable Agriculture and Rural Livelihoods Programme aims to highlight key topics in the field of sustainable agriculture and resource management. Each paper reviews a selected issue of contemporary importance and draws preliminary conclusions for development that are particularly relevant for policymakers, researchers and planners. References are provided to important sources and background material. The Series is published three times a year – in April, August and December – and is supported by the Swedish International Development Cooperation Agency (Sida). The views expressed in this paper are those of the author(s), and do not necessarily represent those of the International Institute for Environment and Development (IIED), The Swedish International Development Cooperation Agency (Sida), or any of their partners.

Dr Ghayur Alam is Director of the Centre For Technology Studies in New Delhi. His main areas of interest include technology policy, intellectual property rights, agricultural biotechnology and the adoption of environmentally suitable technologies in industry and agriculture. He can be contacted at: Centre For Technology Studies, U 24/20, DLF III, Gurgaon, Haryana 122002, India. Email: [email protected] Tel: +91 (0124) 6355942; Fax: +91 (0124) 6358322 2000

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Executive Summary The use of chemical pesticides and fertilisers in Indian agriculture has seen a sharp increase in recent years, and in some areas has reached alarming levels with grave implications for human health, the ecosystem and ground water. It is therefore increasingly urgent that environmentally friendly methods of improving soil fertility and pests and disease control are used. The potential of biopesticides and biofertilisers for promoting sustainable agriculture has been known for many years. A number of government agencies, including the Ministry of Agriculture and the Department of Biotechnology, are engaged in supporting research, production and application of these agents. However, in spite of these efforts, their use in India is small. This paper investigates the potential of and constraints in the use of biopesticides and biofertilisers, taking the state of Haryana as a case study. It explores the factors responsible for the limited use of these agents, based on detailed discussions with a large number of farmers, various agencies engaged in the promotion of biopesticides and biofertilisers, State Agricultural Department officials, and shopkeepers. The study found that for the use of biopesticides, a key problem was that departments promoting Integrated Pest Management (IPM) have very little knowledge and experience of biopesticides, and most state agricultural universities, on whose recommendations pest control methods are promoted, do not tend to recommend biopesticides. In the absence of active promotion by the agriculture department, the demand for these products has not developed, and most private shops and dealers do not stock and sell biopesticides. The paper recommends that the agricultural departments and universities pay greater attention to the promotion of biopesticides, that IPM training is improved, and that there is a greater focus on cropping techniques and varieties which do not require such a dependence on pesticides. In the case of biofertilisers, their poor quality and performance is a major factor in their limited uptake by farmers. This is primarily linked to inappropriate strains and inefficient production technology. As a result it is recommended that research and development to identify more suitable strains, to develop better production technology and quality control methods is greatly increased, and that in the meantime the various grants and subsidies on biofertilisers are diverted to support these R&D programmes.

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A Study of Biopesticides and Biofertilisers in Haryana, India Ghayur Alam

Introduction The use of chemical pesticides and fertilisers in Indian agriculture has seen a sharp increase in recent years. In some areas, such as Haryana, Punjab and west Uttar Pradesh, it has reached alarming levels. The heavy use of these chemicals has already caused grave damage to health, ecosystems and ground water. It is therefore increasingly urgent that environmentally friendly methods of improving soil fertility and pests and disease control are used. The potential of biopesticides and biofertilisers for promoting sustainable agriculture has been known for many years. A number of government agencies, including the Ministry of Agriculture and the Department of Biotechnology, are engaged in supporting research, production and application of these agents. However, in spite of these efforts, their use in India is small. This paper investigates the potential of and constraints in the use of biopesticides and biofertilisers, and explores the factors responsible for the limited use of these agents. It is based on a study in the state of Haryana, a state which represents the problem of excessive use of pesticides and fertilisers, common in many parts of India. The paper also suggests policy measures for the promotion of biopesticides and biofertilisers in the state. The study is based on detailed discussions with a large number of farmers, various agencies engaged in the promotion of biopesticides and biofertilisers, State Agricultural Department officials, and shopkeepers. The study was carried out in 1999 as part of a research project on agricultural problems, undertaken by the Agricultural Economics Research Centre, University of Delhi.

The Potential for Biopesticides About 80,000 tons of pesticides are used in agriculture in India annually (Srinivasan, 1997), mostly in cotton and rice. While cotton is planted on about 5% of the total cultivable area (on about 8 million hectares out of a total of 170 million), it accounts for about 45% of pesticide application (Dhaliwal and Pathak, 1993). Rice accounts for another 23%. Vegetables and fruit also account for a significant proportion (Table 1).

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Table 1. Cropwise consumption of pesticide in India (%) Cotton Paddy Jowar Fruits and Vegetables Wheat Arhar Other Total

44.5 22.8 8.9 7.0 6.4 2.8 7.6 100.00

Source: Dudani and Sengupta, 1991

The intensive use of pesticides in agriculture is a cause of serious concern. The problem is especially serious because of the development of resistance to pesticides in important pests and the presence of pesticide residue in agricultural and dairy products. Pesticide resistance in agriculture was first noticed in India in 1963 when a number of serious pests were reported to have become resistant to DDT and HCH (two of the most commonly used pesticides during the 1960s and 1970s). Since then the number of pests with pesticide resistance has increased. The most serious problem of resistance is witnessed in cotton, for which American bollworm is a serious pest. The bollworm has developed resistance to almost all pesticides in a number of regions, and is particularly serious in parts of Punjab, Haryana, Andhra Pradesh, Karnataka and Maharashtra. Other important pests of cotton, white fly and jassid, have also developed pesticide resistance in some places. Growing pesticide resistance has meant that a large proportion of agricultural production is lost to pests. According to some estimates, these losses amount to between 2030% of total production (Mehrotra, 1989). The losses are particularly serious in cotton. For example, cotton production in Punjab declined by about 50% during 1997 and 1998,1 causing a number of cotton farmers to commit suicide in the affected areas.2 Pesticide resistance has mainly been caused by excessive and indiscriminate use of pesticides (Jayaraj, 1989). Pesticides of spurious quality, which are commonly sold in small towns and villages, have also contributed to resistance in many areas. For example, in Bidar (Karnataka) where the problem of pest resistance has become extremely serious, more than 50 brands of pesticides were found to be sub-standard in 1998-99. In another incident, the licenses of 115 pesticide producers were cancelled in Punjab for selling

1 “Another bad season for cotton farmers”, Hindustan Times, September 17, 1998. 2 For example, in Punjab 133 farmers were reported to have committed suicide in 1998 due to crop failure caused by pest attack. “Another farmer in debt trap commits suicide”, Hindustan Times, October 4, 1998.

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sub-standard pesticide.3 Sub-standard pesticides contribute to resistance as the pests are repeatedly exposed to a low concentration of pesticides. This contributes to the build-up of resistance, without destroying the pests. The other important problem caused by the excessive and inappropriate use of chemical pesticides concerns the presence of pesticide residue in food. Many of the pesticides currently being used have a tendency to survive in plants for a long time. They also enter the food chain and are found in meat and dairy products. The problem of pesticide residue is already a serious threat to health and environment in India. The incidence of pesticide residue is much higher in India than in developed countries. For example, according to one study, more than 80% of milk samples tested in India were found to contain residues of DDT and HCH (Handa, undated). According to another study, residue of DDT and benzene hexachloride, both suspected carcinogens, were found in breast milk samples collected from mothers in Punjab. The amount of residue was very high and babies were ingesting 21 times the amount of these chemicals considered acceptable through their mothers’ milk (Jumanah, 1994). Compared to this, only 0.17% of samples tested in the US in 1990 were found to contain residues over the acceptable limits.4 Similarly, in a study in the UK, only 1% of the samples were found to contain residues above the prescribed limit.5 It is clear that the excessive use of chemical pesticides in agriculture is a serious cause of concern. It is, therefore, important that alternative, environmentally friendly methods of plant protection are adopted, such as integrated pest management (IPM) techniques, including the use of biopesticides.

Biopesticides and Bio-control Agents Biopesticides are derived from animals, plants and micro-organisms such as bacteria and viruses. The advantages of biopesticides are: • They are inherently less harmful than chemical pesticides; • They are more target specific than chemical pesticides affecting only the target pests and their close relatives. In contrast, chemical pesticides often destroy friendly insects, birds and mammals. • They are often effective in small quantities. Also, they decompose quickly and do not leave problematic residues. The most commonly used biopesticides include Bacillus thuringiensis (Bt), Baculoviruses and neem. In addition to these, trichoderma, which is a fungicide, is also used. Biocontrol agents, such as Trichogramma, are parasites and predators of pests and their 3 “Another bad season for cotton farmers”, Hindustan Times, September 17, 1998. 4 “Current Pesticide Residue Levels in Food are Safe”, Pesticide Outlook (5)1, Feb 94. Cambridge. 5 “Latest UK Pesticide Residue Results Published”, Pesticide Outlook, Dec 1994, pp8. Cambridge.

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eggs. These biopesticides and bio-control agents are briefly described below: • Bacillus thuringiensis (Bt). Bacillus thuringiensis is the most commonly used biopesticide globally. It is primarily a pathogen of lepidopterous pests which are some of the most damaging. These include American bollworm in cotton and stem borers in rice. When ingested by pest larvae, Bt releases toxins which damage the mid gut of the pest, eventually killing it. Bt based pesticides are being marketed by three companies in India. The total sale in 1999 was about 70 tons.6 • Baculoviruses. These are target specific viruses which can infect and destroy a number of important plant pests. They are particularly effective against the lepidopterous pests of cotton, rice and vegetables. Their large-scale production poses certain difficulties, so their use has been limited to small areas. They are not available commercially in India, but are being produced on a small scale by various IPM centres and state agricultural departments. • Neem. Derived from the neem tree (Azadirachta indica), this contains several chemicals, including ‘azadirachtin’, which affects the reproductive and digestive process of a number of important pests. Recent research carried out in India and abroad has led to the development of effective formulations of neem, which are being commercially produced. As neem is non-toxic to birds and mammals and is non-carcinogenic, its demand is likely to increase. However, the present demand is very small. Although more than 100 firms are registered to produce neem-based pesticides in India, only a handful are actually producing it. Furthermore, very little of the production is sold locally, most being for export markets. • Trichoderma. Trichoderma is a fungicide effective against soil born diseases such as root rot. It is particularly relevant for dryland crops such as groundnut, black gram, green gram and chickpea, which are susceptible to these diseases. Three companies are marketing trichoderma in India. • Trichogramma. Trichogramma are minute wasps which are exclusively egg-parasites. They lay eggs in the eggs of various lepidopteran pests. After hatching, the Trichogramma larvae feed on and destroy the host egg. Trichogramma is particularly effective against lepidopteran pests like the sugarcane internode borer, pink bollworm and sooted bollworms in cotton and stem borers in rice. They are also used against vegetable and fruit pests. Trichogramma is the most popular bio-control agent in India, mainly because it kills the pest in the egg stage, ensuring that the parasite is destroyed before any damage is done to the crop. A number of countries produce Trichogramma on a large scale. For example, in the former Soviet Union more than 10 biological factories were reported to produce about 50 billion Trichograma and other parasites per season. Similarly, more than 50 commercial insectaries are reported 6 Dr MC Sharma, pers. comm. Director, Biotech International, New Delhi.

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to be producing Trichogramma and other parasites in the USA and Canada. A number of communes in China are also known to produce Trichogramma on a large scale. Whilst India does not have technology to produce Trichogramma on a large scale, they are being produced in small scale facilities for local use, mostly by sugar mills and cooperatives, state agricultural departments, IPM centres and agricultural universities. Recently, some companies have started marketing Trichogramma through direct selling. But the volume of sale is very small. Trichogramma eggs have to be used within a short period (before the eggs hatch). This limits their production and marketing on a large scale, and is also the reason why Trichogramma is not sold through dealers and shopkeepers.

Promotion and effectiveness of Integrated Pest Management and biopesticides The Ministry of Agriculture and the Department of Biotechnology are responsible for promoting biopesticides, the former via the Central IPM Centre (Faridabad), the National Centre for IPM (NIPM) under the Indian Council For Agricultural Research (ICAR) and the Directorate of Biological Control. As a part of the Department of Biotechnology’s demonstration programme, biopesticides have been demonstrated on about 55,000 hectares (Wahab, 1998). The Department has also supported a pilot plant at the Tamil Nadu Agricultural University (Coimbatore) to develop and demonstrate production and application technologies for baculoviruses, trichoderma and Trichogramma. Some Integrated Pest Management (IPM) demonstrations have shown success in controlling pests without the use of chemical pesticides. For example, NIPM carried out a demonstration in rice in a village in west UP on 100 acres in 1999. NIPM totally substituted chemical pesticides with the bio-control agent Trichogramma, which is effective against both stem borer and leaf folder. According to NIPM, the control of pests was complete and the yields were between 6-7 tons/hectare. Compared to this, the yield in the area where chemical pesticides were applied was only 3.5 to 4 tons per hectare (Damodran, 1999). In another successful demonstration by NIPM on cotton in Maharashtra during 199899, Baculoviruses, neem and Trichogramma were found to be more effective in controlling pests than chemical pesticides. The yield in these plots was about 1 ton/hectare, compared to yields of only 300 to 500 kilograms/hectare in the fields where chemical pesticides were used.7

7 “Integrated Pest Management Module for Dryland Regions - ICAR Trials in Cotton Fields Successful”. Hindu Business Line, 4.1.1999.

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The Potential for Biofertilisers The growth in agricultural production during the last three decades has been accompanied by a sharp increase in the use of chemical fertilisers, causing serious concern (Marothia, 1997). Foremost among these concerns is the effect of excessive fertiliser (especially nitrogenous fertilisers) on the quality of soil and ground water.8 Biofertilisers are considered to be an important alternative source of plant nutrition. They are biologically active products, including bacteria, algae or fungi, with the ability to provide plants with nutrients. Most biofertilisers belong to one of two categories: nitrogen fixing and phosphate solubilising. Nitrogen fixing biofertilisers fix atmospheric nitrogen into forms which are readily useable by plants. These include rhizobium, azatobacter, azospirillum, blue green algae (BGA) and azolla. While rhizobium requires symbiotic association with the root nodules of legumes to fix nitrogen, others can fix nitrogen independently. Phosphate solubilising micro-organisms (PSM) secrete organic acids which enhance the uptake of phosphorus by plants by dissolving rock phosphate and tricalcium phosphates. PSMs are particularly valuable as they are not crop specific and can benefit all crops (Table 2). Table 2. Major biofertilisers and target crops Biofertiliser Rhizobium Azatobacter Azospirillum Blue green algae (BGA) Azolla Phosphate solubilising microorganisms (PSMs)

Target Crop Leguminous crops (Pulses, oilseeds, fodder) Wheat, rice, vegetables rice, sugarcane rice rice all

Production of biofertilisers in India The idea of using micro-organisms to improve land productivity has been around in India for at least 70 years, but it was only in the 1990s that large scale production of various biofertilisers commenced. Presently, a number of agricultural universities, state agricultural departments and commercial enterprises produce various biofertilisers. The promotion of biofertilisers is mainly carried out by the National Biofertiliser Development Centre (Ghaziabad), which was set up in 1987. The main objectives of the National Centre are to: 8 Water containing excess of nitrates can affect the blood’s ability to transport oxygen, with serious health implications (WHO, 1963).

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• produce and market biofertilisers of required quality; • isolate and maintain biofertiliser strains suitable to various agro-climatic regions; • train agricultural extension workers; • promote biofertilisers through field demonstrations; • prepare quality parameters; • test samples of biofertilisers produced by others; • provide technical and financial assistance to units producing biofertilisers. The National Centre has the capacity to produce 375 tons of biofertilisers per year. In addition to this, 58 commercial production units have been set up with government support. India’s total production in 1998-99 was reported to be 16,000 tons.9 Rhizobium accounts for the largest proportion (40%) of the total production in India. This is followed by azatobacter. With the increase in the price of phosphate fertilisers, the potential for the use of PSM has also increased.

Effectiveness of biofertilisers A considerable amount of research has been done to establish the effectiveness of biofertilisers on various crops, in different agro-climatic regions. Most agricultural universities, the ICAR and the National Biofertiliser Development Centre have carried out a number of field trials to document the effectiveness of these micro-organisms. These programmes show that the use of biofertilisers can have a significant effect on the yield of most crops. However, their effectiveness is found to vary greatly, depending largely on soil condition, temperature and farming practices. As an example, Table 3 shows the effect of azatobacter on yield. Table 3. Effect of azatobacter on crop yield Crop

Increase in yield over yields obtained with chemical fertilisers (%)

Food grains Wheat Rice Maize Sorghum

8-10 5 15-20 15-20

Crop

Increase in yield over yields obtained with chemical fertilisers (%)

Other Potato Carrot Cauliflower Tomato Cotton Sugarcane

13 16 40 2-24 7-27 9-24

Source: Das, 1991

9 Dr. T. Singh, pers. comm., Director, National Biofertiliser Development Centre.

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The Case Study: Karnal and Bhiwani Districts, Haryana A field study was initiated in two districts in Haryana to try to understand why biofertilisers and biopesticides were not being adopted on a wide scale. The study focused on two districts: Karnal and Bhiwani. While Karnal represents intensive agriculture with a high degree of irrigation, Bhiwani represents dryland farming, with low level irrigation. The potential for biofertilisers and pesticides is described below, followed by the results of our interviews with farmers to establish why biofertilisers and biopesticdes have not been taken up more widely.

The Potential for Biopesticides and Biofertilisers in Haryana The problems caused by excessive pesticide use are particularly serious in rice and cotton in Haryana, both important crops in our study districts. The American bollworm, jassid and white fly in cotton; and stem borer in rice; have developed resistance to chemicals in many parts of Haryana, including parts of the districts studied. In this situation there is great potential for biopesticides. The potential of biofertilisers is evidenced by the fact that about 90% of Haryana’s soil is deficient in nitrogen, indicating severe nutrient deficiency (Dahiya et al., 1993). The dryland districts such as Bhiwani, Mohindergarh, Sirsa and Faridabad are particularly low in nitrogen, and soils are short of organic matter due to poor vegetative cover, high temperatures and the light texture of soil. Biofertilisers could play a role in providing the much needed nutrients and improving soil conditions in these dryland areas, which account for about 28% of the state’s total cultivable area. Biofertilisers can also reduce the intensity of chemical fertiliser consumption, especially in irrigated areas. With the increase in cropping intensity (see below), the use of chemical fertilisers has increased significantly in these areas. The use of organic manure, on the other hand, has not increased. As a result, many parts of Haryana face deteriorating soil conditions and increasing ground water contamination. The suitability of biofertilisers for various crops grown in Haryana has been shown through demonstrations conducted by the Hissar Centre of the National Biofertiliser Development Centre (NBDC). Azatobacter and azospirillum, which can be used for a wide range of crops, are estimated to have particularly large potential. For example, NBDC experiments showed an increase in yield between 3 and 25% with the application of azotobacter in cotton. Similarly, in the case of wheat, use of azotobacter resulted in yield increases between 2 and 20%.10

10 National project on use and development of biofertilisers. Biofertiliser News, 1(2), December 1993.

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The potential for the use of rhizobium is largely confined to the dryland areas of Haryana, where pulses are commonly grown, and where the soils show poor to moderate nodulation.11

Karnal District In Karnal the main nutrient and pest problems relate to the district’s high cropping intensity. Wheat-rice rotation has been common for some time now, and cropping intensity has recently increased further with the introduction of short duration rice varieties such as Govinda (90 days). Planting these varieties allows farmers to take two rice crops between April and October. The first paddy crop is planted in April-May, as soon as wheat has been harvested. This rice crop is ready for harvest by mid July. This is followed immediately by the transplanting of fresh paddy seedlings. The second rice crop is harvested by the end of October, to be followed by wheat, which is sown by early November. This very high intensity of cropping has worsened both the soil quality and pest problem in parts of Karnal. It is extremely damaging to the soil condition, as large amounts of nutrients are used continuously without replenishment. As a new crop is planted as soon as the older crop is harvested (sometimes both activities are done simultaneously), there is no time for proper land preparation and for using organic manure. As the use of chemical fertilisers has increased to provide the required nutrients, soil and water conditions have deteriorated. The problem of pests and pesticide use in Karnal is largely confined to rice. Growing two rice crops without a break is one factor. The continuation of rice plants in the same field, and the high degree of moisture, enable pests to multiply without a break, leading to particularly intense pest attacks in the second crop. Another reason is the popularity of certain basmati varieties which are highly susceptible to pests and diseases. This is particularly serious in one of the most popular of these varieties, called duplicate basmati. This variety was introduced about five years ago from West UP, and became very popular because of its high yields,12 and totally replaced the desi (traditional) basmati variety in many areas. After performing well for three years, the variety began to be affected by pests (stem borer, leaf folder and white back plant hopper) and diseases (sheath blight, blast and bacterial leaf blight) two years ago. The attack was particularly severe last year, forcing many farmers to stop planting basmati in general, and duplicate basmati in particular. In one of the villages we studied, Kuuchhpura, farmers made up to 15 pesticide applications last year but could not save the crop. This year, very few farmers have planted basmati in the village.

11 The assimilation of atmospheric nitrogen by the roots of pulse (and other leguminous) crops is carried out by the nodules formed in the roots of these plants. The low degree of nodulation suggests that their ability to assimilate atmospheric nitrogen is low and that they could benefit from the use of rhizobium. 12 Compared to the average yield of 10 quintal/acre from desi basmati, the yields of duplicate basmati were about 20 quintal/acre.

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The problem of pesticide resistance in stem borer is now common in Karnal, largely caused by the indiscriminate and excessive use of pesticides. Another important reason relates to the fact that farmers in Karnal do not spray their fields themselves. This is done by professional workers who are sent by the shops selling pesticides. As these workers are paid by the area covered, they do a rushed job. The spraying is not uniform: while some parts of the fields get very little, others get excessive pesticides. Secondly, in order to save time they use about one third of the water prescribed to make the pesticide solution. The non-uniform spray of highly concentrated pesticide solution is reported to be a major reason for the development of resistance in rice pests in many parts of the district.13

Bhiwani District In Bhiwani, the focus of the study is on cotton and gram, which, along with wheat and mustard are the main crops in the area. The use of chemical fertilisers is comparatively low in Bhiwani, being used only on wheat and cotton, and not at all on gram and mustard. But, as in Karnal, use of organic manure is not common and the condition of the soil is poor. Three biofertilisers have potential for Bhiwani: rhizobium for gram and azatobacter and PSM for wheat. The potential of rhizobium is reported to be particularly high in Bhiwani because the level of nodulation is very low. The District Agriculture Department is responsible for the sale of rhizobium in Bhiwani. Being a major gram growing district, it was allocated the largest amount of rhizobium last year and its sale to farmers is subsidised at the rate of 50%. The main pest problem in Bhiwani concerns cotton, which is attacked by American, pink and spotted bollworm, white fly and jassid. These pests have become resistant to most pesticides. According to a study of pesticide use in Bhiwani in 1998, about 70% of farmers reported that they were unable to control pests with pesticides (Saini and Jaglan, 1998). Some of these farmers had used up to 11 pesticide applications. The pest problem in Bhiwani is closely linked with the spread of irrigation facilities. Large parts of Bhiwani district are irrigated by the Indira Gandhi Canal, which suffers from large scale seepage. This has led to a rise in the groundwater level from 50-60 feet below the surface in the past to 5-10 feet at present in many areas. As a result, water logging and high humidity are serious problems in many areas of the district. Apart from causing direct damage, this has also created favourable conditions for the growth of pests. Consequently, the problem of pests has become extremely serious in the district during the last five years. The pest problem caused the area under cotton to decline in the second half of the 1990s from 57, 000 hectares in 1996-97 to 51,000 hectares in 1999-2000.14 As in rice 13 Information from the District Agricultural Officers. 14 Information provided by the State Agricultural Department, Bhiwani.

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in Karnal, the pest problem in cotton in Bhiwani is closely related to the susceptibility of the varieties being planted. The cultivation of cotton in this area is comparatively new: it was introduced in the 1970s. Most of the varieties introduced since then are long staple, American types. Although they fetch high prices, they are highly susceptible to various cotton pests. The problem of pests and the excessive use of pesticides in Bhiwani is mostly confined to the American varieties. Desi varieties, which are comparatively resistant to pests and diseases, require less use of pesticides. We observed a shift back in favour of desi cotton in one of the divisions of Bhiwani following severe losses to pests to the American varieties. Whilst many more farmers would prefer to shift to desi cotton varieties, as they provide stable yields, their wholesale prices are too low. In addition it appears that the state agriculture department prefers to promote long staple American varieties, as they have large domestic and export markets.

Farmers’ Perspectives We selected 11 villages from the two districts, six villages from Karnal and five from Bhiwani, in which to interview farmers to establish their awareness and use of biofertilisers and biopesticides. A total of 74 farmers from these villages were interviewed, and were mainly selected because they had attended one of the demonstration programmes carried out by government agencies to promote IPM, biopesticides and biofertilisers (58 of the farmers, or about 80% of the sample). However, some farmers who had not been to the programmes were also interviewed (16 farmers). All the farmers were men; only men had participated in the demonstration programmes, and we were told that men take the decisions about the types of fertilisers and pesticides to be used. The farmers included in the study represent the range of small, medium and large farmers. While 29% of the farmers have less than 5 acres of land, 46% have between 5 and 20 acres. 25% of the farmers have landholdings larger than 20 acres. In terms of education, about one third of the farmers have studied up to class 10 or more. A semi-structured questionnaire was used for interviews, which were conducted in farmers’ homes.

Findings: Biopesticides Although biopesticides and bio-control agents are important components of IPM, the IPM programmes being conducted by various agencies put very little emphasis on these agents. None of the farmers we interviewed had ever used biopesticides, and few were even aware they existed. We found that none of the farmers had even used neem, widely believed to be commonly used by Indian farmers. In fact, we found that IPM itself was not being practised by most farmers. While some of the farmers were aware of IPM practices, such as the need for monitoring and

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augmenting natural enemies of pests, very few farmers have adopted these practices. None of the farmers practised IPM fully, but about 15% practised partial IPM. In most cases this meant delaying the first spray of pesticides until damage by pests becomes evident. The situation is particularly bad in Bhiwani, where 85% of farmers reported not using IPM at all and only 9% reported using some aspects of IPM. Compared to this, 20% of farmers reported using limited IPM in Karnal. This is despite the fact that most of the farmers included in the study participated in the IPM demonstration programmes conducted by the Central IPM.

Why is IPM not practised? We found four important reasons for the low acceptance of IPM: 1. Lack of awareness. This reason was found to be particularly important in Bhiwani, where 77% of farmers were unaware of the concepts of IPM. Compared to this, fewer than 3% of farmers in Karnal were unaware of IPM. Clearly, there is a big districtwise difference in the success of IPM demonstration programmes and state agricultural extension workers in familiarising farmers with IPM. In Karnal these agencies have been successful in at least making farmers aware of the need to practise IPM. 2. Lack of skills. Almost all the farmers, including all of those who were aware of IPM, reported that they lacked the skills necessary to practise IPM. Their ability to practise IPM was, for example, severely constrained by the fact that most of them could not differentiate between harmful and beneficial insects. In fact, many farmers thought that all insects were a potential threat to their crop and had to be destroyed. They were also not able to work out economic thresholds15 to determine the timings of pesticide application. 3. Lack of faith in IPM. This factor was found to be very important amongst 60% of farmers in Karnal. Although almost all of them were aware of IPM, they felt that they did not have sufficient faith in it to reduce the use of chemical pesticides. Many of them felt that the support from the agricultural department was not adequate for them to try IPM practices, which were considered risky. As the CIPM personnel do not keep in touch with the farmers after IPM demonstrations, they felt that they would not get adequate advice and support if things went wrong. Similarly, the local extension workers (ADOs) are not sufficiently trained in IPM to instil confidence in the farmers. The issue of skills and confidence is obviously linked to the intensity of training provided by the IPM agencies to farmers and extension workers. We found that the training is very basic and superficial, being conducted for three to four days in a village, during which 30 villagers and five extension workers are trained. The farmers felt that the training was not intensive and did not impart sufficient skills for them to feel competent and confident in following IPM practices. 15 The economic threshold is the level of pest population at which the damage to crop justifies the use of pest control methods.

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4. IPM practices are difficult and cumbersome. About 70% of the farmers in both districts who were aware of IPM, felt that the IPM practices were too cumbersome and time consuming to be used regularly. Both the monitoring of pest populations and the calculation of economic thresholds were considered by farmers to be impractical. In Karnal, where cropping intensity is high, the farmers felt that they did not have time to keep a close watch on their fields to monitor pests and calculate economic thresholds.

Whose advice is taken? An important reason for the failure of the IPM programme, and the lack of biopesticide use, is related to the fact that most farmers depend on shopkeepers for advice on pesticide application. More than 80% of the farmers reported that shopkeepers, dealers and representatives of pesticide manufacturers were their most important sources of information about pest control methods (Table 4). Table 4. Importance of source of advice for pesticide application Other Farmers Karnal Bhiwani Total

12 (30) 10 (30) 22 (30)

Extension workers and agricultural university 18 (45) 9 (26) 27 (36)

Shops/manufacturers/ dealers 33 (83) 27 (80) 60 (81)

Number of responses=74. Note that some farmers listed more than one source of advice as being equally important Note: Figures in parenthesis indicate percentages.

Compared to the manufacturers and sellers of pesticides, agricultural extension workers play a small role, especially in Bhiwani, where only 26% of farmers reported them to be important. The role of shopkeepers and dealers is particularly important because many farmers (58%) purchase their pesticides on credit. This gives the shopkeepers strong control over the amount and choice of pesticides used. It also makes it easier for the shopkeepers to sell spurious pesticides. Finally, we found that the knowledge of the State Agricultural Department about biopesticides was extremely limited. This was particularly true of the village level workers (ADOs), but also the case even in the Central IPM office in Faridabad. Considering the importance given to the use of biopesticides by national government agencies, the neglect of biopesticides at the state and district level is difficult to understand. The main emphasis is on the monitoring of pest populations and the use of economic thresholds, which farmers find too difficult and time consuming. Further, the Haryana

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Agricultural University recommends the use of only two biopesticides (Bt and neem) on only one vegetable crop. On all other crops, including cotton and rice, the recommendations include only chemical pesticides.

Findings: Biofertilisers Few (19%) farmers have ever used biofertilisers in the two districts. Their number was especially small in Karnal, where only three out of 40 farmers had used them. In Bhiwani about 75% of farmers were not even aware of biofertilisers; the proportion of such farmers was even higher in Karnal (85%). The most important reason for this lack of awareness is the fact that agriculture extension workers do not promote biofertilisers. On the whole, only 15% of farmers had been told about biofertilisers by the extension workers. The emphasis on biofertilisers was particularly low in Karnal, where only one farmer out of 40 had heard about them from extension workers. The District Agricultural Departments do not have a positive attitude towards biofertilisers. They feel that their quality is poor, and their performance totally unreliable. Therefore, they are not prepared to risk their reputation and good will with the farmers by recommending them. The extension services run by the Haryana Agriculture University (krishi vigyan kendra) feel that in areas of wheat/paddy rotation, such as Karnal, the potential of biofertilisers is low. The farmers in these areas can get the same yield by using the recommended dose of chemical fertilisers. As these fertilisers are easy to use, the farmers prefer them. Biofertilisers have to be stored and applied in conditions which are suitable for the multipication of micro-organisms. This requires special facilities and care, which farmers are often unable to provide. Chemical fertilisers, on the other hand, can be stored and applied without special care. In fact, the KVK in Karnal does not recommend the use of biofertilisers at all. Nevertheless, the extension workers in Bhiwani are required to sell a fixed number of rhizobium packets. This explains the larger number of farmers who are aware of biofertilisers, and have used them in this district. But we found that a large proportion of the rhizobium allotted to the district is not sold to the farmers, and is allowed to go to waste. The ADOs say that the quality and performance is so poor that the farmers are not interested in buying it. The quota is shown as sold in official records, and the payment is made by the ADOs from their salary.16 The fact that the rhizobium meant for sale in various pulse growing districts is not being used by farmers is widely known to both the State Agricultural Department and the National Biofertiliser Development 16 For example, one of the ADOs in Bhiwani was given a quota of 2000 packets of rhizobium this year. He could manage to sell only about 200 packets, mostly to his contact farmers. But these have not actually been used by the farmers. He feels that the contact farmers accept biofertilisers because they want to stay in the good books of the ADOs, from whom they receive subsidised or free goods, such as seed kits. He will have to pay to the Agricultural Department Rs. 8,000/- (@Rs. 4.00 a packet).

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Centre. However, every year the practice of fixing quotas and reporting of sale is carried out, as if rhizobium is actually being used. Out of 19 farmers who were aware of biofertilisers, 14 had used them, showing that farmers are prepared to try biofertilisers. However, most of these farmers stopped using them after one crop - only three were still using them. Two reasons were reported to be important for the discontinuation of use: lack of availability and poor performance.

Availability Many farmers who stopped using biofertilisers reported that this was partly because the supply was extremely unreliable. This was largely because biofertilisers were not being sold by most shops. While none of the shops stock biofertilisers in Karnal, two shops in Bhiwani do. The shopkeepers, in turn, say that they do not stock biofertilisers because sales are poor. One of the Bhiwani shops, for example, has been stocking biofertilisers from National Fertilisers Ltd. for the last four years but has sold only 30 packets.

Quality It is clear that the poor quality and performance of biofertilisers present serious problems. Most studies suggest that the biofertilisers being sold in the market are contaminated and have a low count of micro-organisms. It is therefore not surprising that their performance is poor and uneven. For example, in a survey of rhizobium carried out by ICRISAT, 90% of samples from India were found to have a rhizobia count lower than that required for effective performance (Singleton et al., 1996). Incidentally, this problem exists in most developing countries. For example, in a survey of 12 developing countries, only 19% of the samples met the standards prevalent in developed countries (Singleton et al., 1996). The poor performance of biofertilisers in India is primarily linked to inappropriate strains and inefficient production technology. Essentially, the production of bacterial biofertilisers requires the selection of strains appropriate for a particular crop in a given agro-climate. These strains are mass multiplied by adding bacterial culture to a suitable sterilised broth, either using the shake flask method (for small scale production) or the fermenter method (for large scale production). When an adequate growth of bacteria is achieved, the solution is mixed with a carrier such as lignite or charcoal and is packaged. As agro-climatic conditions and soil characteristics vary widely, a large range of strains of each biofertiliser needs to be isolated for each area. The problem of identifying suitable strains is particularly serious in north India, as many of the strains do not survive the very hot temperatures prevalent in these areas. Until strains which can tolerate wide variations in temperature can be identified, the performance of biofertilisers will remain uneven. The Haryana Agriculture University is reported to be working in this direction and has developed improved strains for pearl millet, wheat, mustard, potatoes, and flowering plants. These are, however, yet to be used in large scale production.

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Furthermore, the production of biofertilisers is prone to contamination, which reduces the effectiveness of micro-organisms. It is, therefore, vitally important that throughout the process extreme care is taken to maintain sterile conditions. It is also important that precautions are taken to avoid contamination during the packaging, storage and application of biofertilisers. The production technology employed in India is inefficient and is responsible for most of the contamination common in Indian biofertilisers. Generally, production is undertaken by the flask method, which is unsuitable for large scale production. Although some firms use fermenters, they lack the sophisticated controls and monitoring facilities necessary to regulate factors such as pH, temperature and aeration. As a result the quality of the bacterial broth is often poor and uneven. Another problem relates to the fact that Indian producers do not sterilise the carriers used for mixing the bacterial solution. For example, both the producers in Haryana, the Hissar Biofertiliser Centre and the HAU, use non-sterilised charcoal, as they do not have facilities to sterilise large amounts of charcoal in a short time. This is an important cause of the poor quality and short shelf life of these biofertilisers (Singh et al., 1999). Although India has ISI (Indian Standards Institution) standards for some of the biopesticides (rhizobium and azatobacter), they are not enforced. This is reportedly because the ISI lacks facilities to test biofertilisers.

Conclusions Biopesticides The problem of pests, the development of pesticide resistance and the excessive use of pesticides need to be seen in the totality of the agricultural system. Our study shows that in Karnal and Bhiwani the problem is linked to the increase in cropping intensity (three crops in Karnal), the expansion of irrigation facilities (Bhiwani), the release and adoption of susceptible varieties (govinda and basmati rice in Karnal, and American cotton varieties in Bhiwani), purchase of pesticides on credit (in both the districts) and inappropriate agricultural practices (the use of contract labour for pesticide application, using power spraying machines in Karnal). In the circumstances, mere reliance on pest control, without correcting the basic problem in the system, will not produce sustainable results. The efforts of various government agencies to popularise integrated pest management (IPM), and the use of biopesticides have had little impact. IPM departments have very little knowledge and experience of biopesticides, and most state agricultural universities, on whose recommendations pest control methods are promoted, do not include the use of biopesticides in their recommendations. In the absence of active promotion by the agriculture department, the demand for these products has not developed. It is for this reason that most private shops and dealers do not stock and sell biopesticides.

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The following policy measures need to be taken urgently in order to reduce excessive use of chemical pesticides. • Focus on sustainable agriculture by promoting: a) disease and pest resistant, and especially traditional, varieties; b) judicious inter-cropping and c) reduced crop intensity. • Improvement in the intensity of training for IPM. The focus should be on the quality of training and not on the number of farmers trained. The training should be followed by regular contact with the trained farmers for providing continous support. • Promotion of the use of biopesticides by the state agricultural departments and IPM workers. The state agricultural universities, which have decisive influence over what pest control methods are promoted by governmental agencies, should pay greater attention to biopesticides.

Biofertilisers Despite the Indian government’s efforts to promote the production and use of biofertilisers, our study found that biofertilisers have found little acceptance among farmers in Haryana. The problems of unavailability of biofertilisers and their poor quality are linked. On the one hand, we find that both the State Agriculture Department and shopkeepers are unwilling to stock and sell biofertilisers as they feel that their quality is unreliable. On the other hand, the low demand for biofertilisers has prevented large investment in advanced production and storage facilities, which are required for improving the quality. It is, therefore, clear that the two problems have to be seen in their totality, and a new policy is needed, some elements of which are as follows: • The present policy of providing grants and low interest loans to biofertiliser producers should be abolished; this has resulted in the setting up of a large number of inefficient plants, which cannot produce good quality biofertilisers. • The policy of marketing biofertilisers at very low prices should also be stopped. These prices are too low to attract adequate investment in modern manufacturing facilities. Take the example of rhizobium. A 200 gram packet of biofertiliser, which is supposed to replace about 30 kilograms of urea (a commonly used chemical fertiliser), is purchased by the Agricultural Department for Rs. 8/ packet. This price is not enough to justify investment in facilities such as charcoal sterilisation plants and cold chain for storage and transportation. Rhizobium is sold to farmers at a subsidised rate of Rs. 4/-. Our discussions with farmers suggest they feel that nothing so cheap can provide much nutrition to the plants, and do not value it. The price of biofertilisers should have some relationship with the price of the chemical fertiliser it replaces. Only then will the producers, the shopkeepers and the farmers begin to take biofertilisers seriously. • The storage and application of biofertilisers require special facilities and skills, which most producers, shopkeepers and farmers do not possess. It is important that greater

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R&D efforts are focused on developing biofertilizers which are easier to store and apply. • Research and development to identify more suitable strains, and to develop better production technology and quality control methods has to be increased greatly. The money saved through the abolishment of various grants and subsidies should be invested in these R&D programmes. We recommend that the promotion and production of biofertilisers should be suspended until these steps are taken. The present government policy of promoting biofertilisers without ensuring good quality and performance has actually harmed their cause, creating a widespread feeling among farmers and extension workers that biofertilisers do not work. It will be better if the production and promotion of biofertilisers is suspended until biofertilisers of improved quality can be made available in adequate quantity. Until then all efforts should be focused on developing technology, setting up modern production facilities and developing infrastructure that will produce and deliver biofertilisers of the required quality.

Acknowledgements The study was funded by the Agricultural Economics Research Center, University of Delhi. The author is grateful to Professor Prem Vashishtha, Director, Agricultural Economics Research Center, University of Delhi for his support to the study. The views expressed in the paper, however, are solely the responsibility of the author.

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Handa SK. Undated. Monitoring of pesticide residues in the Indian environment. In: David, BV. (ed). Pest Management and Pesticides: Indian scenario. Namrutha Publishers, Madras, India. Jayaraj S. 1989. Advances in biological means of pest control. The Hindu Survey of Indian Agriculture. Hindu Newspaper Group, India. Jumanah, F. 1994. Pesticide Policies in Developing Countries: Do they encourage excessive use? World Bank Discussion Papers 238, The World Bank, Washington DC. Marothia, DK. 1997. Agricultural technology and environmental quality: an institutional perspective. Indian Journal of Agricultural Economics, 25(3): 477-479. Mehrotra, KN. 1989. Pesticide resistance in insect pests: Indian scenario. Pesticide Research Journal 1(2):95-103, December 1989. Saini, RK. and Jaglan, RS. 1998. Adoption of insect-pest control practices by Haryana farmers in cotton: a survey. Journal of Cotton Research and Development, 12(2): 198. Singh T,.Ghosh, TK., Tyagi, MK. and Duahn, JS. 1999. Survival of Rhizobia and level of contamination in charcoal and lignite. Annal of Biology 15(2):155-158. Singleton, PW., Boonkerd, N., Carr, TJ. and Thompson, JA. 1996. Technical and market constraints limiting legume inoculant use in Asia. In: Extending Nitrogen Fixation Research to Farmers’ Fields: Proceedings of an International Workshop on Managing Legume Nitrogen Fixation in the Cropping System of Asia, 20-24 Aug 1996, ICRISAT Asia Centre, India. Srinivasan G. 1997. Panel for reduced use of chemical pesticides. Hindu Business Line, November 5, 1997. Wahab, S. 1998. Bio-control and economics of IPM in India. RIS Biotechnology and Development Review, October 1998, 31-39. WHO. 1963. International Standards for Drinking Water. World Health Organisation, Geneva.

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27. Indigenous Soil and Water Conservation in Africa. 1991. Reij. C.

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13. Crop-Livestock Interactions for Sustainable Agriculture. 1989. Wolfgang Bayer and Ann Waters-Bayer. 14. Perspectives in Soil Erosion in Africa: Whose Problem? 1989. M. Fones-Sondell. 15-16.

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17. Development Assistance and the Environment: Translating Intentions into Practice. 1989. Marianne Wenning. 18. Energy for Livelihoods: Putting People Back into Africa’s Woodfuel Crisis. 1989. Robin Mearns and Gerald Leach. 19. Crop Variety Mixtures in Marginal Environments. 1990. Janice Jiggins. 20. Displaced Pastoralists and Transferred Wheat Technology in Tanzania. 1990. Charles Lane and Jules N. Pretty. 21. Teaching Threatens Sustainable Agriculture. 1990. Raymond I. Ison.

28. Tree Products in Agroecosystems: Economic and Policy Issues. 1991. J.E.M. Arnold. 29. Designing Integrated Pest Management for Sustainable and Productive Futures. 1991. Michel P. Pimbert. 30. Plants, Genes and People: Improving the Relevance of Plant Breeding. 1991. Angelique Haugerud and Michael P. Collinson. 31. Local Institutions and Participation for Sustainable Development. 1992. Norman Uphoff. 32. The Information Drain: Obstacles to Research in Africa. 1992. Mamman Aminu Ibrahim. 33. Local Agro-Processing with Sustainable Technology: Sunflowerseed Oil in Tanzania. 1992. Eric Hyman. 34. Indigenous Soil and Water Conservation in India’s Semi-Arid Tropics. 1992. John Kerr and N.K. Sanghi. 35. Prioritizing Institutional Development: A New Role for NGO Centres for Study and Development. 1992. Alan Fowler. 36.

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37. Livestock, Nutrient Cycling and Sustainable Agriculture in the West African Sahel. 1993. J.M. Powell and T.O. Williams.

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38. O.K., The Data’s Lousy, But It’s All We’ve Got (Being a Critique of Conventional Methods. 1993. G. Gill.

23. Low Input Soil Restoration in Honduras: the Cantarranas Farmer-to-Farmer Extension Programme. 1990. Roland Bunch.

39. Homegarden Systems: Agricultural Characteristics and Challenges. 1993. Inge D. Hoogerbrugge and Louise O. Fresco.

24. Rural Common Property Resources: A Growing Crisis. 1991. N.S. Jodha.

40. Opportunities for Expanding Water Harvesting in Sub-Saharan Africa: The Case of the Teras of Kassala. 1993. Johan A. Van Dijk and Mohamed Hassan Ahmed.

22. Microenvironments Robert Chambers.

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25. Participatory Education and Grassroots Development: The Case of Rural Appalachia. 1991. John Gaventa and Helen Lewis. 26. Farmer Organisations in Ecuador: Contributions to Farmer First Research and Development. 1991. A. Bebbington.

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42. Community First: Landcare in Australia. 1994. Andrew Campbell.

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43. From Research to Innovation: Getting the Most from Interaction with NGOs in Farming Systems Research and Extension. 1994. John Farrington and Anthony Bebbington. 44. Will Farmer Participatory Research Survive in the International Agricultural Research Centres? 1994. Sam Fujisaka. 45. Population Growth and Environmental Recovery: Policy Lessons from Kenya. 1994. Mary Tiffen, Michael Mortimore and Francis Gichuki. 46. Two Steps Back, One Step Forward: Cuba’s National Policy for Alternative Agriculture. 1994. Peter Rosset and Medea Benjamin. 47. The Role of Mobility Within the Risk Management Strategies of Pastoralists and Agro-Pastoralists. 1994. Brent Swallow. 48. Participatory Agricultural Extension: Experiences from West Africa. 1995. Tom Osborn. 49. Women and Water Resources: Continued Marginalisation and New Policies. 1995. Francis Cleaver and Diane Elson. 50. New Horizons: The Economic, Social and Environmental Impacts of Participatory Watershed Development. 1995. Fiona Hinchcliffe, Irene Guijt, Jules N. Pretty and Parmesh Shah. 51. Participatory Selection of Beans in Rwanda: Results, Methods and Institutional Issues. 1995. Louise Sperling and Urs Scheidegger. 52. Trees and Trade-offs: A Stakeholder Approach to Natural Resource Management. 1995. Robin Grimble, Man-Kwun Chan, Julia Aglionby and Julian Quan. 53. A Role for Common Property Institutions in Land Redistribution Programmes in South Africa. 1995. Ben Cousins.

57. The Conditions for Collective Action: Land Tenure and Farmers’ Groups in the Rajasthan Canal Project. 1996. Saurabh Sinha. 58. Networking for Sustainable Agriculture: Lessons from Animal Traction Development. 1996. Paul Starkey. 59. Intensification of Agriculture in Semi-Arid Areas: Lessons from the Kano Close-Settled Zone, Nigeria. 1996. Frances Harris. 60. Sustainable Agriculture: Impacts on Food Production and Food Security. 1996. Jules Pretty, John Thompson and Fiona Hinchcliffe. 61. Subsidies in Watershed Development Projects in India: Distortions and Opportunities. 1996. John M. Kerr, N.K. Sanghi and G. Sriramappa. 62. Multi-level Participatory Planning for Water Resources Development in Sri Lanka. 1996. K. Jinapala, Jeffrey D. Brewer, R. Sakthivadivel. 63. Hitting a Moving Target: Endogenous Development in Marginal European Areas. 1996. Gaston G.A. Remmers. 64. Poverty, Pluralism and Extension Practice. 1996. Ian Christoplos. 65. Conserving India’s Agro-Biodiversity: Prospects and Policy Implications. 1997. Ashish Kothari. 66. Understanding Farmers’ Communication Networks: Combining PRA With Agricultural Knowledge Systems Analysis. 1997. Ricardo Ramirez. 67. Markets and Modernisation: New Directions for Latin American Peasant Agriculture. 1997. Julio A. Berdegué and Germán Escobar.

54. Linking Women to the Main Canal: Gender and Irrigation Management. 1995. Margreet Zwarteveen.

68. Challenging ‘Community’ Definitions in Sustainable Natural Resource Management: The case of wild mushroom harvesting in the USA. 1997. Rebecca McLain and Eric Jones.

55. Soil Recuperation in Central America: Sustaining Innovation After Intervention. 1995. Roland Bunch and Gabinò López.

69. Process, Property and Patrons: Land Reform In Upland Thai Catchments. 1997. Roger Attwater.

56. Through the Roadblocks: IPM and Central American Smallholders. 1996. Jeffery Bentley and Keith Andrews.

70. Building Linkages for Livelihood Security in Chivi, Zimbabwe. 1997. Simon Croxton and Kudakwashe Murwira.

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71. Propelling Change from the Bottom-Up: Institutional Reform in Zimbabwe. 1997. J. Hagmann, E. Chuma, M. Connolly and K. Murwira. 72. Gender is not a Sensitive Issue: Institutionalising a Gender-Oriented Participatory Approach in Siavonga, Zambia. 1997. Christiane Frischmuth. 73. A Hidden Threat to Food Production: Air Pollution and Agriculture in the Developing World. 1997. F. Marshall, Mike Ashmore and Fiona Hinchcliffe. 74. Policy Research and the Policy Process: Do the Twain ever Meet? 1998. James L. Garrett and Yassir Islam. 75. Lessons for the Large-Scale Application of Process Approaches from Sri Lanka. 1998. Richard Bond. 76. Malthus Revisited: People, Population and the Village Commons in Colombia. 1998. Juan Camilo Cardenas. 77. Bridging the Divide: Rural-Urban Interactions and Livelihood Strategies. 1998. Cecilia Tacoli. 78. Beyond the Farmer Field School: IPM and Empowerment in Indonesia. 1998. Peter A. C. Ooi. 79 The Rocky Road Towards Sustainable Livelihoods: Land Reform in Free State, South Africa. 1998. James Carnegie, Mathilda Roos, Mncedisi Madolo, Challa Moahloli and Joanne Abbot. 80 Community-based Conservation: Experiences from Zanzibar. 1998. Andrew Williams, Thabit S. Masoud and Wahira J. Othman. 81 Participatory Watershed Research and Management: Where the Shadow Falls. 1998. Robert E. Rhoades. 82 Thirty Cabbages: Greening the Agricultural ‘Life Science’ Industry. 1998 William T. Vorley. 83 Dimensions of Participation in Evaluation: Experiences from Zimbabwe and the Sudan. 1999. Joanne Harnmeijer, Ann Waters-Bayer and Wolfgang Bayer 84 Mad Cows and Bad Berries. 1999. David Waltner-Toews.

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85. Sharing the Last Drop: Water Scarcity, Irrigation and Gendered Poverty Eradication. 1999. Barbara van Koppen. 86. IPM and the Citrus Industry in South Africa. 1999. Penny Urquhart 87. Making Water Management Everybody’s Business: Water Harvesting and Rural Development in India. 1999. Anil Agarwal and Sunita Narain 88. Sustaining the Multiple Functions of Agricultural Biodiversity. 1999. Michel Pimbert 89. Demystifying Facilitation in Participatory Development. 2000. Annemarie Groot and Marleen Maarleveld 90. Woodlots, Woodfuel and Wildlife: Lessons from Queen Elizabeth National Park, Uganda. 2000. Tom Blomley 91. Borders, Rules and Governance: Mapping to catalyse changes in policy and management. 2000. Janis B. Alcorn 92. Women’s Participation in Watershed Development in India. 2000. Janet Seeley, Meenakshi Batra and Madhu Sarin 93. A Study of Biopesticides and Biofertilisers in Haryana, India. 2000. Ghayur Alam 94. Poverty and Systems Research in the Drylands. 2000. Michael Mortimore, Bill Adams and Frances Harris

Gatekeeper papers can be purchased from IIED’s bookshop. Contact The Bookshop, 3 Endsleigh Street, London WC1H ODD, UK. Telephone: +44 (0)20 7388 2117 Facsimile: +44 (0)20 7388 2826 E-mail: [email protected] Internet: http://www.iied.org/ For further information about the series contact: The Sustainable Agriculture and Rural Livelihoods Programme at the same address, or e-mail: [email protected]

GATEKEEPER SERIES NO.SA93

The Sustainable Agriculture Livelihoods Programme

and

Rural

The Sustainable Agriculture and Rural Livelihoods Programme of IIED promotes and supports the development of socially and environmentally aware agriculture through policy research, training and capacity strengthening, networking and information dissemination, and advisory services. The Programme emphasises close collaboration and consultation with a wide range of institutions in the South. Collaborative research projects are aimed at identifying the constraints and potentials of the livelihood strategies of the Third World poor who are affected by ecological, economic and social change. These initiatives focus on the development and application of participatory approaches to research and development; resource conserving technologies and practices; collective approaches to resource management; the value of wild foods and resources; rural-urban interactions; and policies and institutions that work for sustainable agriculture.

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ISSN 1357-9258

Nutr Cycl Agroecosyst (2009) 84:167–178 DOI 10.1007/s10705-008-9235-6

Dissolution of phosphorus from animal bone char in 12 soils G. P. Warren Æ J. S. Robinson Æ E. Someus

Received: 1 May 2008 / Accepted: 28 November 2008 / Published online: 14 December 2008 Ó Springer Science+Business Media B.V. 2008

Abstract Heat-treated animal bone char (ABC) has not previously been evaluated for its potential as a phosphorus (P) fertilizer. ABC, Gafsa phosphate rock (GPR) and triple superphosphate fertilizer (TSP) were incubated in 12 soils. Dissolved-P was assessed by extraction with NaOH and bioavailability with the Olsen extractant. The rate of P dissolution from ABC was described almost equally well by the Elovich and Power equations. After 145 days, the fraction of P dissolved ranged from 0 to 73% and to 56% for ABC and GPR, respectively. The most important soil properties determining P dissolution from ABC were pH and P sorption. P dissolution was not significant at soil pH [6.1 (ABC) and [5 (GPR) and the lower the pH, the greater the Dissolved-P. Dissolved-P also correlated positively and significantly with inorganic P sorption, measured by the Freundlich isotherm and the P sorption index of Bache and Williams (1971). Soil pH and P sorption index could be combined in multiple regression equations that use readily

G. P. Warren (&)
J. S. Robinson Department of Soil Science, The University of Reading, P.O. Box 233, Reading RG6 6DW, UK e-mail: [email protected] E. Someus Terra Humana Ltd, Sze´chenyi u. 59, 1222 Budapest, Hungary

measured soil properties to predict the potential for ABC dissolution in a soil. Dissolution of P from GPR correlated with soil pH and exchangeable acidity. In comparison with GPR, ABC was a better source of available P, assessed by Olsen-P. In most soils, ABC increased Olsen-P immediately after application, including soils of relatively high pH in which GPR was ineffective. ABC is a P fertilizer of solubility intermediate between GPR and TSP. Keywords Available P
Biochar
Fertilizer
Phosphorus
Phosphate rock

Introduction It is probable that bones have always been regarded as a valuable manure, and by about the end of the eighteenth century, their manurial value was attributed to phosphates (Smith 1959). Bone products remain advocated and widely used in domestic gardening (Royal Horticultural Society 2002). However, by the 1950s, for most commercial farming, bone and P fertilizers derived from it were supplanted by fertilizers made from mineral deposits (Smith 1959). This lack of interest in bone as a fertilizer for commercial purposes may explain the observation that reliable data on the plant availability of P from recycled products of P-containing wastes such as sewage sludge, meat and bone are

123

168

rare (Romer 2006). Nevertheless, trials in arable fields can show a slow release of P from bone, comparable to that of phosphate rock (PR) directly applied to soil (Bekele and Hofner 1993) or, in certain soils, an effectiveness as good as superphosphate fertilizer (Ramos 1982). Reasons for looking at alternative and renewable sources of P include the future depletion of economically recoverable PR reserves and the need to restrict introduction of toxic metals to agricultural soil via fertilizer, for which bone is a clean P source. For example, reviews show that cadmium concentrations range up to only 3.03 mg kg-1 in cattle and pig bone (Doyle 1979) but up to 556 mg kg-1 in PR (Van Kauwenbergh 1997). However, concerns have arisen about the transmission of diseases through animal byproducts and in the European Union, regulations control their disposal (EU 2002). Controlled thermal treatment exceeding about 400°C can be used to make a form of biochar that is free of infective agents, rich in P, and that we call animal bone char (ABC). ABC appears potentially an effective P fertilizer, but it has not been tested for this purpose. To assess its value and limitations as a P fertilizer, information is required about its rate of dissolution in soil and soil properties that may influence its dissolution. A substantial body of information exists on the dissolution rate of P from PR directly applied to soil. The requirements for P dissolution are a source of acidity, and sinks for P and Ca (Rajan et al. 1996), which must be provided by the soil/plant system. Sedimentary carbonate fluorapatites are the PRs that are most widely exploited for agriculture (Khasawneh and Doll 1978). Chemical and X-ray diffraction evidence show that the inorganic phases of bone should also be classed as carbonate apatites (LeGeros 1994), so it appears that P dissolution from bone, ABC and phosphate rock should be controlled by the same soil factors. However, this hypothesis has not been tested. The first aim of the work was therefore to measure the dissolution of P from ABC, in comparison with well-known soluble and slowly-soluble P fertilizers, relate P dissolution from ABC to a wide range of soil characteristics, and test the hypothesis that P dissolution is controlled by the same soil properties for ABC as for PR. The second aim was to assess the ability of ABC to improve plant-available P in soil.

123

Nutr Cycl Agroecosyst (2009) 84:167–178

Materials and methods Soils Soils were obtained from 12 locations, chosen to provide a range of types and to include some with severe P deficiency. Sampling was from the 0 to 20 cm horizon using multiple auger holes or pits. Stones were removed with a coarse sieve (approx 2 cm aperture), the soil air-dried for 2 or 3 days at room temperature or in a well-ventilated oven at 30°C and the soil ground to pass a sieve of 2 mm mesh. Table 1 gives their main properties. P sources The ABC (batch SM7) was supplied by Terra Humana Ltd. It was derived from cattle bone, and prepared by heating at 400°C for 45 min. Gafsa Phosphate Rock (GPR), from Tunisia, was a carbonate fluorapatite containing some accessory calcitic materials (Hammond et al. 1986). A fully soluble fertilizer, Triple Superphosphate (TSP, containing 20% P), was used to provide a benchmark for agronomic effectiveness, against which to compare the slowly soluble sources, and to assess the potential of soils for immobilization of free phosphate. To minimise the potential effect of particle size, all P sources were crushed gently in a pestle and mortar to pass a 2 mm aperture sieve. Analytical methods For the ABC and PR, P extracted by neutral ammonium citrate was measured by the method of Mackay et al. (1990), P extracted by water was at a solid:solution ratio of 1:50 for 1 h at 20°C, and surface area was measured by gas adsorption. Measurements of Olsen-P (0.5 M NaHCO3 adjusted to pH 8.5), pH in water and 0.01 M CaCl2, exchangeable acidity, organic C and clay were made as described by Rowell (1994). Total C was measured by combustion (Leco model SC444 analyser) and total P by dissolution in H2SO4/H2O2/Li2SO4/Se solution at 360°C and colorimetric analysis (Anderson and Ingram 1993). CEC and exchangeable cations were measured by the unbuffered method of Sumner and Miller (1996). pH in KCl and pH buffer capacity

Forest

were measured by the method of Robinson et al. (1992). The P sorption index of Bache and Williams (1971) was measured, being the quotient X/logC, where X equals P sorbed (mg P 100 g-1 soil) and C the P concentration in solution (lmol P l-1). Two indices were measured, one with P addition at the usual P addition rate of 1.5 g P kg-1 (Pindex-1500) and also at a low rate of 300 mg P kg-1 (Pindex-300), comparable to the actual rate of added P used in the incubation experiment. To measure the P sorption isotherm, samples of soil were equilibrated with endover-end shaking for 16 h at 20°C in 0.03 M KCl (soil:solution = 1:20), with P additions to result in final concentrations in the range 0 to 20 mg P l-1. In many soils the amount of readily extractable P was high and so there was substantial desorption of soil P at low initial solution P concentrations, making it difficult to fit equations to describe the P sorption isotherm. Therefore the data for sorbed P were adjusted by adding Olsen-P to estimate pre-existing labile P, and then fitted to the Freundlich isotherm:

5.41 5.152

1.05

Vegetable

Arable 6.83

13.88

12.53

21.89

0.081

-0.010

Arable Grass Fallow

Grass Fallow 1.14 1.92

3.13 5.37

0.144

0.298 0.282

1.24 3.02

Arable

0.29 1.23 0.615

Forest

Vegetable

7.91 0.044

3.95

37.19 -0.022

26.45

Vegetable

Veg/Grass 2.84

21.96

4.25

35.80

0.075

0.063

Vegetable 11.51 3.72 0.044

169

3.4

37.03

The product of the Freundlich parameters, ab, was also used in the regression analyses because at a P concentration of 1, a equals the amount of P sorbed, and ab equals the P buffer capacity at the same concentration. Phosphorus sorption properties of the soils are given in Table 2. Field capacity for water was estimated by flooding soil with water and allowing it to drain freely for 24 h. Experimentation showed that for most soils, wetting air-dry soil to 60% of the field capacity gave soil that was moist to touch and the texture in a reasonable state if plants were to have been grown. Pwllpeiran, Neuhaus and Florasca required wetting to 75% field capacity. Water contents were measured by oven-drying overnight at 105°C. All results are presented on an oven-dry basis.

8 16.1

30.0

10.73

24.33 8.8

5.1

18 53.0

21.7

17 31.6

12.7

8.85 18.02

12.84 5.5

5.0 5.4 2 17

17.0 75 4.7

46.1 40.2

11.7 37.3

7.51 5.0 5 25.9

8.8

32.73

12.59 7.4

8.3

14 26.4

13.6

20 78.7

14.4 Israel

Kenya

Zambia

Germany

Cameroon UK

UK

Hungary

UK

Hula

Kiboko

Misamfu

Neuhaus

Odja Pwllpeiran

Rosemaund

Szentes

Whiteknights

Compost

Netherlands

Hungary Florascaa

a

20.40

72.50 6.8

6.1 23.2

170.2

52

92

8.3

2.4

ð1Þ

Incubation procedure

Droevendaal

68 18.8 Italy Albenga

Olsen P (mg kg-1) Country

Clay (%)

12.0

7.9

12.68

P ¼ a Cb

Soil

Table 1 Characteristics of the soils as sampled

Organic C (g kg-1)

pH, water

pH buffering (mmol kg-1 pH-1)

Exchangeable acidity (cmol kg-1)

CEC (cmol kg-1)

Exchangeable Ca (cmol kg-1)

Land use

Nutr Cycl Agroecosyst (2009) 84:167–178

Air dry soil (300 g) was mixed with the P amendment, if used, water added to a water content of 60 or 70% field capacity (range 35–70% moisture content) and mixed again. The treatments were Control (no P), ABC, GPR and TSP, with additions at rates providing 500 mg P kg-1 soil. There were three replicates of each treatment. The soils were incubated at 20°C in

123

170 Table 2 Phosphorus sorption properties of the soils

Nutr Cycl Agroecosyst (2009) 84:167–178

Soil

P sorption index (cg kg-1) -1

P addition rate (mg kg ) 300

Freundlich isotherm parameters a (mg kg-1)

b (l kg-1)

1500

Albenga

2.56

4.8

61.9

0.233

Droevendaal

8.29

10.9

125.3

0.325

Florasca

19.97

29.6

194.6

0.537

Hula

12.21

25.3

193.2

0.372 0.274

Kiboko

4.37

6.2

42.0

Misamfu

7.84

13.9

106.6

0.313

Neuhaus

2.99

5.2

67.9

0.237

8.68

12.6

97.4

0.326

18.74

27.3

264.8

0.370

Odja Pwllpeiran Rosemaund

5.82

9.1

66.6

0.352

Szentes

8.02

14.2

96.4

0.397

14.64

23.6

205.4

0.352

Whiteknights

the dark in polyethylene containers with ventilation holes. Soil water content was maintained by occasional addition of purified water to weight. At days 1, 5, 13, 34, 70 and 145, soil samples were taken from each replicate for Olsen P and P dissolution analysis. For some soils, there were minor deviations from this sampling plan to fit with the calendar. At the end of the incubation period, a portion of the remaining soil was air-dried at 30°C and ground to pass a 2-mm aperture sieve prior to storage for additional analysis.

(RCF = 2,800g) to remove precipitated humic acid, and the P concentration measured colorimetrically. In calculation of the results for P extracted by NaOH, allowance was made for P in the NaCl solution that was entrained in the moist soil immediately before addition of NaOH. Dissolved-P was defined as the difference between treated soil and Control soil (the mean value) for the P extracted by NaOH.

Description of dissolution rates for ABC Dissolved-P in soil A two-step sequential extraction was performed following the method of Mackay and Syers (1986). Soil (containing 0.8 g oven-dry mass) was weighed into a pre-weighed polymer centrifuge tube (50 ml). NaCl solution (1.0 M, 40 ml) was added and the tube shaken end-over-end for 30 min. Following centrifugation (RCF = 500g), the supernatant was carefully decanted and the tube with moist soil reweighed. NaOH solution (0.5 M, 40 ml) was added and the tube shaken with a vortex mixer to re-disperse the soil. The sample was shaken end-over-end for 16 h, centrifuged (RCF = 2,800g) and the supernatant filtered (Whatman 42 filter). P in the NaCl extract was measured colorimetrically by the molybdenum blue and ascorbic acid method (Kuo 1996). An aliquot of the NaOH extract was neutralized with 1 M H2SO4, centrifuged

123

The following equations with two fitted parameters are commonly used to describe the kinetics of soil processes such as sorption and dissolution (Sparks 1989):
ð2Þ First order: Q ¼ a 1  ebT Elovich: Q ¼ a þ b ln (T)

ð3Þ

Powerequation: Q ¼ a Tb

ð4Þ

where Q is the quantity of product at time T in days, and a and b are fitted parameters. In presentation of results, a and b are re-used in the different equations, but this does not imply any relationship or connection between the same parameter symbol used in different equations. Dissolved-P was used for Q. The results were fitted by linear regression for the Elovich equation and by non-linear regression for First order and Power equations.

Nutr Cycl Agroecosyst (2009) 84:167–178

171

Statistics

Olsen-P in soil

All statistical calculations were made with Genstat (Lawes Agricultural Trust 2006).

The addition of ABC produced an immediate significant increase in Olsen-P after one day of incubation in all soils except Albenga and Szentes (Table 4). The increase, relative to the control, ranged from 6.1 mg kg-1 (Hula) to 44.9 mg kg-1 (Whiteknights). In most soils where ABC caused immediate OlsenP increase, Olsen-P increased further over the incubation period, and by the end of incubation the value was changing little. In Szentes soil with ABC, OlsenP remained unchanged, while in Albenga, Florasca and Hula, Olsen-P declined (Table 4). In Florasca and Hula soils, ABC initially gave an increase in Olsen-P, but not after 145 days. GPR gave an immediate increase in Olsen-P only in Odja, Neuhaus, Misamfu and Whiteknights soils. In the same four soils plus Pwllpeiran, there was a significant increase in Olsen-P during incubation. In Albenga and Florasca, there were decreases in OlsenP during incubation with GPR, in parallel with those seen in those soils incubated with ABC. TSP caused a significant initial increase in Olsen-P for all soils (Table 4), but the size of the increase differed between soils and for all TSP treated soils, Olsen-P was much less than the Control value plus 500 mg P kg-1. During incubation, Olsen-P declined in all soils except Szentes and Whiteknights. This suggests that a substantial and variable portion of the soluble P was sorbed in all soils. The net sorption was

Results ABC and Gafsa PR The ABC and GPR contained similar concentrations of total P (13.4 and 12.5%, respectively). However, ABC contained very much more P in all extractable forms; for example, 244 mg kg-1 water extractable P compared with 42 mg kg-1 in GPR (Table 3). Organic C was a minor component (10.4%) of ABC.

Table 3 Properties of ABC and Gafsa PR ABC

GPR

Total P (%)

13.4

12.5

Neutral ammonium citrate extractable P (%)

11.5

4.1

Olsen P (mg kg )

1498

116

Water extractable P (mg kg-1)

244

42

Total C (%)

12.50

2.13

Organic C (%)

10.4

0.38

Surface area (m2 g-1)

82.2

16.5

pH (water)

7.6

6.4

-1

Table 4 Olsen-P (mg kg-1) in soils after incubation without P and with ABC, GPR and TSP Soil

Day 1

Day 145

Control

ABC

GPR

TSP

Control

ABC

GPR

TSP

Albenga

54.6

55.6

53.2

429.0

46.6

44.7

41.7

240.1

Droevendaal

52.1

63.8

52.0

235.5

50.2

68.7

50.7

160.1

Florasca

55.2

62.3

58.6

234.7

39.2

41.2

38.9

122.7

Hula

14.2

20.3

15.1

303.3

13.4

14.9

13.3

73.7

Kiboko

13.8

20.5

13.8

432.9

13.9

25.6

12.7

239.0

Misamfu

5.1

48.2

15.0

323.6

5.3

70.8

36.6

167.3

Neuhaus

68.4

88.5

72.1

329.0

67.7

127.8

93.1

271.1 133.5

Odja

1.5

25.0

7.2

179.9

1.4

65.0

34.8

Pwllpeiran

14.2

30.9

16.0

193.8

12.1

47.1

26.5

66.5

Rosemaund

15.0

26.9

15.6

304.9

12.8

44.0

19.1

148.2

Szentes

13.9

16.9

13.8

285.5

11.0

13.1

11.4

287.8

Whiteknights

7.5

52.4

44.6

168.2

11.2

146.7

118.1

174.0

s.e. (df = 71)

1.223

1.223

1.223

62.7

1.611

1.611

1.611

22.77

123

123

81.6

87.8 84.8 55.0 0.0214 0.2117 10.3 118.9 4.54 44.42 14.9 104.2 0.0380 0.144

4.42

1.29 11.40

42.16 14.5

4.22 29.3

35.6 0.0114

0.0505 0.192

0.054

75.6

292.8

Rosemaund

Whiteknights

4.35

240.3 Pwllpeiran

15.1

4.56 43.77 14.9 31.7 0.0189 0.072 16.5 229.2 Odja

3.47 12.10 11.4 33.5 0.0852 0.197 83.6 Neuhaus

7.87

2.19 22.70 7.19 81.0 0.0746 0.261 170.5 Misamfu

9.89

1.90

1.53 2.63

8.19 6.40

5.08 21.5

29.0 0.186

0.414 0.782

0.403 4.73

2.77

18.8

88.6 84.1

81.9 60.0

80.5 0.0332

0.0254 0.1963

0.3119 7.92

3.37 33.6

56.7

36.3

87.4

10.0

51.6

81.8 84.3 73.3 0.0423 0.2973 10.7 60.4

39.7 39.3 0.0616 0.1740 9.56 39.9

86.2 42.7 0.0166 0.1660 5.65 87.5

10.8

50.1 29.0

23.6 0.0577

0.0422 0.1702

0.0899 4.70

5.12 31.0

22.2

Elovich First order s.e. b s.e. a

31.7

Dissolved-P was expressed as a percentage of the amount of P added, and abbreviated to PD34 and PD145, for 34 and 145 days’ incubation respectively. In five soils, PD145 was not significantly different from zero (Table 6). The highest soil pH for significant P dissolution from ABC was 6.14 (Droevendaal soil).

59.3

Proportion of dissolved-P and soil pH

Kiboko

Data for Dissolved-P from ABC were successfully fitted to the First order, Elovich and Power equations for eight soils (Table 5). For Kiboko soil, there was significant dissolution averaged over all times and thus in parameter a, but the change from Day 1 to 145 and thus the curvature of the relationship between Dissolved-P and time was not significant. For the remaining four soils, there was no significant ABC dissolution. For most soils, the Elovich and Power equation fitted almost equally well, judged by variance accounted for (Table 5), but since the Power equation gave the best fit for more soils than any other equation, it was used to describe the dissolution rate in subsequent work.

Droevendaal

ABC dissolution rate

s.e.

estimated by the difference between TSP and Control treatments for Olsen-P. Hula and Pwllpeiran soils showed the greatest TSP sorption. It was correlated significantly with P sorption, assessed by the two P sorption indices, and highly significantly with Freundlich sorption isotherm parameter a (Fig. 1).

b

Fig. 1 Olsen-P derived from TSP applied at 500 mg P kg-1, at Day 145 of incubation, in relation to Freundlich parameter a of the soil P sorption isotherms

s.e.

300

a

200

s.e.

100

Freundlich parameter a

b

0

s.e.

0

a

50

% Variance accounted for

100

Power equation parameters

150

Elovich parameters

200

First order parameters

y = -0.6847x + 236.79 R 2 = 0.51

250

Soil

Olsen-P from TSP, mg/kg

300

Power

Nutr Cycl Agroecosyst (2009) 84:167–178

Table 5 Fitted parameters of the First order, Elovich and Power equations, used to describe Dissolved-P from ABC (mg kg-1) in relation to time (days) for eight soils

172

Nutr Cycl Agroecosyst (2009) 84:167–178

173

Table 6 Dissolved-P from ABC, GPR and TSP after 145 days’ incubation, as a percentage of P applied (PD145) Soil

PD145

Effect of P source on soil pH (water)

ABC

GPR

TSP

ABC

GPR

TSP

Florasca

-2.8

Albenga

-1.9

-4.1

55.7

-0.06

0.06

-0.51

-0.8

-0.4

0.00

0.09

-0.74

Hula

-0.3

-0.0

5.9

-0.03

0.02

-0.50

Szentes

0.1

-0.1

56.1

-0.05

0.11

-0.86

Kiboko

8.0

0.6

60.2

0.07

0.11

-0.56

Droevendaal

16.5

1.3

89.8

0.24

0.19

-0.11

Neuhaus

16.9

6.5

56.5

0.43

0.23

-0.29

Rosemaund

19.4

4.6

85.1

0.59

0.34

-0.22

Misamfu

39.6

20.6

82.4

0.98

0.83

0.21

Odja

49.3

28.2

88.8

0.26

0.29

0.10

Pwllpeiran

54.1

23.3

93.7

1.10

0.96

0.19

Whiteknights

68.0

52.5

80.1

0.32

0.46

0.02

Soils are placed in rank order of increasing PD145 for ABC. The effect of P source on soil pH was measured on soils after incubation. The SEM (df = 72) was 3.00 for PD145 and 0.081 for effect of P source on soil pH

For GPR, PD145 was significant in only four soils (Table 6). Compared with ABC, a lower pH was required for P dissolution, less than 5.03 (Misamfu soil). Both ABC and GPR caused significant increases in pH for seven of the soils (Table 6). These soils were the same seven where PD145 for ABC was significant. TSP normally lowered pH. The relationships of PD34 and PD145 with pH appeared curved because there are four soils with high pH values and non-significant P dissolution, while at soil pH less than about 7.0, the relationship between pH and PD145 was much closer to linear (Fig. 2). It was considered that if P dissolution did not occur above about pH 7, then the weaker influence of other soil

80 70

PD145 (%)

60 50 40 30

pH KCl

20

pH water

10 0 -10 2

4

6

8

10

soil pH

Fig. 2 Relationships between ABC dissolved at 145 days (PD145) and initial soil pH in 12 soils. Fitted quadratic lines are shown for pH in water (dashed) and KCl (solid)

properties could be masked for those soils of pH \7. Therefore, the correlations to assess factors influencing ABC dissolution were based only on the eight soils with measurable P dissolution from ABC, comprising the seven with significant PD145, plus Kiboko. Although the PD145 for Kiboko soil was not significant, the fitted dissolution curves did demonstrate significant P dissolution on average (rate parameter a). Correlations between ABC dissolution and soil properties Significant inverse correlations were found between PD34 and PD145, and soil pH (Table 7). Significant positive correlations were found between PD34 and PD145, and the following properties relating to P sorption: Freundlich parameters a and ab, and P sorption index at both rates of P addition. Fitted parameter a of the Power equation for dissolution rate correlated significantly with soil pH, but not P sorption properties, while parameter k showed no correlation with soil properties. However, dissolution rate parameter a was significantly correlated with exchangeable acidity and exchangeable Al. In most soils, PD145 was greater than PD34, but the incidence and closeness of significant correlations with soil parameters was the same for these two assessments of P dissolution (Table 7). Therefore, it was decided to use PD145 as the principal assessment

123

174

Nutr Cycl Agroecosyst (2009) 84:167–178

Table 7 Extract from the matrix of correlation coefficients between dissolved-P at 34 and 145 days (PD34 and PD145 respectively) for ABC, PD145 for GPR, power equation

parameters a and k for dissolution of ABC, and soil properties, for the eight soils with measurable P dissolution from ABC

GPR

ABC

ABC

PD145

PD34

PD145

Power Eq-a

PD34 (ABC)

0.955***

PD145 (ABC)

0.957***

0.957***

1

Power Eq-a

0.930***

0.890**

0.866**

1

Power Eq-k

0.675

0.675

0.707*

0.309

-0.508

-0.494

Olsen P

Power Eq-k

1

-0.536

1

-0.456

-0.263

Pindex-300

0.673

0.801*

0.816*

0.549

0.693

Pindex-1500 Freundlich-a

0.746* 0.638

0.864** 0.776*

0.869** 0.776*

0.657 0.544

0.664 0.656

Freundlich-b

0.484

0.583

0.626

0.389

0.612

Freundlich-ab

0.625

0.766*

0.770*

0.52

0.667

pH, water

-0.835**

-0.823*

-0.801*

-0.846**

-0.510

pH, CaCl2

-0.807*

-0.786*

-0.759*

-0.822*

-0.501

pH, KCl

-0.888**

-0.872**

-0.845**

-0.924**

-0.480

pH Buffer capacity

0.617

0.517

0.510

0.548

0.085

Exchangeable acidity

0.844**

0.704

0.685

0.835**

0.083

-0.286

-0.268

0.670

0.649

CEC Exchangeable Al

-0.252 0.818*

-0.359 0.807*

-0.139 0.055

Exchangeable Ca

-0.523

-0.498

-0.476

-0.613

-0.145

Exchangeable K

-0.382

-0.506

-0.494

-0.413

-0.641

Exchangeable Mg

-0.355

-0.420

-0.378

-0.486

-0.261

Exchangeable Mn

0.182

0.239

0.302

-0.005

0.661

Exchangeable Na Clay

-0.262 0.215

-0.180 0.322

-0.136 0.377

-0.449 0.037

0.153 0.602

Organic C

0.408

0.507

0.503

0.262

0.463

Total C

0.420

0.526

0.524

0.269

0.498

Total P

-0.192

0.016

0.043

-0.382

0.461

*, ** and *** denote correlations significant at the 5, 1 and 0.1% levels respectively

of P dissolution because it related to more soil properties than dissolution rate parameter a, and being a larger value than PD34 was considered to be a more reliable measurement. Multiple correlations of PD145 with soil properties were investigated and the best was with pH (KCl) and Pindex-300 (% variance accounted for = 91.9%; Fig. 3): PD145 ¼72:1  12:2  pHðKClÞ

ð5Þ þ 2:22  Pindex-300 An alternative multiple regression with a good fit existed with pH in water and Pindex-1500 (% variance accounted for = 84.5%):

123

PD145 ¼57:6  8:62  pHðwaterÞ þ 1:70  Pindex-1500

ð6Þ

Correlations between GPR dissolution and soil properties Significant correlations were found between PD145 for GPR and soil pH, exchangeable acidity and Al, and Pindex-1500 (Table 7). PD145 for ABC (PD145[ABC]) and for GPR (PD145[GPR]) were very closely correlated (r = 0.957, Table 7), although PD145[GPR] was consistently lower, as shown by the regression equation:

Nutr Cycl Agroecosyst (2009) 84:167–178

175

exists as hydroxyapatite and that dissolution was to H2PO4-, then the dissolution equation is:

80 70

PD145 (%)

60

Ca5 ðPO4 Þ3 OH þ 7Hþ ! 5Ca2þ þ 3H2 PO4  þ H2 O

50 40 30 20 10 0

0

20

40

60

80

Fitted Value

Fig. 3 Multiple regression equation describing PD145 (ABC dissolved at 145 days) in relation to soil pH and soil P sorption index, for eight soils with significant P dissolution. Fitted value = 72.1 - 12.2 9 pH(KCl) ? 2.22 9 Pindex-300

PD145½GPR ¼ 0:781  PD145½ABC  9:34

ð7Þ

Exchangeable acidity in Whiteknights soil Exchangeable acidity was measured in the dried Whiteknights soil after incubation. This soil was analysed because it gave the highest PD145 and should therefore demonstrate most clearly the demands made on soil acidity for P dissolution. Dissolution of GPR and ABC consumed a large part of the exchangeable acidity (Table 8). Estimates for the actual and theoretical consumption of acidity on dissolution of ABC were compared. The difference in total exchangeable acidity between ABC and control treatments was 32.2 mmol kg-1. This difference was caused by consumption of acidity in order to dissolve ABC in Whiteknights soil. Whiteknights soil pH after incubation with ABC was 3.83, and pKa values for steps 1 and 2 of orthophosphoric acid are 2.12 and 7.21, so it is expected that H2PO4- is the dissolution product at pH 3.83. If it is assumed that P in ABC Table 8 Exchangeable acidity (cmol kg-1) in Whiteknights soil after 145 days’ incubation Treatment

Al acidity

H acidity

Total acidity

Control

4.34

0.70

5.05

ABC

1.43

0.40

1.83

GPR

1.74

0.36

2.11

TSP

3.12

0.66

3.78

SED (df = 10)

0.089

0.063

0.073

ð8Þ It shows that dissolution of 3 mol of P require 7 mol of acidity (H?); therefore 500 mg kg-1 of P would require (7/3) 9 (500/30.97) = 37.7 mmol kg-1. PD145 shows that 68% of ABC was dissolved (Table 6), thus consuming 25.6 mmol kg-1 acidity, while the measured consumption was 32.2 mmol kg-1. Given that there is substitution of both cations and anions in the ABC, and other components such as carbonate that may consume acidity, this is considered to be reasonable agreement. Thus the acidity required to dissolve ABC was provided largely by the inorganic exchangeable acidity.

Discussion Influence of soil properties on ABC dissolution The data for dissolution rate of ABC were interpreted by fitting to three Eqs. 2–4 that have been commonly used to assess dissolution rates of materials added to soil. For most soils, the Power Function (4) gave the best fit, assessed by the % variance accounted for (Table 5). Equations 2 and 3 may be justified by theoretical mechanisms for dissolution reactions (Chien et al. 1980a). However, although the relationship is empirical, equations of the form of (4) in respect of time describe well the time course of desorption of phosphate from soil and soil components (Barrow 1979). Equation 4 fitted the data best for the eight soils in which significant P dissolution took place. Therefore, its fitted parameters were the logical ones to correlate with soil properties and parameter a showed significant correlations with soil properties related to acidity (Table 7). However, for this purpose of investigating the influence of soil properties on ABC dissolution, the simple percentages of Dissolved-P from ABC (PD34 or PD145) were preferred, being correlated with more soil properties, and would be much easier to measure in future work, since one measurement only is needed instead of a time series.

123

176

Soil acidity was clearly a major constraint on P dissolution from ABC. This is shown by (i) the significant correlations of PD145 with soil pH (Table 7), (ii) the increases in soil pH when P dissolution occurred from ABC (Table 6), (iii) the significant correlation of dissolution rate parameter a with exchangeable acidity and Al, and (iv) the consumption of exchangeable acidity in Whiteknights soil (Table 8). Dissolution of calcium phosphates such as ABC releases Ca and H2PO4- into soil solution (Eq. 8), and therefore the reaction will not proceed if soluble Ca and H2PO4- concentrations rise too far. A sink for P dissolved was also an important soil property that influenced P dissolution from ABC. This was shown by significant correlations of PD34 and PD145 with the two P sorption indices and the ‘‘extensive’’ parameter a of the P sorption isotherms (Table 7). The latter relates to the P sorption capacity of the soil (Holford 1982), whereas the parameter b is an affinity parameter (Holford 1982) for P sorption, and was not correlated with the extent of ABC dissolution, again suggesting that the capacity of the soil to sorb released P is an important influence. Dissolution of PR has been shown to be positively affected by the size of Ca sink (Robinson et al. 1992), but there was no significant correlation of PD145 with CEC or exchangeable Ca, either alone or in multiple regressions. This suggests that the sink for Ca was not an important factor in assisting P dissolution from ABC. After addition of 500 mg kg-1 soluble P as TSP, the P remaining extractable as Olsen-P was lower in soils with higher P sorption as expected (Fig. 1). This shows that soluble P released by dissolution from ABC is sorbed in the soil, reducing its plant availability, but providing a bigger sink and therefore encouraging P dissolution. The complementary nature of the P sink with acidity is illustrated by the very close multiple correlation of the two with PD145 (Eqs. 5, 6). The two multiple correlations of PD145 with pH and P sorption (Eqs. 5, 6) suggest that relationships could be obtained to predict the likely extent of ABC dissolution in a soil from its known properties. Equation 5 gave the closer correlation, but Eq. 6 uses variants of the measurements that are more commonly in routine use for other purposes, and so are better suited for predictive use.

123

Nutr Cycl Agroecosyst (2009) 84:167–178

Comparison of P dissolution from ABC and GPR In general, initial soil pH is a good predictor of PR dissolution (Rajan et al. 1996), and we found the same applied to dissolution of ABC. An approximate cut-off pH value could be identified above which P dissolution was insignificant, for GPR ([5.03) and ABC ([6.14). For both ABC and GPR, the closest correlations with soil properties were with pH, while the correlation of GPR dissolution was less close with P sorption (Table 7). For the eight soils with significant ABC dissolution, the relationship between soil pH and PD145 approximated to linear below pH 7 (Fig. 2), and other linear relationships between soil pH and PR dissolution have been found, e.g., in acid New Zealand soil (Bolan and Hedley 1990). Correlation of P dissolution parameters for North Carolina PR in 16 Colombian acid soils showed significant effects of P sorption, pH and exchangeable Al (Chien et al. 1980b). The same effects were found in this work with GPR, but Chien et al. (1980b) found additional correlations with clay and organic matter, which were not found in our group of soils. However, we can conclude that the generally established controlling principles for P dissolution from PR also apply to ABC. Agronomic effectiveness of ABC Recent data on the availability of P to plants from modern recycling products are rare (Romer 2006). Studies show that products such as MBM (meat and bone meal), steamed bone meal and bone chips give P responses to pot and field grown crops (Romer 2006; Jeng et al. 2006; Klock and Taber 1996). ABC is manufactured using much higher temperatures (ca. 400°C) than the previously mentioned materials and contains less organic matter. It was therefore expected to have different surface properties and different dynamics of dissolution and availability when compared with PR and the above-mentioned materials. Olsen-P is a widely accepted laboratory index of the plant-available P in soil, and it is useful in both acid and calcareous soils (Kuo 1996), a particular advantage in the present work where a wide soil pH range was intended. At the end of the incubation period, the soils where significant P dissolution from ABC occurred (Table 6) were the same ones that

Nutr Cycl Agroecosyst (2009) 84:167–178

gave significant increases in Olsen-P (Table 4), showing that P dissolution is a guide to the P availability to plants and that ABC will be an effective P fertilizer in many soils. When P dissolution occurred, the majority took place in the first 20 days. Because the mobility of P in soil is low, the early availability of P is essential for proper crop development (Hedley et al. 1995). ABC showed a clear benefit to Olsen-P over GPR for most soils (Tables 4, 5). In two soils, Florasca and Hula, ABC improved Olsen-P at Day 1 although not at Day 145, and these soils were high pH soils where GPR was completely insoluble. Thus, for most soils, ABC provides a limited but immediately available P pool in soil, combined with further P release thereafter, a pattern of release that appears well timed to suit crop requirements. This pattern is different to the one for TSP, where Olsen-P starts at a much higher concentration than with ABC and then declines because of the reaction of dissolved phosphate with soil (Table 4). However, it should be noted that for slowly-soluble fertilizers, Olsen-P gives a measure of the availability of immediate reaction products only and underestimates plant-available P (Menon and Chien 1995; Saggar et al. 1992). Thus in comparison with TSP, plant-available P from ABC may be better than our data suggest. It is clear that ABC is a fertilizer with P supply characteristics intermediate between traditional slow-release (PR) and fully soluble (TSP) fertilizers. The results call for pot and field trials to test this conclusion.

Conclusions The soil properties that influenced P dissolution from ABC were the same as those that control P dissolution from PR, as originally hypothesised. In particular, the most important soil properties were those related to soil acidity, and the more exchangeable acidity and lower the pH, the greater the dissolution of ABC. The size of the sink for Dissolved-P was the other significant control on ABC dissolution, and the two could be combined in multiple regression Eqs. 5 and 6 that use readily measured soil properties to predict the potential for ABC dissolution in a soil. This conclusion is based on a correlation study with a wide range of soils, and calls for detailed mechanistic studies on the

177

mineralogical and surface properties of ABC and P dissolution from it. The above conclusion implies that the knowledge of the soils and circumstances when PR is useful as a fertilizer applies also to ABC. However, in a direct comparison with GPR, which is well-characterised and widely accepted as a relatively soluble PR, ABC was much better in providing available P, as assessed by the Olsen method. It could even supply some available P immediately after application to soils of high pH, in which GPR was ineffective. Therefore, ABC is predicted to have a wider range of application than PR, so that the soils for which it is suitable and rates of ABC addition need to be assessed under field conditions. Because of its apparent potential as a P fertilizer, field trials are now in progress. Acknowledgements This work was financially supported by the European Union, Framework VI (Contract no. FOOD-CT2005-514082). We thank the anonymous reviewers for their helpful comments.

References Anderson JM, Ingram JSI (1993) Tropical soil biology and fertility. A handbook of methods. CABI, Wallingford Bache BE, Williams EG (1971) A phosphate sorption index for soils. J Soil Sci 22:289–301. doi:10.1111/j.1365-2389. 1971.tb01617.x Barrow NJ (1979) The description of desorption of phosphate from soil. J Soil Sci 30:259–270. doi:10.1111/j.1365-2389. 1979.tb00983.x Bekele T, Hofner W (1993) Effects of different phosphate fertilizers on yield of barley and rape seed on reddish brown soils of the Ethiopian highlands. Fert Res 34:243– 250. doi:10.1007/BF00750570 Bolan NS, Hedley MJ (1990) Dissolution of phosphate rocks in soils II. Effect of pH on the dissolution and plant availability of phosphate rock in soil with pH dependent charge. Fert Res 24:125–134. doi:10.1007/BF01073580 Chien SH, Clayton WR, McClellan GH (1980a) Kinetics of dissolution of phosphate rocks in soils. Soil Sci Soc Am J 44:260–264 Chien SH, Leo´n LA, Tejeda HR (1980b) Dissolution of North Carolina phosphate rick in acid Colombian soils as related to soil properties. Soil Sci Soc Am J 44:1267–1271 Doyle JJ (1979) Toxic and essential elements in bone—a review. J Anim Sci 49:482–497 EU (2002) Animal by-products regulations (EC) No 1774/ 2002. Official Journal of the European Communities 10.10.2002. L 273/1-95 Hammond LL, Chien SH, Mokwunye AU (1986) Agronomic value of unacidulated and partially acidulated phosphate rocks indigenous to the tropics. Adv Agron 40:89–140. doi:10.1016/S0065-2113(08)60281-3

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178 Hedley MJ, Mordtvedt JJ, Bolan NS, Syers JK (1995) Phosphorus fertility management in agroecosystems. In: Tiessen H (ed) Phosphorus in the global environment. Transfers cycles and management. Wiley, Chichester, pp 59–92 Holford ICR (1982) The comparative significance and utility of the Freundlich and Langmuir parameters for characterizing sorption and plant availability of phosphate in soils. Aust J Soil Res 20:233–242. doi:10.1071/SR9820233 Jeng AS, Haraldsen TK, Grønlund A, Pedersen PA (2006) Meat and bone meal as nitrogen and phosphorus fertilizer to cereals and rye grass. Nutr Cycl Agron 76:183–191. doi:10.1007/s10705-005-5170-y Khasawneh FC, Doll EC (1978) The use of phosphate rock for direct application to soils. Adv Agron 30:159–206. doi: 10.1016/S0065-2113(08)60706-3 Klock KA, Taber HG (1996) Comparison of bone products for phosphorus availability. Hortic Tech 6:257–260 Kuo S (1996) Phosphorus. In: Sparks DL (ed) Methods of soil analysis Part 3 chemical methods. Soil Science Society of America and American Society of Agronomy, Madison, pp 869–919 Lawes Agricultural Trust (2006) Genstat release 9 reference manual. VSN International Hemel Hempstead, UK LeGeros RZ (1994) Biological and synthetic apatites. In: Brown PW, Brent Constanz (eds) Hydroxyapatite and related materials. CRC Press, Boca Raton, pp 3–28 Mackay AD, Syers JK (1986) Effect of phosphate, calcium and pH on the dissolution of a phosphate rock in soil. Fert Res 10:175–184 Mackay AD, Brown MW, Currie LD, Hedley MJ, Tillman RW, White RE (1990) Effect of shaking procedures on the neutral ammonium citrate soluble phosphate fraction in fertiliser materials. J Sci Food Agric 50:443–457. doi: 10.1002/jsfa.2740500403 Menon RG, Chien SH (1995) Soil testing for available phosphorus in soils where phosphate rock-based fertilizers are used. Fert Res 41:179–187. doi:10.1007/BF00748307

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Nutr Cycl Agroecosyst (2009) 84:167–178 Rajan SS, Watkinson JH, Sinclair AG (1996) Phosphate rocks for direct application to soils. Adv Agron 57:78–146 Ramos MG (1982) Efficiency of eight phosphates for wheat and soybean on an argillaceous Dark Red Latosol. Rev Bras Cienc Do Solo 6:38–42 Robinson JS, Syers JK, Bolan NS (1992) Importance of proton supply and Ca-sink size in the dissolution of phosphate rock materials of different reactivity. J Soil Sci 43:447– 459. doi:10.1111/j.1365-2389.1992.tb00151.x Romer W (2006) Plant availability of P from recycling products and phosphate fertilizers in a growth-chamber trial with rye seedlings. J Plant Nutr Soil Sci 169:826–832. doi: 10.1002/jpln.200520587 Rowell DL (1994) Soil science: methods and applications. Longman, Harlow Royal Horticultural Society (2002) www.rhs.org.uk/NR/rdon lyres/C46FFCC8-FAE1-4DD8-A9BA-4D00137F8892/0/c_ and_e_manures.pdf. Accessed 28 February 2008 Saggar S, Hedley MJ, White RE, Gregg PEH, Perrott KW, Cornforth IS (1992) Development and evaluation of an improved soil test for phosphorus: 2 Comparison of the Olsen and mixed cation–anion exchange resin tests for predicting the yield of ryegrass grown in pots. Fert Res 33:135–144. doi:10.1007/BF01051168 Smith AM (1959) Manures and fertilisers. Nelson, London Sparks DL (1989) Kinetics of soil chemical processes. Academic Press, London Sumner ME, Miller WP (1996) Cation exchange capacity and exchange coefficients. In: Sparks DL (ed) Methods of soil analysis Part 3 chemical methods. Soil Science Society of America and American Society of Agronomy, Madison, pp 1201–1229 Van Kauwenbergh SJ (1997) Cadmium and other minor elements in world resources of phosphate rock. In: Proceedings No. 400 International Fertiliser Society, York, UK pp 1–40

Oil Mallee charcoal properties CEC meq/100g

volatiles%dry

ash%dry

fixed C%wet

fixed C%dry

s.area m2/g

0

20

40

60

80

100

% pH(CaCl2) 8.4 EC 25 uS/m N 1.2% P 0.12% K 0.7% Ca 2.8% Zn 38 ppm

deep banding charcoal at Pindar April 2005; Ausplow Deep Blade System. thanks to John Ryan

DEEP BANDED MALLEE CHARCOAL

1 t/ha at broad-acre rate for row spacing of 600 mm

visible effect at 6 t/ha rate

6 t/ha in 100 mm wide band

TRIAL SITES

PINDAR; sandy clay loam 40ppm av. P

KALANNIE; yellow sand 44ppm av. P

Pindar

Kalannie 2

Kalannie 1

2500

55 kg/ha soluble fertiliser - May sown

grain yield, kg/ha

2000

1500

110 kg/ha soluble fertiliser - June sown 1000

500

0 0

1

2

3

4

5

6

rate of deep banded charcoal, t/ha

poor yield increase with recommended rates of soluble fertiliser

7

half rate

full rate

2500

+340 kg/ha

grain yield, kg/ha

2000

1500

Pindar 1000

500

0 0

1

2

3

4

5

6

rate of deep banded charcoal, t/ha

18% yield increase with half rates of soluble fertiliser at 6 t/ha char

7

mineral plus microbes

2500

grain yield, kg/ha

2000

+640 kg/ha 1500

1000

500

0 0

1

2

3

4

5

6

7

rate of deep banded charcoal, t/ha

46% yield increase with at least 1.5 t/ha char added to the mineral fertiliser

values of yield increases Trial site# and fertiliser 1. 100 kg/ha mineral+1 1. 30 kg/ha soluble 2 2. 110 kg/ha soluble 3 3. 110 kg/ha soluble*

yield benefit

banded charcoal

broad acre equivalent kg/ha

kg/ha

value ($/ ha) for wheat at

carbon value

kg/ha

t/ha

charcoal

carbon

$150/t

$250/t

$/kg C#

640

1.5

250

56

96

160

2.84

344

6.0

1000

225

52

86

0.38

76

6.0

1000

225

11

19

0.08

83

3.0

620*

140

12

21

0.15

#

~$3/kg = $3000/t of carbon!

wheat at $250/t

Mineral+

half rate of soluble

full rate of soluble

2.6

2.4

grain yield, t/ha

2.2

Pindar

2.0

1.8

1.6

1.4

1.2

1.0 10

15

20

25

30

35

grains per head

grains/ head explained 42% of yield variation = drought stress effect (the crop needed an ‘irrigation’ to survive 2005)

40

55 kg/ha Sol.

30 kg/ha Sol.

Min+

50

root colonisation; flowering, %

45

Pindar

40

at flowering

35 30 25 20 15 10 5 0 0

1

2

3

4

5

6

deep banded charcoal, t/ha

char increased AMF colonisation (especially the inoculated microbes)

7

HS

LS

M+

35

30

3

6

0

Grains per head

6 25 3

0

3

6

Pindar

20

0

at flowering 15

10 0

5

10

15

20

25

30

35

40

45

50

root colonisation September %

AMF colonisation associated with grains/head - may have helped reduce drought stress – fungal hyphae extend root system

S55

S30

M+

S110

30

25 biomass at tillering, g/m

2

SYMBIOTIC ? 20

PARASITIC ?

15

10

5

0 0

1

2

3

4

5

6

banded charcoal, t/ha

char increased early growth for lower soluble P conditions But decreased early growth for higher soluble P conditions

7

Interpretations • Valuable yield increases from char addiction – broadacre agriculture, low native AMF

• Very efficient Carbon sequestration with low rates of low C char – Few soil effects, long term benefits?

• Char seems to have increased drought tolerance by encouraging symbiotic fungi. • Higher levels of soluble P may suppress symbiosis – more value in low fertility situations.

Improving wheat production with deep banded Oil Mallee Charcoal in Western Australia 1 2 3 4

Paul Blackwell , Syd Shea , Paul Storer , Zakaria Solaiman , Mike Kerkmans5, and Ian Stanley6 1Department

of Agriculture and Food, Geraldton WA 2 Oil Mallee Company of Australia 3Western Mineral Fertilisers 4University of Western Australia 5Oil Mallee Association of WA 6 "Bungadale", Kalannie , WA

location • Mostly winter rain WESTERN AUSTRALIA

from May to October

• Many sandy soils with organic matter <1%

GERALDTON Pindar Kalannie PERTH

•Usually grows > 50% of Australia’s wheat

WHEAT BELT

20 years R&D into charcoal and soil fungi in Japan and Indonesia

helped develop Oil Mallee concept with John Bartle of CALM

Makoto Ogawa

Syd Shea

Director of Oil Mallee company

ALLEY planting

MALLEE in WA potential ~10 Mt/yr biomass

BLOCK planting

from Ogawa, M. 1994.Symbiosis of People and Nature in the Tropics. Farming Japan Vol.. 28 – 5, p10 21. CHARCOAL improves the MICRO-HABIAT of beneficial soil microbes

Some new fertiliser suppliers are using beneficial soil microbes and mineral fertilisers. Is charcoal a better source of microporosity than zeolite?

Research questions • Will charcoal improve crop yields from poor soil in a dry Mediterranean environment? – (50% increase in Sumatra; Yamato et al., 220% increase in Brazil; Lehmann & Rondon)

• How much soluble fertiliser • Will mineral fertiliser and inoculated soil microbes enable more yield with charcoal?

Soil biological nutrition model with charcoal charcoal particle

plant root

Symbiotic fungi (AM) mineral particle

THE OIL MALLEE INDUSTRY processing Mallee for eucalyptus oil

OIL DISTILLATION HARVESTING

Pyrolysis with an open pan ‘Moki’ method at Kalannie by Shea, Stanley and Okimori March 2005; air temp. = 40oC+! Yasuyuki Okimori

wood charcoal (Jarrah)

mallee charcoal (‘05 trials)

Mallee biomass after oil extraction

Oil Mallee charcoal properties CEC meq/100g

volatiles%dry

ash%dry

fixed C%wet

fixed C%dry

s.area m2/g

0

20

40

60

80

100

% pH(CaCl2) 8.4 EC 25 uS/m N 1.2% P 0.12% K 0.7% Ca 2.8% Zn 38 ppm

deep banding charcoal at Pindar April 2005; Ausplow Deep Blade System. thanks to John Ryan

DEEP BANDED MALLEE CHARCOAL

1 t/ha at broad-acre rate for row spacing of 600 mm

visible effect at 6 t/ha rate

6 t/ha in 100 mm wide band

TRIAL SITES

PINDAR; sandy clay loam 40ppm av. P

KALANNIE; yellow sand 44ppm av. P

Pindar

Kalannie 2

Kalannie 1

2500

55 kg/ha soluble fertiliser - May sown

grain yield, kg/ha

2000

1500

110 kg/ha soluble fertiliser - June sown 1000

500

0 0

1

2

3

4

5

6

rate of deep banded charcoal, t/ha

poor yield increase with recommended rates of soluble fertiliser

7

half rate

full rate

2500

+340 kg/ha

grain yield, kg/ha

2000

1500

Pindar 1000

500

0 0

1

2

3

4

5

6

rate of deep banded charcoal, t/ha

18% yield increase with half rates of soluble fertiliser at 6 t/ha char

7

mineral plus microbes

2500

grain yield, kg/ha

2000

+640 kg/ha 1500

1000

500

0 0

1

2

3

4

5

6

7

rate of deep banded charcoal, t/ha

46% yield increase with at least 1.5 t/ha char added to the mineral fertiliser

values of yield increases Trial site# and fertiliser 1. 100 kg/ha mineral+ 1 1. 30 kg/ha soluble 2 2. 110 kg/ha soluble 3 3. 110 kg/ha soluble*

yield benefit

banded charcoal

broad acre equivalent kg/ha

kg/ha

value ($/ ha) for wheat at

carbon value

kg/ha

t/ha

charcoal

carbon

$150/t

$250/t

$/kg C#

640

1.5

250

56

96

160

2.84

344

6.0

1000

225

52

86

0.38

76

6.0

1000

225

11

19

0.08

83

3.0

620*

140

12

21

0.15

#

~$3/kg = $3000/t of carbon!

wheat at $250/t

Mineral+

half rate of soluble

full rate of soluble

2.6

2.4

grain yield, t/ha

2.2

Pindar

2.0

1.8

1.6

1.4

1.2

1.0 10

15

20

25

30

35

grains per head

grains/ head explained 42% of yield variation = drought stress effect (the crop needed an ‘irrigation’ to survive 2005)

40

55 kg/ha Sol.

30 kg/ha Sol.

Min+

50

root colonisation; flowering, %

45

Pindar

40

at flowering

35 30 25 20 15 10 5 0 0

1

2

3

4

5

6

deep banded charcoal, t/ha

char increased AMF colonisation (especially the inoculated microbes)

7

HS

LS

M+

35

30

3

6

0

Grains per head

6 25 3

0

3

6

Pindar

20 0

at flowering 15

10 0

5

10

15

20

25

30

35

40

45

50

root colonisation September %

AMF colonisation associated with grains/head - may have helped reduce drought stress – fungal hyphae extend root system

S55

S30

M+

S110

30

25 biomass at tillering, g/m

2

SYMBIOTIC ? 20

PARASITIC ?

15

10

5

0 0

1

2

3

4

5

6

banded charcoal, t/ha

char increased early growth for lower soluble P conditions But decreased early growth for higher soluble P conditions

7

Interpretations • Valuable yield increases from char addiction – broadacre agriculture, low native AMF

• Very efficient Carbon sequestration with low rates of low C char – Few soil effects, long term benefits?

• Char seems to have increased drought tolerance by encouraging symbiotic fungi. • Higher levels of soluble P may suppress symbiosis – more value in low fertility situations.

Questions • Can these results be repeated? – pot trials UWA, small plot trials.

NLP submission

• How low is the char requirement of the mineral fertiliser? – 2007 small plot trials

• How long can the char effect last? – – – –

resowing Pindar and Kalannie trials NLP submission ARWA support a research potential seminar in June KEY information for potential Char economics

INTEGRATED WOOD PROCESSING (IWP) plant at NARROGIN

5MW plant = $6.2M over 20 years; est. Bell and Bennett (2002)

Ogawa and Okimori (2004)

Ogawa and Okimori (2004)

A BENEFICIAL SYSTEM?

THANKYOU Sylvain Pottier Yasuyuki Okimori and Makoto Ogawa of Kansai Environmental Engineering Centre, Kansai Electric Co. Ltd and General Environmental Technos Co., Ltd. and the Oil Mallee Company for financial support Ausplow Ltd for the use of their plot airseeder. Andrew Donken Victor Dodd and Doug Cail Dave Gartner, Ben Parkin and Chris Gazey United Farmers Cooperative and Hans Schoof for soil testing and interpretation. Stephen Davies, Bill Bowden, John Bartle, and Tony Vyn for field advice and assistance.

CSIRO PUBLISHING

Australian Journal of Experimental Agriculture, 2007, 47, 1377–1382

www.publish.csiro.au/journals/ajea

Determining the agronomic value of composts produced from garden organics from metropolitan areas of New South Wales, Australia K. Y. Chan A,B,E, C. Dorahy A,C and S. Tyler A,D ACentre

for Recycled Organics in Agriculture. Department of Primary Industries, Locked Bag 4, Richmond, NSW 2753, Australia. CNSW Department of Primary Industries, PMB 8, Camden, NSW 2570, Australia. D432 Zara Road, Chillingham, NSW 2484, Australia. ECorresponding author. Email: [email protected] BNSW

Abstract. About 0.3 million t/year of composted garden organics (CGO) including mulches and soil conditioners are produced annually in New South Wales, Australia, although only a small proportion of this material (<4%) is used in agriculture. A lack of information on product characteristics and agronomic performance has limited the development of agricultural markets for CGO products. These CGO products are the coarse and fine fractions separated by screening after composting. This paper presents the results of a survey of CGO mulches and soil conditioners (unblended or blended with a mixture of other organic materials including biosolids, animal manures and paper), which are commercially produced in the metropolitan areas of New South Wales and assesses their agronomic and soil amendment values in terms of chemical and biological properties. It also evaluates the short-term effects of applying increasing rates (0, 25, 50 and 100 t/ha) of selected composted soil conditioners on radish growth in a pot experiment. The mulch products had low nutrient concentrations but had high carbon (C) contents (mean C = 45%) and C/Nitrogen (N) ratios (mean C/N = 72) and are most suitable for use as surface mulch. The unblended soil conditioners were low in nutrients, particularly N (average total N = 1.0%, range 0.9–12%), and had lower and variable C contents. The pot trial results indicated lack of growth response of radish at application rates up to 100 t/ha of unblended soil conditioners from garden organics. The blended soil conditioners were more variable in quality and as confirmed by pot trial results produced highly variable plant responses. The high variability in product quality and performance of the soil conditioners, particularly the blended products might be related to the source and type of blending material as well as the composting conditions used in the manufacturing process. These results highlight the need to improve compost quality and consistency and the need for further research to advance understanding of the benefits using CGO in terms of improving soil quality, crop productivity and net economic returns to growers. Introduction Composts produced from plant and animal residuals have been used by farmers worldwide for many hundreds of years to increase crop productivity and improve soil quality but they are not typically used as a component of Australian agricultural production systems. However, Australian farmers are increasingly seeking alternatives to conventional inputs to provide plant nutrients and improve soil health as indicated by the increasing interest in the use of organic fertilisers instead of inorganic fertilisers. Across Australia, government legislation (Resource NSW 2001; Victorian Consolidation Legislation 2005) and strategies (Resource NSW 2003; Zero Waste SA 2005) focus on diverting materials from landfills and the beneficial re-use of these materials. For example, in New South Wales (NSW), Australia, over 600000 tonnes of garden organics, such as grass clippings, prunings and other vegetation, are collected from households and municipal areas each year and composted to produce ~0.3 m t/year of composted garden organics (CGO) (DEC © CSIRO 2007

2004). After composting, the product is usually screened into coarse and fine fractions, to produce mulches and soil conditioners, respectively. Most (87%) of the recycled organics generated in the Sydney metropolitan area are consumed in the urban amenity market segments including landscaping, and domestic garden applications (DEC 2004). However, the urban amenity market is approaching saturation (WMAA 2005), whereas only ~4% of the CGO are currently used in agriculture (DEC 2004). Given the large area of arable agricultural land in NSW (>100000 km2; ABS 2001) the size of the agricultural market is virtually unlimited. As a prerequisite for developing agricultural markets for composts, there is a need to understand the characteristics of CGO and demonstrate their agronomic value to farmers. However, little information is available on the quality and agronomic performance of the CGO currently being produced in NSW.

10.1071/EA06128

0816-1089/07/111377

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Australian Journal of Experimental Agriculture

The objectives of this paper are: (i) to present the results of a survey of CGO being commercially produced in the metropolitan areas, particularly in the Sydney region; (ii) to assess their agronomic and soil amendment values in terms of physical, chemical and biological properties; and (iii) to evaluate the short-term performance of selected soil conditioners in a pot experiment. Materials and methods Survey of CGO A survey of 13 composting facilities in the Sydney region and other major metropolitan areas of NSW was conducted in 2004. All the facilities surveyed employed open-windrow systems, the dominant form of composting in most parts of Australia (Wilkinson et al. 2002). At each facility, finished compost products that were ready for market were collected. Composite samples (10–20 kg) of composted soil conditioners and mulches were obtained by shovelling 1–2 kg of compost from 10 random positions in the standing pile into plastic bags. The composite samples were thoroughly mixed and stored at 4°C before analysis. In total, nine CGO mulches, 10 CGO soil conditioners and 12 blended CGO soil conditioners were collected and studied in this research. Soil conditioners refer to the fine compost fraction (<8–10 mm) produced from garden organics as the only feedstock. Blended CGO soil conditioners are fine compost fraction produced from either co-composting a mixture of garden organics and other organic residuals, such as biosolids, poultry litter and cattle feedlot manure or mixing CGO soil conditioners with other organic residuals. CGO characterisation The samples of mulches and soil conditioners were analysed for a range of chemical, physical and biological properties. Immediately after sampling, moist samples were analysed for pH, electrical conductivity, ammonium, nitrate and soluble phosphorus (P) concentration following the procedures described in Standards Australia (2003). The CGO soil conditioners were also tested for phytotoxicity and microbial activity. The phytotoxicity bioassay involved germinating radish seeds on a sample of soil conditioner and assessing early root growth against a minimum length requirement of 60 mm (Standards Australia 2003). Microbial activity was measured using the Food and Drug Administration (FDA) enzymatic test (Schnurer and Rosswall 1982). Subsamples of mulches and soil conditioners were dried and ground (<2 mm) and analysed for total carbon (C), organic nitrogen (N), total sulfur (S), total P, pH, electrical conductivity (EC), total copper (Cu), total zinc (Zn) and total iron (Fe). pH and EC were determined on 1 :5 sample/water extract following Rayment and Higginson (1992). Total C, N and S were determined using Leco combustion (Rayment and Higginson 1992). Total P, total Cu, total Zn, total boron and total Fe were determined using an inductively coupled plasma mass spectrometer after acid digestion (USEPA 1996). Pot experiment Four soil conditioners and six blended soil conditioners were used in the pot experiment (Table 1). The blended soil conditioners contained biosolids, poultry litter, cattle feedlot

K. Y. Chan et al.

manure and paper pulp and represented the range of materials commonly used in compost manufacturing in NSW. All the compost samples were brought to ~40% moisture content and left at room temperature for 4 days before application. The soil used for the pot trial was collected from 0–10 cm of a grey Dermosol (Isbell 1996) located at the Centre for Recycled Organic in Agriculture, near Camden (70 m Australia Height Datum at 34.07536°S, 150.6956°E), NSW. The site had a long history of cropping and cultivation but was under lucerne pasture at the time of sampling. The soil properties were: pHCa (4.5); organic C (12.9 g/kg); extractable P (21 mg/kg); water content field capacity (–10 kPa) (0.28 kg/kg); clay content (260 g/kg). Treatments and experimental design Treatments involved 10 soil conditioners and four rates of soil conditioner application, namely 0, 25, 50 and 100 t/ha on an oven dry basis. The experiment followed a randomised complete block design with four replications. Pots (115-mm internal diameter and 100-mm tall) with individual trays were used. The quantity of oven dry soil conditioners equated to 0, 25, 50 and 100 g/pot for the four application rates, respectively. 900 g of oven dry equivalent of the screened soil was packed into each pot. The appropriate amount of soil conditioner was then added to the respective pot and thoroughly mixed. The individual pots were then watered to field capacity (28% by weight) and left for 24 h in the glasshouse before sowing. Ten radish seeds (Raphanus sativus L. cv. Long Scarlet) were sown in each pot and these were thinned to five after plant emergence. The pots were placed on four benches, each of which represented an experimental block. All of the pots were randomised within each block. During the experiment, all the pots were maintained at approximately field capacity and watered by hand on a regular basis. After 26 days, the radish plants were harvested and the fresh weight of both the tops and roots recorded. The harvested plants were dried at 60°C to constant weight and re-weighed to determine dry weight. Statistical analyses The different properties of the compost products were compared using 1-way ANOVA in GENSTAT (VSN International Ltd 2003). For the pot trial, results of both fresh weight and dry weight of Table 1. Descriptions of the blended and unblended soil conditioners derived from composted garden organics (CGO) used in the pot experiment Sample no.

Type of conditioner

Description

2 3 6 28 1 5

Soil conditioner Soil conditioner Soil conditioner Soil conditioner Blended soil conditioner Blended soil conditioner

11 14 16 17

Blended soil conditioner Blended soil conditioner Blended soil conditioner Blended soil conditioner

CGO CGO CGO CGO CGO/biosolids CGO compost/poultry litter/cow manure CGO/biosolids CGO/paper compost CGO/poultry litter CGO/poultry litter

Agronomic value of composted garden organics

Australian Journal of Experimental Agriculture

the radish using different soil conditioners and rate of application were analysed using 2-way ANOVA. Differences between treatments were statistically significant at 5% probability unless otherwise stated. Product variability was assessed by examining the ranges as well as coefficients of variation (CV) of the different chemical parameters of the different categories of composting products. Linear regression analysis was also undertaken in GENSTAT to determine; (i) whether radish dry weight was correlated with any of the compost chemical parameters measured; and (ii) correlation, if any, between results of FDA test and phytotoxicity bioassay. Results Product quality Apart from size grading, the mulches had very different properties compared with the soil conditioners (Table 2). The mulches had lower total N, total P, total Ca and total magnesium concentrations but higher C and C/N than the soil conditioners. Mean C content of the mulches was 44.6%, which is nearly twice that of the soil conditioners. Mean C/N of the mulches was 71.7 compared with 25.5 of the soil conditioners. Comparing the two categories of soil conditioners revealed the blended soil conditioners had higher average EC, mineral N and total S (Table 2) than the unblended soil conditioners. They were also higher in heavy metals, as indicated by the Zn and Cu concentrations in Table 2. Mean FDA values as well as CV were similar between the two groups of soil conditioners (Table 3). Similarly, mean root length, as a measure of phytotoxicity, was not significantly different between the unblended CGO soil conditioners and the blended products.

Product variability While the C content of the mulches was fairly uniform (range 41–47%, CV = 4.5%), nutrient concentrations (total N and total P) were more variable (CV >20%) (Table 2). Total N concentration in the mulches varied more than 2-fold (range 0.5–1.0%), resulting in a similar magnitude of variation in the C/N ratio (range 41–104). Higher variability was found in the soluble/available nutrients, namely, soluble P and mineral N (CV >50%). Compared with the mulches, soil conditioners were more variable in C content (15–32%, CV = 25.8%). While the C content of the blended soil conditioners was similar to those of the unblended soil conditioners, they were highly variable with respect to most of the chemical parameters measured (Table 2). For example, mineral N concentration ranged from 1.3 to 530 mg/kg (Table 2). The results from the phytotoxicity bioassays (Table 3) showed that despite similar mean values, the blended soil conditioners were more variable than the unblended soil conditioners (CV 65.8 v. 13.7%; Table 3). In fact, 42% of the blended products had root length <60 mm, the critical value below which the medium is classified as phytotoxic (Standards Australia 2003). In contrast, similar CV was found for the FDA results of the two categories of soil conditioners. Pot experiment For the soil conditioners, no significant changes in fresh weight of radish harvested 26 days after sowing with increasing application rates up to 100 t/ha were observed (Fig. 1). In contrast, radish fresh weight increased in response to increasing application rate in five out of the six blended soil conditioners

Table 2. Mean, range (in parentheses) and coefficient of variation (CV%) of basic chemical properties total elemental composition of mulches, soil conditioners (SC) and blended soil conditioners (blended SC) produced from composted garden organics in the metropolitan areas of New South Wales Within rows, mean values followed by different letters are statistically different (P < 0.05) Parameter

Mulch

1379

SC (mean and range)

Blended SC

Mulch

SC (CV%)

Blended SC

pH (1:5 solid :water) Electric conductivity (dS/m) Soluble P (mg/kg) NH4-N (mg/kg) NO3-N (mg/kg) Mineral N (mg/kg) C:N

6.53a (5.0–7.3) 1.22a (0.39–1.95) 2.7a (0.9–5.3) 13.2a (0.7–63.7) 0.9a (0–2) 26.7a (0.7–65.7) 71.7a (41.1–104.4)

Chemical properties 6.89a (5.2–7.5) 7.13a (5.9–7.9) 1.96a (1.24–3.12) 3.08b (1.34–4.68) 2.2a (0.9–7.1) 11.2a (0.2–43.4) 6.6a (0.4–57.4) 78.0b (0.6–231) 2.9a (0–16) 74.0b (0–527) 15.8a (0.6–57.4) 202.1b (1.3–530) 25.5b (13.6–32.0) 19.9b (9.4–28.0)

11.1 40.7 50.2 164.4 95.4 159.5 27.0

11.3 20.5 76.9 140.8 198.4 98.4 26.6

7.7 50.9 119.0 107.7 205.0 106.5 37.5

C (%) N (%) Ca (%) K (%) Mg (%) Na (%) P (%) S (%) Fe (%) B (mg/kg) Zn (mg/kg) Cu (mg/kg)

44.6a (41–47) 0.66a (0.5–1.0) 0.71a (0.51–1.10) 0.40a (0.14–0.52) 0.14a (0.11–0.19) 0.14a (0.11–0.18) 0.07a (0.03–0.13) 0.11a (0.06–0.17) 0.41a (0.19–0.76) 11.9a (6.1–15.0) 64.6a (48–87) 39.4a (11–110)

Elemental composition 25.1b (15–32) 20.6b (14–31) 1.00b (0.9–1.2) 1.21b (0.5–2.1) 1.44b (0.74–2.20) 2.23b (1.00–4.30) 0.50a (0.38–0.57) 0.44a (0.12–0.75) 0.25b (0.19–0.38) 0.29b (0.21–0.44) 0.14a (0.10–0.20) 0.16a (0.07–0.27) 0.16b (0.05–0.24) 0.38b (0.09–0.82) 0.13a (0.09–0.16) 0.19b (0.07–0.28) 1.19b (0.70–1.50) 1.43b (0.90–2.60) 11.9a (8.9–16.0) 10.2a (2.8–17.0) 153.3b (120–200) 190.3c (63–330) 59.6b (30–190) 84.8c (25–240)

4.6 26.0 28.2 30.0 21.4 21.4 45.3 36.4 43.9 33.1 21.9 89.2

25.8 15.2 33.3 16.0 24.0 21.4 28.6 15.4 20.2 23.0 22.1 84.4

29.3 44.1 54.2 54.6 24.1 31.3 70.1 31.6 37.1 47.2 41.2 75.5

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Australian Journal of Experimental Agriculture

K. Y. Chan et al.

Table 3. FDA and phytotoxicity tests of soil conditioners (SC) and blended soil conditioners (blended SC) produced from composted garden organics in the metropolitan areas of New South Wales Mean values in the same row followed by different letters are statistically different (P < 0.05) Parameter

SC

FDA (µg fluorescein/g soil.min) Root length (mm)A AThe

Blended SC (mean and range)

25.6a (10.7–40.1) 98a (78–115)

Fresh top weight (g/pot)

11

(a)

16 1 5

30 25

17 20 15 2 6 14 3 28

10 5 0

Dry top weight (g/pot)

3.5

16 11

(b)

1 17 5

3.0 2.5 2.0 1.5

2

1.0

6 14 3

0.5

28

0

20

44.1 13.7

Blended SC (CV%) 58.6 65.8

phytotoxity test using radish plant roots following Standards Australia (2003).

evaluated. The only exception was the blended soil conditioner containing paper pulp (no. 14), which did not affect radish fresh weight at any rate of application compared with the nil treatment (Fig. 1a). It had the lowest total N concentration (0.5%) and negligible mineral N (1.3 mg/kg; Table 2). Three of the blended soil conditioners (no. 1, 11 and 17) showed continuing increases in radish fresh weight with increasing application rates. Two of the samples (no. 5 and 16) showed increases up to 50 t/ha and then remained unchanged at higher application rates. Both had high mineral N concentration but were found to be phytotoxic (root length <20 mm long).

35

22.7a (8.9–52.9) 63a (16–112)

SC

40

60

80

100

Application rate (t/ha) Fig. 1. (a) Fresh weight and (b) dry weight of radish tops (g/pot) in response to increasing application rates (0, 25, 50 and 100 dry t/ha) of soil conditioners () and blended soil conditioners () produced from composted garden organics.

The nature of radish dry weight production in response to increasing application rates of unblended and blended soil conditioners was similar to that observed for fresh weight production (Fig. 1). Regression of dry weight with mineral N, total N and C/N ratio of the soil conditioners all resulted in statistically significant correlation coefficients. Dry weight of radish was found to be positively correlated with mineral N and total N but negatively correlated with C/N ratio. The highest correlation coefficient (r2 = 0.788) was obtained in the case of C/N ratio. The equation is: DW = 4.931 – (0.135 × CN) (r2 = 0.788, n = 10, P < 0.001)

(1)

where DW is dry weight of radish at harvest and CN is C/N ratio of the soil conditioners. Therefore, dry matter production of radish was negatively related to C/N ratio of the soil conditioners. Discussion The mulches had low nutrient concentrations (e.g. mean mineral n = 27 mg/kg) and high C/N ratios (mean 72) suggesting they are unlikely to be a source of nutrients for growing plants. However, the mulches are likely to be suitable as compost blankets for controlling weeds, conserving water and protecting the soil surface against erosion (DEC 2005). Compared with the other organic amendments (cow manure, N = 1.5%, P = 0.5%, potassium (K) = 1.2%; blood and bone, N = 5.3%, P = 5.2%; poultry manure, N = 3.1%, P = 2.5%, K = 1.6%; sewage sludge, N = 2.0%, P = 1.0% (Burgess 1993)), soil conditioners produced from garden organics as the only feedstock were generally low in total N (1%), P (0.07%) and K (0.5%). In fact, average total N of the soil conditioners was less than a third of that of the poultry manure (Table 2). According to Verdonck (1998), the total N of whole green compost (before screening) ranged from 0.6 to 0.8%. Cook et al. (1998) used a green waste compost with a total N concentration of 1% to grow barley and found that the only significant yield increase was observed at the highest rate of compost application (150 t/ha). The low nutrient concentrations in the soil conditioners of our study can be partly attributed to the nature of the feedstock, which consisted of grass clippings and tree prunings. The mean C/N ratio for the unblended soil conditioner was 25.5, which is higher than the recommended optimal C/N range of 15 to 20 :1 for mature compost (Verdonck 1998). Composts with C/N ratios above 25 to 30 :1 usually immobilises inorganic N (Sullivan and Miller 2001). The pot trial results confirmed the low nutrient availability of the soil conditioners produced from garden organics alone and their unsuitability as soil amendments when applied as sole source of fertilisation. The significant reverse

Agronomic value of composted garden organics

relationship between dry matter of radish plants and C/N ratio (Eqn 1) suggested the usefulness of the ratio as an indicator of compost maturity. Garcia et al. (1992) also suggested that C/N is a good indicator of maturity for composts made from feedstock of high C/N ratio. The FDA test is a measure of microbiological activity based on enzymatic activities (Schnurer and Rosswall 1982). Recently, the test has been evaluated as an indicator of microbiological activity and hence of compost stability during composting process, with conflicting results (Garcia-Gomez et al. 2003; Saviozzi et al. 2004; Ntougias et al. 2006). While Garcia-Gomez et al. (2003) concluded that the FDA test could be used in place of respiration rate as a measure of stability during composting of olive wastes, results of Saviozzi et al. (2004) for composting of urban wastes indicated that FDA values did not alter during the entire composting process and as such was not a sensitive indicator of stability compared with the standard respiration test. In the present study, similar FDA results between the two categories of soil conditioners suggested that they had similar level of microbiological activity, even though 42% of the blended soil conditioners were found to be phytotoxic as measured by the root length bioassay test. Linear regression analyses indicated that the FDA results were not significantly (P > 0.05) correlated with the root length bioassay results and, therefore, suggested that it is unsuitable as an indicator of compost stability. Further research is needed to resolve the discrepancy and to assess the usefulness of FDA test as an indicator of compost stability. The high variability in the chemical composition of the CGO compost products observed in this survey of NSW supported earlier reports from other parts of Australia (Wilkinson et al. 2000; Wilkinson et al. 2002). Such high variability and, therefore, uncertainty about the consistency of compost products has been identified as a barrier to market acceptance in Australian agriculture (Wilkinson et al. 2002). The variability in the chemical composition of the CGO compost products is probably related to the differences in the composition of the organic feedstock and the degree of maturity of the products. Garden organics can vary in total N concentrations depending on the proportions of leafy material, such as grass clippings and more woody material like tree trunks and branches. This is influenced by several factors, such as the size of the operation, geographical location, season, rainfall patterns and method of garden organic collection (Wilkinson et al. 2002; Dorahy et al. 2005). For example, more grass clippings are generated during the summer months, which can lower the C/N ratio in composts produced during this period. Degree of maturity is determined by the conditions and duration of the composting process (Chen and Inbar 1993). Immature compost products are often biologically unstable and have the potential to reduce crop yield (Dick and McCoy 1993; Paulin et al. 2001). In our survey, nearly half of the blended soil conditioners were found to be phytotoxic and, therefore, immature. Results of the pot trial highlighted the variable short-term plant responses, which were a direct reflection of the variability of the soil conditioners. CGO soil conditioners have the potential to play an important role as a source of C for improving soil quality in the longer term through increasing aggregate stability, water holding capacity and microbial activity (Dick and McCoy 1993; Gibson et al.

Australian Journal of Experimental Agriculture

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2002). However, the unblended and blended CGO soil conditioners evaluated in our survey had mean C concentrations of 25 and 21%, respectively, and some were as low as 14–15%, which was much lower than expected. This suggests inorganic materials, such as sand and clay were somehow enriched during processing. If these products are to be promoted for use as a source of organic matter, then the total C concentrations will need to be increased. The long-term benefit of CGO soil conditioners in improving soil quality of organic matter impoverished soil needs to be demonstrated in field experiments. The generally higher variability of the blended soil conditioners compared with the unblended soil conditioners reflected the variety of materials used for blending. The survey results further highlighted how the type of blending material can influence the properties, such as nutrient status, and agronomic performance of the final product. For example, the blended soil conditioners containing biosolids were higher in N and heavy metals than those containing other organic residuals. The pot trial results emphasised that additional effort is still required to improve product consistency, given that the soil conditioners containing the same blending material (e.g. poultry litter in no. 16 and 17) did not perform equally, with respect to increasing radish growth (Fig. 1). Compost quality and consistency can be improved by selecting feedstock and blending materials more judiciously, as well as controlling the composting process more carefully. Farmers will only buy CGO soil conditioners and mulches if there is a demonstrated value from using them, either through improving soil quality and crop productivity or providing a net economic return. Such information is not available and limits the potential to develop agricultural markets for CGO. Consequently, further research is required to quantify the beneficial characteristics of these products and promote these benefits to farmers and the broader community. Conclusions Our survey of CGO commercially produced in the metropolitan areas of NSW has revealed that mulches and soil conditioners have variable physical, chemical and biological properties. Similarly, our pot experiment revealed the short-term agronomic performance of a selection of unblended and blended soil conditioners was inconsistent. Product variability can be reduced and product quality can be improved by more careful selection of feedstocks and blending materials, as well as better control of the composting process. Further research is required to quantify the benefits these products have in terms of improving soil quality, crop productivity and net economic returns to farmers. These issues need to be addressed if viable agricultural markets for CGO are to be developed. Acknowledgements Financial support provided by NSW Department of Environment and Conservation is acknowledged. We also thank the compost producers for their cooperation in undertaking this study.

References ABS (2001) 2001 agricultural census data. Australian Bureau of Statistics. Available at http://www.abs.gov.au [Verified 15 August 2007]

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Burgess J (1993) Organic fertilisers – an introduction. Agfact AC.20, NSW Agriculture, NSW, Australia. Chen Y, Inbar Y (1993) Chemical and spectroscopical analyses of organic matter transformation during composting in relation to compost maturity. In ‘Science and engineering of composting: design, environmental, microbiological and utilisation aspects’. (Eds HAJ Hoitink, HM Keener) pp. 551–600. (Ohio State University: Wooster, OH) Cook JA, Keeling AA, Bloxham PF (1998) Effect of green waste compost on yield parameters in spring barley (Hordeum vulgare) v. Hart Acta Horticulturae 469, 283–286. [International Society of Horticulture Science] DEC (2004) Draft aggregated analysis of the Department of Environment and Conservation’s 2002/03 survey of organics processing in NSW. Department of Environment and Conservation (NSW), Parramatta, NSW, Australia. DEC (2005) Recycled organics in catchment management. Final Report. (DEC 2005/363) Department of Environment and Conservation (NSW), Parramatta, NSW, Australia. Available at http://www.environment. nsw.gov.au/resources/2005363_ORG_CatchMgtRpt.pdf [Verified 15 August 2007] Dick WA, McCoy EL (1993) Enhancing soil fertility by additions of compost. In ‘Science and engineering of composting: design, environmental, microbiological and utilisation aspects’. (Eds HAJ Hoitink, HM Keener) pp. 622–644. (Ohio State University: Wooster, OH) Dorahy C, Chan KY, Gibson TS, Tyler S (2005) Identifying potential agricultural and horticultural markets for composted garden organics in New South Wales. Centre for Recycled Organics in Agriculture, NSW DPI. Garcia C, Hernandez T, Costa F, Ayuso M (1992) Evaluation of the maturity of municipal waste compost using simple chemical parameters. Communications in Soil Science and Plant Analyses 23, 1501–1512. Garcia-Gomez A, Roig A, Bernal MP (2003) Composting of the solid fraction of olive mill wastewater with olive leaves: organic matter degradation and biological activity. Bioresource Technology 86, 59–64. doi:10.1016/S0960-8524(02)00106-2 Gibson TS, Chan KY, Sharma G, Shearman R (2002) ‘Soil carbon sequestration using recycled organics – a review of the scientific literature.’ NSW Agriculture consultancy report prepared for Department of Environment and Conservation, NSW. Available at http://www.environment.nsw.gov.au/resources/SPD_ORG_0208Soil CarbonSeq.pdf [Verified 15 August 2007] Isbell RF (1996) ‘The Australian soil classification.’ (CSIRO Publishing: Melbourne) Ntougias S, Ehaliotis C, Papadopoulou KK, George Zervakis G (2006) Application of respiration and FDA hydrolysis measurements for estimating microbial activity during composting processes. Biology and Fertility of Soils 42, 330–337. doi:10.1007/s00374-005-0031-z Paulin R, Reid A, Solin E (2001) Marketing composted organics to horticulture. Report to WA Waste Management and Recycling Fund GRW/1/98 and GRW/6/98. Department of Agriculture, Western Australia.

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Rayment GE, Higginson FR (1992) Australian laboratory handbook of soil and water chemical methods. In ‘Australian soil and land survey handbook’. pp. 17–23. (Inkata Press: Melbourne) Resource NSW (2001) Waste Avoidance and Recovery Act 2001. NSW Consolidated Act. Available at http://www.austlii.edu.au/au/legis/ nsw/consol_act/waarra2001364/ [Verified 15 August 2007] Resource NSW (2003) Waste Avoidance and Resource Recovery Strategy. NSW Government 2003. Available at http://www.environment.nsw.gov.au/resources/warr2003_fullreport.pdf [Verified 15 August 2007] Saviozzi R, Cardelli R, Levi-Minzi R, Riffaldi R (2004) Evolution of biochemical parameters during composting of urban wastes. Compost Science & Utilization 12, 153–160. Schnurer JS, Rosswall T (1982) Fluorescein diacetate hydrolysis a measure of total microbial activity in soil and litter. Applied and Environmental Microbiology 432, 1256–1261. Standards Australia (2003) ‘Australian standard composts, soil conditioners and mulches – AS4454–2003.’ (Standard Australia International Ltd: Sydney) Sullivan DM, Miller RO (2001) ‘Compost quality attributes, measurements and variability.’ (CRC Press: Boca Raton, FL) USEPA (1996) USEPA Method 3050B (Acid digestion of sediments, sludges and soils). Test methods for evaluating solid waste, physical/chemical methods. USEPA. Verdonck O (1998) Compost specifications. Acta Horticulturae 469, 169–176. Victorian Consolidation Legislation (2005) Sustainability Victoria Act 2005. Victorian Acts. Available at http://www.austlii.edu.au/au/ legis/vic/consol_act/sva2005277/ [Verified 15 August 2007] VSN International Ltd (2003) ‘GENSTAT for Windows.’ 7th edn. (Lawes Agricultural Trust: Rothamsted, UK) Wilkinson K, Tee E, Hood V (2000) Does AS4454 adequately benchmark compost quality? In ‘Compost 2000 Down Under Conference.’ pp. 1–7. (Compost Australia: Melbourne) Wilkinson K, Paulin R, Tee E, O’Malley P (2002) Grappling with compost quality down-under. In ‘Proceedings of the 2002 international symposium on composting and compost utilization. 6–8 May 2002, Columbus, Ohio’. (Eds SC Michel Jr, RF Rynk, HAJ Hoitink) pp. 527–539. (Ohio State University: Columbus) WMAA (2005) Compost industry supply chain – industry position paper. Waste Management Association of Australia, Compost Australia. Available at http://www.wmaa.asn.au/director/divisions/compost/ Roadmap%20Strategies%20And%20Actions.cfm [Verified 20 September 2007] Zero Waste SA (2005) South Australia’s waste strategy 2005–2010. Government of South Australia, Adelaide. Available at http://www.zerowaste.sa.gov.au/pdf/waste_strategy/zw_waste_strategy _final.pdf [Verified 15 August 2007]

Manuscript received 4 April 2006, accepted 4 April 2007

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J. Plant Nutr. Soil Sci. 2008, 171, 893–899

DOI: 10.1002/jpln.200625199

893

Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal Christoph Steiner1,2*, Bruno Glaser1, Wenceslau Geraldes Teixeira3, Johannes Lehmann4, Winfried E.H. Blum5, and Wolfgang Zech1 1

Institute of Soil Science and Soil Geography, University of Bayreuth, 95440 Bayreuth, Germany Current address: Biorefining and Carbon Cycling Program, The University of Georgia, Athens, USA 3 Embrapa Amazonia Ocidental, CP 319–69011–970 Manaus, Brazil 4 Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853, USA 5 Institute of Soil Research, University of Natural Resources and Applied Life Sciences (BOKU), 1180 Vienna, Austria 2

Abstract Leaching losses of N are a major limitation of crop production on permeable soils and under heavy rainfalls as in the humid tropics. We established a field trial in the central Amazon (near Manaus, Brazil) in order to study the influence of charcoal and compost on the retention of N. Fifteen months after organic-matter admixing (0–0.1 m soil depth), we added 15N-labeled (NH4)2SO4 (27.5 kg N ha–1 at 10 atom% excess). The tracer was measured in top soil (0–0.1 m) and plant samples taken at two successive sorghum (Sorghum bicolor L. Moench) harvests. The N recovery in biomass was significantly higher when the soil contained compost (14.7% of applied N) in comparison to only mineral-fertilized plots (5.7%) due to significantly higher crop production during the first growth period. After the second harvest, the retention in soil was significantly higher in the charcoal-amended plots (15.6%) in comparison to only mineral-fertilized plots (9.7%) due to higher retention in soil. The total N recovery in soil, crop residues, and grains was significantly (p < 0.05) higher on compost (16.5%), charcoal (18.1%), and charcoal-pluscompost treatments (17.4%) in comparison to only mineral-fertilized plots (10.9%). Organic amendments increased the retention of applied fertilizer N. One process in this retention was found to be the recycling of N taken up by the crop. The relevance of immobilization, reduced N leaching, and gaseous losses as well as other potential processes for increasing N retention should be unraveled in future studies. Key words: biochar Brazil / carbon / nitrogen cycling / slash-and-burn / soil organic matter / Terra Preta

Accepted January 2, 2008

1 Introduction The fertility of highly weathered Ferralsols in the tropics is low, and soil organic matter (SOM) plays a major role in sustaining soil productivity. Thus, long-term intensive use is not sustainable without nutrient inputs where SOM stocks are depleted (Tiessen et al., 1994). Due to low nutrient-retention capacity and high permeability of these soils, strong tropical rainfalls cause rapid leaching of mobile nutrients such as those applied with mineral N fertilizers (Hölscher et al., 1997a; Giardina et al., 2000; Renck and Lehmann, 2004). To overcome these limitations of poor soil, low nutrient-retention capacity and accelerated SOM decay require alternatives to slash-and-burn (the prevalent agricultural practice in the tropics) and alternative fertilization methods (Ross, 1993; Fernandes et al., 1997). Instead of burning, involving a quick release of nutrients (Kuhlbusch et al., 1991; Hölscher et al., 1997b; Giardina et al., 2000; Hughes et al., 2000) and CO2 (Fearnside, 1997), fallow vegetation could be applied as mulch (Sommer et al., 2004), compost, or charcoal (Lehmann et al., 2002). Depending on the mineralization rate, organic fertilizers such as compost, mulch, or manure applications release nutrients in a gradual manner (Burger and Jackson, 2003). This may be different for very recalcitrant organic addi-

tions such as charcoal. According to Duxbury et al. (1989) and Sombroek et al. (1993), it is important to separate effects due to OM per se (maintenance and improvement of water infiltration, water-holding capacity, structure stability, CEC, healthy soil-biological activity) from those due to its decomposition (source of nutrients).

Only relatively small amounts of charcoal are produced by the traditional slash-and-burn technique. Charcoal represents only 1.7% of the preburn biomass if a forest is converted into cattle pasture (Fearnside et al., 2001). Producing charcoal for soil amelioration from aboveground biomass instead of converting it to CO2 through burning might be an alternative to slash-and-burn (Lehmann et al., 2002; Steiner et al., 2004b; Lehmann et al., 2006).

The existence of so-called “Terra Preta de Índio” (Indian black earth) suggests that a human-induced accumulation of SOM can be maintained over centuries (Sombroek et al., 1993). These soils are exceptionally fertile, and their productivity is most likely linked to an anthropogenic accumulation of P and Ca associated with bone apatite (Lima et al., 2002) and black C (BC) as charcoal (Glaser et al., 2001).

* Correspondence: Dr. Ch. Steiner; e-mail: [email protected]

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The sustained fertility of charcoal-containing Terra Preta and the frequent use of charcoal as a soil conditioner (Steiner et al., 2004b) in Brazil provided the incentive to study the effects of charcoal application on N cycling. Charcoal acted as an adsorber which reduced N leaching in previous pot experiments (Lehmann et al., 2002, 2003), and charcoal additions proved to sustain fertility if an additional nutrient source is given in a field trial (Steiner et al., 2007). Charcoal plus fertilizer improved plant growth and doubled grain production in comparison to the fertilizer without charcoal. Plant biomass production sharply decreased within 1 y when only mineral fertilizer was applied, but could be maintained for a longer period of time when OM was added. The authors proposed that charcoal can improve soil chemical, biological, and physical properties, but could not completely discern the mechanisms of fertility enhancement (Steiner et al., 2007). Stable isotopes such as 15N can serve as valuable tracers to study plant resource acquisition and as a means to understand how plants interact with their abiotic and biotic environments (Dawson et al., 2002). Therefore, our objective was to compare the effect of organic amendments such as charcoal and compost on retention of 15N-labeled mineral fertilizer in a highly weathered Ferralsol under humid tropical field conditions.

2 Materials and methods 2.1 Study location and experimental setup

J. Plant Nutr. Soil Sci. 2008, 171, 893–899 The charcoal derived from secondary forest wood and was considered rather as soil conditioner than fertilizer due to the charcoal’s low nutrient contents (Tab. 1). It was manually crushed to particle sizes <2 mm. The applied 11 Mg ha–1 corresponded to the amount of charcoal-C which could be produced by a single slash-and-char event of a tropical secondary forest on Xanthic Ferralsols in central Amazonia (Lehmann et al., 2002). The amount of C added with charcoal was chosen as a reference value for adding the compost. Compost was prepared from biomass of a secondary forest, fruit residues, manure, and kitchen waste. On February 3, 2001, organic materials were mixed with hand hoes into the top soil (0–0.1 m) of the plots, and the first mineral fertilization was done on March 19, 2001 [30 N kg ha–1 as (NH4)2SO4, 35 kg P ha–1 as simple superphosphate, 50 kg K ha–1 as KCl, and 2100 kg lime ha–1]. The fields were cropped twice (rice Oryza sativa L. and sorghum Sorghum bicolor L. Moench) prior the second fertilization on April 16 (see Tab. 1 for treatment description). All crop residues remained on the field, and only grains were removed. Sorghum was planted again on April 18, 2002 in a density of 25 plants m–2 producing two harvests by ratooning (July 21 and October 16, 2002). Only these two harvests are subject of the present paper and designated as 1st (HI) and 2nd (HII) harvest. Table 1: Treatments, organic amendments, and harvest remnants (from previous harvests remained in the field). Mineral fertilization (F) was applied after the second harvest in April 2002, 15N-labeled N (55), P (40), K (50), lime (430) [kg ha–1]. Token

The experiment was conducted within a larger field trial established 30 km N of Manaus, Amazonas, Brasil (3°8′ S, 59°52′ W, 40–50 m asl) at the Embrapa-Amazônia Ocidental (Empresa Brasileira de Pesquisa Agropecuaria) experimental research station. The natural vegetation is evergreen tropical rainforest with a mean annual precipitation of 2530 mm (1971–1997) having its seasonal maximum between December and May, a mean annual temperature of 25.8°C (1987–1997), and relative humidity of 85% (Correia and Lieberei, 1998). The soil was classified as a highly weathered Xanthic Ferralsol (FAO, 1990), finetextured with high clay content. It is strongly aggregated and has medium contents of organic C (24 g kg–1), low pH values of 4.7 (in H2O), low CEC of 1.6 cmolc kg –1, and low base saturation (BS) of 11% (Steiner et al., 2007). This experiment is part of a long-term field trial established in January 2001 (Steiner et al., 2007). The main objective was to study different organic-amendment combinations based on equal amounts of C additions. Fifteen different treatments were established in five repetitions after clearing of approx. 3600 m2 secondary forest and removing the aboveground biomass. The treatments were applied on 4 m2 plots (2 m × 2 m) forming an entire field area of 1600 m2 (45 m × 35 m) with a minimum distance to the surrounding vegetation of 10 m. For this study, five mineral-fertilized (F) treatments were chosen, four of them with compost (CO + F) and/or charcoal (CC + F) application (Tab. 1). The treatment receiving compost only (CO) served to provide a reference value for N isotope composition in soil and plants. This treatment was used as a control for all treatments as d15N did not differ between the treatments without tracer application [(NH4)2SO4 fertilized or not].  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Organic matter

1st harvest (HI) remnantsa

2nd Total harvest (HII) remnantsa

[Mg dry matter ha–1] COb

compost (67)

5.13 1.98

0.27

2.25

CO + F

compost (67)

6.24

1.51

7.75

CC + F

charcoal (11)

F

1.11

6.24

2.55

0.72

3.27

½CC + ½CO + F charcoal (5,5), compost (33,5)

4.74

1.10

5.85

CC + ½CO + F

4.28

1.10

5.38

charcoal (11), compost (33,5)

F = mineral fertilizer; CO = compost; CC = charcoal previous harvests July 7, 2001 and February 6, 2002 b unfertilized control treatment, reference value for 15N natural abundance; previous mineral fertilization: March 2001 [kg ha–1] N (30), P (35), K (50), lime (2100); compost contained 10.1, 0.73, 2.85, 3.27, and 1.51 g kg–1 N, P, K, Ca, and Mg, respectively; charcoal contained 5.39, 0.03, 0.23, 0.82, and 0.17 g kg–1 N, P, K, Ca, and Mg, respectively. a

2.2 Tracer application, sampling, and calculations The chosen treatments (F, CC + F, CO + F, ½CC + ½CO + F, and CC + ½CO + F) received 15N isotope enrichment using 15N-labeled (NH ) SO with 10 atom% 15N excess. The tra4 2 4 cer was mixed in a ratio 1:1 with conventional (NH4)2SO4 and www.plant-soil.com

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Nitrogen retention with compost and charcoal 895

applied at a rate of 55 kg N ha–1 in April 2002 (second fertilization). Additionally, 40 kg P ha–1, 50 kg K ha–1, and 430 kg ha–1 of lime was applied. Soil and plant samples were taken at each harvest and analyzed for d15N. Only the top 0.1 m of soil was sampled, this was also the depth down to which the organic amendments were mixed. Two soil samples were taken per plot to form one composite sample. Soils were airdried and ground before isotope analysis. Representative plant samples were taken from the entire crop by using the center 1.4 × 1.4 m (49 plants) of each plot. Plant samples were dried at 70°C for 48 h and ground. The remaining fertilizer N in soil or plant biomass was calculated after Eq. 1 (Boutton, 1996). Nf
d15 Nf ˆ Nf
d15 Nc ‡Y
d15 NNPK ,

(1)

Nf = nitrogen content of biomass or soil in N-fertilized treatment, d15Nf = measured d15N value of biomass or soil in N-fertilized treatment, d15Nc = measured d15N value of biomass or soil in unfertilized control treatment (only CO served as valid control treatment as d15N did not differ between treatments without tracer application), d15NNPK = d15N of (NH4)2SO4 10 atom% (= 29330.3‰).

15N

excess

The amount of 15N remaining in soil or in plant biomass (Y) was calculated according to Eq. 2. The subtraction of d15Nc in the denominator was neglected because it is small (approx. 10 and 20 for soil and biomass, respectively) in comparison to d15NNPK. Yˆ

Nf
d15 Nf

Nf
d15 Nc

15

d NNPK

.

(2)

The percentage of N taken up by biomass or remaining in the soil was calculated according to Eq. 3: N% ˆ

Y
100, N…NH4 †2 SO4

(3)

where N(NH4)2SO4 = amount of tracer fertilized [27.5 kg ha–1 (NH4)2SO4 10 atom% 15N excess].

2.3 Analyses of soil and plant samples Soil and plant samples were analyzed for their C and N contents by dry combustion with an automatic C/N-Analyzer (Elementar, Hanau, Germay). Total N isotope composition in soil and plants was determined using an Elemental Analyzer (Carlo Erba NA 1500, Carlo Erba Reagenti, Rodano, Italy; for Dumas combustion) connected to an isotope-mass spectrometer (FINNIGAN MAT delta E; Thermo Finnigan, San Jose CA) via a split interface.  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2.4 Statistical analyses Treatment effects were analyzed by one-way analysis of variance (ANOVA). Significant treatment effects were detected using the Fisher’s LSD (last significant difference) test. Statistical analyses and figures were performed using SPSS 12.0 (SPSS Inc.) and SigmaPlot 7.0.

3 Results and discussion While the soil C contents were significantly increased by the organic amendments (CO and CC), the N values were only significantly enhanced in comparison to the F plots if CO was applied (Fig. 1). After the second harvest (HII), the N and C contents on solely compost-amended plots (CO) did not differ from those receiving only mineral fertilizer. The OM-amended and N-fertilized plots had significantly higher C and N contents than the F plots. All organic amendments significantly increased the C : N ratio after the first harvest. This difference was even more distinct after the second harvest but only on charcoal-containing plots (Fig. 1). Neither the N concentrations in the biomass nor the measured d15N values differed significantly (data not shown). The significantly higher mineral N uptake by plants growing on the compost-amended plots (CO + F) was due to a significantly higher plant biomass production (Tab. 2). Wardle et al. (1998) found greater tree-seedling growth, N uptake, and enhanced efficiency of nutrient uptake in boreal forest soils when charcoal was added. The authors assumed that adsorption of phenolics by the charcoal diminished adverse effects on plant growth, both as allelopathic agents, and through complexing N, thus reducing its availability to plants. In our case, soil analyses indicate that other nutrients than N were more important to enhance plant growth leading to N sequestration in biomass (Steiner et al., 2007). This assumption is corroborated by the study of Alfaia et al. (2000) who found only a 16% rice grain-yield increase due to (NH4)2SO4 fertilization, but significant losses of fertilized N. In the soil, the situation was rather different. After the second harvest (HII), significantly more fertilizer N remained in the soil amended with charcoal (15.6% of applied N) than on plots without organic amendment (9.7%). The compost treatment showed intermediate values (12.6%) (Fig. 2). In the soil, the increased retrieval of N rather than higher total soil N contents caused the significantly enhanced N recovery. Only remaining crop residues could have caused the increase in encountered 15N from HI to HII. However, the treatment ½CC + ½CO + F showed a much larger increase in soil 15N encountered from HI to HII than the F treatment but had slightly less crop-residue input (Tab. 2). Only the compost treatment (CO + F) generated significantly more crop residue 15N than the control group but this additional residue return did not significantly affect the soil 15N at HII. At least to some extent the accrued crop residues after HII added to the soil’s N pool as shown by the shift in isotope values (data not shown) because soil sampling was done 7–14 d after the harvest. Belowground biomass was not www.plant-soil.com

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J. Plant Nutr. Soil Sci. 2008, 171, 893–899

Figure 1: Contents of C and N in of the soil at the first (HI) and second harvest (HII). The error bars show the mean ± standard error. The Fisher’s LSD (least significant difference) value is plotted to scale significant mean separation (p < 0.05).

assessed and can contribute significantly to N cycling as the root biomass pool can be assumed to be at least half as large as the aboveground biomass pool (Lacerda et al., 2004; Hattori et al., 2005). Lehmann and Zech (1998) found 30% of sorghum roots in Kenya below 0.3 m. We sampled only the upper 0.1 m, thus N could have been recycled from deeper soil layers.

The significantly increased uptake of applied N by plants on plots with additional compost and the significantly higher N retention in the soil due to charcoal additions may be explained by either reduced N leaching (Lehmann et al., 2003) or reduced gaseous N losses (Yanai et al., 2007). Reduced N leaching may be a result (1) of either improved retention of the applied NH‡ 4 by electrostatic adsorption to exchange sites provided by the com-

Table 2: Biomass production, N uptake, and withdrawal (grains) at the first (HI) and second harvest (HII). Different letters in the same column indicate significant differences (p < 0.05) between treatments (Fisher’s LSD test, n = 5). HI

HII

HI

crop residues grains

crop residues grains

N residues

HII N grains

[Mg dry matter ha–1]

Treatment

N residues

N grains

[kg ha–1]

F

1.38

b

0.28

c

0.50

c

0.14

c

11.3

c

4.7

c

4.9

b

2.3

CO

1.50

b

0.28

c

0.56

c

0.16

bc

19.8

b

5.8

c

7.5

b

3.2

c bc

CO + F

2.69

a

0.96

a

1.17

a

0.80

a

29.8

a

15.5

a

13.1

a

12.6

a

CC + F

1.85

b

0.42

bc

0.72

bc

0.28

bc

17.3

bc

7.1

c

7.0

b

4.6

bc

½CC + ½CO + F

1.76

b

0.65

b

0.80

abc

0.33

bc

18.9

bc

11.8

ab

8.7

b

6.1

bc

CC + ½CO + F

2.08

ab

0.49

bc

0.97

ab

0.49

ab

19.7

b

8.1

bc

9.1

ab

8.5

ab

F = mineral fertilizer; CO = compost; CC = charcoal Crop residues remained in the field; mean C 44.8, N 9.97 g kg–1, C : N = 44.16; mean N content of grains = 16.9 g kg–1

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Figure 2: Amount of mineral N fertilizer remaining in the soil (Ferralsol, a and b) and in the crop (sorghum, c and d) after the first (HI, a and c) and second harvest (HII, b and d) as a percentage. Means and standard errors (p < 0.05, Fisher’s LSD test, n = 5).

post or charcoal or (2) of immobilization of N by microbial biomass. Lehmann et al. (2003) made microbial immobilization responsible for decreases in foliar N contents and total N uptake as a response to charcoal additions due to their higher C : N ratio. However, their pot experiment used larger amounts of applied charcoal (67.6 and 135.2 Mg C ha–1) than our study. The C : N ratio in the soil studied here was found to be significantly higher in the charcoal treatments at both harvest times (Fig. 1) in comparison to the control. Decomposition of a portion of newly applied charcoal and concurrent N immobilization is most likely a transient phenomenon as charcoal is much more stable than other organic additions (Baldock and Smernik, 2002). In the studied permeable soils under high-rainfall conditions, temporary immobilization of mobile nutrients might be desirable. The results of the 15N experiments by Burger and Jackson (2003) suggest a very dynamic role of microbially bound N and highlight the importance of N immobilization that is taking place simultaneously with inorganic-N production by mineralization. They concluded that greater C availability stimulates microbial activity resulting in greater N demand, promoting immobilization and recycling of NO3 . The resilience of soil C in charcoalamended plots shows the refractory nature of charcoal (Kuhlbusch and Crutzen, 1995). While the stability of charcoal leads to low C losses, nutrient release by mineralization is most likely lower than from other organic materials. As charcoal is expected to be an extremely recalcitrant form of OM, it is unknown to what extent charcoal C favors N immobilization. In previous studies, the same plots showed significantly increased plant growth and potential for microbial-population growth in mineral-fertilized soils amended with charcoal and in Terra Preta, but lower microbial respiration in the absence of an easily degradable C source (glucose) compared to soils without charcoal (Steiner et al., 2004a, 2007). It has been shown that charcoal amendments can significantly enhance nitrification in pine-forest soils (DeLuca et al., 2006). The authors suggest that charcoal alters  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

the activity of the nitrifying community and removes inhibiting phenols. We could not elucidate alterations in nitrification and its possible consequences for leaching and denitrification, although Birk (2005) found evidence that the organic amendments increased the presence of anaerobic bacteria which possibly are denitrifiers. Dinkelmeyer et al. (2003) found a rapidly decreasing total recovery (in plants and soil) of 15N (87% to 54% to 24% at 1, 3, and 12 months after N application, respectively), but they assessed a complex and deep-rooting agroforestry system to a soil depth of 5 m. They found a minimum of 13% Nfertilizer efficiency when applied to peach palm (Bactris gasipaes) and a maximum of 38% if applied to cupuassu (Theobroma grandiflorum). Alfaia et al. (2000) assessed N utilization of a rice crop grown in central Amazona and found a N-fertilizer efficiency of only 7.8%, 10.0%, and 1% in shoot, grain, and root biomass, respectively. We found a maximum recovery in plant biomass of 15% and total recovery of 22% 3 months after N application at HI. Already after 4 d, Renck and Lehmann (2004) found applied 15N in the soil solution to a depth of 0.6 m and to a depth of 5 m after 1 week at the same study site. They found that the largest part of applied 15N in the top soil was leached as organic N. The total fluxes of organic N were similar to those of NO3 in the topsoil. According to Lehmann et al. (2002), the NH‡ 4 adsorbability of charcoal is largely dependent on soluble OM, as an addition of DOC from a manure extract increased NH‡ 4 adsorption. Therefore charcoal might have reduced leaching of organic N in addition to the inorganic forms. The organic amendments might likewise have altered denitrification but leaching is most likely the predominant N loss in the studied soil and the relative proportion could not be clarified in this study. The charcoal’s low biodegradability (Kuhlbusch and Crutzen, 1995), low nutrient content (Ogawa, 1994; Antal and Grønli, 2003), and high porosity and specific surface area (Braida et al., 2003) makes charcoal a rather exceptional SOM conwww.plant-soil.com

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stituent. Terra Preta research has shown that oxidation on the edges of the aromatic backbone and adsorption of other OM to charcoal is responsible for the increased CEC, though the relative importance of these two processes remains unclear (Liang et al., 2006).

4 Conclusion We conclude that both the higher retention of N in the soil and the increased uptake by biomass are responsible for the significantly enhanced N cycling in plots that received charcoal. Soil charcoal amendments improve the efficiency of mineral N fertilizer.

Acknowledgments

J. Plant Nutr. Soil Sci. 2008, 171, 893–899 DeLuca, T. H., Kenzie, M. D. M., Gundale, M. J., Holben, W. E. (2006): Wildfire-produced charcoal directly influences nitrogen cycling in Ponderosa pine forests. Soil Sci. Soc. Am. J. 70, 448–453. Dinkelmeyer, H., Lehmann, J., Renck, A., Trujillo, L. Jr., J. P. d. S., Gebauer, G., Kaiser, K. (2003): Nitrogen uptake from 15N-enriched fertilizer by four tree crops in an Amazonian agroforest. Agroforest. Syst. 57, 213–224. Duxbury, J. M., Smith, M. S., Doran, J. W., Jordan, C., Szott, L., Vance, E. (1989): Soil Organic Matter as a Source and a Sink of Plant Nutrients, in Coleman, D. C., Oades, J. M., Uehara, G. (eds.): Dynamics of Soil Organic Matter in Tropical Ecosystems. University of Hawaii Press, Honolulu, pp. 33–67. FAO (1990): Soil map of the world, revised legend. FAO, Rome, Italy. Fearnside, P. M. (1997): Greenhouse gases from deforestation in Brazilian Amazonia: Net committed emissions. Climatic Change. 35, 321–360.

The research was conducted within SHIFT ENV 45, a German–Brazilian cooperation and financed by BMBF, Germany and CNPq, Brazil (BMBF No. 0339641 5A, CNPq 690003/ 986). A financial contribution was given by the doctoral scholarship program of the Austrian Academy of Sciences. We are grateful for the fieldworkers’ help particularly Luciana Ferreira da Silva and Franzisco Aragão Simão and the laboratory technician Marcia Pereira de Almeida. Jago Birk helped during an internship on the field and in the laboratory.

Fearnside, P. M., Lima, P. M., Graça, A., Rodrigues, F. J. A. (2001): Burning of Amazonian rainforest: burning efficiency and charcoal formation in forest cleared for cattle pasture near Manaus, Brazil. Forest Ecol. Manage. 146, 115–128.

References

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Hölscher, D., Möller, R. F., Denich, M., Fölster, H. (1997b): Nutrient input-output budget of shifting agriculture in Eastern Amazonia. Nutr. Cycl. Agroecosys. 47, 49–57.

Boutton, T. W. (1996): Stable carbon isotope ratios of soil organic matter and their use as indicators of vegetation and climate change, in Boutton, T. W., Yamasaki, S. (eds.): Mass Spectrometry of Soils. Marcel Dekker, New York, pp. 47–82. Braida, W. J., Pignatello, J. J., Lu, Y. F., Ravikovitch, P. I., Neimark, A. V., Xing, B. S. (2003): Sorption hysteresis of benzene in charcoal particles. Environ. Sci. Technol. 37, 409–417. Burger, M., Jackson, L. E. (2003): Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates in organic and conventional cropping systems. Soil Biol. Biochem. 35, 29–36. Correia, F. W. S., Lieberei, R. (1998): Agroclimatological information about the experimental field of the SHIFT-area, ENV 23, 42, 45, 52. Third SHIFT Workshop, Manaus. BMBF, Berlin, Germany, pp. 389–396. Dawson, T. E., Mambelli, S., Plamboeck, A. H., Templer, P. H., Tu, K. P. (2002): Stable isotopes in plant ecology. Annu. Rev. Ecol. Syst. 33, 507–559.

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J. Plant Nutr. Soil Sci. 2008, 171, 893–899 central Amazon? 17th World Congress of Soil Science, Bangkok, Thailand, The International Union of Soil Sciences, pp. 1–12. Lehmann, J., da Silva Jr., J. P., Steiner, C., Nehls, T., Zech, W., Glaser, B. (2003): Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil 249, 343–357. Lehmann, J., Gaunt, J., Rondon, M. (2006): Bio-char sequestration in terrestrial ecosystems–a review. Mitig. Adapt. Strat. Glob. Change. 11, 403–427. Liang, B., Lehmann, J., Solomon, D., Grossman, J., O′Neill, B., Skjemstad, J. O., Thies, J., Luizão, F. J., Petersen, J., Neves, E. G. (2006): Black carbon increases cation exchange capacity in soils. Soil Sci. Soc. Am. J. 70, 1719–1730. Lima, H. N., Schaefer, C. E. R., Mello, J. W. V., Gilkes, R. J., Ker, J. C. (2002): Pedogenesis and pre-Colombian land use of “Terra Preta Anthrosols” (“Indian black earth”) of Western Amazonia. Geoderma 110, 1–17. Ogawa, M. (1994): Symbiosis of people and nature in the tropics. Farming Japan 28, 10–30. Renck, A., Lehmann, J. (2004): Rapid water flow and transport of inorganic and organic nitrogen in a highly aggregated tropical soil. Soil Sci. 169, 330–341. Ross, S. M. (1993): Organic matter in tropical soils–Current conditions, concerns and prospects for conservation. Prog. Phys. Geog. 17, 265–305. Sombroek, W. G., Nachtergaele, F. O., Hebel, A. (1993): Amounts, dynamics and sequestering of carbon in tropical and subtropical soils. Ambio 22, 417–426.

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Nitrogen retention with compost and charcoal 899 Sommer, R., Vlek, P. L. G., Sá, T. D. d. A., Vielhauer, K., Coelho, R. d. F. R., Fölster, H. (2004): Nutrient balance of shifting cultivation by burning or mulching in the Eastern Amazon–evidence for subsoil nutrient accumulation. Nutr. Cycl. Agroecosys. 68, 257–271. Steiner, C., Teixeira, W. G., Lehmann, J., Zech, W. (2004a): Microbial Response to Charcoal Amendments of Highly Weathered Soils and Amazonian Dark Earths in Central Amazonia – Preliminary Results, in Glaser, B., Woods, W. I.: Amazonian Dark Earths: Explorations in Space and Time. Springer Verlag, Heidelberg, pp. 195–212. Steiner, C., Teixeira, W. G., Zech, W. (2004b): Slash and Char: An Alternative to Slash and Burn Practiced in the Amazon Basin, in Glaser, B., Woods, W. I.: Amazonian Dark Earths: Explorations in Space and Time. Springer Verlag, Heidelberg, pp. 183–193. Steiner, C., Teixeira, W. G., Lehmann, J., Nehls, T., Macêdo, J. L. V. d., Blum, W. E. H., Zech, W. (2007): Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant Soil 291, 275–290. Tiessen, H., Cuevas, E., Chacon, P. (1994): The role of soil organic matter in sustaining soil fertility. Nature 371, 783–785. Wardle, D. A., Zackrisson, O., Nilsson, M. C. (1998): The charcoal effect in Boreal forests: mechanisms and ecological consequences. Oecologia 115, 419–426. Yanai, Y., Toyota, K., Okazaki, M. (2007): Effects of charcoal addition on N2O emissions from soil resulting from rewetting air-dried soil in short-term laboratory experiments. Soil Sci. Plant Nutr. 53, 181–188.

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DOI: 10.1002/jpln.200625199

893

Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal Christoph Steiner1,2*, Bruno Glaser1, Wenceslau Geraldes Teixeira3, Johannes Lehmann4, Winfried E.H. Blum5, and Wolfgang Zech1 1

Institute of Soil Science and Soil Geography, University of Bayreuth, 95440 Bayreuth, Germany Current address: Biorefining and Carbon Cycling Program, The University of Georgia, Athens, USA 3 Embrapa Amazonia Ocidental, CP 319–69011–970 Manaus, Brazil 4 Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853, USA 5 Institute of Soil Research, University of Natural Resources and Applied Life Sciences (BOKU), 1180 Vienna, Austria 2

Abstract Leaching losses of N are a major limitation of crop production on permeable soils and under heavy rainfalls as in the humid tropics. We established a field trial in the central Amazon (near Manaus, Brazil) in order to study the influence of charcoal and compost on the retention of N. Fifteen months after organic-matter admixing (0–0.1 m soil depth), we added 15N-labeled (NH4)2SO4 (27.5 kg N ha–1 at 10 atom% excess). The tracer was measured in top soil (0–0.1 m) and plant samples taken at two successive sorghum (Sorghum bicolor L. Moench) harvests. The N recovery in biomass was significantly higher when the soil contained compost (14.7% of applied N) in comparison to only mineral-fertilized plots (5.7%) due to significantly higher crop production during the first growth period. After the second harvest, the retention in soil was significantly higher in the charcoal-amended plots (15.6%) in comparison to only mineral-fertilized plots (9.7%) due to higher retention in soil. The total N recovery in soil, crop residues, and grains was significantly (p < 0.05) higher on compost (16.5%), charcoal (18.1%), and charcoal-pluscompost treatments (17.4%) in comparison to only mineral-fertilized plots (10.9%). Organic amendments increased the retention of applied fertilizer N. One process in this retention was found to be the recycling of N taken up by the crop. The relevance of immobilization, reduced N leaching, and gaseous losses as well as other potential processes for increasing N retention should be unraveled in future studies. Key words: biochar Brazil / carbon / nitrogen cycling / slash-and-burn / soil organic matter / Terra Preta

Accepted January 2, 2008

1 Introduction The fertility of highly weathered Ferralsols in the tropics is low, and soil organic matter (SOM) plays a major role in sustaining soil productivity. Thus, long-term intensive use is not sustainable without nutrient inputs where SOM stocks are depleted (Tiessen et al., 1994). Due to low nutrient-retention capacity and high permeability of these soils, strong tropical rainfalls cause rapid leaching of mobile nutrients such as those applied with mineral N fertilizers (Hölscher et al., 1997a; Giardina et al., 2000; Renck and Lehmann, 2004). To overcome these limitations of poor soil, low nutrient-retention capacity and accelerated SOM decay require alternatives to slash-and-burn (the prevalent agricultural practice in the tropics) and alternative fertilization methods (Ross, 1993; Fernandes et al., 1997). Instead of burning, involving a quick release of nutrients (Kuhlbusch et al., 1991; Hölscher et al., 1997b; Giardina et al., 2000; Hughes et al., 2000) and CO2 (Fearnside, 1997), fallow vegetation could be applied as mulch (Sommer et al., 2004), compost, or charcoal (Lehmann et al., 2002). Depending on the mineralization rate, organic fertilizers such as compost, mulch, or manure applications release nutrients in a gradual manner (Burger and Jackson, 2003). This may be different for very recalcitrant organic addi-

tions such as charcoal. According to Duxbury et al. (1989) and Sombroek et al. (1993), it is important to separate effects due to OM per se (maintenance and improvement of water infiltration, water-holding capacity, structure stability, CEC, healthy soil-biological activity) from those due to its decomposition (source of nutrients).

Only relatively small amounts of charcoal are produced by the traditional slash-and-burn technique. Charcoal represents only 1.7% of the preburn biomass if a forest is converted into cattle pasture (Fearnside et al., 2001). Producing charcoal for soil amelioration from aboveground biomass instead of converting it to CO2 through burning might be an alternative to slash-and-burn (Lehmann et al., 2002; Steiner et al., 2004b; Lehmann et al., 2006).

The existence of so-called “Terra Preta de Índio” (Indian black earth) suggests that a human-induced accumulation of SOM can be maintained over centuries (Sombroek et al., 1993). These soils are exceptionally fertile, and their productivity is most likely linked to an anthropogenic accumulation of P and Ca associated with bone apatite (Lima et al., 2002) and black C (BC) as charcoal (Glaser et al., 2001).

* Correspondence: Dr. Ch. Steiner; e-mail: [email protected]

 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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The sustained fertility of charcoal-containing Terra Preta and the frequent use of charcoal as a soil conditioner (Steiner et al., 2004b) in Brazil provided the incentive to study the effects of charcoal application on N cycling. Charcoal acted as an adsorber which reduced N leaching in previous pot experiments (Lehmann et al., 2002, 2003), and charcoal additions proved to sustain fertility if an additional nutrient source is given in a field trial (Steiner et al., 2007). Charcoal plus fertilizer improved plant growth and doubled grain production in comparison to the fertilizer without charcoal. Plant biomass production sharply decreased within 1 y when only mineral fertilizer was applied, but could be maintained for a longer period of time when OM was added. The authors proposed that charcoal can improve soil chemical, biological, and physical properties, but could not completely discern the mechanisms of fertility enhancement (Steiner et al., 2007). Stable isotopes such as 15N can serve as valuable tracers to study plant resource acquisition and as a means to understand how plants interact with their abiotic and biotic environments (Dawson et al., 2002). Therefore, our objective was to compare the effect of organic amendments such as charcoal and compost on retention of 15N-labeled mineral fertilizer in a highly weathered Ferralsol under humid tropical field conditions.

2 Materials and methods 2.1 Study location and experimental setup

J. Plant Nutr. Soil Sci. 2008, 171, 893–899 The charcoal derived from secondary forest wood and was considered rather as soil conditioner than fertilizer due to the charcoal’s low nutrient contents (Tab. 1). It was manually crushed to particle sizes <2 mm. The applied 11 Mg ha–1 corresponded to the amount of charcoal-C which could be produced by a single slash-and-char event of a tropical secondary forest on Xanthic Ferralsols in central Amazonia (Lehmann et al., 2002). The amount of C added with charcoal was chosen as a reference value for adding the compost. Compost was prepared from biomass of a secondary forest, fruit residues, manure, and kitchen waste. On February 3, 2001, organic materials were mixed with hand hoes into the top soil (0–0.1 m) of the plots, and the first mineral fertilization was done on March 19, 2001 [30 N kg ha–1 as (NH4)2SO4, 35 kg P ha–1 as simple superphosphate, 50 kg K ha–1 as KCl, and 2100 kg lime ha–1]. The fields were cropped twice (rice Oryza sativa L. and sorghum Sorghum bicolor L. Moench) prior the second fertilization on April 16 (see Tab. 1 for treatment description). All crop residues remained on the field, and only grains were removed. Sorghum was planted again on April 18, 2002 in a density of 25 plants m–2 producing two harvests by ratooning (July 21 and October 16, 2002). Only these two harvests are subject of the present paper and designated as 1st (HI) and 2nd (HII) harvest. Table 1: Treatments, organic amendments, and harvest remnants (from previous harvests remained in the field). Mineral fertilization (F) was applied after the second harvest in April 2002, 15N-labeled N (55), P (40), K (50), lime (430) [kg ha–1]. Token

The experiment was conducted within a larger field trial established 30 km N of Manaus, Amazonas, Brasil (3°8′ S, 59°52′ W, 40–50 m asl) at the Embrapa-Amazônia Ocidental (Empresa Brasileira de Pesquisa Agropecuaria) experimental research station. The natural vegetation is evergreen tropical rainforest with a mean annual precipitation of 2530 mm (1971–1997) having its seasonal maximum between December and May, a mean annual temperature of 25.8°C (1987–1997), and relative humidity of 85% (Correia and Lieberei, 1998). The soil was classified as a highly weathered Xanthic Ferralsol (FAO, 1990), finetextured with high clay content. It is strongly aggregated and has medium contents of organic C (24 g kg–1), low pH values of 4.7 (in H2O), low CEC of 1.6 cmolc kg –1, and low base saturation (BS) of 11% (Steiner et al., 2007). This experiment is part of a long-term field trial established in January 2001 (Steiner et al., 2007). The main objective was to study different organic-amendment combinations based on equal amounts of C additions. Fifteen different treatments were established in five repetitions after clearing of approx. 3600 m2 secondary forest and removing the aboveground biomass. The treatments were applied on 4 m2 plots (2 m × 2 m) forming an entire field area of 1600 m2 (45 m × 35 m) with a minimum distance to the surrounding vegetation of 10 m. For this study, five mineral-fertilized (F) treatments were chosen, four of them with compost (CO + F) and/or charcoal (CC + F) application (Tab. 1). The treatment receiving compost only (CO) served to provide a reference value for N isotope composition in soil and plants. This treatment was used as a control for all treatments as d15N did not differ between the treatments without tracer application [(NH4)2SO4 fertilized or not].  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Organic matter

1st harvest (HI) remnantsa

2nd Total harvest (HII) remnantsa

[Mg dry matter ha–1] COb

compost (67)

5.13 1.98

0.27

2.25

CO + F

compost (67)

6.24

1.51

7.75

CC + F

charcoal (11)

F

1.11

6.24

2.55

0.72

3.27

½CC + ½CO + F charcoal (5,5), compost (33,5)

4.74

1.10

5.85

CC + ½CO + F

4.28

1.10

5.38

charcoal (11), compost (33,5)

F = mineral fertilizer; CO = compost; CC = charcoal previous harvests July 7, 2001 and February 6, 2002 b unfertilized control treatment, reference value for 15N natural abundance; previous mineral fertilization: March 2001 [kg ha–1] N (30), P (35), K (50), lime (2100); compost contained 10.1, 0.73, 2.85, 3.27, and 1.51 g kg–1 N, P, K, Ca, and Mg, respectively; charcoal contained 5.39, 0.03, 0.23, 0.82, and 0.17 g kg–1 N, P, K, Ca, and Mg, respectively. a

2.2 Tracer application, sampling, and calculations The chosen treatments (F, CC + F, CO + F, ½CC + ½CO + F, and CC + ½CO + F) received 15N isotope enrichment using 15N-labeled (NH ) SO with 10 atom% 15N excess. The tra4 2 4 cer was mixed in a ratio 1:1 with conventional (NH4)2SO4 and www.plant-soil.com

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Nitrogen retention with compost and charcoal 895

applied at a rate of 55 kg N ha–1 in April 2002 (second fertilization). Additionally, 40 kg P ha–1, 50 kg K ha–1, and 430 kg ha–1 of lime was applied. Soil and plant samples were taken at each harvest and analyzed for d15N. Only the top 0.1 m of soil was sampled, this was also the depth down to which the organic amendments were mixed. Two soil samples were taken per plot to form one composite sample. Soils were airdried and ground before isotope analysis. Representative plant samples were taken from the entire crop by using the center 1.4 × 1.4 m (49 plants) of each plot. Plant samples were dried at 70°C for 48 h and ground. The remaining fertilizer N in soil or plant biomass was calculated after Eq. 1 (Boutton, 1996). Nf
d15 Nf ˆ Nf
d15 Nc ‡Y
d15 NNPK ,

(1)

Nf = nitrogen content of biomass or soil in N-fertilized treatment, d15Nf = measured d15N value of biomass or soil in N-fertilized treatment, d15Nc = measured d15N value of biomass or soil in unfertilized control treatment (only CO served as valid control treatment as d15N did not differ between treatments without tracer application), d15NNPK = d15N of (NH4)2SO4 10 atom% (= 29330.3‰).

15N

excess

The amount of 15N remaining in soil or in plant biomass (Y) was calculated according to Eq. 2. The subtraction of d15Nc in the denominator was neglected because it is small (approx. 10 and 20 for soil and biomass, respectively) in comparison to d15NNPK. Yˆ

Nf
d15 Nf

Nf
d15 Nc

15

d NNPK

.

(2)

The percentage of N taken up by biomass or remaining in the soil was calculated according to Eq. 3: N% ˆ

Y
100, N…NH4 †2 SO4

(3)

where N(NH4)2SO4 = amount of tracer fertilized [27.5 kg ha–1 (NH4)2SO4 10 atom% 15N excess].

2.3 Analyses of soil and plant samples Soil and plant samples were analyzed for their C and N contents by dry combustion with an automatic C/N-Analyzer (Elementar, Hanau, Germay). Total N isotope composition in soil and plants was determined using an Elemental Analyzer (Carlo Erba NA 1500, Carlo Erba Reagenti, Rodano, Italy; for Dumas combustion) connected to an isotope-mass spectrometer (FINNIGAN MAT delta E; Thermo Finnigan, San Jose CA) via a split interface.  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2.4 Statistical analyses Treatment effects were analyzed by one-way analysis of variance (ANOVA). Significant treatment effects were detected using the Fisher’s LSD (last significant difference) test. Statistical analyses and figures were performed using SPSS 12.0 (SPSS Inc.) and SigmaPlot 7.0.

3 Results and discussion While the soil C contents were significantly increased by the organic amendments (CO and CC), the N values were only significantly enhanced in comparison to the F plots if CO was applied (Fig. 1). After the second harvest (HII), the N and C contents on solely compost-amended plots (CO) did not differ from those receiving only mineral fertilizer. The OM-amended and N-fertilized plots had significantly higher C and N contents than the F plots. All organic amendments significantly increased the C : N ratio after the first harvest. This difference was even more distinct after the second harvest but only on charcoal-containing plots (Fig. 1). Neither the N concentrations in the biomass nor the measured d15N values differed significantly (data not shown). The significantly higher mineral N uptake by plants growing on the compost-amended plots (CO + F) was due to a significantly higher plant biomass production (Tab. 2). Wardle et al. (1998) found greater tree-seedling growth, N uptake, and enhanced efficiency of nutrient uptake in boreal forest soils when charcoal was added. The authors assumed that adsorption of phenolics by the charcoal diminished adverse effects on plant growth, both as allelopathic agents, and through complexing N, thus reducing its availability to plants. In our case, soil analyses indicate that other nutrients than N were more important to enhance plant growth leading to N sequestration in biomass (Steiner et al., 2007). This assumption is corroborated by the study of Alfaia et al. (2000) who found only a 16% rice grain-yield increase due to (NH4)2SO4 fertilization, but significant losses of fertilized N. In the soil, the situation was rather different. After the second harvest (HII), significantly more fertilizer N remained in the soil amended with charcoal (15.6% of applied N) than on plots without organic amendment (9.7%). The compost treatment showed intermediate values (12.6%) (Fig. 2). In the soil, the increased retrieval of N rather than higher total soil N contents caused the significantly enhanced N recovery. Only remaining crop residues could have caused the increase in encountered 15N from HI to HII. However, the treatment ½CC + ½CO + F showed a much larger increase in soil 15N encountered from HI to HII than the F treatment but had slightly less crop-residue input (Tab. 2). Only the compost treatment (CO + F) generated significantly more crop residue 15N than the control group but this additional residue return did not significantly affect the soil 15N at HII. At least to some extent the accrued crop residues after HII added to the soil’s N pool as shown by the shift in isotope values (data not shown) because soil sampling was done 7–14 d after the harvest. Belowground biomass was not www.plant-soil.com

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Figure 1: Contents of C and N in of the soil at the first (HI) and second harvest (HII). The error bars show the mean ± standard error. The Fisher’s LSD (least significant difference) value is plotted to scale significant mean separation (p < 0.05).

assessed and can contribute significantly to N cycling as the root biomass pool can be assumed to be at least half as large as the aboveground biomass pool (Lacerda et al., 2004; Hattori et al., 2005). Lehmann and Zech (1998) found 30% of sorghum roots in Kenya below 0.3 m. We sampled only the upper 0.1 m, thus N could have been recycled from deeper soil layers.

The significantly increased uptake of applied N by plants on plots with additional compost and the significantly higher N retention in the soil due to charcoal additions may be explained by either reduced N leaching (Lehmann et al., 2003) or reduced gaseous N losses (Yanai et al., 2007). Reduced N leaching may be a result (1) of either improved retention of the applied NH‡ 4 by electrostatic adsorption to exchange sites provided by the com-

Table 2: Biomass production, N uptake, and withdrawal (grains) at the first (HI) and second harvest (HII). Different letters in the same column indicate significant differences (p < 0.05) between treatments (Fisher’s LSD test, n = 5). HI

HII

HI

crop residues grains

crop residues grains

N residues

HII N grains

[Mg dry matter ha–1]

Treatment

N residues

N grains

[kg ha–1]

F

1.38

b

0.28

c

0.50

c

0.14

c

11.3

c

4.7

c

4.9

b

2.3

CO

1.50

b

0.28

c

0.56

c

0.16

bc

19.8

b

5.8

c

7.5

b

3.2

c bc

CO + F

2.69

a

0.96

a

1.17

a

0.80

a

29.8

a

15.5

a

13.1

a

12.6

a

CC + F

1.85

b

0.42

bc

0.72

bc

0.28

bc

17.3

bc

7.1

c

7.0

b

4.6

bc

½CC + ½CO + F

1.76

b

0.65

b

0.80

abc

0.33

bc

18.9

bc

11.8

ab

8.7

b

6.1

bc

CC + ½CO + F

2.08

ab

0.49

bc

0.97

ab

0.49

ab

19.7

b

8.1

bc

9.1

ab

8.5

ab

F = mineral fertilizer; CO = compost; CC = charcoal Crop residues remained in the field; mean C 44.8, N 9.97 g kg–1, C : N = 44.16; mean N content of grains = 16.9 g kg–1

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Nitrogen retention with compost and charcoal 897

Figure 2: Amount of mineral N fertilizer remaining in the soil (Ferralsol, a and b) and in the crop (sorghum, c and d) after the first (HI, a and c) and second harvest (HII, b and d) as a percentage. Means and standard errors (p < 0.05, Fisher’s LSD test, n = 5).

post or charcoal or (2) of immobilization of N by microbial biomass. Lehmann et al. (2003) made microbial immobilization responsible for decreases in foliar N contents and total N uptake as a response to charcoal additions due to their higher C : N ratio. However, their pot experiment used larger amounts of applied charcoal (67.6 and 135.2 Mg C ha–1) than our study. The C : N ratio in the soil studied here was found to be significantly higher in the charcoal treatments at both harvest times (Fig. 1) in comparison to the control. Decomposition of a portion of newly applied charcoal and concurrent N immobilization is most likely a transient phenomenon as charcoal is much more stable than other organic additions (Baldock and Smernik, 2002). In the studied permeable soils under high-rainfall conditions, temporary immobilization of mobile nutrients might be desirable. The results of the 15N experiments by Burger and Jackson (2003) suggest a very dynamic role of microbially bound N and highlight the importance of N immobilization that is taking place simultaneously with inorganic-N production by mineralization. They concluded that greater C availability stimulates microbial activity resulting in greater N demand, promoting immobilization and recycling of NO3 . The resilience of soil C in charcoalamended plots shows the refractory nature of charcoal (Kuhlbusch and Crutzen, 1995). While the stability of charcoal leads to low C losses, nutrient release by mineralization is most likely lower than from other organic materials. As charcoal is expected to be an extremely recalcitrant form of OM, it is unknown to what extent charcoal C favors N immobilization. In previous studies, the same plots showed significantly increased plant growth and potential for microbial-population growth in mineral-fertilized soils amended with charcoal and in Terra Preta, but lower microbial respiration in the absence of an easily degradable C source (glucose) compared to soils without charcoal (Steiner et al., 2004a, 2007). It has been shown that charcoal amendments can significantly enhance nitrification in pine-forest soils (DeLuca et al., 2006). The authors suggest that charcoal alters  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

the activity of the nitrifying community and removes inhibiting phenols. We could not elucidate alterations in nitrification and its possible consequences for leaching and denitrification, although Birk (2005) found evidence that the organic amendments increased the presence of anaerobic bacteria which possibly are denitrifiers. Dinkelmeyer et al. (2003) found a rapidly decreasing total recovery (in plants and soil) of 15N (87% to 54% to 24% at 1, 3, and 12 months after N application, respectively), but they assessed a complex and deep-rooting agroforestry system to a soil depth of 5 m. They found a minimum of 13% Nfertilizer efficiency when applied to peach palm (Bactris gasipaes) and a maximum of 38% if applied to cupuassu (Theobroma grandiflorum). Alfaia et al. (2000) assessed N utilization of a rice crop grown in central Amazona and found a N-fertilizer efficiency of only 7.8%, 10.0%, and 1% in shoot, grain, and root biomass, respectively. We found a maximum recovery in plant biomass of 15% and total recovery of 22% 3 months after N application at HI. Already after 4 d, Renck and Lehmann (2004) found applied 15N in the soil solution to a depth of 0.6 m and to a depth of 5 m after 1 week at the same study site. They found that the largest part of applied 15N in the top soil was leached as organic N. The total fluxes of organic N were similar to those of NO3 in the topsoil. According to Lehmann et al. (2002), the NH‡ 4 adsorbability of charcoal is largely dependent on soluble OM, as an addition of DOC from a manure extract increased NH‡ 4 adsorption. Therefore charcoal might have reduced leaching of organic N in addition to the inorganic forms. The organic amendments might likewise have altered denitrification but leaching is most likely the predominant N loss in the studied soil and the relative proportion could not be clarified in this study. The charcoal’s low biodegradability (Kuhlbusch and Crutzen, 1995), low nutrient content (Ogawa, 1994; Antal and Grønli, 2003), and high porosity and specific surface area (Braida et al., 2003) makes charcoal a rather exceptional SOM conwww.plant-soil.com

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stituent. Terra Preta research has shown that oxidation on the edges of the aromatic backbone and adsorption of other OM to charcoal is responsible for the increased CEC, though the relative importance of these two processes remains unclear (Liang et al., 2006).

4 Conclusion We conclude that both the higher retention of N in the soil and the increased uptake by biomass are responsible for the significantly enhanced N cycling in plots that received charcoal. Soil charcoal amendments improve the efficiency of mineral N fertilizer.

Acknowledgments

J. Plant Nutr. Soil Sci. 2008, 171, 893–899 DeLuca, T. H., Kenzie, M. D. M., Gundale, M. J., Holben, W. E. (2006): Wildfire-produced charcoal directly influences nitrogen cycling in Ponderosa pine forests. Soil Sci. Soc. Am. J. 70, 448–453. Dinkelmeyer, H., Lehmann, J., Renck, A., Trujillo, L. Jr., J. P. d. S., Gebauer, G., Kaiser, K. (2003): Nitrogen uptake from 15N-enriched fertilizer by four tree crops in an Amazonian agroforest. Agroforest. Syst. 57, 213–224. Duxbury, J. M., Smith, M. S., Doran, J. W., Jordan, C., Szott, L., Vance, E. (1989): Soil Organic Matter as a Source and a Sink of Plant Nutrients, in Coleman, D. C., Oades, J. M., Uehara, G. (eds.): Dynamics of Soil Organic Matter in Tropical Ecosystems. University of Hawaii Press, Honolulu, pp. 33–67. FAO (1990): Soil map of the world, revised legend. FAO, Rome, Italy. Fearnside, P. M. (1997): Greenhouse gases from deforestation in Brazilian Amazonia: Net committed emissions. Climatic Change. 35, 321–360.

The research was conducted within SHIFT ENV 45, a German–Brazilian cooperation and financed by BMBF, Germany and CNPq, Brazil (BMBF No. 0339641 5A, CNPq 690003/ 986). A financial contribution was given by the doctoral scholarship program of the Austrian Academy of Sciences. We are grateful for the fieldworkers’ help particularly Luciana Ferreira da Silva and Franzisco Aragão Simão and the laboratory technician Marcia Pereira de Almeida. Jago Birk helped during an internship on the field and in the laboratory.

Fearnside, P. M., Lima, P. M., Graça, A., Rodrigues, F. J. A. (2001): Burning of Amazonian rainforest: burning efficiency and charcoal formation in forest cleared for cattle pasture near Manaus, Brazil. Forest Ecol. Manage. 146, 115–128.

References

Glaser, B., Guggenberger, G., Haumaier, L., Zech, W. (2001): Persistence of Soil Organic Matter in Archaeological Soils (Terra Preta) of the Brazilian Amazon Region, in Rees, R. M., Ball, B. C., Campbell, C. D., Watson, C. A.: Sustainable management of soil organic matter. CABI Publishing, Wallingford, pp. 190–194.

Alfaia, S. S., Guiraud, G., Jacquin, F., Muraoka, T., Ribeiro, G. A. (2000): Efficiency of nitrogen-15labelled fertilizers for rice and ryegrass cultivated in an Ultisol of Brazilian Amazonia. Biol Fertil. Soils 31, 329–333.

Fernandes, E. C. M., Motavalli, P. P., Castilla, C., Mukurumbira, L. (1997): Management control of soil organic matter dynamics in tropical land-use systems. Geoderma 79, 49–67. Giardina, C. P., Sanford, R. L., Dockersmith, I. C., Jaramillo, V. J. (2000): The effects of slash burning on ecosystem nutrients during the land preparation phase of shifting cultivation. Plant Soil 220, 247–260.

Antal, M. J., Grønli, M. (2003): The art, science, and technology of charcoal production. Ind. Eng. Chem. Res. 42, 1619–1640.

Hattori, T., Inanaga, S., Araki, H., An, P., Morita, S., Luxová, M., Lux, A. (2005): Application of silicon enhanced drought tolerance in Sorghum bicolor. Physiol. Planta. 123, 459–466.

Baldock, J. A., Smernik, R. J. (2002): Chemical composition and bioavailability of thermally altered Pinus resinosa (Red pine) wood. Org. Geochem. 33, 1093–1109.

Hölscher, D., Ludwig, B., Möller, R. F., Fölster, H. (1997a): Dynamic of soil chemical parameters in shifting agriculture in the Eastern Amazon. Agr. Ecosyst. Environ. 66, 153–163.

Birk, J. J. (2005): Einfluss von Holzkohle und Düngung auf die mikrobielle Zersetzergemeinschaft und den Streuumsatz in amazonischen Ferralsols. Master thesis (unpublished), University of Bayreuth, Germany.

Hölscher, D., Möller, R. F., Denich, M., Fölster, H. (1997b): Nutrient input-output budget of shifting agriculture in Eastern Amazonia. Nutr. Cycl. Agroecosys. 47, 49–57.

Boutton, T. W. (1996): Stable carbon isotope ratios of soil organic matter and their use as indicators of vegetation and climate change, in Boutton, T. W., Yamasaki, S. (eds.): Mass Spectrometry of Soils. Marcel Dekker, New York, pp. 47–82. Braida, W. J., Pignatello, J. J., Lu, Y. F., Ravikovitch, P. I., Neimark, A. V., Xing, B. S. (2003): Sorption hysteresis of benzene in charcoal particles. Environ. Sci. Technol. 37, 409–417. Burger, M., Jackson, L. E. (2003): Microbial immobilization of ammonium and nitrate in relation to ammonification and nitrification rates in organic and conventional cropping systems. Soil Biol. Biochem. 35, 29–36. Correia, F. W. S., Lieberei, R. (1998): Agroclimatological information about the experimental field of the SHIFT-area, ENV 23, 42, 45, 52. Third SHIFT Workshop, Manaus. BMBF, Berlin, Germany, pp. 389–396. Dawson, T. E., Mambelli, S., Plamboeck, A. H., Templer, P. H., Tu, K. P. (2002): Stable isotopes in plant ecology. Annu. Rev. Ecol. Syst. 33, 507–559.

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Hughes, R. F., Kauffman, J. B., Cummings, D. L. (2000): Fire in the Brazilian Amazon 3. Dynamics of biomass, C, and nutrient pools in regenerating forests. Oecologia 124, 574–588. Kuhlbusch, T. A. J., Crutzen, P. J. (1995): Toward a global estimate of black carbon in residues of vegetation fires representing a sink of atmospheric CO2 and a source of O2. Global Biogeochem. Cycl. 9, 491–501. Kuhlbusch, T. A., Lobert, J. M., Crutzen, P. J., Warneck, P. (1991): Molecular nitrogen emissions from denitrification during biomass burning. Nature 351, 135–137. Lacerda, C. F., Cambraia, J., Oliva, M. A., Ruiz, H. A. (2004): Influência do cálcio sobra o crescimento e solutos em plântulas de sorgo estressadas com cloreto de sódio. R. Bras. Ci. Solo. 28, 289–295. Lehmann, J., Zech, W. (1998): Fine root turnover of irrigated hedgerow intercropping in Northern Kenya. Plant Soil 198, 19–31. Lehmann, J., da Silva Jr., J. P., Rondon, M., Cravo, M. d. S., Greenwood, J., Nehls, T., Steiner, C., Glaser, B. (2002): Slash and char – a feasible alternative for soil fertility management in the

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J. Plant Nutr. Soil Sci. 2008, 171, 893–899 central Amazon? 17th World Congress of Soil Science, Bangkok, Thailand, The International Union of Soil Sciences, pp. 1–12. Lehmann, J., da Silva Jr., J. P., Steiner, C., Nehls, T., Zech, W., Glaser, B. (2003): Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil 249, 343–357. Lehmann, J., Gaunt, J., Rondon, M. (2006): Bio-char sequestration in terrestrial ecosystems–a review. Mitig. Adapt. Strat. Glob. Change. 11, 403–427. Liang, B., Lehmann, J., Solomon, D., Grossman, J., O′Neill, B., Skjemstad, J. O., Thies, J., Luizão, F. J., Petersen, J., Neves, E. G. (2006): Black carbon increases cation exchange capacity in soils. Soil Sci. Soc. Am. J. 70, 1719–1730. Lima, H. N., Schaefer, C. E. R., Mello, J. W. V., Gilkes, R. J., Ker, J. C. (2002): Pedogenesis and pre-Colombian land use of “Terra Preta Anthrosols” (“Indian black earth”) of Western Amazonia. Geoderma 110, 1–17. Ogawa, M. (1994): Symbiosis of people and nature in the tropics. Farming Japan 28, 10–30. Renck, A., Lehmann, J. (2004): Rapid water flow and transport of inorganic and organic nitrogen in a highly aggregated tropical soil. Soil Sci. 169, 330–341. Ross, S. M. (1993): Organic matter in tropical soils–Current conditions, concerns and prospects for conservation. Prog. Phys. Geog. 17, 265–305. Sombroek, W. G., Nachtergaele, F. O., Hebel, A. (1993): Amounts, dynamics and sequestering of carbon in tropical and subtropical soils. Ambio 22, 417–426.

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Nitrogen retention with compost and charcoal 899 Sommer, R., Vlek, P. L. G., Sá, T. D. d. A., Vielhauer, K., Coelho, R. d. F. R., Fölster, H. (2004): Nutrient balance of shifting cultivation by burning or mulching in the Eastern Amazon–evidence for subsoil nutrient accumulation. Nutr. Cycl. Agroecosys. 68, 257–271. Steiner, C., Teixeira, W. G., Lehmann, J., Zech, W. (2004a): Microbial Response to Charcoal Amendments of Highly Weathered Soils and Amazonian Dark Earths in Central Amazonia – Preliminary Results, in Glaser, B., Woods, W. I.: Amazonian Dark Earths: Explorations in Space and Time. Springer Verlag, Heidelberg, pp. 195–212. Steiner, C., Teixeira, W. G., Zech, W. (2004b): Slash and Char: An Alternative to Slash and Burn Practiced in the Amazon Basin, in Glaser, B., Woods, W. I.: Amazonian Dark Earths: Explorations in Space and Time. Springer Verlag, Heidelberg, pp. 183–193. Steiner, C., Teixeira, W. G., Lehmann, J., Nehls, T., Macêdo, J. L. V. d., Blum, W. E. H., Zech, W. (2007): Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant Soil 291, 275–290. Tiessen, H., Cuevas, E., Chacon, P. (1994): The role of soil organic matter in sustaining soil fertility. Nature 371, 783–785. Wardle, D. A., Zackrisson, O., Nilsson, M. C. (1998): The charcoal effect in Boreal forests: mechanisms and ecological consequences. Oecologia 115, 419–426. Yanai, Y., Toyota, K., Okazaki, M. (2007): Effects of charcoal addition on N2O emissions from soil resulting from rewetting air-dried soil in short-term laboratory experiments. Soil Sci. Plant Nutr. 53, 181–188.

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Introduction to the Pioneer Works of Charcoal Uses in Agriculture, Forestry and Others in Japan Makoto Ogawa Osaka Institute of Technology Introduction In Asian countries, the highly intensive agriculture has been popular since ancient days because of high population density, limited arable field and rice plant cultivation. Therefore, various traditional cultivation techniques had developed in order to raise the productivity of crops. Any kinds of wastes, the excretions of human and live stocks, straw, leaf litter, grass、sewages and rice husk charcoal has been used as for the fertilizers and soil amendments not only in agriculture but also gardening or greening. Particularly wood ash containing some cinders was used as an important material for soil amendment and mineral supply. In Japan where the domestic supply of energy sources has been limited, the forest resources, fire wood and charcoal were a most important energy source until the beginning of 20th century. Charcoal production and consumption increased depending on the increase of population and reached to the maximum, 2.7 million ton per year in 1947. It may be estimated that the wood, mainly broad leaved trees, of about 10 million ton was carbonized by the traditional kiln at that time (1). However, according to the rapid increase of the imported fossil fuels in 1960s, so called “Fuel Revolution” progressed, and the productivity of charcoal decreased to the minimum, about 30 thousand ton per year in 1980s. The abrupt changes in the people’s daily life and the relations between human and forest caused the decrease of Matsutake mushroom, mycorrhizal fungus and the outbreak of pine wilting disease (2). In 1970s, under such a circumstance, late Dr. Kishimoto S. and Sugiura G. who were the experts of charcoal and wood vinegar production began the movement to make revive charcoal and to encourage the new use. In 1980 they published a book “ Introduction to charcoal making on Sunday ” (3) and distributed the knowledge of popular charcoal making and use. They contributed largely toward the present prosperity of charcoal business in Japan and Asia. The author, Ogawa M. and his colleagues started the studies on the utilization of charcoal in agriculture and forestry on their requests in 1980 and reported the effects of bark charcoal on soy bean and pine tree in 1983 (4) (5). Being encouraged by their activities and the extension of organic farming in Japan, the application and studies of charcoal in agriculture began actively in 1980s. In 1986, “Technical Research Association for Multiuse of Carbonized Materials” (TRA) was established by the financial support of Forest Agency, and the studies of new charcoal use launched being participated with 13 private companies for 3 years. The studies on the effects of charcoal and wood vinegar were conducted covering the various fields; the improvement of carbonization Page 1 of 15

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technology, soil amendment in agriculture and greening, activation of microorganisms and water purification. The research result with some general comments was published in 1990 and widely distributed (6). By the report, the effects of charcoal and wood vinegar were recognized in public and authorized as a specific material of soil amendment by MAFF (Ministry of Agriculture, Forestry and Fishery) in1990. Contrary to the government expectation to raise the charcoal production in rural area, the cheaper charcoals which are imported from Southeast Asia being produced from coconut and oil palm shells has reached to the same amount with those in domestic. In this paper, only the publications written by Japanese are introduced, because it seems to be unavailable in other countries.

1. Charcoal Utilization in Agriculture and Gardening 1. Rice husk charcoal The oldest description on charcoal use in agriculture is found in a text book, “ Nogyo Zensho ( Encyclopedia of Agriculture )” written by Yasusada Miyazaki in 1697 (7). He described in it; “After roasting every wastes, the dense excretions should be mixed with it and stocked for a while. This manure is efficient for the yields of any crops. It is called the fire manure”. Probably the similar knowledge had been popular in China and Korea since ancient time. In Asian countries, the rice husk charcoal which can be carbonized by simple method in field soon after harvesting has been one of the most common materials for soil amendment. It seems that the rice husk charcoal has been used for several thousand years since the beginning of rice cultivation in Asia, because rice husk with high content of silica is hardly decomposed and unavailable for the manure. The custom to use rice husk charcoal mixed with the excretions had spread among farmers particularly in wheat cultivation until about 60 years ago. It seems to be reasonable, because the charcoal can absorb and keep chemical nutrients and deodorize the stench. However, this method was too popular to investigate for scientists, and so the roles of charcoal in agriculture had been neglected for long time. After the information on wood charcoal use circulated in1980’s, the roles of rice husk charcoal have been noticed in the research field of agriculture. Recently Ezawa T. et al. (8) reported that rice husk and its charcoal enhanced A (arbuscular) mycorhiza formation of some crop plants and improved the soil physical properties when each of them was added into top soil. Ishii T. et al. (9) also reported the same effects on the A mycorrhiza formation of citrus seedlings. Komaki Y. et al. (10) suggested that a small amount of rice husk charcoal was effective on the growth of Catharanthus roseus, but the browning of leaves appeared with the excessive application because of high concentration of potassium and higher pH than wood charcoal. Takagi K. et al. (11) proposed a practical method to reduce the outflow of pesticides and herbicides from paddy field utilizing the absorbing ability of rice husk charcoal. Also he tried to fix the bacteria with high decomposing ability of pesticide into rice husk charcoal and succeeded to reduce the outflow from golf course (12).  At present, the carbonizing method has developed from the traditional method to the sophisticated facility equipped at the rice mill. Dried rice husk can be carbonized Page 2 of 15

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automatically and continuously in the self-burning kiln and the extra heat is utilized for small scale power generation (13). Recently the facility and system have been exported to South East Asia by the company. Probably it is possible to apply to the wheat and barley husks and other crop plant residues. In Asian countries, the studies of charcoal use in agriculture have been mostly carried out by JICA experts. In Indonesia, Igarashi T. started the experiment to produce the rice husk charcoal with simple method and to cultivate soy bean and maize with the charcoal in 1989 (14). Igarashi T. et al. (15) applied the charcoal together with magnesium phosphate and lime respectively and tried to rotate soy bean with maize. The charcoal application enhanced root nodule formation, plant growth and the yields significantly. The effect was sustained also in the second crop of maize without any supply of fertilizers, and the after effect was observed up to 10th rotation. In particular, the growth and yield of maize treated with the charcoal were more than that in the control plot cultivated only by chemical fertilizer. He also tried to apply the charcoal in several areas with different soil condition and reported that the effect seemed to be different from the soil properties and the kind of crops (16). Since the publication of experiment results, charcoal use is advancing in Indonesia. In Thailand, Oka H. et al. (17) studied the effects of rice husk charcoal on the growth, yield and nitrogen fixation rates of soy bean which was planted in the infertile sandy soil. He reported that the amount of upper ground biomass, root, soy bean yield and the rate of nitrogen fixation in soil increased significantly. In field, the application of 10 ton per hectare was most efficient, and the effect appeared evidently in the second crop of sorghum and the third of soy bean. The soil physical properties, porosity, water holding capacity, pH and CEC were also improved, although the values were different depending on soil type. In Philippine, Noguti A. et al. (18) confirmed the effect of rice husk charcoal on the growth of beans in an infertile acidic red soil. In this experiment the rice husk charcoal of 2.5 t / ha and lime of 1.5 t/ha were applied and mixed with top soil 15 cm in depth, chemical fertilizer was applied and the root nodule bacteria inoculated. The number of root nodule and nitrogen fixing rates increased in the plot with lime, but it was more stimulated evidently by the addition of charcoal. The inoculation of root nodule bacteria and the application of rice husk charcoal induced the same effect with single use of lime. It seems to be meaningful economically in Philippine where the use of lime is rather costly for farmers. 2) Wood and bark charcoal In 1983, Ogawa M. et al. (4, 5) reported that the bark charcoal powders containing a small amount of chemical fertilizers were efficient for the mycorrhiza formation of pine tree and the A mycorrhiza and root nodule formations of soy bean plant. In the experiment of soy bean plant (19), the bark charcoal of broad leaved tree was mixed with 1 % (W / W) of the inorganic fertilizer (N: P: K (8: 8: 8)), urea, super lime phosphate, ammonium sulfate and oil cake powder respectively. These charcoal fertilizers were stocked for one week and scattered over soil surface at 500 g / m2 and 1500g / m2 each before plowing. Soy bean seedlings without root nodules were planted in each plot. The plots in which applied the inorganic chemical fertilizer, 100 g / m2 and 200 g / m2 and the control plot without any treatments were set to compare the efficiency.

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Soy bean yields which were harvested from the plots with charcoal fertilizers of 500 g / m2 were mostly equal to those from the plots with 100 and 200 g of chemical fertilizer. By this method the amount of chemicals could be saved remarkably to 1/20. Root nodule formation was stimulated by charcoal fertilizers, but it was suppressed by the ones with ammonium sulfate and synthetic chemical fertilizer. A mycorrhiza infection rates and the spore numbers increased in the plots treated with charcoal fertilizers. It seems that the better growth of soy bean plants resulted from the enhanced root growth and propagation of symbiotic microorganisms being activated by the charcoal0.. The soil microbial flora in each plot changed with the application of charcoal fertilizers. Charcoal fertilizers with higher pH than 8 inhibited the propagation of soil fungi, but enhanced that of bacteria and Actinomycetes soon after the treatment and then returned to the normal state gradually. It was prospected that the emission of carbon dioxide increased temporarily being caused by the high microbial activity. At the same time, the free living nitrogen fixing bacteria could be isolated on the nitrogen free medium. From the inoculation test of the charcoal which was sterilized and buried in soil for a week, it was certain that the charcoal became the habitat for root nodule bacteria (19). The charcoal which was carbonized under high temperature is usually alkaline and porous substance, and there is no substrate for saprophytic microorganisms. When the charcoal was added into soil, at first the plant root grows toward the charcoal with enough water and air. Next some microorganisms which can endure under high alkalinity can propagate in or around charcoal. It seems that the charcoal provides a better habitat for the root and symbiotic microorganisms. These research results were confirmed also in the TRA. Wood charcoal was efficient to improve the soil properties, but the mixtures with chemical fertilizers, zeolite, wood vinegar and organic fertilizer exhibited the better effects than charcoal itself on tea plant, citrus and vegetables (20), rice plant and apple tree (21) and some leguminous plants and grass for greening (22). It was found that root nodule bacteria could be immobilized with high frequency in the white and hard charcoal with fine pores. So, Takagi S. (23) proposed the method to make the inoculum of root nodule bacteria of leguminous plants utilizing the charcoal. On the other hand, A mycorrhizal fungi showed the better growth on black charcoal which was carbonized at 400-500 degree Celsius. The spore of Gigaspora margarita was formed in black volcanic soil with high carbon content (24). The application of wood charcoal to the plant associated with Frankia was effective also for the actinorhiza formation (25). In general, it is certain from these results that the white charcoal with the fine pore and high pH is suitable for the immobilization of bacteria and the black one for that of fungi. After the study of TRA Oohira T. et al. (26) reported that the oak charcoal with finer pores than that of pine was suitable for the immobilization of bacteria and Actinomycetes than that of pine. Meanwhile, the immobilizing ability of pine charcoal could be improved by mixing of acetic acid. Matsubara Y. et al. (27) reported that coconut shell charcoal and the inoculation of A mycorrhizal fungi were effective to suppress the infection of soil born pathogen Fusarium spp.. The research results of charcoal use in various fields were distributed not only in Japan but also in Asian countries mainly by Ogawa M. (28) (29) (30). Page 4 of 15

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3) Charcoal compost and wood vinegar   In Japan, the compost making from litter and excretions and its use has been very common for long time. Ash or carbonized material was an essential material to accelerate the decomposition stimulating the bacterial activity and to neutralize the acidity. It is also well known that the charcoal absorbs smell and liquid. In 1980s, a private company invented the method to produce charcoal compost which was made from fresh chicken dung and palｍ shell charcoal tip (31). In the process of compost making, the more the charcoal is used, the faster the decomposition progresses with exothermic reaction. Under aerobic condition Bacillus group became dominant and produces antibiotics. Kobayasi (32) reported that these antibiotics inhibited the growth of some soil born pathogens, Pythium, Rhizoctonia, Phytophtra and Fusarium and were effective to suppress root diseases of various plants. At present the charcoal compost (Haipuro) has been sold as a biological fungicide by the company. Following this instance, various kinds of organic composts have been produced from other livestock excretions and charcoal and sold in market. It had been also well known that the liquid flowing out of charcoal kiln was useful. Actually it had been used in forestry nursery bed as a pesticide and at road side as a herbicide. Kishimoto S. et al. (33) published a text book in which they recommended the utilization of wood vinegar in agriculture, forestry, animal husbandry and food processing describing the methods for the purification, distillation and filtration. Wood vinegar is a byproduct which is obtained from the carbonization process cooling the smoke by air or water. This liquid contains the volatile substances emitted with pyrolysis; water soluble fraction is wood vinegar and the oily one is wood tar. The chemical composition is different depending on raw materials. Major components of broad leaved trees are 81 % water, acetic acid 8-10 %, methanol 2.44 %, acetone 0.56 % and soluble tar 7 %, and that of conifers are rich in water, acetic acid 3.5 % and the others concentrations are lower than that of broad leaved trees (34). The chemical components of wood vinegar containing many organic substances are unstable, so it has been sold as the material complex. It has been recognized since 1960s that the wood vinegars extracted from broad leaved trees are more efficient for the growth and rooting of various plants than that of conifers. The effects were confirmed also in the study of TRA (35) (36) (37). The concentrated liquid of wood vinegar with strong acidity shows the effects to kill microorganisms, plants and some larvae, but the diluted one to stimulate rooting, plant growth and microbial propagation. There are many reports of the application in field practice and generally the effects have been well known by users, but there are a few available scientific reports on the mechanisms because of the chemical property.

2. Utilization in Forestry and Greening 1.

Rehabilitation and reforestation of trees and pine forest by charcoal and mycorrhiza Page 5 of 15

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In 1980, Ogawa et al. (38) tried to apply the bark charcoal powders with a small amount of chemical fertilizers and succeeded to promote the growth of pine, Pinus thunbergii and cultivate the mycorrhizal fungi, Rhizopogon rubescens which is a dominant mycorrhizal species in the young stand with infertile basic sand Some chemical fertilizers, urea, ammonium sulfate, super lime phosphate and synthetic chemical fertilizer, were added to bark charcoal powder with 0.1-1.0% (W / W) respectively. These materials were buried into the trenches 30 cm in depth and width after cutting the roots and covered by sand. The regenerated fresh roots grew inside the charcoal layers vigorously after 3 months and the mushrooms appeared abundantly along the trenches 9 months later. After a year, the amounts of pine root and mycorrhiza increased remarkably in the charcoal layers. In addition, the growth of shoots and the color of needles became better than before treatment. These apparent effects probably resulted from the regeneration of root and the formation of mycorrhiza. It might be caused from the enhanced nutrient uptake and the water absorption through mycorrhiza. The water content in the charcoal was eminently higher and it was kept 40 % even in mid summer comparing with 5 % outside the charcoal layer (39). After releasing the experiment result the similar phenomena were confirmed by many researchers in local forest experiment stations, because it is an edible mushroom in Japan. For example Hirasa T. (40) devised the growing method of seedling with the mycorrhiza and the cultivation method in field. The same method has been widely accepted by professional gardeners and applied to various kinds of tree species to make revive the famous trees in shrine, temple and park. Usually the charcoal powder, maximum 1 cm in diameter, has been buried into trench or hole together with a small amount of phosphate fertilizer and the spores of suitable mycorrhizal fungi to host plant. Sometimes the root system was exposed removing top soil and covered by charcoal powder as well. Also in nursery, the charcoal fertilizer is mixed with pot soil to improve soil properties and inoculate the mycorrhizal fungi (41). Both pine wilting disease by the insect and nematode and oak wilting by the insect and fungi have been spreading mainly in western Japan for several decades, and now it has become so serious problem in forestry. Pinus densiflora forest in low land mostly disappeared in the southwest and reaches to northern most area of Honshu. Pinus thunbergii forest which had been planted along the seacoast to prevent natural disasters was also declining. Therefore, the practical methods of the rehabilitation and reforestation of pine forest have been expected eagerly in rural areas. Mycorrhiza formation is essential to Pinus species which generate the forests as a pioneer plant at the dry site with infertile soil. These fungi also prefer to propagate in dry and infertile soil condition. Therefore, it has been well known through the ecological study of pine forest (2) that the man-made pine forest should be kept at the primary stage of plant succession by cutting all of under shrubs and raking out the litter layer. Ogawa M. proposed to rehabilitate and reforest the coastal pine forest using charcoal and mycorrhizal fungi publishing a monograph (41). In the established forest, the same methods described previously have been applied. Meanwhile, in the place from which all of pine tree entirely destroyed, the under shrubs and top soil are completely removed before planting. Page 6 of 15

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Then pine seedlings with the inoculated mycorrhizal fungi, Rhizopogon, Pithoritus, Suillus species, are planted together with the charcoal powder. The survival rates of these seedlings were much higher than that without mycorrhiza and charcoal. As such a trial, growing tree and burying charcoal, seems to be one of the practical methods for carbon sequestration, Ogawa M. and his colleagues have promoted the movement to make revive “White Sand and Green Pine” which is one of the symbolic scenery of Japan in order to contribute the prevention of natural disasters and the countermeasure for global warming. 2) Rehabilitation of tropical rain forest and forestation in semiarid region Ogawa M. who was working in the rehabilitation project of tropical rain forest in 1989 found that a dominant species, Dipterocarpaceae, forms the ectomycorrhiza with several fungal species among which Scleroderma columnare enhanced the seedling growth efficiently in nursery. He tested the effect of charcoal powder on the growth of Shorea species and found that the small amount of charcoal 2 % in volume was effective to stimulate the mycorrhizal formation and the growth (42). Kikuti J. and M. Ogawa (43) devised the practical inoculation method in which several saplings with the mycorrhiza were planted inside the nursery bed and the pots were set under the canopy. By this method the mycelium of mycorrhizal fungi penetrates through holes of the pot and naturally infected. Mori S. et al. (44) found the rice husk charcoal is also effective and established the more convenient method. Rice husk charcoal is not so harmful even if it was added too much. The nursery technique to inoculate the mycorrhizal fungi with charcoal was also used in the forestation project of pine in northern China and obtained the successful results (45). The material such as charcoal which has higher water holding capacity is efficient to stimulate the rooting and to supply water to the root through mycorrhiza even under severe dry condition. It can be expected the charcoal will be used in dry land farming like date palm plantation and the greening to stop the desertification (46).

3. Utilization of charcoal and wood vinegar in animal husbandry and fishery Charcoal powder had been commonly used to cure the intestinal disorders of animals. In 1980s the utilization of charcoal and wood vinegar extended into the fields of animal husbandry and the fish aquaculture. One of the wood vinegar makers invented in 1970s the tablet of charcoal powder containing wood vinegar and sold as a medicine of live stocks being formally recognized MAFF (33). When animals take the drug with the feed, it is said that the quality of meat, fat and egg can be improved being affected with the high activity of intestinal microorganisms (47). Recently the use for pig and poultry increased to avoid the antibiotics and to prevent the epidemics. In general, charcoal powder has the strong ability to absorb the smell of excretions and liquid. Especially the charcoal carbonized under lower temperature than 300 degree Celsius shows the strong adsorption of ammonium (48). The mixture of charcoal and wood vinegar has been used in barn as the deodorant and absorbent of liquid. It seems that these effects result from the complex reactions of charcoal and wood vinegar, but there is a few available scientific Page 7 of 15

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data (33). The material containing wood vinegar also is used in the aquaculture of eel and fish to keep water clean (33). Sometimes high quality charcoal which is carbonized under higher temperature has been also used for water purification in the fish tank. From experiences it is said that fish likes to spawn around the charcoal, probably because some algae propagate on the wood charcoal and carbon fiber

4. Trials of carbon sequestration by charcoal use in agriculture and forestry 1. Developing charcoal industry In 2000, the fundamental law concerning to the establishment of recycling social system was enacted in Japan, and it was acquired to reuse any wastes as much as possible. Particularly the incineration of waste woods was prohibited in order to reduce the discharge of CO2 and dioxin. The total amount of waste woods mainly from construction has reached to 4.6 million ton per year, but the domestic use is only 60 % still now. Therefore, some construction companies have switched from the incineration to the carbonization and intended to use the charcoal not only in agriculture but also for the humidity control of house and building, because it is necessary to reduce the high humidity of traditional wooden building in Japan. The function of charcoal for humidity control was studied intensively for several decades ago (49) (50). Recently the construction companies have begun to spread the charcoal bag not only over the under floor but above the ceiling (51). Meanwhile it was also reported that the treatment was efficient to reduce an asthma and atopic dermatitis by diminishing the population of molds and tick (52) (53). According to the development of charcoal utilization, carbonization technology is developing from the simple kiln to the automatic mass production facilities. The newly devised carbonizers including various kinds of movable batch type kiln, rotary kiln, swing kiln and etc has been sold for the mass production of waste wood charcoal. In some cases the extra gas has been used for thermal electric power generation. At the same time, the studies to establish the industrial standards and function of carbonized materials have started, and the charcoal industry begins to be renewed in 2000s.

2.

New materials of charcoal

Recently the raw materials of charcoal are ranging from waste woods to some flammable substances. Among them the carbonization of bamboo and its utilization has been widely noticed as one of the dealing methods of bamboo forest which is recently occupying the wide ranges in southwest Japan. Bamboo charcoal with somewhat different structure and functions from wood charcoal has been used for the purification of water and air. Up to several years ago, all of garbage from urban life had been burned in the incineration plant, but now some cities began to carbonize the garbage and try its utilization. But there are some problems to be solved, because the water content is usually so high that it consumes too Page 8 of 15

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much energy for desiccation, and some products are unsuitable for agricultural use because of the high concentration of heavy metals and salt (54). Therefore, the thermal electric power plants have tried to burn the garbage charcoal mixing with coal and oil (55). The wastes disposed from food processing and live stock excretions have been also carbonized and used in agriculture with compost (55). 3) Carbon Sequestration by Forestation and Carbonization (CFSC) On January 8 in 1991, Ogawa M. puts forward a new idea “The earth’s green saved with charcoal” writing an article in Nihon Keizai Shinbun (Nikkei). He described in this paper the outline of this concept; The carbon dioxide emitted into air can be fixed by photosynthesis into the planted tree; If the waste wood will be carbonized and used in agriculture and other fields, a vast amount of carbon will be stocked for long term in soil, and at the same time the sustainable production of crops and trees will be realized. In 1990s it has been recognized gradually in Japan that the carbonization are meaningful as a counter measure against global warming through the production of renewable energy and the uses for soil amendment in agriculture. However, the raw materials of carbonization in this project must be restricted only the plant residues, because it induces large scale deforestation as well as other biomass energy productions. After COP3, Ogawa M. (56) (57) proposed the idea “Carbon Sequestration by Forestation and Carbonization (CSFC Project)” in Japan and Asia. In Indonesia and Malaysia, the large scale plantations of Acacia mangium for paper pulp and that of oil palm for biomass energy are expanding after clear cutting of the natural forests. Fast growing species in monoculture has been cut in rotation of every 8 to 10 years, and still now the slash burn fields are also spreading in wide area. The sustainability of tree plantation and cropland in tropical region has always become very serious problem. It needs to develop the more efficient techniques for soil amendment to sustain the high productivity. It is certain that the charcoal use is one of the most reliable and low-cost procedures being harmonized the nature. The same opinion was proposed in the review written by Glaser B. et al. (58). If charcoal is easily weathered in field, the idea may be meaningless. But it has been actually exhibited that the charcoal has remained for one thousand years or more without weathering at the ruin of ancient coin studio and in the old tombs in Japan and Korea. After the observation of stability in sulfuric acid, sodium hydrate or under ultra violet light for short term (personal communication), Kawamoto K. et al. (59) examined the durability of wood charcoal against ozone and estimated the half-life of the charcoal in air. The weight of saw dust charcoal carbonized at 400ºC was not affected with 8.5% ozone, while the one done at 1000ºC burned with 4.9% ozone. There were observed minute pores on the surface of charcoal carbonized at 1000ºC. The half-life of charcoal which was carbonized at 1000ºC and treated by ozone in air was about 50,000 years. From these results it is suggested that wood charcoal is stable on a geological time scale. On the other hand, Yamato M. et al. (60) reported the changes in soil chemical properties and the crop yields when the bark charcoal of Acacia mangium, which was made of waste from pulp industry, was applied as soil amendment for the cultivation of maize, cowpea and peanut Page 9 of 15

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in Sumatra, Indonesia. The yields of maize and peanut significantly increased after the application of bark charcoal under the fertilized condition in an infertile soil. The amount of root and the colonization rate of A mycorrhiza increased especially in maize. The application of charcoal improved the soil chemical properties by neutralizing soil pH and increasing total nitrogen, available phosphate contents, cation exchange capacity, amount of exchangeable cations and base saturation. Moreover, it induced the decreasing of exchangeable Al ion which seems to be harmful for the root growth. The effects of charcoal application appeared more evidently in tropical region than those in Japan. Root nodule formations of leguminous plants were also stimulated by charcoal. Formerly it was reported that the population of free living nitrogen fixing bacteria increased around the charcoal buried in tropical soil (28). Probably a small amount of nitrogen seems to be accumulated into soil by charcoal application also in slash burn cultivation. According to these results in Indonesia, the feasibility study of CSFC project was conducted with the existing project of an industrial plantation and pulp production by Okimori Y. et al. (61) in Indonesia Sumatra as an example of Clean Development Mechanism (CDM) project. It was prospected that a total of 368,000 t / year of biomass residue and waste which were disposed from plantation and pulp mill could be transformed into charcoal of 77,000 t / year, if conventional charcoal producing methods are used. It was also expected that the carbon emission reduction by the project reaches to 62,000 t-C / year (or 230,000 t-CO2). In addition, this project can contribute to local economy providing the employment chance for 2,600 people, and will make realize the sustainable industrial plantation by soil amendment with charcoal. A similar trial was conducted also in Indonesian JICA project as a small scale example, and the research result was reported by JICA (62). In this project it was confirmed that the applications of charcoal were efficient both for the seedling growth of Acacia and the tree growth in field. In Western Australia, the multipurpose project of mallee eucalyptus plantation has been carried out by Oil Mallee Company and Shea S. (63) in order to prevent the salinization of arable soil. Another feasibility study of the project was conducted by Ogawa M. et al. (64) in West Australia joining to the existing project. They proposed to carbonize wood waste and to use the charcoal for soil amendment in wheat field. In this study, it was prospected that the total carbon sink would reach 1,035,450 Mg-C with 14 % by aboveground biomass, 33.1 % by belowground biomass and 52 % by charcoal in soil, if the plantation will be kept for 35 years. Meanwhile, the effects of eucalyptus charcoal on the growth and yield of wheat were evidently confirmed by Paul J. (in printing). Ｔhe feasibility study of carbon sequestration in which various kinds of waste wood out of construction, saw mill, trimmed branch and others were recycled by carbonization was conducted by RITE (Research Institute of Environment and Industry) as summarized in the previous paper(64). It was focused on the effective use of surplus heat from a garbage incinerator for carbonizing woody materials. It was prospected from the study that the waste wood of 936.0 Mg-C / year would be converted into the net carbon sink of 298.5 Mg-C / year by carbonization, with the fixed carbon recovery of the system being 31.9 %.

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The life cycle assessment has been conducted also in Japan on the case of carbonization of waste wood and the use of charcoal for construction and greening. By this study it was certified that the CSFC project is significant and useful for carbon sequestration also in carbon and energy balance (unpublished). From these research results, it is expected that CSFC project will be recognized as a concrete, easy and low cost counter measure when the global warming will intensify more seriously in the near future. Today the charcoal uses in various fields are extending through the release of technical informations, and the charcoal production industry is growing as one of environment businesses not only in Japan but also among Asian countries.

Literature cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

Matsutake Kenkyu Konwakai ed. (1982) “ How to Cultivate Matsutake in Field” pp. 158 Soobun, Tokyo (in Japanese) Ogawa M. (1978) “ Biology of Matsutake ” pp.333 Tsukiji Shokan, Tokyo (in Japanese) Kishimoto S. & G. Sugiura (1980) “ Introduction to Charcoal Making on Sunday” pp. 250 Sougou Kagaku Shuppan Tokyo (in Japanese) Ogawa M., Y. Yambe & G. Sugiura (1983) Effects of charcoal on the root nodule formation and VA mycorrhiza formation of soy bean. The Third International Mycological Congress (IMC3) Abstract: 578 Ogawa M., Y. Yambe & G. Sugiura (1983) Cultivation of the hypogenous mushroom, Rhizopogon rubesscens. IMC3 Abstract: 577 Technical Research Association for Multiuse of Carbonized Materials(TRA) ed. (1990) “ The Research Report on The New Uses of Wood Charcoal and Wood Vinegar” Technical Research Association for Multiuse of Carbonized Materials Tokyo pp. 374 (in Japanese) Miyazaki Y. (1697) “ Nougyouzennsho ( Encyclopedia of Agriculture ) ” Vol. 11, 91-104 in “ Nihon Nousho Zenshu” Vol. 12 (revised edition) Nousangyoson Bunka Kyokai, Tokyo (in Japanese) Ezawa T. et al. (2002) Enhancement of the effectiveness of indeginous arbuscular mycorrhizal fungi by inorganic soil amendments. Soil Sci. Plant Nutr ., 48 48(6):897-900 Ishii T. & K. Kadoya (1994) Effects of charcoal as a soil conditioner on citrus growth and VA mycorrhizal development. J. Japan, Soc. Hort. Sci . 63 63(3):529-535 (10) Komaki et al. (2002) Utilization of chaff charcoal for medium of flower bed seedlings and its effect on the growth and quality of Madagascar periwinkle ( Catharanthus roseus) seedlings. Japan. Soc. Soil Sci. Plant Nutr., 73 73(1):49-52 (in Japanese) (11)Takagi K. & S. Takanashi (2003) Development of a technique for reducing herbicide runoff from paddy field using PCPP-1 model and rice husk charcoal powder. Proceedings 3rd international Conference on Contaminants in the Soil Environment in the Australasia –Pacific Region: 50 Beijing China (12)Takagi K. & Y. Yoshida (2003) In situ bioremediation of herbicides simazinePage 11 of 15

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polluted soils in a golf course using degrading bacteria –enriched charcoal. Proceedings International Workshop on Material Circulation through Agro Ecosystems in East Asia and Assessment of its Environmental Impact : 58-60 Tsukuba, Japan (13)Kansai Sangyo Co. Ltd (1991) “ Challenge toward Nature Farming ” Kansai Sangyo pp. 56 (in Japanese) (14) Ogawa M. (1991) Effective utilization of charcoal as a material for soil amendment. AICAF Expert Bulletin 12 12(3):1-13 (in Japanese) (15) Igarashi T. (1996) Soil improvement effect of FMP & CRH in Indonesia. JICA Pamphlet pp. 30 (16) Igarashi K. (2002) “Handbook for soil amendment of tropical soil”. AICAFF : 127-134 (in Japanese) (17) Oka H. et al. (1993) Improvement of sandy soil in the northeast by using carbonized rice husks. JICATechnical Report 13 13: 42-40 (in Japanese) (18) Noguchi A. et al. (1993) Effect of rice husk charcoal application on the growth and nitrogen fixation of Phaseolus vulgaris. JICA Internal Report (in Japanese) (19) Ogawa M. & Y. Yambe (1986) Effects of charcoal on VA mycorrhiza and nodule formations of soy bean. Studies on Nodule Formation and Nitrogen Fixation in Legume Crops; Bulletin of Green Energy Program Group II No.88:108-134 MAFF (with English summary) (20) Ishigaki K. et al. (1990) The effect of the soil amendment materials with charcoal and wood vinegar on the growth of citrus, tea plant and vegetables. TRA Report : 107-120 (in Japanese) (21) Okutu M. et al. (1990) The effect of the soil amendment materials with charcoal and wood vinegar on the growth of rice plant, apple tree and vegetables. TRA Report : 121131 (in Japanese) (22) Sano H. et al. (1990) Effects of the materials for greening with charcoal on the growth of herbaceous plants and trees (1). TRA Report : 155-165 (in Japanese) (23) Takagi S. (1990) Immobilization method of root nodule bacteria within charcoal and effective inoculation method to the legumes. TRA Report : 229-248 (in Japanese) (24) Soda R. et al. (1990) Spore propagation of VA mycorrizal fungi TRA Report : 199-212 (25) Aiba F. (1990) Effects of the materials for greening with charcoal on the growth of herbaceous plants and trees (2). TRA Report: 167-170 (in Japanese) (26) OOhira T. et al. (1992) Function of charcoal as microbial carrier in soil. J. Antibact. Antifung. Agents 20 20(10): 511-517 (with English summary) Page 12 of 15

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(27) Matsubara Y. et al. (2002) Incidence of Fusarium root rot in Asparagus seedlings infected with arbuscular mycorrhizal fungus as affected by several soil amendment. J. Japn. Soc. Hort. Sci . 71 71(3): 3370-374 (28) Ogawa M. (1987) “ Symbiotic microorganisms connecting soil and plants-Ecology of mycorrhiza” pp.241 Nosangyoson Bunka Kyokai, Tokyo (in Japanese) (29) Ogawa M. (1991) Carbonized material as a soil amendment. AICAFF Expert Bulletin 12 12(3): 1-13 (in Japanese) (30) Ogawa M. (1994) Symbiosis of people and nature in the tropics. Farming Japan 28 28(5): 10-34 (31) King Coal Co. Ltd Pamphlet (2006) Hi-pro 251 (32) Kobayashi N. (2001) Charcoal utilization in agriculture (1) Nogyo Denka 54 54(13):1619 (in Japanese) (33) Kishimoto S. et al. (1997) “ Charcoal and Wood vinegar” pp.317 Sourinsha, Tokyo (in Japanese) (34) Yatagai M. (1990) Purification and utilization of wood vinegar and the deodorization by charcoal. TRA Report : 297- 313 (in Japanese) (36) Ishii H. et al. (1990) Effects of purified wood vinegar on the growth of crop plants. TRA Report : 343- 362 (35) Nogi S. (1990) Purification of wood vinegar and the growth promoting effects for fruit trees. TRA Report : 314-330 (37) Hayashi R. (1990) Effects of purified wood vinegar as soil amendment and leaf surface spray. TRA Report : 331-341 (38) Ogawa M. (1983) Charcoal and the mushroom Rhizopogon rubescens. Forestry and Forest Products Research Institute News (JOUHOU) 223 223(2): 1-3 (in Japanese) (39) Ogawa M. ed. (1992) “ Cultivation of wild mushroom” pp.173 Ringyo Kairyo Fukyu Sousho 110 Zenkoku Ringyo Fukyu Kyokai, Tokyo (in Japanese) (40) Hirasa T. (1992) Effects of charcoal granule buried in rhizosphere of Pinus thunbergii on the production of syoro mushroom ( Rhizopogon rubescens ). Bulletin of Shimane Forestry Research Center 43 43: 25-30 (with English summary) (41) Ogawa M. (2007) “ Reviving pine tree with charcoal and mycorrhiza” pp.323 Tsukiji Shokan Tokyo (in Japanese) (42) Ogawa M. (2006) Inoculation method of Scleroderma column are onto Dipterocarps. Suzuki K. et al. ed “ Plantation Technology in Tropical Forest Science” 185-197 Springer Page 13 of 15

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(43) Kikuti J. & Ogawa M. (1999) Development of nursery techniques utilizing microorganisms. RETROF: “ Research Report on Rehabilitation of Tropical Forest” 155182 (44) Mori S. & Marjenah (2000) A convenient method for inoculating Dipterocarp seedlings with the ectomycorrhizal fungus, Scleroderma columnare. Guhardja H. et al. Eds. “ Rainforest Ecosystems of East Kalimantan” Ecological Studies 140: 251-255 (45) Takami K. (2003) “ Apricot bore fruit in our village” pp. 280 Nihon Keizai Shinbun, Tokyo (in Japanese) (46) Ogawa M. (1998) Utilization of symbiotic microorganisms and charcoal for desert greening. Green Age 14 14: 5-11 (47) Article in “ Monthly Swine Magazine ( YOTON JOHO )” 35 35(2) (2007) (in Japanese) (48) Honma S. (2000) Chemical structure and ammonia adsorption ability of Todomatsu ( Abies sachalinensis) wood carbonized in nitrogen and air atmospheres. J. Wood Sci. 46 46(4): 348-354 (with English summary) (49) Nakano T. et al. (1996) Improvements of the under floor humidity in woody building and water content of wood material. Mokuzai Kogyo 51 51(5): 198-202 (in Japanese) (50) Abe I. et al. (1995) Humidity control capacity of microporous carbon. Seikatu Eisei 39 39(6): 333-336 (in Japanese) (51) Kitamura T. (2005) Evaluation of the humidity control capacity of the waste wood charcoal. J. Mat. Cycle & Waste Manage . 16 16(6): 501-507 (in Japanese) (52) Morita H. (2005) The effect of humid controlling charcoal on the environmental antigenic allergy. Proceedings of 35th Annual Meeting of Japanese Society for Dermatoallergology: 115. (53) Taketani T. (2006) Evaluation of the effect of humid controlling charcoal on the infantile bronchial asthma. Allergy 55 55(3, 4): 467 (54) Abe I. et al. (2001) “ Carbonization of all wastes ,urban wastes, sewage, garbage and waste woods, and their utilization” Proceedings of the symposium on the production of charcoal and activated charcoal from wastes and their utilization. pp. 294, NIS Inc. (in Japanese) (55) Shinogi Y. et al. (2003) Basic characteristics of low-temperature carbon products from waste sludge. Advances in Environmental Research, 7 : 661-665 (56) Ogawa M. (1998) Greening with symbiotic microorganisms and charcoal in desert region. Monthly Bulletin Oversea Agricultural Development News 239 239: 10-17 (in Japanese)

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(57) Ogawa M. (1999) Utilization of symbiotic microorganisms and charcoal in tropical agriculture and forestry and CO2 fixation. Soil Microorganisms 53 53(2): 73-79. (in Japanese) (58) Glaser B et al. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal- a review. Biol Fertil Soils (2002) 35 35: 219-220 (59) Kawamoto K. et al. (2005) Reactivity of wood charcoal with ozone. J. Wood Sci . 51 51: 66-72 (60) Yamato M. et al. (2006) Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Sci. Plant Nut... 52 52: 489-495 (61) Okimori Y. et al. (2003) Potential of CO2 emission reduction by carbonizing biomass wastes from industrial tree plantation in South Sumatra, Indonesia. Mitigation and Adaptation Strategies for Global Change 8 : 261-280 (62) JICA (2002) “ Demonstration studies on carbon fixing forest management project ”. pp. 20 with appendices, JICA (63) Shea S. (1999) Potential for carbon sequestration and product displacement with oil mallees, In Proceedings: The Oil Mallee Profitable Landcare Seminar, Oil Mallee Association, Perth, Australia (64) Ogawa M. et al. (2006) Carbon sequestration by carbonization of biomass and forestation: Three case studies. Mitigation and Adaptation Strategies for Global Change 11 11: 429-444 .

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J. Japan. Soc. Hort. Sci. 63(3) : 529-535.

Effects

of Charcoal

1994.

as a Soil Conditioner

Vesicular-Arbuscular

Mycorrhizal

on Citrus

Growth

and

Development

Takaaki Ishii1 and Kazuomi Kadoya2 I Faculty of Education , Ehime University, Matsuyama, Ehime 790 2College of Agriculture , Ehime University, Matsuyama, Ehime 790

Summary

Effects of several kinds of charcoal applied to soil on citrus growth and vesiculararbuscular mycorrhizal (VAM) development were investigated. Satsuma mandarin (Citrus unshiu Marc.) trees on trifoliate orange (Poncirus trifoliata Raf.) rootstocks were transplanted to root boxes using the soil mixed with charcoal derived from rice husk, citrus juice sediment or western spruce bark. The trees were inoculated with the spores of Glomus fasciculatum (Thaxter) Gerdemann and Trappe emend. Walker and Koske. Elongation of the roots in the charcoal treatments was more vigorous than that in the charcoal-free control. The fresh weigths of the root, shoot and the whole tree increased in response to charcoal application. The intensity of VAM infection in any charcoal treatment was higher than that in the control. In particular, the percentage of the infection in the rice husk charcoal plot was 41.5 and P concentration in the leaf exceeded that of the control. In a Citrus iyo orchard, the percentage of VAM infection was 52% in the rice husk charcoal plot, the highest among plots. The intensity in the Bahia grass (Paspalum notatum Flugge.) plot was next, followed by the third highest rate found in the abandoned plot which had not been cultivated in recent years. The lowest percentage of VAM infection was in a clean-culture plot. A microscopic observation also revealed that in a charcoal-treated plot there were many sites where VAM fungi infected the root.

them (Dixon et al., 1988; Edriss et al., 1984; Ishii et al., 1992b; Menge et al., 1978; Nemec, 1979). These fungi improve mineral nutrition of the host by increasing P uptake from a P deficient soil

Introduction

A classic book written in Japan (Miyazaki, 1697) explained that soybean plants vigorously flourished with a minimum of care when their seeds were sowed with charcoal. Recently, Ogawa

(Antunes and Cardoso, 1991; Ferguson and Menge, 1986; Graham and Timmer, 1985; Krikun and Levy, 1980; Nemec, 1979; Tang et al., 1984). Higher concentration of minor elements, especially Zn (Krikun and Levy, 1980) and Cu (Timmer and Leyden, 1980), were also observed after an inoculation with VAM fungi. Because the fungi provided essential elements for citrus growth, the infected trees could grow more rapidly and appeared healthier than non-infected trees. This phenomenon was especially noticeable in soils of low fertility (Nemec, 1979). Furthermore, VAM fungi inoculation may increase tolerance to water stress by regulating stomatal opening through hormone synthesis (Graham et al., 1987). In our reports, the photosynthesis and transpiration rates of VAM fungi-infected satsuma mandarin trees grow-

(1987) reported that charcoal applied to the soil could stimulate the activity of soil microorganisms and promote the formation of root nodules and vesicular-arbuscular mycorrhizae in soybean roots. VAM symbioses are exceptionally common among terrestrial flowering plants (Harley and Harley, 1987). Among these plants, there is a wide range of dependency on VAM fungi for plant growth. Citrus is also infected by several kinds of VAM fungi and is considered highly dependent on Received for publication

7 February

1994.

Parts of this paper were presented at the 1989 Meeting and 1990 Spring Meeting of the Japanese for Horticultural

Spring Society

Science.

529

530

T. Ishii

and K. Kadoya

ing in P-deficient soil surpassed those of non-VAM trees stressed by high temperatures in August

coal

(Shrestha et al., 1992). Interestingly, an inoculation of VAM fungi improved the fruit quality of satsuma mandarin trees. In particular, it enhanced the Hunter's a/b value of peel color and the sugar content in juice (Ishii et al., 1992b). In the citrus orchards where high quality fruit was produced, the percentage of VAM infection in the root was very high (Shrestha et al., 1993). On the other hand, phytotoxic substances exist in the bark and sawdust extracts from several woody forest species, especially in the bark extracts of hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc. ex Endl.) which are condensed tannins (Ishii and Kadoya, 1993). In soils to which unfermented organic matter were added, ethylene has often been detected at concentrations high enough to inhibit the growth of citrus trees (Ishii and Kadoya, 1984). The problem of growth inhibition is solved, however, if the organic matter with

the

phytotoxic substances is first transformed into charcoal and then used as a soil amendment. The purpose of this study is to investigate effects of several kinds of charcoal applied to soil on citrus growth and VAM development.

were The

an

EC

and

in

pH

mixtures meter,

with

taining

300 ~

after 50

340

of

In

tree

and

3.8

sulfate, the

to

were

solution trees.

Roots were

(1

In

P

which

the

personal

on

onto root

(NEC

and

K The

of

calcium

(8

:

Hoagland

2

by

minor

administered

plates

were

to

of

with

MG

boxes from using

an

-10

a special

root

sheets

measured,

equipped

and

g

plastic

lengths

a

excluded. glass

mediagraph

Japan)

5

was

was the

P

deducted.

A

transparent

computer

essor

the

pH.

g

from phosphate,

mixture

soil

6.4

annum

with

liter/tree)

1989,

appearing traced

with

per

first

sulfate the

citrus prefecture,

calcium

supplied

improve

from

K

were

. pot Glomus

fertilized

of

con-

with

respectively;

charcoal

trees

each

was g

were

greenhouse

Ehime

sulfate,

carbonate-magnesium

element

of and

fasciculatum

isolated

ammonium

in

weight)

by

meter

roots

Glomus

city,

each P,

potassium

control

1

inoculum

inoculated

Matsuyama

of

of

contents

pH

soil

from

grass

1988, g

mixture and

of

obtained

Bahia

in

3.2

to (EC)

a

of

originally

orchards

N,

50

the

weight

spores

was

fasciculatum

of

with

planting,

g fresh

inoculum

Japan.

of conductivity

respectively.

treated

cultures

proportion

electric measured

months

The

a

and

were

Two

Tokyo,

Materials

mixed

weight.

image

with

a

software

a proc-

stylus

pen,

program.

Methods In

Experiment 1. Effects of charcoal application

on citrus

early

moved root,

growth and VAM development In this experiment, we examined the effects of charcoal application on the growth and VAM development of 'Aoshima' satsuma mandarin trees on trifoliate orange rootstocks for two years. In early April of 1988, three two-year-old satsuma mandarin trees per plot were transplanted individually to root boxes (40 cm × 40 cm × 40 cm) containing the mixtures of river sand and a specific charcoal. Before planting, the roots were carefully washed to remove the soil which had nourished the trees. The control soil lacked charcoal. The charcoal used was made by using a chimney (15 cm in diameter and 1.8 m in length) with some holes for aeration or an oil drum (200 liter) equipped with a chimney (15 cm in diameter and 1.8 m in length). The charcoal sources were rice husk, citrus juice sediment and western spruce bark. The charcoal derived from western spruce bark was broken into 5 ~ 10 mm pieces. The sand and char-

December

from and

the

the shoot

at

ured

in

The

colorimetrically

(1920,

by

1921).

sampled

and

seconds.

After

ments

50%

distilled

the

rootlets

were

growing

tip,

the

ethanol, treatment,

and

Hayman of

centage following

VAM of

13

in :

FAA

5

:

stained

by

(1970),

were

infection VAM equation

by infection :

cut the

was

were for

into

a

Ten

calculated

acid:

segments of

microscopy.

segwere

acetic

for

few

2 - cm

segments

technique

analyzed light

Deniges

rootlets water

v/v/v). the

meas-

of

(formalin:

200,

were

was

feeder

with

For were

residues

content method

Undamaged

fixed

per

the

retotal,

samples

the

P

were the

measured.

leaf

rinsed

behind

immediately

P, and

N HC].

trees then

were

leaf

overnight, 2.4

the and

weights of

550 •Ž

dissolved

1989, boxes,

fresh

determination

ashed

ty

of root

the

Phillips intensiThe with

perthe

J. Japan. Soc. Hort. Sci. 63(3) : 529-535. 1994.

Experiment

2. Soil management and the intensity VAM infection in citrus roots

of

In late April of 1987, 4 experimental plots of 5 trees each were prepared in a Citrus iyo (15 - yearold trees on trifoliate orange rootstock) orchard in Matsuyama city, Ehime prefecture. The experimental plots were as follows : 1) charcoal as a soil amendment, 2) abandoned culture, 3) sod culture with Bahia grass, and 4) clean culture by using herbicides such as paraquat dichloride and N- (phosphonomethyl) glycine (3 times in a year). The charcoal plot had two pits (60 × 60 cm in width and 40 cm in depth) circling a tree and filled with 6 kg of rice husk charcoal. Paraquat dichloride was applied once annually. In the Bahia grass plot, the grass was mowed once each summer. Except for the abandoned plot, the rest received 32 kg N, 23 kg P, and 25 kg K per 10 a annually. The application of agrochemicals, such as fungicides and pesticides, followed the guidelines of disease and pest control for Ehime prefecture. In early September of 1988, root samples were obtained from 3 to 5 places of each plot at a depth of 5-10 cm, and then the intensity of VAM infection was determined by the methods described above. The root structure was observed with a scanning electron microscope (SEM, JEOL type JSM - T200, Tokyo, Japan). The apical 20 mm of 20 elongating roots from each plot were rinsed with distilled water for a few seconds and the apices were immediately fixed in Karnovsky solution (Karnovsky, 1965) at room temperature for 24 hr. After being dehydrated through graded solutions of ethyl alcohol-acetone, they were divided into 4 segments in 100% acetone. These segments were then immersed in acetone for 2 hr, critical-point-dried, mounted on aluminum stubs with silver conducting paint, and coated with a thin layer of gold using an ion-coater (Eiko Engineering type IB -2, Tokyo, Japan). The roots were observed in a SEM and photographed. Results Experiment

1.

No differences observed. was

The

higher

western

in soil pH among EC

than

spruce

value that

bark

treatments

of the charcoal

of the control. charcoal

The

treatment

were

treatments EC

in the

was

about

13

times

higher

531

than

that

of the

control

plot

(Table 1). This is because NaCl permeated into the bark during sea storage after being imported into Japan from North America. Soils treated with 3 kinds of charcoal had significant effects on growth, leaf P concentration, and VAM development in roots of satsuma mandarin trees. About 2 months after the onset of this experiment, except in the western spruce bark charcoal treatment, roots appeared on the glass plates, and their elongation rates indicated that roots in the charcoal-treated plots were more vigorous than ones in the control. As of November 8, 1989, the root length in any charcoal treatment was about 1.5 times longer than that in the control. The total fresh weights and the fresh weights of roots and shoots increased with charcoal treatments. The growth increments varied little among the kinds of charcoal (Table 2). The intensity of VAM infection in any charcoal treatment was higher than that in the control; that of the rice husk charcoal treatment attaining 41.5% (Table 3). Hardly any significant differences in leaf P concentration among treatments with western spruce bark charcoal, citrus juice sediments charcoal and the control were observed; but leaf P concentration in the rice husk charcoal treatment, which significantly stimulated VAM infection, was higher than that in the control (Table

3).

Experiment

2.

The intensiy of VAM infection in the rice husk charcoal plot was 52%, the highest among plots. The intensity in the Bahia grass sod plot was second highest, whereas that of the abandoned plot was third. The lowest percentage of VAM infection was in the clean culture plot where herbicides were used 3 times a year (Table 4). The hyphae, vesicles and arbuscles of VAM fungi were fre-

Table 1. The pH and electric conductivity (EC) of soils treated with charcoal (Experiment 1) .

532

T. Ishii

Table

Table

2.

and

K. Kadoya

Effect of charcoal application on the growth of satsuma mandarin trees (Experiment

1) .

3. Effect of charcoal application on vesiculararbuscular mycorrhizal (VAM) development and leaf phosphorus (P) concentration in satsuma mandarin trees (Experiment 1) .

Table 4. Effect of soil management on VAM development in Citrus iyo trees (Experiment 2) .

quently observed on/in citrus roots sampled from the charcoal-treated plots (Fig. 1). The SEM photomicrographs also indicated that in the charcoaltreated plot there were many sites where VAM fungi infected and penetrated into the root (Figs. 2 and 3). Discussion In Japan, is a very

it has effective

long

been

known

soil conditioner

that which

charcoal promotes

plant growth. Charcoal application may result in improving physical properties of soil, its fertility, and

biological

indicated

that

conditions. citrus

The growth

present and

experiment

VAM

develop-

Fig.

1. Photomicrograph

of VAM fungal

structures

in

Citrus iyo roots stained with typan blue. a : fungal hyphae ( × 100), b : vesicle ( × 150), c : arbuscle ( × 600).

ment in the root were stimulated by applying charcoal to soil. This stimulation of citrus growth by charcoal is attributed to an increase in the percentage of VAM infection in the roots. Ogawa (1987) also reported that the enhanced colonization by symbiotic microorganisms, such as Rhizobium and VAM fungi, by charcoal application, invigorated soybean plants.

J. Japan. Soc. Hort. Sci. 63(3) : 529-535. 1994.

Fig. 2. SEM photomicrograph

533

of VAM fungi in Citrus iyo roots.

Left : × 200, Right : × 1000.

gi by fungicides such as thiophanate methyl, benomyl, iprodione, and copper fungicides is severe. In the case of herbicides, Kobayashi (1988) showed that the germination of Gigaspora margarita spores was severely repressed by 48 ppm paraquat dichloride or 410 ppm N- (phosphonomethyl) glycine. In our experiment, the percentage of VAM infcetion in the herbicide-treated clean culture plot is lower than that of the abandoned plot. The pH value of water extracts from charcoal was high (Ishii and Kadoya, 1990), indicating that charcoal ameliorated soil acidity. Generally, soil pH is low in citrus orchards in Japan, so that the percentage of VAM infection in the root is low and the number of VAM spores in the soil is small

Fig. 3. SEM photomicrograph

of a VAM spore

(Glomus spp.) and invasion into roots (× 1000).

The

increased

(Ishii et al., 1989b, 1992a). By neutralizing soil acidity, charcoal may be improving the growth and development of VAM fungi. There are very few reports on VAM development in citrus trees grown in Japan. When roots of satsuma mandarin and Citrus iyo trees from 24 orchards in Ehime prefecture (in southwestern

VAM infections

of its hyphae

by charcoal

ap-

plication may be because charcoal absorbs many kinds of toxic substances and agrochemicals which inhibit root growth and microbial activity. It has also been shown that some agrochemicals inhibit the germination of VAM spores (Kobayashi, 1988; Ogawa, 1987). The growth inhibition of VAM fun-

Japan) were observed for VAM infections, were not extensive except for an orchard

they with

good soil conditions which produced 9 ~ 10 t satsuma mandarin fruit per 10 a every year (Ishii et al., 1989b). Numerous VAM spores in the soil and VAM -infected plants are generally observed in woodlands and non-cultivated fields. This indicates that there are many factors which restrict

534

T. Ishii

and

the existence and growth of VAM fungi in orchards because of our present soil management practices, such as the usage of agrochemicals and chemical fertilizers. The average annual amount of P applied is about 20 kg per 10 a. That P, especially soluble P, is detrimental to VAM development in citrus roots was reported earlier (Antunes and Cardoso, 1991; Graham and Timmer, 1985). Several kinds of VAM fungi, however, live in our soil in spite of many malpractices in our present soil management (Ishii et al., 1992a). We suggested that VAM formation in citrus roots could be effectively increased through application of charcoal to the soil or introduction of a sod culture system. In particular, the application of charcoal is very effective for VAM development. Contrarily, an excess of charcoal inhibits citrus growth (Ishii and Kadoya, 1990). This inhibition by an excessive application of charcoal might be concerned with an increment of soil pH value. Therefore, an appropriate amount of charcoal to be applied is less than 2 t per 10 a (this is approximately equivalent to 2% charcoal, Table 2). Furthermore, such an effect of charcoal may be strengthened by mixing charcoal and soil. VAM fungi develop well in citrus orchards where Bahia grass is used for sod (Ishii et al., 1993). We have also indicated that the intensity of VAM formation on some weeds grown in citrus orchards was higher than that on citrus trees (Ishii et al., 1989a). However, sod culture in commercial citrus orchards has been unsuccessful in Japan; most citrus growers believe that a clean culture is best for the production of high-quality fruits. Thus, our soil management system must be re-evaluated. The prevailing cultural system in which large quantities of agrochemical and chemical fertilizers are used, should be thoroughly revamped so that a cultural system which maintains beneficial soil microorganisms is adopted. In conclusion, any application of charcoal to the soil is a practical method to improve soil properties and to foster the development of symbiotic microorganisms including VAM fungi. Literature Antunes,

Cited Growth

and

nutrient status of citrus plants as influenced mycorriza and phosphorous application. Plant

V. and E. J. B. N. Cardoso.

1991.

by and

K. Kadoya

Soil 131 : 11-19. Deniges, G. 1920. Reaction de coloration extremement sensible des phosphates et des arseniates. Compt. rend. 171 : 802-804. Deniges, G. 1921. Determination quantitative des plus faibles quantites de phosphates dans les produits biologiques par la methode ceruleomolybdique. Compt. rend. Soc. biol. 84 : 875-877. Dixon, R. K., H. E. Garrett and G. S. Cox. 1988. Cytokinin activities in Citrus jambhiri Lush. seedlings colonized by vesicular-arbuscular mycorrhizal fungi. Tree 2 : 39-44. Edriss, M. H., R. M. Davis and D. W. Burger. 1984. Influence of mycorrhizal fungi on cytokinin production in sour orange. J. Amer. Soc. Hort. Sci. 109 : 587-590. Ferguson, J. J. and J. A. Menge. 1986. Response of citrus seedlings to various field inoculation methods with Glomus deserticola in fumigated nursery soils. J. Amer. Soc. Hort. Sci. 111 : 288-292. Graham, J. H. and L. Timmer. 1985. Rock phosphate as a source of phosphorus for vesicular-arbuscular mycorrhizal development and growth of citrus in a soilless medium. J. Amer. Soc. Hort. Sci. 110 : 489-492. Graham, J. H., J. P. Syvertsen and M. L. Smith, Jr. 1987. Water relations of mycorrhizal and phosphorus-fertilized non-mycorrhizal citrus under drought stress. New Phytol. 105 : 411-419. Harley, J. L. and E. L. Harley. 1987. A check-list of mycorrhiza in the British flora. New Phytol. 105 : 1-102. Ishii, T. and K. Kadoya. 1984. Growth of citrus trees as affected by ethylene evolved from organic materials applied to soil. J. Jap. Soc. Hort. Sci. 53 : 320-330. Ishii, T., K. Tatsumi and K. Kadoya. 1989a. VA mycorrhizal development of citrus trees as affected by soil managements. J. Jap. Soc. Hort. Sci. 58 (Suppl. 1): 32-33. (In Japanese). Ishii, T., K. Tatsumi and K. Kadoya. 1989b. Distribution and ecological aspects of vesicular-arbuscular mycorrhizal fungi in citrus orchards. Mem. Coll. Agr., Ehime Univ. 34 : 65-71. Ishii, T. and K. Kadoya. 1990. Use of charcoal as a soil conditioner applied to citrus orchards. J. Jap. Soc. Hort. Sci. 59 (Suppl. 1): 36-37. (In Japanese). Ishii, T., Y. H. Shrestha and K. Kadoya. 1992a. VA mycorrhizal fungi in citrus soils and the relationship between soil factors and number of the spores. J. Jap. Soc. Hort. Sci. 61 (Suppl. 2): 166-167. (In Japanese). Ishii, T., Y. H. Shrestha and K. Kadoya. 1992b. Effect of vesicular-arbuscular (VA) mycorrhizal fungi on tree growth, fruit development and quality, and water stress of satsuma mandarin trees. J. Jap.

535

J. Japan. Soc. Hort. Sci. 63(3) : 529-535. 1994. Soc. Hort. Sci. 62 (Suppl. 1): 26-27. (In Japanese). Ishii, T., J. Hamada, K. Ishizaki, Y. H. Shrestha and K. Kadoya. 1993. Effect of sod culture system by Bahia grass (Paspalum notatum Flugge.) on vesicular-arbuscular mycorrhizal development of satsuma mandarin trees. J. Jap. Soc. Hort. Sci. 62 (Suppl. 2): 98-99. (In Japanese). Ishii, T. and K. Kadoya. 1993. Phytotoxic constituents in the bark and sawdust extracts of Chamaecyparis obtusa and Cryptomeria japonica and their effects on the growth of seedlings of trifoliate orange (Poncirus trifoliate Ref.) and rice (Oryza sativa L.). J. Jap. Soc. Hort. Sci. 53 : 320-330. Karnovsky, M. J. 1965. A formaldehyde-glutaraldehyde fixative of high osmolality for use in electron microscopy. J. Cell Biol. 27 : 137A-138A. Kobayashi, N. 1988. Factors affecting the germination of spores of Gigaspara margarita . Microorganisms 31 : 13-28. Krikun, J. and Y. Levy. 1980. Effect of vesicular arbuscular mycorrhiza on citrus growth and mineral composition. Phytoparasitica 8 : 195-200. Menge, J. A., E. L. V. Johnson and R. G. Platt. 1978. Mycorrhizal dependency of several citrus cultivars under three nutrient regimes. New Phytol. 81 : 553-559. Miyazaki, S. 1697. Nougyou-Zensho. In : Yamada, T., J. Iinuma, M. Oka and S. Morita (eds.). The complete works of ancient agricultural books in Japan. Ru-

ral Culture Association, 1988. (In Japanese). Nemec, S. 1979. Response of six citrus rootstocks to three species of Glomus , a mycorrhizal fungus. The citrus industry 5 : 5-14. Ogawa, M. 1987. Mutualistic microorganisms at the plant-soil interface. Rural Culture Association. (In Japanese). Phillips, J. M. and D. S. Hayman. 1970. Improved procedures for clearing roots and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection. Trans. Br. Mycol. Soc. 55 : 158-161. Shrestha, Y. H., T. Ishii and K. Kadoya. 1992. Effect of vesicular-arbuscular (VA) mycorrhizal fungi on photosynthesis and transpiration, and the distribution of photosynthates of fruit-bearing satsuma mandarin trees. J. Jap. Soc. Hort. Sci. 62 (Suppl. 1): 28-29. (In Japanese). Shrestha, Y. H., T. Ishii and K. Kadoya. 1993. A relation of vesicular-arbuscular mycorrhizal development and fruit quality of satsuma mandarin. J. Jap. Soc. Hort. Sci. 62 (Suppl. 2): 96-97. (In Japanese). Tang, Z., Q. Zhang and S. Hou. 1984. The effects of mycorrhizal fungus on phosphate uptake by citrus in.red earth. Acta Mycologia Sinica 3 : 170-177. Timmer, L. W. and R. F. Leyden. 1980. The relationship of mycorrhizal infection to phosphorus-induced copper deficiency in sour orange seedlings. New Phytol. 85 : 15-23.

炭 施 用 が カ ンキ ツの樹 体 生 長 お よびVA菌

根 形 成 に及 ぼ す影 響

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摘 炭 施 用 が カ ン キ ツ の 樹 体 生 長 お よ びVA菌 及 ぼ す 影 響 を 調 査 した.イ

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あ る い は カ ンキ ツ ジ ュ ー ス か す か ら作 っ た 炭 で 処 理 し

ま た 葉 内 の リ ン 含 量 も増 加 した.一

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園 に お け る炭(イ

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の 結 果,ボ tum ッ ク ス の ガ ラ ス ず れの炭 施用 区 にお い

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生 体 重,

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ヒア グ ラス 草生 区 行 裸 地 区(3.6%)の

Microbial Fertilizers in Japan

6/25/09 7:07 AM

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Microbial Fertilizers in Japan

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Michinori Nishio National Institute of Agro-Environmental Sciences Kannondai 3-1-1, Tsukuba, Ibaraki 305 Japan, 1996-10-01 This Bulletin discusses microbial products in Japan, where they are used on many farms, particularly by organic farmers who hope that these products will improve nutrient uptake by plants and the quality of their products. It discusses the use of charcoal and rhizobia to stimulate nutrient uptake, and the use of arbuscular mycorrizal fungi (AMF) to help establish vegetation on barren land. The range of commercial AMF products available in Japan is briefly described, and their use and effectiveness in Japanese agriculture. Abstracts in Other Languages: 中文, 日本語, !"#

Abstract Introduction In 1961, Japan enacted the "Fundamental Law of Agriculture", which encouraged farmers to selectively produce vegetables, fruits, forage crops and livestock as well as rice, instead of staple foods such as wheat, barley and corn. The aim of the law was to raise farmers' incomes in response to the rapid growth of the Japanese economy. Consumption of vegetables, fruits, milk, eggs and meats increased with economic growth. Farmers adopted the strategy of increasing crop yields by applying large amounts of chemical fertilizers and pesticides. During the 1960s and 1970s, the yield of many crops per unit area increased dramatically as the result of intensive use of chemical inputs and various soil amendments. At present, however, the yield of many crops in Japan has reached a plateau. Moreover, the negative effects of heavy applications of chemical inputs are becoming apparent, in terms of both production and the environment, especially in the case of vegetables. Physiological disturbance of plant metabolism is common, due to the accumulation of excess plant nutrients in the soil. The spread of soil-borne diseases is a threat to vegetable production, especially where monoculture is prevailing. Pollution of underground and surface water by nitrates is sometimes reported from vegetable producing areas. Quality deterioration, in terms of a decrease in the content of vitamins http://www.agnet.org/library/eb/430/

Page 1 of 16

Microbial Fertilizers in Japan

6/25/09 7:07 AM

areas. Quality deterioration, in terms of a decrease in the content of vitamins and sugars, is becoming a subject of concern. All these factors are giving farmers an interest in the function and utilization of soil microorganisms, as a way of repairing the damage from the overuse of chemical inputs. Many farmers in Japan are showing a strong interest in the utilization of microorganisms to help: Stimulate plant nutrient uptake; Provide biological control of soil-borne diseases; Hasten the decomposition of straw and other organic wastes; Improve soil structure; and Promote the production of physio-logically active substances in the rhizosphere or in organic matter. The main incentive for farmers to use microorganisms seems to be that they hope to increase the yield or quality of their crops at a relatively low cost, without a large investment of money and labor. Although many microbial materials are sold commercially, most of them are not microbiologically defined, i.e. the microorganisms contained in the products are not identified, and the microbial composition is not fixed. Many of these commercial products are advertised as if they could solve any problem a farmer is likely to encounter. Because most extension advisors lack any knowledge of microbial products, confusion and trouble frequently occur. In this report I would like to describe the present situation of microbial technologies in Japan, focusing on the practical use of various products and their potential.

Utilization of Arbuscular Mycorrhizal Fungi More than 50% of upland and grassland soils in Japan are volcanic ash soils (Andosols), which transform phosphate into unavailable forms by chemical bonding with aluminum ions. Phosphate availability is therefore one of the strongest limiting factors on Japanese upland and grassland farms. At present, this problem is being overcome by a heavy basal dressing of a mixture of superphosphate and fused phosphate. Although these heavy applications have contributed to a remarkable increase in yields of many crops, many vegetable fields have accumulated phosphate at levels which inhibit plant growth. On the other hand, most grasslands are still deficient in phosphate, because enough chemical phosphate is being applied only when they are reclaimed. Therefore, there are two types of Andosols in Japan; one contains a sufficient amount of phosphate, and one does not. In both cases, there have been attempts to use arbuscular mycorrhizal fungi (AMF) or vesicular-arbuscular mycorrhizal fungi (VAM) for soil amelioration.

Utilization of Indigenous Amf by the Application of Charcoal The idea that the application of charcoal stimulates indigenous AMF in soil and thus promotes plant growth is relatively well-known in Japan, although the actual application of charcoal is limited due to its high cost. The concept originated in the work of M. Ogawa, a former soil microbiologist in the Forestry and Forest Products Research Institute in Tsukuba. He and his colleagues applied charcoal around the roots of pine trees growing by the seashore, and found that Japanese truffles became plentiful. He also tested http://www.agnet.org/library/eb/430/

Page 2 of 16

Microbial Fertilizers in Japan

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seashore, and found that Japanese truffles became plentiful. He also tested the application of charcoal to soybean with a small quantity of applied fertilizer, and demonstrated the stimulation of plant growth and nodule formation (Ogawa 1983). His findings with regard to legumes were taken up for further study by the National Grassland Research Institute (Nishio and Okano 1991).

Stimulation of Alfalfa Growth by Charcoal Application Table 1 shows the results obtained with alfalfa in pot experiments. The soil used was a volcanic ash soil with very low phosphate availability. Although alfalfa growth was very poor without applied fertilizer, it was improved by the application of small amounts of fertilizer, and even more by the application of charcoal with the fertilizer. Four sets of pots were prepared. Each set received the same amount of fertilizer (2 g N, 4.4 g P and 8.3 g K/m2). Set [F] received only fertilizer. The others received fertilizer and also rhizobia [F+R], 1,000g/m of charcoal [F+C], and rhizobia plus charcoal [F+R+C]. The charcoal used was a commercial product made of bark from several kinds of deciduous broadleaved trees. Particle composition was >2mm, 24%; 1-2mm, 18%, and <1mm; 58%. Compared to the sets which received fertilizer alone, or fertilizer plus rhizobia, the charcoal application stimulated plant growth by 1.7 - 1.8 times [F+C] and 1.4 - 1.8 times [F+R+C], measured at 38 days after sowing. At this stage the stimulatory effect of rhizobia on plant growth was not marked, because the plants had met most of their requirements by absorbing the applied nitrogen fertilizer, and nodule development was still at an early stage. At 58 days, when the nitrate added had been completely exhausted, plants not inoculated with rhizobia ([F] and [F + C]) ceased to grow, and their leaves turned yellow due to nitrogen deficiency. The soil used did not contain any indigenous rhizobia effective on alfalfa, so that roots not inoculated with R. meliloti did not show any acetylene reduction activity. At this stage, the stimulatory effect of charcoal on growth was observed only in the plants inoculated with rhizobia. The shoot weight of the [F + R + C] plants was 1.7 times greater than that of the [F + R] plants.

Stimulation of Nutrient Uptake by Charcoal Application The amount of nutrients (N, P, K) absorbed by the shoots showed a trend similar to that of the shoot fresh weight (Table 1). The amount of N fixed by the nodules and transported to the shoots was calculated by subtracting the N content of the shoots of the plants not inoculated with rhizobia from the N content of the inoculated plants ([F+R]-[F], [F+R+C] - [F+C]). The addition of charcoal increased this amount of N 2.8-4.0 times, and the ARA by 6.2 times (Table 2). Added charcoal also increased the nodule weight by 2.3 times. Fig. 1 shows the relationship between the increment of P and N associated with rhizobial inoculation in comparison with the non-inoculated alfalfa ([F+R] - [F] and [+R+C] - [F+C]). A significant correlation was observed between the increments of P and N, suggesting that the stimulation of nitrogen fixation by charcoal addition may be due to the stimulation of P uptake. http://www.agnet.org/library/eb/430/

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by charcoal addition may be due to the stimulation of P uptake.

Relationship between Charcoal Application and Amp The relative values of the shoot fresh weight and the degree of AMF infection were determined on the basis of the values of [F+R]. A significant correlation was observed between the shoot weight and AMF infection (Fig. 2). When the soil was sterilized by chloropicrin, alfalfa growth was greatly reduced, even with the application of the same amount of fertilizer shown in Table 1. The stimulatory effect of charcoal on plant growth also diminished. On the other hand, vigorous plant growth and the stimulatory effects of charcoal addition were clearly observed when the sterilized soil was mixed with a large amount of native soil (Fig. 3). This clearly indicates that the stimulatory effect of added charcoal may appear only when a certain level of indigenous AMF are present.

Mechanism Whereby Charcoal Stimulates the Growth of Amf Charcoal may stimulate the growth of AMF by the following mechanism. Charcoal particles have a large number of continuous pores with a diameter of more than 100!m. They do not contain any organic nutrients, because of the carbonization process. The large pores in the charcoal may offer a new microhabitat to the AMF, which can obtain organic nutrients through mycelia extended from roots. This may enable the AMF to extend their mycelia far out from the roots, thus collecting a larger amount of available phosphate.

Utilization of Amf for Establishment of Green Cover on Barren Land Barren land with poor vegetation cover, such as bare slopes beside roads and on mountains, or large fresh deposits of volcanic debris, are subject to serious soil erosion. The ordinary method of establishing plant cover on sloping barren land is to seed grass or transplant tree seedlings, together with fertilization of the soil. At the early stages of plant development, however, when plant cover is not yet well established, heavy rainfall can cause soil erosion and leach out fertilizers. This retards plant establishment. To overcome the problem, a new technology is now being developed. T. Marumoto of Yamaguchi University and his colleagues have developed a new soil mulching sheet made of a plastic random-fiber sheet of webbing. It contains plant seeds, fertilizer (including a coated nitrogen fertilizer and culture media composed of organic materials (peat soil + bark manure), zeolite and bentonite (Marumoto 1996). The sheet is stretched out over the soil surface, and helps prevent soil erosion at the early stages of vegetation growth. Shoots and roots of seedlings can easily push through the sheet and develop further. Marumoto also attempted to stimulate the growth of grasses and trees by inoculating the sheet with AMF and ectomycorrhizal fungi. Table 3 shows one of their experiments, in which a commercial product of AMF (Gigarospora margarita) was inoculated on the soil surface beneath a sheet containing mixed grass seeds. After six months, the dry weight of the grass increased by 1.4-1.6 times compared to the control, and the level of infection by AMF was clearly enhanced by the inoculation. http://www.agnet.org/library/eb/430/

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by AMF was clearly enhanced by the inoculation. Marumoto et al. demonstrated the effectiveness of their sheet by applying it to more than 50 field sites, including bare slopes of building construction sites, sites where golf courses were being developed, road construction sites and fresh deposits of volcanic debris. They are now attempting to improve their technology by utilizing mycorrhizal fungi. Their experiments show that the selection of plant species suited to the targeted soil, and also of species of endo- and ecto-mycorrhizal fungi suited to the host plant, are very important.

Utilization of the Commercial Amf Products in Vegetable Production A number of AMF products for inoculation are sold commercially in Japan. In May 1994, Idemitsu Industry, one of the biggest oil companies in Japan, launched its AMF product (Yorifuji and Suzuki 1955). The Central Glass Company then began to sell its AMF products through Tosho Central Trading Company. Before these two companies, Kyowa Fermentation Industry had been the first company in Japan to produce an AMF product and subject it to marketing tests, but abandoned actual marketing since it judged there would be little profit, in the context of Japanese intensive agriculture. Several other companies are now investigating the application of AMF to agriculture, and intend to market new products in the near future. As the sales of chemical fertilizers fall, affected by the environmental conservation movement and by the increasing costs of production, fertilizer companies are searching for alternative added-value technologies, of which AMF is one. In addition to stimulating the nutrient uptake by plants, it is hoped that AMF will prevent the infection by pathogens of roots. If they are found in fact to do this, a very large market demand might be expected, because soil-borne plant diseases are the most serious limiting factor in Japan's vegetable production, where continuous cropping is widespread. Since the microbiological industry generally needs a relatively small investment, at least at the start, companies other than fertilizer producers are also competing to develop and sell AMF products.

Brief Description of Commercial Amf Products Idemitsu Industry uses mainly strains of Glomus, with complementary strains of Gigaspora and Scutellospora. Central Glass uses strains of Gigaspora. Although the specificity of AMF is generally said not to be high, researchers at these companies have demonstrated that different strains may sometimes vary greatly in their ability to infect the roots of certain plants. Therefore, AMF products are composed of multiple strains, all with confirmed infection abilities. Spores and mycelia produced by the cultivation of host plants are packed with mineral carriers or peat moss. One AMF product sold by Idemitsu Industry has a water content of 15%, and should be stored at temperatures lower than 20°C. Activity can be maintained for at least two years if the product is stored at 5°C.

Effectiveness of Commercial Amf Products AMF products are used mainly on vegetables such as eggplant, tomato, strawberry, sweet pepper, leek, asparagus and lettuce. They are not used much on flowers or fruit trees, although they probably will be in future. They http://www.agnet.org/library/eb/430/

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much on flowers or fruit trees, although they probably will be in future. They will probably not be used on low-value crops such as cereals, soybean and pasture, because of the cost-benefit relationship. In most cases, nursery beds are inoculated with AMF products, and the inoculated seedlings are planted out in the field. Usually nursery beds also receive 150-205 kg/ha of P2O5 fertilizer. Although this amount of phosphate seems to be excessive in terms of producing full AMF activity, the growth of seedlings has been reported to be increased significantly, by 20% or more, by AMF inoculation. Final yields of marketable produce were reported to be increased by 20-50%. Vegetable farmers regard large, healthy seedlings as important in achieving higher yields and preventing soilborne diseases. A more noticeable stimulation of seedling growth could be expected if phosphate applications were reduced to a lower level. Even so, farmers might not be satisfied if lower phosphate applications resulted in smaller seedlings. In intensive agriculture, the objective is not a reduction in chemical fertilizers, but a higher yield of better quality. Organic farming using reduced inputs might be able to utilize AMF products more effectively.

Utilization of Phosphate Solubilizing Microorganisms Japan has only very small amounts of rock phosphate, and most of its soils immobilize phosphate ions into unavailable forms. Rock phosphate which can be mined by current technology is predicted to become exhausted in about 100 years' time. Therefore, there is a strong interest in developing alternative sources of phosphate fertilizer. Many countries are studying the direct utilization of rock phosphate. Australia has developed "biosuper", i.e. pellets composed of rock phosphate, sulfur and sulfur-oxidizing bacteria. Japanese scientists are very interested in the solubilization of bound phosphate in soil which has accumulated phosphate from repeated, heavy applications of phosphate fertilizer. While more than 70% of total phosphate is present in organic forms, such as inositol phosphate in volcanic ash soils, there are very few indigenous microorganisms with a strong ability to decompose inositol phosphate in the soil. On the contrary, Japanese soils contain many indigenous heterotrophic microorganisms which solubilize mineral bound phosphates by the excretion of chelating organic acids. In grassland soils, phosphate solubilizing microorganisms made up 1% of bacterial populations and 10% of fungal populations (Nishio 1985). Tinker (1980) raised doubts on the utilization of heterorophic phosphate solubilizing microorganisms, because they need a large amount of organic matter before they can excrete organic acids. Even if phosphate is solubilized, phosphate ions are incorporated into the microbial biomass, so roots cannot absorb enough of them. Thus, we adopted the following strategy: a) The addition of a large amount of organic matter makes phosphate solubilizing (PS) microorganisms proliferate and these solubilize bound phosphate. b) Solubilized phosphates are incorporated into the microbial biomass during other microbial multiplication, using organic matter. c) Once the organic matter becomes exhausted, the microbial biomass http://www.agnet.org/library/eb/430/

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c) Once the organic matter becomes exhausted, the microbial biomass decreases and releases phosphate into the soil. d) The death of the microbial biomass can be accelerated by various soil treatments, including tillage, drying, liming and sterilization. e) Plants can absorb phosphate after microbial proliferation has ceased. f) The absorption of phosphate by plants can be accelerated by inoculation with AMF.

Experimental Evidence Each step described above has been experimentally confirmed (Kimura and Nishio 1989). Fig. 4 shows the difference in biomass P (P retained in biomass) between the soils with and without compound phosphate. When the soil was incubated for 7 days by adding sucrose and ammonium sulfate, the biomass P significantly increased, utilizing Ca-, Al-, and Fe-phosphates and low-quality rock phosphate. However, no significant increase was observed with varicite (crystallized aluminum phosphate) over this short period. This indicates that insoluble phosphates which are not crystallized can be solubilized by indigenous microorganisms when abundant carbon sources are supplied. The rate of increase in soil biomass P fell, and available phosphate increased, after the depletion of carbon sources, or after soil treatments such as chloropicrin fumigation, air-drying or grinding (Fig. 5). This indicates that after the exhaustion of organic matter, microbial biomass falls, releasing phosphate into the soil, and that the release of available phosphate can be accelerated by soil treatments. To demonstrate the stimulatory effect of AMF on plant absorption of phosphate released from soil biomass, an experiment was conducted using dry yeast as an alternative to dead soil biomass. Fig. 6 shows that the simultaneous addition of dry yeast and AMF had a marked effect on both the growth of alfalfa and phosphate absorption by the plant.

Implications Although this experimental evidence merely shows the principles underlying the technology, this is very useful when we attempt to utilize heterotrophic phosphate-solubilizing (PS) microorganisms in soil. It indicates that PS microorganisms need the addition of a large amount of organic matter as a substrate (excretes from roots are not sufficient); Phosphate solubilized by PS micro-organisms is seldom absorbed directly by the plant as long as a large amount of organic matter remains, because other heterotrophs incorporate phosphate into biomass; thus, Growth retardation of the plant may be a possibility just after the application of organic matter. To avoid growth retardation, seeding or transplanting should be delayed. If rock phosphate, basic sludge or other low-grade phosphate is added, presolubilization of bound phosphate in the compost is one way of avoiding growth retardation.

Utilization of Microbial Materials in Organic Farming The number of farmers following organic farming is increasing each year in Japan. The Ministry of Agriculture, Forestry and Fisheries adopted guidelines for organic commodities in 1993. These define organic produce as being http://www.agnet.org/library/eb/430/

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for organic commodities in 1993. These define organic produce as being produced in fields to which no chemically synthesized inputs, except for those permitted, have been applied for at least three years. Since crop production with no chemical inputs at all is very difficult in Japan, many farmers instead try to make minimal use of chemical fertilizer and pesticides. Produce grown in this way is regarded as being related to organic food. In terms of the plant nutrient supply, there are two types of organic farming. One provides plant nutrients from local resources, and the other uses commercial organic fertilizers. Most organic farmers in Japan use the latter type, i.e. commercial organic fertilizers, made from rape seed meal or soybean meal (both residues of oil extraction), meat and fish meal, bone meal etc. These supply sufficient plant nutrients to give relatively high yields. Local resources include green manures, composted livestock manure etc.

Utilization of Microbial Materials to Make &Quot;Bokashi&Quot; Most Japanese organic farmers utilize what is known as `bokashi', in addition to compost. `Bokashi' is organic fertilizer which is briefly composted, to make it less attractive to pests. If rape seed or soybean meal is directly applied to soil, a certain fly ("tanebae") lays eggs in it. The maggots feed on young seedlings just after germination and cause serious damage. Fishmeal also attracts field mice, which dig tunnels under the seed beds. To avoid damage of this kind, farmers developed on their own initiative a technique of composting organic fertilizers for a short period. Typical ingredients are shown in Table 4. These are mixed, and inoculated with microorganisms. Water is added to give a moisture content of 50-55%, and the compost is heaped into a pile. When the temperature of the pile reaches 50-55°C, the pile is mixed and spread out. After the compost has cooled down, it is again heaped in a pile. This microbial decomposition and cooling is repeated three or four times. The materials are then spread out to dry, and finally packed in bags for storage. The name of the product, `bokashi', means in Japanese "obscuring the direct effectiveness". The concentration of nitrogen in bokashi is much lower than in chemical fertilizer, ranging from 2 to 5% total nitrogen. Since the original ingredients are dried materials, there are not enough microorganisms present to begin immediate decomposition of the organic matter. To avoid anaerobic fermentation, with its unpleasant odor, the compost is inoculated with aerobic microorganisms which multiply rapidly. Because these microorganisms need oxygen and have no heat-tolerance, the pile is mixed and spread every one or two days. During the process of composting, easily decomposable organic matter is decomposed through the production of microbial biomass, liberating ammonium ions. The ammonium is retained on soil particles. The microbial biomass contributes to the slower release of nutrients with the residual ingredients. Overall, the aim of the process seems to be, firstly, to decompose substances which attract pests, and secondly, to create a slower-acting organic fertilizer. The production of bokashi in Japan seems to be increasing. Many organic farmers engaged in vegetable production use bokashi when they limit the water supply to plants. Plants under water stress increase the osmotic pressure in their fluid by increasing concentrations of mono- and oligohttp://www.agnet.org/library/eb/430/

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pressure in their fluid by increasing concentrations of mono- and oligosaccharides instead of starch. This results in a higher level of sugars and vitamins in the vegetables, as well as a longer post-harvest storage life. These attributes raise the quality of the produce. When vegetables are being cultivated in a state of water stress, the application of ordinary chemical fertilizers is very difficult, because a rapid increase in the concentration of mineral nutrients in a small amount of soil water frequently damages plant growth. Although slow-acting fertilizers can avoid these difficulties, organic farmers prefer bokashi because it is organic. Although many microbial products are sold in Japan, except in a few special cases, they are not microbiologically defined, i.e. the microorganisms they contain are not identified, and merely described in terms of their hoped-for results. Products which not only identify the microorganisms, but quantify them, are very rare. Fortunately, the microorganisms effective in bokashi production are not restricted to a special group, but are very common species which can multiply rapidly in ordinary composting materials. No serious problems have occurred in bokashi production, with one interesting exception.

Is &Quot;Em&Quot; Really an Effective Microorganism? What is "EM"? This exception is "EM", standing for "effective microorganisms". EM products were developed by T. Higa of Ryukyu University, Okinawa. They contain abundant anaerobic lactic acid bacteria and yeasts, as well as other microorganisms. The utilization of these anaerobic microorganisms is a distinctive feature which distinguishes EM from other microbial products. EM first attracted notice in garbage treatment by local governments that were struggling to cope with the increasing amount of garbage. The EM manufacturer claimed that individual households could make "compost" of good quality in one or two weeks using a sealed plastic bag or container containing cooking refuse mixed with an EM product. Although anaerobic fermentation usually generates an unpleasant odor, EM products were claimed to suppress any bad smells by producing lactic acid. Higa claimed that the "compost" thus prepared could be used in a home garden or distributed to farmers. This idea attracted local governments, who hoped it would cut down on the cost of garbage treatment, as well as citizens who appreciated the importance of recycling. The "compost" thus prepared, however, has a very high water content, because water vapor cannot escape from a sealed bag. It also contains a large amount of available organic matter, because the decomposition of organic matter is incomplete, as with the making of silage or pickles. Incorporating available organic matter into the soil causes an explosive proliferation of pathogenic "sugar fungi" such as Physium and Rhizoctonia. Therefore, many crop failures have occurred when seeds were sown just after application of the "compost". Some farmers' groups are now making bokashi from this garbage compost by drying it, mixing it with other materials, and composting this mixture further. "EM Bokashi" Apart from compost made from household wastes, farmers are also making bokashi, using EM products under anaerobic conditions, from other ordinary organic materials. Higa claims in his book that a revolution in agriculture is possible, since the use of EM products increases greatly the yield of crops. For http://www.agnet.org/library/eb/430/

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possible, since the use of EM products increases greatly the yield of crops. For example, rice fertilized with EM bokashi produced brown rice yields of more than 12 mt/ha. I. Goto and a colleague of Tokyo Agricultural University carried out some field experiments in cooperation with the EM company. They analyzed EM bokashi supplied by the company and also bokashi supplied by farmers, and showed that the samples contained on average 40 kg N, 30 Kg P2O5 and 13 kg K2O per 1000 kg, much the same as ordinary bokashi (Goto and Muramoto 1995). EM recommends the application of 1000 kg/ha of EM bokashi, but the input of 40 kg of nitrogen contained in this amount is not sufficient for the full growth of vegetables. Goto examined the crops of farmers who use EM bokashi, and found that the yield of lettuce from 1000 kg of EM bokashi was much the same as that from ordinary commercial organic fertilizer, when the nitrogen levels were adjusted. He also found that farmers generally applied 30 mt/ha of cattle manure in addition to the EM bokashi, and pointed out that the yields obtained by the farmers may have been greatly supported by the manure. When in fact vegetables were cultivated with only 1000 kg/ha EM bokashi alone in the fields of the University, he found that the yields of many vegetables were only half those obtained by ordinary practices (Muramoto and Goto 1995). Later, researchers of EM reported that when the nitrogen level was adjusted to 100 kg/ha, EM bokashi (2500 kg/ha) yielded the same quantity of lettuce as chemical fertilizer (Iwahori et al. 1996). Therefore, they insisted that the standard amount of EM bokashi which should be applied was 2500 kg/ha for lettuce, and criticized Goto for using an insufficient amount. These experiments seem to show that EM bokashi is no revolutionary step forward, because when it is used, vegetables need the same level of nitrogen as when they are given chemical fertilizers. Goto claims that EM bokashi is nothing but ordinary bokashi, and has no special qualities (Goto et al. 1996).

Utilization of Azolla in Organic Paddy Fields Although Azolla has seldom been utilized by Japanese farmers, regardless of experimental results in research institutes, the recent trend towards organic farming shows signs of changing the situation. A common practice in organic rice production is to release ducklings, usually hybrids of domestic ducks and wild ones, into paddy fields. The webs of their feet disturb the soil surface in the shallow water, and remove the young seedlings of weeds, thus controlling weeds without herbicides. I. Watanabe, who studied Azolla at the International Rice Research Institute, speculated that this soil disturbance would suspend soil particles in the water, thus increasing the availability of phosphate adsorbed on soil particles to Azolla floating on the water surface. He made contact with a farmer and proposed his idea. They carried out experiments in 1995 in the farmer's paddy field, inoculating Azolla in early May without fertilizer. The Azolla increased very rapidly, and covered the whole field just like a carpet. The Azolla biomass was estimated to be 28 mt/ha on June 25. Subsequently, some of the Azolla was eaten by birds, and was reduced by about 30% by July 14. Since the Azolla supplied too much nitrogen to the rice, some of the plants collapsed, and the yield of brown rice was only 4.36-4.5 mt/ha (Huruno 1995). This experiment is likely to trigger off widespread utilization of Azolla in Japan. http://www.agnet.org/library/eb/430/

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Michinori Nishio National Institute of Agro-Environmental Sciences Kannondai 3-1-1, Tsukuba, Ibaraki 305 Japan, 1996-10-01 This Bulletin discusses microbial products in Japan, where they are used on many farms, particularly by organic farmers who hope that these products will improve nutrient uptake by plants and the quality of their products. It discusses the use of charcoal and rhizobia to stimulate nutrient uptake, and the use of arbuscular mycorrizal fungi (AMF) to help establish vegetation on barren land. The range of commercial AMF products available in Japan is briefly described, and their use and effectiveness in Japanese agriculture. Abstracts in Other Languages: 中文, 日本語, !"#

Abstract Introduction In 1961, Japan enacted the "Fundamental Law of Agriculture", which encouraged farmers to selectively produce vegetables, fruits, forage crops and livestock as well as rice, instead of staple foods such as wheat, barley and corn. The aim of the law was to raise farmers' incomes in response to the rapid growth of the Japanese economy. Consumption of vegetables, fruits, milk, eggs and meats increased with economic growth. Farmers adopted the strategy of increasing crop yields by applying large amounts of chemical fertilizers and pesticides. During the 1960s and 1970s, the yield of many crops per unit area increased dramatically as the result of intensive use of chemical inputs and various soil amendments. At present, however, the yield of many crops in Japan has reached a plateau. Moreover, the negative effects of heavy applications of chemical inputs are becoming apparent, in terms of both production and the environment, especially in the case of vegetables. Physiological disturbance of plant metabolism is common, due to the accumulation of excess plant nutrients in the soil. The spread of soil-borne diseases is a threat to vegetable production, especially where monoculture is prevailing. Pollution of underground and surface water by nitrates is sometimes reported from vegetable producing areas. Quality deterioration, in terms of a decrease in the content of vitamins http://www.agnet.org/library/eb/430/

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areas. Quality deterioration, in terms of a decrease in the content of vitamins and sugars, is becoming a subject of concern. All these factors are giving farmers an interest in the function and utilization of soil microorganisms, as a way of repairing the damage from the overuse of chemical inputs. Many farmers in Japan are showing a strong interest in the utilization of microorganisms to help: Stimulate plant nutrient uptake; Provide biological control of soil-borne diseases; Hasten the decomposition of straw and other organic wastes; Improve soil structure; and Promote the production of physio-logically active substances in the rhizosphere or in organic matter. The main incentive for farmers to use microorganisms seems to be that they hope to increase the yield or quality of their crops at a relatively low cost, without a large investment of money and labor. Although many microbial materials are sold commercially, most of them are not microbiologically defined, i.e. the microorganisms contained in the products are not identified, and the microbial composition is not fixed. Many of these commercial products are advertised as if they could solve any problem a farmer is likely to encounter. Because most extension advisors lack any knowledge of microbial products, confusion and trouble frequently occur. In this report I would like to describe the present situation of microbial technologies in Japan, focusing on the practical use of various products and their potential.

Utilization of Arbuscular Mycorrhizal Fungi More than 50% of upland and grassland soils in Japan are volcanic ash soils (Andosols), which transform phosphate into unavailable forms by chemical bonding with aluminum ions. Phosphate availability is therefore one of the strongest limiting factors on Japanese upland and grassland farms. At present, this problem is being overcome by a heavy basal dressing of a mixture of superphosphate and fused phosphate. Although these heavy applications have contributed to a remarkable increase in yields of many crops, many vegetable fields have accumulated phosphate at levels which inhibit plant growth. On the other hand, most grasslands are still deficient in phosphate, because enough chemical phosphate is being applied only when they are reclaimed. Therefore, there are two types of Andosols in Japan; one contains a sufficient amount of phosphate, and one does not. In both cases, there have been attempts to use arbuscular mycorrhizal fungi (AMF) or vesicular-arbuscular mycorrhizal fungi (VAM) for soil amelioration.

Utilization of Indigenous Amf by the Application of Charcoal The idea that the application of charcoal stimulates indigenous AMF in soil and thus promotes plant growth is relatively well-known in Japan, although the actual application of charcoal is limited due to its high cost. The concept originated in the work of M. Ogawa, a former soil microbiologist in the Forestry and Forest Products Research Institute in Tsukuba. He and his colleagues applied charcoal around the roots of pine trees growing by the seashore, and found that Japanese truffles became plentiful. He also tested http://www.agnet.org/library/eb/430/

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seashore, and found that Japanese truffles became plentiful. He also tested the application of charcoal to soybean with a small quantity of applied fertilizer, and demonstrated the stimulation of plant growth and nodule formation (Ogawa 1983). His findings with regard to legumes were taken up for further study by the National Grassland Research Institute (Nishio and Okano 1991).

Stimulation of Alfalfa Growth by Charcoal Application Table 1 shows the results obtained with alfalfa in pot experiments. The soil used was a volcanic ash soil with very low phosphate availability. Although alfalfa growth was very poor without applied fertilizer, it was improved by the application of small amounts of fertilizer, and even more by the application of charcoal with the fertilizer. Four sets of pots were prepared. Each set received the same amount of fertilizer (2 g N, 4.4 g P and 8.3 g K/m2). Set [F] received only fertilizer. The others received fertilizer and also rhizobia [F+R], 1,000g/m of charcoal [F+C], and rhizobia plus charcoal [F+R+C]. The charcoal used was a commercial product made of bark from several kinds of deciduous broadleaved trees. Particle composition was >2mm, 24%; 1-2mm, 18%, and <1mm; 58%. Compared to the sets which received fertilizer alone, or fertilizer plus rhizobia, the charcoal application stimulated plant growth by 1.7 - 1.8 times [F+C] and 1.4 - 1.8 times [F+R+C], measured at 38 days after sowing. At this stage the stimulatory effect of rhizobia on plant growth was not marked, because the plants had met most of their requirements by absorbing the applied nitrogen fertilizer, and nodule development was still at an early stage. At 58 days, when the nitrate added had been completely exhausted, plants not inoculated with rhizobia ([F] and [F + C]) ceased to grow, and their leaves turned yellow due to nitrogen deficiency. The soil used did not contain any indigenous rhizobia effective on alfalfa, so that roots not inoculated with R. meliloti did not show any acetylene reduction activity. At this stage, the stimulatory effect of charcoal on growth was observed only in the plants inoculated with rhizobia. The shoot weight of the [F + R + C] plants was 1.7 times greater than that of the [F + R] plants.

Stimulation of Nutrient Uptake by Charcoal Application The amount of nutrients (N, P, K) absorbed by the shoots showed a trend similar to that of the shoot fresh weight (Table 1). The amount of N fixed by the nodules and transported to the shoots was calculated by subtracting the N content of the shoots of the plants not inoculated with rhizobia from the N content of the inoculated plants ([F+R]-[F], [F+R+C] - [F+C]). The addition of charcoal increased this amount of N 2.8-4.0 times, and the ARA by 6.2 times (Table 2). Added charcoal also increased the nodule weight by 2.3 times. Fig. 1 shows the relationship between the increment of P and N associated with rhizobial inoculation in comparison with the non-inoculated alfalfa ([F+R] - [F] and [+R+C] - [F+C]). A significant correlation was observed between the increments of P and N, suggesting that the stimulation of nitrogen fixation by charcoal addition may be due to the stimulation of P uptake. http://www.agnet.org/library/eb/430/

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by charcoal addition may be due to the stimulation of P uptake.

Relationship between Charcoal Application and Amp The relative values of the shoot fresh weight and the degree of AMF infection were determined on the basis of the values of [F+R]. A significant correlation was observed between the shoot weight and AMF infection (Fig. 2). When the soil was sterilized by chloropicrin, alfalfa growth was greatly reduced, even with the application of the same amount of fertilizer shown in Table 1. The stimulatory effect of charcoal on plant growth also diminished. On the other hand, vigorous plant growth and the stimulatory effects of charcoal addition were clearly observed when the sterilized soil was mixed with a large amount of native soil (Fig. 3). This clearly indicates that the stimulatory effect of added charcoal may appear only when a certain level of indigenous AMF are present.

Mechanism Whereby Charcoal Stimulates the Growth of Amf Charcoal may stimulate the growth of AMF by the following mechanism. Charcoal particles have a large number of continuous pores with a diameter of more than 100!m. They do not contain any organic nutrients, because of the carbonization process. The large pores in the charcoal may offer a new microhabitat to the AMF, which can obtain organic nutrients through mycelia extended from roots. This may enable the AMF to extend their mycelia far out from the roots, thus collecting a larger amount of available phosphate.

Utilization of Amf for Establishment of Green Cover on Barren Land Barren land with poor vegetation cover, such as bare slopes beside roads and on mountains, or large fresh deposits of volcanic debris, are subject to serious soil erosion. The ordinary method of establishing plant cover on sloping barren land is to seed grass or transplant tree seedlings, together with fertilization of the soil. At the early stages of plant development, however, when plant cover is not yet well established, heavy rainfall can cause soil erosion and leach out fertilizers. This retards plant establishment. To overcome the problem, a new technology is now being developed. T. Marumoto of Yamaguchi University and his colleagues have developed a new soil mulching sheet made of a plastic random-fiber sheet of webbing. It contains plant seeds, fertilizer (including a coated nitrogen fertilizer and culture media composed of organic materials (peat soil + bark manure), zeolite and bentonite (Marumoto 1996). The sheet is stretched out over the soil surface, and helps prevent soil erosion at the early stages of vegetation growth. Shoots and roots of seedlings can easily push through the sheet and develop further. Marumoto also attempted to stimulate the growth of grasses and trees by inoculating the sheet with AMF and ectomycorrhizal fungi. Table 3 shows one of their experiments, in which a commercial product of AMF (Gigarospora margarita) was inoculated on the soil surface beneath a sheet containing mixed grass seeds. After six months, the dry weight of the grass increased by 1.4-1.6 times compared to the control, and the level of infection by AMF was clearly enhanced by the inoculation. http://www.agnet.org/library/eb/430/

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by AMF was clearly enhanced by the inoculation. Marumoto et al. demonstrated the effectiveness of their sheet by applying it to more than 50 field sites, including bare slopes of building construction sites, sites where golf courses were being developed, road construction sites and fresh deposits of volcanic debris. They are now attempting to improve their technology by utilizing mycorrhizal fungi. Their experiments show that the selection of plant species suited to the targeted soil, and also of species of endo- and ecto-mycorrhizal fungi suited to the host plant, are very important.

Utilization of the Commercial Amf Products in Vegetable Production A number of AMF products for inoculation are sold commercially in Japan. In May 1994, Idemitsu Industry, one of the biggest oil companies in Japan, launched its AMF product (Yorifuji and Suzuki 1955). The Central Glass Company then began to sell its AMF products through Tosho Central Trading Company. Before these two companies, Kyowa Fermentation Industry had been the first company in Japan to produce an AMF product and subject it to marketing tests, but abandoned actual marketing since it judged there would be little profit, in the context of Japanese intensive agriculture. Several other companies are now investigating the application of AMF to agriculture, and intend to market new products in the near future. As the sales of chemical fertilizers fall, affected by the environmental conservation movement and by the increasing costs of production, fertilizer companies are searching for alternative added-value technologies, of which AMF is one. In addition to stimulating the nutrient uptake by plants, it is hoped that AMF will prevent the infection by pathogens of roots. If they are found in fact to do this, a very large market demand might be expected, because soil-borne plant diseases are the most serious limiting factor in Japan's vegetable production, where continuous cropping is widespread. Since the microbiological industry generally needs a relatively small investment, at least at the start, companies other than fertilizer producers are also competing to develop and sell AMF products.

Brief Description of Commercial Amf Products Idemitsu Industry uses mainly strains of Glomus, with complementary strains of Gigaspora and Scutellospora. Central Glass uses strains of Gigaspora. Although the specificity of AMF is generally said not to be high, researchers at these companies have demonstrated that different strains may sometimes vary greatly in their ability to infect the roots of certain plants. Therefore, AMF products are composed of multiple strains, all with confirmed infection abilities. Spores and mycelia produced by the cultivation of host plants are packed with mineral carriers or peat moss. One AMF product sold by Idemitsu Industry has a water content of 15%, and should be stored at temperatures lower than 20°C. Activity can be maintained for at least two years if the product is stored at 5°C.

Effectiveness of Commercial Amf Products AMF products are used mainly on vegetables such as eggplant, tomato, strawberry, sweet pepper, leek, asparagus and lettuce. They are not used much on flowers or fruit trees, although they probably will be in future. They http://www.agnet.org/library/eb/430/

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much on flowers or fruit trees, although they probably will be in future. They will probably not be used on low-value crops such as cereals, soybean and pasture, because of the cost-benefit relationship. In most cases, nursery beds are inoculated with AMF products, and the inoculated seedlings are planted out in the field. Usually nursery beds also receive 150-205 kg/ha of P2O5 fertilizer. Although this amount of phosphate seems to be excessive in terms of producing full AMF activity, the growth of seedlings has been reported to be increased significantly, by 20% or more, by AMF inoculation. Final yields of marketable produce were reported to be increased by 20-50%. Vegetable farmers regard large, healthy seedlings as important in achieving higher yields and preventing soilborne diseases. A more noticeable stimulation of seedling growth could be expected if phosphate applications were reduced to a lower level. Even so, farmers might not be satisfied if lower phosphate applications resulted in smaller seedlings. In intensive agriculture, the objective is not a reduction in chemical fertilizers, but a higher yield of better quality. Organic farming using reduced inputs might be able to utilize AMF products more effectively.

Utilization of Phosphate Solubilizing Microorganisms Japan has only very small amounts of rock phosphate, and most of its soils immobilize phosphate ions into unavailable forms. Rock phosphate which can be mined by current technology is predicted to become exhausted in about 100 years' time. Therefore, there is a strong interest in developing alternative sources of phosphate fertilizer. Many countries are studying the direct utilization of rock phosphate. Australia has developed "biosuper", i.e. pellets composed of rock phosphate, sulfur and sulfur-oxidizing bacteria. Japanese scientists are very interested in the solubilization of bound phosphate in soil which has accumulated phosphate from repeated, heavy applications of phosphate fertilizer. While more than 70% of total phosphate is present in organic forms, such as inositol phosphate in volcanic ash soils, there are very few indigenous microorganisms with a strong ability to decompose inositol phosphate in the soil. On the contrary, Japanese soils contain many indigenous heterotrophic microorganisms which solubilize mineral bound phosphates by the excretion of chelating organic acids. In grassland soils, phosphate solubilizing microorganisms made up 1% of bacterial populations and 10% of fungal populations (Nishio 1985). Tinker (1980) raised doubts on the utilization of heterorophic phosphate solubilizing microorganisms, because they need a large amount of organic matter before they can excrete organic acids. Even if phosphate is solubilized, phosphate ions are incorporated into the microbial biomass, so roots cannot absorb enough of them. Thus, we adopted the following strategy: a) The addition of a large amount of organic matter makes phosphate solubilizing (PS) microorganisms proliferate and these solubilize bound phosphate. b) Solubilized phosphates are incorporated into the microbial biomass during other microbial multiplication, using organic matter. c) Once the organic matter becomes exhausted, the microbial biomass http://www.agnet.org/library/eb/430/

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c) Once the organic matter becomes exhausted, the microbial biomass decreases and releases phosphate into the soil. d) The death of the microbial biomass can be accelerated by various soil treatments, including tillage, drying, liming and sterilization. e) Plants can absorb phosphate after microbial proliferation has ceased. f) The absorption of phosphate by plants can be accelerated by inoculation with AMF.

Experimental Evidence Each step described above has been experimentally confirmed (Kimura and Nishio 1989). Fig. 4 shows the difference in biomass P (P retained in biomass) between the soils with and without compound phosphate. When the soil was incubated for 7 days by adding sucrose and ammonium sulfate, the biomass P significantly increased, utilizing Ca-, Al-, and Fe-phosphates and low-quality rock phosphate. However, no significant increase was observed with varicite (crystallized aluminum phosphate) over this short period. This indicates that insoluble phosphates which are not crystallized can be solubilized by indigenous microorganisms when abundant carbon sources are supplied. The rate of increase in soil biomass P fell, and available phosphate increased, after the depletion of carbon sources, or after soil treatments such as chloropicrin fumigation, air-drying or grinding (Fig. 5). This indicates that after the exhaustion of organic matter, microbial biomass falls, releasing phosphate into the soil, and that the release of available phosphate can be accelerated by soil treatments. To demonstrate the stimulatory effect of AMF on plant absorption of phosphate released from soil biomass, an experiment was conducted using dry yeast as an alternative to dead soil biomass. Fig. 6 shows that the simultaneous addition of dry yeast and AMF had a marked effect on both the growth of alfalfa and phosphate absorption by the plant.

Implications Although this experimental evidence merely shows the principles underlying the technology, this is very useful when we attempt to utilize heterotrophic phosphate-solubilizing (PS) microorganisms in soil. It indicates that PS microorganisms need the addition of a large amount of organic matter as a substrate (excretes from roots are not sufficient); Phosphate solubilized by PS micro-organisms is seldom absorbed directly by the plant as long as a large amount of organic matter remains, because other heterotrophs incorporate phosphate into biomass; thus, Growth retardation of the plant may be a possibility just after the application of organic matter. To avoid growth retardation, seeding or transplanting should be delayed. If rock phosphate, basic sludge or other low-grade phosphate is added, presolubilization of bound phosphate in the compost is one way of avoiding growth retardation.

Utilization of Microbial Materials in Organic Farming The number of farmers following organic farming is increasing each year in Japan. The Ministry of Agriculture, Forestry and Fisheries adopted guidelines for organic commodities in 1993. These define organic produce as being http://www.agnet.org/library/eb/430/

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for organic commodities in 1993. These define organic produce as being produced in fields to which no chemically synthesized inputs, except for those permitted, have been applied for at least three years. Since crop production with no chemical inputs at all is very difficult in Japan, many farmers instead try to make minimal use of chemical fertilizer and pesticides. Produce grown in this way is regarded as being related to organic food. In terms of the plant nutrient supply, there are two types of organic farming. One provides plant nutrients from local resources, and the other uses commercial organic fertilizers. Most organic farmers in Japan use the latter type, i.e. commercial organic fertilizers, made from rape seed meal or soybean meal (both residues of oil extraction), meat and fish meal, bone meal etc. These supply sufficient plant nutrients to give relatively high yields. Local resources include green manures, composted livestock manure etc.

Utilization of Microbial Materials to Make &Quot;Bokashi&Quot; Most Japanese organic farmers utilize what is known as `bokashi', in addition to compost. `Bokashi' is organic fertilizer which is briefly composted, to make it less attractive to pests. If rape seed or soybean meal is directly applied to soil, a certain fly ("tanebae") lays eggs in it. The maggots feed on young seedlings just after germination and cause serious damage. Fishmeal also attracts field mice, which dig tunnels under the seed beds. To avoid damage of this kind, farmers developed on their own initiative a technique of composting organic fertilizers for a short period. Typical ingredients are shown in Table 4. These are mixed, and inoculated with microorganisms. Water is added to give a moisture content of 50-55%, and the compost is heaped into a pile. When the temperature of the pile reaches 50-55°C, the pile is mixed and spread out. After the compost has cooled down, it is again heaped in a pile. This microbial decomposition and cooling is repeated three or four times. The materials are then spread out to dry, and finally packed in bags for storage. The name of the product, `bokashi', means in Japanese "obscuring the direct effectiveness". The concentration of nitrogen in bokashi is much lower than in chemical fertilizer, ranging from 2 to 5% total nitrogen. Since the original ingredients are dried materials, there are not enough microorganisms present to begin immediate decomposition of the organic matter. To avoid anaerobic fermentation, with its unpleasant odor, the compost is inoculated with aerobic microorganisms which multiply rapidly. Because these microorganisms need oxygen and have no heat-tolerance, the pile is mixed and spread every one or two days. During the process of composting, easily decomposable organic matter is decomposed through the production of microbial biomass, liberating ammonium ions. The ammonium is retained on soil particles. The microbial biomass contributes to the slower release of nutrients with the residual ingredients. Overall, the aim of the process seems to be, firstly, to decompose substances which attract pests, and secondly, to create a slower-acting organic fertilizer. The production of bokashi in Japan seems to be increasing. Many organic farmers engaged in vegetable production use bokashi when they limit the water supply to plants. Plants under water stress increase the osmotic pressure in their fluid by increasing concentrations of mono- and oligohttp://www.agnet.org/library/eb/430/

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pressure in their fluid by increasing concentrations of mono- and oligosaccharides instead of starch. This results in a higher level of sugars and vitamins in the vegetables, as well as a longer post-harvest storage life. These attributes raise the quality of the produce. When vegetables are being cultivated in a state of water stress, the application of ordinary chemical fertilizers is very difficult, because a rapid increase in the concentration of mineral nutrients in a small amount of soil water frequently damages plant growth. Although slow-acting fertilizers can avoid these difficulties, organic farmers prefer bokashi because it is organic. Although many microbial products are sold in Japan, except in a few special cases, they are not microbiologically defined, i.e. the microorganisms they contain are not identified, and merely described in terms of their hoped-for results. Products which not only identify the microorganisms, but quantify them, are very rare. Fortunately, the microorganisms effective in bokashi production are not restricted to a special group, but are very common species which can multiply rapidly in ordinary composting materials. No serious problems have occurred in bokashi production, with one interesting exception.

Is &Quot;Em&Quot; Really an Effective Microorganism? What is "EM"? This exception is "EM", standing for "effective microorganisms". EM products were developed by T. Higa of Ryukyu University, Okinawa. They contain abundant anaerobic lactic acid bacteria and yeasts, as well as other microorganisms. The utilization of these anaerobic microorganisms is a distinctive feature which distinguishes EM from other microbial products. EM first attracted notice in garbage treatment by local governments that were struggling to cope with the increasing amount of garbage. The EM manufacturer claimed that individual households could make "compost" of good quality in one or two weeks using a sealed plastic bag or container containing cooking refuse mixed with an EM product. Although anaerobic fermentation usually generates an unpleasant odor, EM products were claimed to suppress any bad smells by producing lactic acid. Higa claimed that the "compost" thus prepared could be used in a home garden or distributed to farmers. This idea attracted local governments, who hoped it would cut down on the cost of garbage treatment, as well as citizens who appreciated the importance of recycling. The "compost" thus prepared, however, has a very high water content, because water vapor cannot escape from a sealed bag. It also contains a large amount of available organic matter, because the decomposition of organic matter is incomplete, as with the making of silage or pickles. Incorporating available organic matter into the soil causes an explosive proliferation of pathogenic "sugar fungi" such as Physium and Rhizoctonia. Therefore, many crop failures have occurred when seeds were sown just after application of the "compost". Some farmers' groups are now making bokashi from this garbage compost by drying it, mixing it with other materials, and composting this mixture further. "EM Bokashi" Apart from compost made from household wastes, farmers are also making bokashi, using EM products under anaerobic conditions, from other ordinary organic materials. Higa claims in his book that a revolution in agriculture is possible, since the use of EM products increases greatly the yield of crops. For http://www.agnet.org/library/eb/430/

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possible, since the use of EM products increases greatly the yield of crops. For example, rice fertilized with EM bokashi produced brown rice yields of more than 12 mt/ha. I. Goto and a colleague of Tokyo Agricultural University carried out some field experiments in cooperation with the EM company. They analyzed EM bokashi supplied by the company and also bokashi supplied by farmers, and showed that the samples contained on average 40 kg N, 30 Kg P2O5 and 13 kg K2O per 1000 kg, much the same as ordinary bokashi (Goto and Muramoto 1995). EM recommends the application of 1000 kg/ha of EM bokashi, but the input of 40 kg of nitrogen contained in this amount is not sufficient for the full growth of vegetables. Goto examined the crops of farmers who use EM bokashi, and found that the yield of lettuce from 1000 kg of EM bokashi was much the same as that from ordinary commercial organic fertilizer, when the nitrogen levels were adjusted. He also found that farmers generally applied 30 mt/ha of cattle manure in addition to the EM bokashi, and pointed out that the yields obtained by the farmers may have been greatly supported by the manure. When in fact vegetables were cultivated with only 1000 kg/ha EM bokashi alone in the fields of the University, he found that the yields of many vegetables were only half those obtained by ordinary practices (Muramoto and Goto 1995). Later, researchers of EM reported that when the nitrogen level was adjusted to 100 kg/ha, EM bokashi (2500 kg/ha) yielded the same quantity of lettuce as chemical fertilizer (Iwahori et al. 1996). Therefore, they insisted that the standard amount of EM bokashi which should be applied was 2500 kg/ha for lettuce, and criticized Goto for using an insufficient amount. These experiments seem to show that EM bokashi is no revolutionary step forward, because when it is used, vegetables need the same level of nitrogen as when they are given chemical fertilizers. Goto claims that EM bokashi is nothing but ordinary bokashi, and has no special qualities (Goto et al. 1996).

Utilization of Azolla in Organic Paddy Fields Although Azolla has seldom been utilized by Japanese farmers, regardless of experimental results in research institutes, the recent trend towards organic farming shows signs of changing the situation. A common practice in organic rice production is to release ducklings, usually hybrids of domestic ducks and wild ones, into paddy fields. The webs of their feet disturb the soil surface in the shallow water, and remove the young seedlings of weeds, thus controlling weeds without herbicides. I. Watanabe, who studied Azolla at the International Rice Research Institute, speculated that this soil disturbance would suspend soil particles in the water, thus increasing the availability of phosphate adsorbed on soil particles to Azolla floating on the water surface. He made contact with a farmer and proposed his idea. They carried out experiments in 1995 in the farmer's paddy field, inoculating Azolla in early May without fertilizer. The Azolla increased very rapidly, and covered the whole field just like a carpet. The Azolla biomass was estimated to be 28 mt/ha on June 25. Subsequently, some of the Azolla was eaten by birds, and was reduced by about 30% by July 14. Since the Azolla supplied too much nitrogen to the rice, some of the plants collapsed, and the yield of brown rice was only 4.36-4.5 mt/ha (Huruno 1995). This experiment is likely to trigger off widespread utilization of Azolla in Japan. http://www.agnet.org/library/eb/430/

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Plant and Soil 244: 273–279, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.

273

Inoculation with arbuscular mycorrhizal fungi: the status quo in Japan and the future prospects Masanori Saito1,3 & Takuya Marumoto2 1 Department of

Grassland Ecology, National Institute of Livestock and Grassland Science, Nishi-nasuno, Tochigi, 329-2793, Japan; 2 Faculty of Agriculture, Yamaguchi University, Yoshida, Yamaguchi, 753-8515, Japan; 3 Corresponding author∗ Received 21 August 2001. Accepted in revised form 12 December 2001

Key words: charcoal, degraded soil, inoculum, revegetation, VA mycorrhizal fungi

Abstract Inoculation of arbuscular mycorrhizal (AM) fungi has potential benefits in not only sustainable crop production but also environmental conservation. However, the difficulty of inoculum production due to the obligate biotrophic nature of AM fungi has been the biggest obstacle to putting inoculation into practice. Nevertheless, several companies have sought to produce inoculum of AM fungi. Firstly in this review, the present status of inoculum production and its use in Japan is described. Secondly, although the effectiveness of inoculation is primarily limited by environmental and biological factors, some possible ways to improve inoculation performance are discussed. Approaches include use of chemicals to increase spore germination and colonization and soil application of charcoal to provide a microhabitat for AM fungi to colonize and survive.

Introduction Inoculation with arbuscular mycorrhizal (AM) fungi has potential value for improved crop production, and numerous trials have been conducted since the 1970s (Gianinazzi et al., 1990; Jarstfer and Sylvia, 1993, 1999; Kurle and Pfleger, 1994; Menge, 1984; Powell, 1984; Safir, 1994; Sieverding, 1991). However, the difficulty in inoculum production due to the obligate biotrophic nature of AM fungi has been the biggest obstacle to putting inoculation into practice. At present, nevertheless, several companies all over the world have commercialized the inoculum of AM fungi (http://dmsylvia.ifas.ufl.edu/commercial.htm). Sustainability of agricultural systems has been disputed because of environmental pollution and deterioration due to ‘modern’ and ‘intensive’ agriculture (Matson et al., 1997). The significance of AM fungi to the sustainability of the environment has been realized in arable and natural lands because AM fungi affect the plant community structure in various ways (Van ∗ FAX No: +81-287-36-6629. E-mail: [email protected]

der Heijden et al., 1998). Therefore, for rehabilitation of deteriorated or degraded land, inoculation with AM fungi can be considered an effective option (Miller and Jastrow, 1992; Pfleger et al., 1994). Such a trend may encourage the inoculum production companies. The intention of this is not to review numerous papers on inoculum production of AM fungi, but to present the current status of inoculum production and its use in Japan. Secondly, we discuss some possible ways to improve inoculation performance and the future prospects in inoculation technology.

Inoculum production in Japan In the 1940s in Japan, the growth promoting effect of endomycorrhizal fungi on plant growth was established by a pioneering scientist, T. Asai (Asai, 1943, 1944). However, his work was neglected until research on inoculum production of AM fungi boomed in the 1980s in Japan (Ogawa, 1987). In the early 1990s some companies started commercial production of inoculum of AM fungi.

274 The Ministry of Agriculture, Forestry and Fisheries (MAFF) of the Japanese Government has promoted the introduction of various technologies to reduce agrochemical inputs to arable lands for sustainable agriculture. MAFF recognized that AM inocula are useful to reduce phosphate fertilizer application, and in 1996 approved AM inocula as soil amendments by an ordinance of the Soil Productivity Improvement Law. The ordinance regulates the quality of 12 types of amendments such as zeolite, peat, and other organic/inorganic materials that are effective for the improvement of soil productivity. The ordinance specifies that a quality guarantee be labeled on the outside of the product container. In the case of AM fungi, the following items are required; (i) name and address of producer, (ii) raw materials, (iii) symbiotic efficiency, (iv) efficacy, (v) recommended application rate, (vi) storage conditions, (vii) expiration date. In item (ii), carrier material, such as peat or zeolite, is indicated. In item (iii), the symbiotic efficiency is expressed as percentage of colonization by the inoculum of a specific test plant such as Welsh onion under standard conditions. In item (iv), the producer should note that the inoculum is not effective for some crops species belonging to the Brassicaceae and Chenopodiaceae, and that the inoculum may not be effective in soils rich in available phosphate. This quality guarantee is important to expel poor quality microbial inocula from the market place. At present, three companies, Central Glass Co., Idemitsu Kosan Co., and Osaka Gas Co., produce AM inoculum. The MAFF statistics indicate that 28 – 83 tons of the inocula were supplied per year from 1997 to 1999. Much of inoculum was supplied for non-agricultural applications such as rehabilitation of degraded or devegetated landscapes. Because enduse of the inocula is not within the framework of the ordinance, the above statistics do not include the supply for such non-agricultural objectives. Although the detailed procedure for inoculum production is proprietary, these inocula are produced under glasshouse conditions based upon the pot culture technique (Jarstfer and Sylvia, 1993). One company uses expanded clay as a potting medium (Dehne and Backhaus, 1986). Others extract and concentrate the propagules of AM fungi from potting media, and carriers such as peat are mixed with the propagules. The inocula are mainly sold to horticulture farmers. Some formulations are specific for each crop species by taking into account factors such as host plant species,

AM fungal species, and the handling of inoculum into horticultural practices. The cost of inoculum production is a serious problem because the inocula are not competitive in price with phosphorus fertilizer. Even if farmers understand the significance of sustainable agricultural systems, the reduction of phosphorus inputs by using AM fungal inocula alone cannot justify the use of the inocula except in the case of high value crops. Another serious problem is control of phytopathogenic micro-organisms. At present, the inoculum produced is not completely free from pathogens, even though the producers attempt to control pathogens with various agrochemicals. Farmers are very aware of the risk of pathogens, so they do not accept inoculum containing host root residues. Although pieces of root colonized with AM fungi, especially Glomus intraradices and related species, function well as propagules, the companies remove such residue of host roots from their products.

Rehabilitation of a volcanic deposit-affected area Inocula of AM fungi are expected to be substantially beneficial in the establishment of vegetation in degraded or bare landscapes (Miller and Jastrow, 1992; Pfleger et al., 1994; Requena et al., 2001). Currently in Japan, AM fungal inocula has been applied most successfully in revegetation of land by devastated by volcanic activities (Marumoto et al., 1996, 1999). In the Japanese islands, active volcanos sometimes seriously damage large areas and destroy human activities. Newly deposited volcanic materials are very low in nutrients available for plants and very susceptible to erosion. The revegetation process is therefore slow, so the acceleration of revegetation is required not only for environmental conservation but also for the prevention of erosion. In 1990, Mt. Fugendake (32◦ 45 N, 130◦ 19 E) began volcanic activities after 200 years of inactivity. During 1991 – 1994, several large pyroclastic flows completely destroyed the previous vegetation on the mountain slope. More than 1000 ha of the mountain slope and the base of the mountain were covered with a thick pyroclastic deposit. Immediately after volcanic activities ceased in 1995, a revegetation project was started. Because the area to be revegetated was on a steep slope of the volcano and was still a hazard, the workers were not able to access the revegetation project site during the first a few years. Therefore, revegetation materials were

275

Figure 1. Revegetation in a volcano-devastated area of Mt. Fugendake, Japan. (A) Application of bags containing AM fungal inoculum on the pyroclastic flow. (B) Germination of plants from seeds contained in the bag. (C) A landscape of the pyroclastic flow 3 weeks after the application. (D) A landscape in the same site as (C) 3 years after the application.

applied from the air by a helicopter in 1995. A bag of unwoven polyester fabric, weighing about 2 kg, contained plant seeds, AM fungal inocula, slow-release chemical fertilizer, and some carriers such as peat moss. Seeds of various wild grass and shrub species were used: Miscanthus sinensis, Artemisia princeps, Lespedeza cuneata and others. Gigaspora margarita and Glomus sp. were used as the fungal inocula. About 3000 bags per ha were applied to the target-area (Figure 1 A, B). The grass plants that germinated from the bag were highly colonized with AM fungi. Recently, the inoculated fungal species were still proliferating 6 years after application (unpublished). Thus, the AM fungi and some nutrients in the bag supported the growth of the plants contained in the bag in the nutrient poor pyroclastic flow. The site where the bags were located became a base from which the plants revegetated the site and prevented serious erosion (Figure 1 C, D). This ‘bag’ method reduced the amount of revegetation materials, including inoculum, and established plant coverage more effectively than broadcast application of revegetation materials to the whole area. Because the local government urgently requested the

Figure 2. Schematic model of the effectiveness of AM fungal inoculation in relation to indigenous AM fungal potential and soil phosphorus availability.

revegetation project, the cost for inoculum was not taken into account in the program.

Improvement in inoculation performance The effectiveness of AM fungal inoculation is affected by various environmental and biological factors, espe-

276 cially the phosphorus availability in soil and the inoculum potential of indigenous AM fungi (Gianinazzi et al., 1990). In soil low in phosphorus availability and indigenous AM fungi, the effectiveness of inoculation is expected to be the greatest (Figure 2). This was demonstrated in the revegetation project described above. Field trials in Japan with a commercial inoculum indicate that the efficacy is generally highest in Andisols which show high phosphate fixing capacity (Ueda and Kubo, pers. comm.). On the other hand, in soils rich in available phosphorus, the effectiveness is reduced low and the inoculation might even reduce the crop performance (Peng et al., 1993). Although the effectiveness of inoculation is primarily limited by inoculum potential and P availability, there are possible ways to improve inoculation performance. The inoculation process can be divided into three stages: (i) spore germination, (ii) colonization, and (iii) growth of extraradical hyphae and sporulation. The potential improvement of inoculum performance is discussed for each stage of this process.

Figure 3. Effect of temperature regime on spore germination of Gigaspora margarita (modified from Miyamoto et al., 1994). The spores collected from a pot culture medium were mixed with calcined attapulgite and were kept for 1 – 28 days at different temperatures. After the treatment, 200 spores were extracted by wet-sieving, and the germination rates for 2 weeks at 30 ◦ C were examined.

Spore germination The propagules (mainly spores) in the inoculum should be active and should immediately initiate growth after inoculation. Many chemical compounds and unidentified fractions of various extracts have been found to stimulate spore germination and hyphal extension (Azcón–Aguilar et al., 1999; Hepper, 1984; Ishii et al., 1997; Nagahashi and Douds, 2000; Nair et al., 1991). Addition of these compounds to the inoculum may improve the germination rate and increase the colonization potential of the inoculum (Tawaraya et al., 1998). Spores of AM fungi often show dormancy, although this phenomenon has not yet been critically investigated. Storing the spores for a period from some weeks to some months under cold temperature usually breaks spore dormancy (Hepper, 1984; Safir et al., 1990). G. margarita often shows spore dormancy and a very low germination rate unless elevated temperature treatment is used to break the dormancy (Figure 3). Breaking the spore dormancy technique can increase initial colonization and may enhance the effectiveness of the inoculation (Miyamoto et al., 1994). Root colonization Arbuscular mycorrhizal colonization is comprised of a series of complicated processes from recogni-

Figure 4. Effect of charcoal application on the growth of alfalfa and indigenous AM fungi in a pot experiment. Alfalfa was grown in a clay loam infertile Andisol with N (2 g m−2 ) and K (8.3 g m−2 ) fertilization under different phosphate fertilizer application levels. L, M and H in P level was equivalent to 0, 2.2 and 4.4 g P m−2 , respectively. Charcoal made of a mixture of barks from deciduous trees was applied at a rate of 1 kg m−2 (modified from Nishio and Okano, 1991).

tion between the fungi and host plant to arbuscule formation (Nagahashi, 2000). Root exudates contain compounds that promote colonization by AM fungi (Nagahashi, 2000; Tawaraya et al., 1998). Since the colonization process may depend on a balance among phytohormones (Ludwig–Müller, 2000), and some phytohormones affect colonization by AM fungi (Ghachtouli et al., 1996). Application of a flavonoid, formononetin at time of inoculation stimulated colonization by AM fungi (Fries et al., 1998; Koide et al., 1999). Application of such compounds at transplanting may increase inoculation performance.

277 Growth of extraradical hyphae and sporulation Nutrient absorption of mycorrhizal plants from soil depends upon the function of extraradical hyphae. Soil management that assures the extraradical hyphae to be fully functioning may enable improvement of inoculation performance. Application of charcoal to soil stimulated the colonization of crops by indigenous AM fungi (Nishio and Okano, 1991; Ogawa et al., 1983; Saito, 1990) (Figure 4). The effect of charcoal was ascribed to its physioco-chemical properties. Charcoal is porous, weakly alkaline, and does not serve as a substrate for saprophytes. AM fungi sensitive to competition from saprophytes can easily extend their extraradical hyphae into charcoal buried in soil and sporulate in the particles (Ogawa, 1987). Charcoal particles act as a micro-habitat for AM fungi to survive and later grow into the soil, which makes charcoal suitable as a carrier of AM fungal inoculum (Ogawa, 1989). Charcoal can be applied in a large scale in infertile soils rich in indigenous AM fungi, but its cost is not competitive with inorganic fertilizers at least in Japan. Although many inoculation studies have been conducted, there is still little known about how AM fungi proliferate and survive in soil and how they affect the following crop. In arable lands, various crops are cultivated in sequence. Absence of a host plant, cultivation of non-host crops, or long fallow negatively affect the population of AM fungi in soil (Kurle and Pfleger, 1994; Safir, 1994; Thompson, 1987). On the other hand, some mycotrophic crops increase the growth of the succeeding mycotrophic crop (Arihara and Karasawa, 2000; Karasawa et al., 2001). Irrespective of inoculation, therefore, crop sequence should be taken into account when predicting the responses of AM fungi in a sustainable agricultural system.

Future prospects Commercial inoculum production of AM fungi has been increasing during the past decade, although the future prospect of the business is still uncertain. The obligate biotrophic nature of AM fungi inevitably raises the cost for inoculum production. Soilless culture systems seem to be promising, because this enables the production of clean spores (Jarstfer and Sylvia, 1999). A dual culture of transformed carrot hairy root with AM fungi is an excellent system for providing the sterile

spores for research purposes (Glomales in vitro collection; http://www.mbla.ucl.ac.be/ginco-bel/anglais /cadre.htm) but is unsuitable for commercial inoculum production. Even if mass production system of the dual culture of lower production cost was developed (Jolicoeur et al., 1999), it is uncertain whether the use of spores produced from roots transformed by a pathogenic bacterium, Agrobacterium rhizogenes, would be allowed for inoculation in field. In the field application of any microbial inoculum, it is essential to verify that the inoculated microorganisms caused the plant response in field. Various molecular techniques have been developed to distinguish the inoculated strain from other indigenous strains. However, these techniques to identify AM fungi are still not routinely used because of genetic heterogeneity in AM fungi. Although ITS (internal transcribed spacer) sequence of rDNA is widely used for discrimination among strains in other fungal taxa, application of the ITS sequence for identification of AM fungi is complicated. For example, ITS sequences of 3 isolates of G. margarita including BEG34 and two Japanese isolates showed that the sequences were too diverse to discriminate the isolates; the accession number of the sequence data used were AJ006838–50 for isolates BEG34, AB048619–29 for MAFF520052, and AB048607–18 for MAFF520054, respectively (Saito, 2000). Single stranded conformation polymorphism (SSCP) of the large ribosomal subunit gene may be promising to discriminate isolates of several Glomus spp. (Kjøller and Rosendahl, 2000), while the sequence diversity in this region is very high (Clapp et al., 2001). We need more reliable molecular techniques to trace the inoculated fungi. Therefore, from the standpoint of not only basic biological interest but also application, molecular genetics of these multinucleate fungi is of high research priority. It is now well recognized that inoculation of AM fungi has a potential significance in not only sustainable crop production, but also environmental conservation. However, the status quo of inoculation is far from practical technology that can be widely used in the field. Together, a basic understanding of the biology of AM fungi and an improvement in inoculum production and inoculation technology are required to advance management of these fungi.

Acknowledgements The preparation of this paper was supported in part by

278 Promotion of Basic Research Activities for Innovative Biosciences (PROBRAIN), Bio-oriented Technology Research Advancement Institution, Japan. The authors are grateful to Central Glass Co. Ltd., Idemitsu Kosan Co. Ltd., and Osaka Gas Co. Ltd. for valuable information on inoculum production and to Prof. R. Koide for his critical reading of this manuscript. MS is grateful to Dr. Wu Chi–Guang for fruitful discussions on inoculum production.

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Soil Biology & Biochemistry 41 (2009) 1301–1310

Contents lists available at ScienceDirect

Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio

Effect of biochar amendment on soil carbon balance and soil microbial activity S. Steinbeiss a, *, G. Gleixner a, M. Antonietti b a b

Max Planck Institute for Biogeochemistry, Hans-Knoell-Str. 10, 07745 Jena, Germany Max Planck Institute of Colloids and Interfaces, Am Muehlenberg 1, 14476 Potsdam-Golm, Germany

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 July 2008 Received in revised form 16 March 2009 Accepted 21 March 2009 Available online 17 April 2009

We investigated the behavior of biochars in arable and forest soil in a greenhouse experiment in order to prove that these amendments can increase carbon storage in soils. Two qualities of biochar were produced by hydrothermal pyrolysis from 13C labeled glucose (0% N) and yeast (5% N), respectively. We quantified respiratory losses of soil and biochar carbon and calculated mean residence times of the biochars using the isotopic label. Extraction of phospholipid fatty acids from soil at the beginning and after 4 months of incubation was used to quantify changes in microbial biomass and to identify microbial groups utilizing the biochars. Mean residence times varied between 4 and 29 years, depending on soil type and quality of biochar. Yeast-derived biochar promoted fungi in the soil, while glucose-derived biochar was utilized by Gram-negative bacteria. Our results suggest that residence times of biochar in soils can be manipulated with the aim to ‘‘design’’ the best possible biochar for a given soil type. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: Biochar 13 C labeling PLFA Residence times Greenhouse experiment

1. Introduction There is a large imbalance between carbon release to the atmosphere and carbon uptake by other compartments that leads to a continued increase in atmospheric CO2 equivalent to a rate of 4.1 109 tons of carbon per year (IPCC, 2007). Thus, it should be of utmost importance to develop new methods to retain carbon in a stable form that can be stored outside of the atmosphere for longer time periods. In this context, biochars have attracted a lot of research within the last years basically with focus on the application of biochars to soils, where they not only contribute to carbon storage but at the same time act as fertilizers (Glaser et al., 2001; Marris, 2006). Although a positive effect of biochar amendments on crop yields was already known to ancient cultures (Glaser, 2007), to date little is known about the effects of biochar addition on soil microorganisms and consequently on the soil carbon balance. There is a huge variability in physical biochar structures depending on the parent material and the conditions present at their formation, which leads to quite different turnover times in soils (Czimczik and Masiello, 2007). Large charcoal particles originated from forest wildfires have been shown to remain in soils for * Corresponding author at: Institute of Groundwater Ecology, Helmholtz Centre Munich, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany. Tel.: þ49 (0) 89 3187 2916; fax: þ49 (0) 89 3187 3361. E-mail address: [email protected] (S. Steinbeiss). 0038-0717/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2009.03.016

thousands of years (Pessenda et al., 2001; Gouveia et al., 2002; Gavin et al., 2003), however, smaller particles as derived from grassland burning can hardly be detected in steppe ecosystems (Forbes et al., 2006). The physical and chemical structure, e.g. surface area and condensation grade, and the particle size of synthetic biochars can be modified in technical processes (Titirici et al., 2007a,b) opening the question about the stability of synthetic biochars in soils. There have been developed numerous chemical and technical methods to produce charcoals from a variety of biomass materials (Antal and Gronli, 2003; Marris, 2006; Titirici et al., 2007a). Each production method needs a certain energy supply to activate the reactions and results in completely different biochar structures. However, hydrothermal carbonization looks especially promising energy- and process-wise. Once activated in a continuous process, 20–30% of the energy bound to the original biomass are liberated in the process, while keeping practically all carbon bound to the final structure (Titirici et al., 2007b). No extensive biomass material preparation or costly product isolation procedures are required. Also soft, wet and low grade biomass can be carbonized, making industrial biowaste, sludges or green household waste apt to carbonization. A crude estimate of such directly accessible and mostly already collected biowaste sums up to about 25  106 tons per year in Germany, or to 10  109 tons per year worldwide. Thus, we deal with a potential measure to cure at least significant parts of the CO2 problem, appropriate biological stability in soils and an added biological benefit provided. The optimal biochar

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combining fertilizer and carbon storage function in soils would activate the microbial community leading to nutrient release and fertilization and would add to the decadal soil carbon pool. The structural and chemical properties of biochars that are driving their decomposition or stabilization in soils still have to be identified. In our current study, we added two types of hydrothermally synthesized biochar, a highly condensed, nitrogen free biochar expected to be stable in soil, and a nitrogen containing biochar with low condensation grade expected to be easily degradable, to different soils with the aim to answer the following questions: 1) How stable are biochars produced by this method in different soils? 2) How do inherited soil microorganisms react on the addition of such biochars? 3) Is the stability of these biochars tuneable by varying the condensation grade and chemical composition of the biochar?

2. Materials and methods 2.1. Soil sampling and characterization Soils used for the greenhouse experiment were sampled at the continued arable plot of the Jena Experiment (Roscher et al., 2004) and at the old growth forest field site of the Hainich National Park (Knohl et al., 2003), respectively. The soil of the Jena Experiment was classified as Eutric Fluvisol (FAO, 1998) and had a texture of 23% clay, 64% silt and 13% sand (Kreutziger, personal communication). The soil of the Hainich field site was a fertile Cambisol containing 40% clay, 56% silt and 4% sand (Knohl et al., 2003). In September 2007 the top 5 cm of soil were sampled at both field sites, passed through a sieve with a mesh size of 2 mm and partitioned for PLFA extraction (fresh soil), for soil column filling and for chemical analyses (dried at 40  C), respectively. Soil carbon and nitrogen concentrations were measured from ball-milled sub-samples by elemental analysis (Elementaranalysator vario Max CN, Elementar Analysensysteme GmbH, Hanau, Germany) before and after incubation. Organic carbon concentration was determined by calculating the difference between elemental analyses of the total carbon concentration and soil inorganic carbon concentration (Steinbeiss et al., 2008b). For d13C analysis of the soil organic carbon, 3 mg ground sample was weighed in small tin capsules. The arable soil contained about 1.6% inorganic carbon, which was removed by treatment with 120 ml of sulfurous acid (5–6% SO2, Merck, Darmstadt, Germany) prior to isotope analysis (Steinbeiss et al., 2008a). Isotope ratios were measured by a coupling of an elemental analyzer (EA 1110) with an isotope ratio mass spectrometer (DeltaPlusXL, Thermo Finnigan, Bremen, Germany). All values represent repeated measurements with a standard deviation of less than 0.3& and were calibrated versus V-PDB using CO2 as reference gas (Werner and Brand, 2001). Soil analyses were summarized in Table 1.

2.2. Biochar production and characterization Stable carbon isotopes have proven to reliably trace the flow of carbon in various soil organic matter pools (Gleixner et al., 2001) and into soil microorganisms using the compound-specific 13C content of phospholipid fatty acids (Rubino et al., 2007; Kramer and Gleixner, 2008). Moreover, changes in the13C content of various pools enable the determination of mean residence times (Balesdent and Mariotti, 1996; Gleixner et al., 2002). Consequently, the production of isotopically labeled biochars from simple isotopic precursors is most promising investigating synthetic biochars in the soil system. Biochars were produced by hydrothermal pyrolysis (Titirici et al., 2007a,b) using glucose (signature G) and yeast (signature Y) as parent material, respectively. A 13C label was introduced to both biochars adding uniformly 13C labeled glucose (99 atom%, Sigma Aldrich, Seelze, Germany) to the parent materials prior to biochar synthesis. Glucose should be seen as model compound for cellulose, the major structural component of plant biomass. Several investigations have shown that charcoal produced from very different types of biomass always show similar chemical structures (Schmidt and Noack, 2000; Gleixner et al., 2001; Titirici et al., 2007b, in press). Heterocyclic (Ocontaining) pyran and furan ring systems of carbohydrates or phenol type structures that are the backbone of lignin form for example benzene and other polyaromatic hydrocarbons (PAH) due to the aromatization reactions in the charring process. Solid state 13C NMR examinations proof this remarkable structural and compositional similarity of all charcoals made from different sources of biomass (Titirici et al., in press) and therefore we do not expect serious differences between charcoals produced from model compounds and from biomass (Baccile et al., submitted for publication). Yeast acted as a protein, i.e. nitrogen, rich model waste material resulting from bioethanol, beer and wine production (pomace, draff, brewer grains, distiller’s grain or distiller’s wash (Belyea et al., 1998; Pfeffer et al., 2007; Maas et al., 2008; Quintero et al., 2008)) and thus represented a probable commercial source material for the synthesis of nitrogen rich biochars. The yeast we used was provided by a local beer brewery and represents the brewer grains that were separated from the beer product as described in the literature above. The grains were basically made up of the yeast active in the fermentation and additionally contain some rest of barley glume and wheat bran. Element composition and d13C values of the biochars were determined by elemental analysis and EA-IRMS as was described for the soil samples, respectively (Table 1). Thermogravimetry (TGA851e, Mettler-Toledo, Gießen, Germany) was applied to characterize the thermal stability and thus the carbonization grade of the biochars (Meszaros et al., 2007; Pastor-Villegas et al., 2007; Strezov et al., 2007). Samples, biochars and their respective parent materials, were introduced into the oven at 60  C and heated with a rate of 1  C min1 to 850  C in an Argon atmosphere. Scanning electron microscopy (SEM) was performed on a DSM 940 A (Zeiss, Oberkochen, Germany). Infrared-spectra were measured with an IFS 66 FTIR spectrometer (Bruker Optik GmbH, Ettlingen, Germany). Spectra were obtained averaging 128 scans, with a resolution of 4 cm1.

Table 1 Basic characterization of biochars and soils; sd refers to standard deviation of replicated measurements. For d13C values of CO2 gas in the controls the standard error of the calculated y-intercept was given instead (see Methods section for details).

C content (%) N content (%) d13C value (&) d13C value of CO2 gas in the controls (&)

Glucose-derived biochar

sd

Yeast-derived biochar

sd

Arable soil

sd

Forest soil

sd

64.6 0.0 3.6

0.5 0.0 0.15

67.4 5.0 2.8

0.5 0.03 0.30

2.5 0.3 27.7 24.0

0.01 0.0003 0.14 0.8

5.5 0.5 27.1 27.6

0.06 0.005 0.06 0.6

S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

2.3. Experimental design and regular measurements Soil columns were filled with 150 g soil (dry weight); 15 columns were filled with arable soil (signature A) and 15 columns were filled with forest soil (signature F). The soil of six columns of each soil type was mixed with glucose-derived biochar (signatures AG and FG) and further six columns of each soil type were mixed with yeast-derived biochar (signatures AY and FY). Three columns of each soil type were left as control without biochar (signatures A and F). The amount of biochar added to the soil was calculated to correspond to a carbon addition of 30% of the initial soil organic carbon content. Initial soil properties including PLFA analyses were determined from soil samples without incubation (signatures AI and FI) with triple replicates. Soil columns were incubated at 25  C during the day and 20  C during the night. No artificial lighting was applied. Soil moisture was adjusted every three to four days in all columns. No water leached out from the columns. Soil respiration was measured using a carbon dioxide probe (GMP 343, Vaisala, Helsinki, Finland) from week 1 to week 25 with a temporal resolution of 1 week in the beginning (up to week 7) and 2–3 weeks afterwards. The respired gas was collected in weeks 7, 12, 15, 17, 20, 23 and 26 using 2.3 l gas flasks connected via a capillary to the soil columns (filling time 4 h per sample). Sample air was dried chemically using magnesium perchlorate (Fisher Scientific, Loughborough, UK). Each time two flasks were filled the same way with greenhouse air to correct ambient CO2 concentration and isotope ratios of the treatments (d13Ctreatment,korr) (Amundson et al., 1998). Gas CO2 concentration was measured by GC-FID (Agilent technologies, Santa Clara, USA) and stable carbon isotope ratios were determined by isotope ratio mass spectrometry (Finnigan MAT 252, Bremen, Germany). Based on the isotopic difference between the respired CO2 from biochars and from soil organic carbon it was possible to calculate the proportion of biochar-derived carbon in the respired gas for every sampling date (Equation (1)) (Balesdent et al., 1998; Waldrop and Firestone, 2004). To overcome possible treatment effects we determined the control values used in Equation (1) from the gas measurements of the control treatments (A and F), assuming the same processes in the treatments as in the controls. We made Keeling plots combining the measured d13C values for the complete time series of the gas collected from the respective control columns and the reciprocal CO2 concentration (1/CO2). The y-intercept of the linear fit (R2 ¼ 0.96 for A and R2 ¼ 0.97 for F) can be interpreted as the d13C value of biologically produced CO2 during respiration (Amundson et al., 1998) (Table 1).

Fð%Þ ¼

d13 Ctreatment;corr  d13 Ccontrol  100 d13 Cbiochar  d13 Ccontrol

(1)

Mean residence times (T) for the biochars were calculated using measured carbon contents before (ct0) and after incubation (ct) combined with the calculated proportion of biochar carbon in the respiration gas assuming a first order reaction mechanism (Equation (2)) (Gregorich et al., 1996; Gleixner et al., 2002).

T ¼

ðt  t0 Þ lnðct =ct0 Þ

(2)

2.4. Phospholipid fatty acid (PLFA) extraction Phospholipid fatty acids were extracted from fresh sieved soil before incubation and from all treatments after 4 months in the greenhouse. We extracted three replicates of each treatment except of the controls (signatures A, F). There, only one sample per soil

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type was extracted to leave the other two replicates for further continuous measurements. PLFA extraction was performed after standard methods described in the literature (Bligh and Dyer, 1959; Zelles and Bai, 1993). Briefly, soils were shaken for 2 h in a mixture of chloroform, methanol and phosphate buffer. The lipid extracts (chloroform phase) were transferred to silica-filled solid phase extraction columns (SPE). Phospholipids were separated from neutral lipids and glycolipids by eluting with chloroform, acetone and methanol, respectively. The phospholipids in the methanol fraction were hydrolyzed and methylated using a methanolic KOH solution leading to phospholipid fatty acid methyl esters. Quantification of the PLFAs per soil dry weight was performed on a GC-FID system (Agilent Technologies, Santa Clara, USA) using a fused silica column (HP ultra 2, 50 m length  0.32 mm ID, 0.52 mm film thickness). The temperature program started at 140  C (1 min isotherm) followed by a heating rate of 2  C min1 to 270  C, which was held for 9 min, and followed by a final heating rate of 30  C min1 to 320  C. For peak identification retention times of standard measurements were used. Compound-specific isotope ratios of the identified PLFAs were measured by GC–IRMS (DeltaPlusXL, Thermo Finnigan, Bremen, Germany). Gas chromatographic separation was performed with the same parameters as the quantification (see above). To obtain d13C values of the PLFAs, measured isotope values were corrected for the methyl carbon added during methylation (Kramer and Gleixner, 2006). Identified PLFAs were assigned to certain microbial groups, i.e. fungi (C18:2u6,9, C18:1u9), Gram-positive bacteria (branched saturated fatty acids), Gram-negative bacteria (monounsaturated fatty acids) and bacteria in general (straight chain saturated fatty acids) (Zelles, 1997; Baath and Anderson, 2003; Waldrop and Firestone, 2004; Kramer and Gleixner, 2006; Allison et al., 2007). 2.5. Statistical evaluation Statistical evaluation of the data sets was performed with SPSS version 16.0 (SPSS Inc., Chicago, USA). For direct comparison of treatments simple t-tests were used. To test for systematic effects of the soil type, the charcoal type or any interaction of both variables in complete data sets of all treatments analyses of variance (ANOVA) were calculated. Principal component analyses using the proportion of microbial groups in the soil were performed to compare the structure of the microbial community in the different treatments and the respective initial soil samples. Statistical significance was assigned at the p  0.05 level. 3. Results 3.1. Biochar characterization Glucose-derived biochar was highly carbonized and thus thermally stable. Thermogravimetry to a temperature maximum of 850  C in an inert atmosphere led to a total mass loss of about 50% with the highest rate of volatilization at temperatures between 380 and 390  C. In contrast, the parent material, glucose, lost 86% of its initial mass under the same experimental conditions and thermal degradation occurred in several processes with maximum reaction rates already at temperatures of 200  C and 280  C, respectively. The degree of condensation in the yeast-derived biochar was much lower than that of the glucose-derived biochar, indicated by a total mass loss of 72%, which is only 10% less than that of the parent material, yeast, under the same conditions. Thermal degradation of the yeast-derived biochar already started at 200  C,

S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

reached the next maximum reaction rate at 325  C and showed a last process similar to the glucose-derived biochar degradation between 380 and 390  C. Scanning electron microscopy (SEM) showed similar structures of our model biochars (carbonaceous spheres and continuous nanopore systems) as were observed for charcoals produced from different biomass types (e.g. rice grains, oak leafs, pine needles) by hydrothermal pyrolysis (Cui et al., 2006; Titirici et al., 2007b) (Fig. 1). Infrared-spectra reveal a polar surface structure of the model biochars containing phenolic, carbonyl and hydroxyl functional groups. The aromatic structure was more pronounced for the highly condensed glucose-derived biochar, whereas the low condensation grade of the yeast-derived biochar resulted in larger proportions of saturated and unsaturated aliphatic structures (Fig. 2). Infraredspectra of charcoals produced from biomass verify hydroxyl groups, phenolic residues, carbonyl functions, aliphatic double bonds and a certain degree of aromaticity as the typical biochar structure characteristics (Titirici et al., 2007b).

1.1 1.0 0.9 C-H aromatic

Absorbance

1304

0.8 0.7

C-O-C

0.6

CH aliphatic

CH2, CH3 aliphatic C=O

0.5

C=C aromatic

0.4 OH

0.3 4500

4000

3500

3000

2500

2000

1500

1000

500

0

Wavenumber in cm-1 Fig. 2. Infrared-spectra of glucose-derived biochar (straight line) and yeast-derived biochar (dashed line).

3.2. Soil respiration and gas measurements Initial respiration rates differed strongly between the treatments (Fig. 3) but did not correlate to the initial carbon content. In arable soil, both biochar treatments (AG, AY) showed similar respiration rates to the control despite the carbon addition (p ¼ 0.64 and 0.50, respectively). In forest soil, the highest initial respiration was measured in the treatment with labile yeastderived biochar (FY), which was significantly higher (p < 0.001) than both the control (F) and the treatment with glucose-derived biochar (FG). No difference was observed between the treatment with stable glucose-derived biochar in forest soil and the respective control (p ¼ 1.00). Respiration rates strongly decreased within 4 weeks of incubation and had leveled off after 12 weeks to a constant median value of 2 mg C d1 for all treatments. No systematic differences in respiration rates were observed between the treatments, although the FY treatment showed significantly higher respiration rates at some occasions within the first 10 weeks of the experiment (i.e. weeks 4 and 10: p < 0.001 and p ¼ 0.062). Labeling with 13C led to isotopic differences of 24–31& between biochar carbon and soil organic carbon (Table 1) which was used to quantify the proportion of biochar-derived carbon in

the respired CO2. Two major differences were observed between the soil types. First, data variability as well between replicates as between repeated samplings was much higher in arable soil treatments than in forest soil treatments (p < 0.001). Second, the proportion of biochar carbon in the respiration gas was generally lower in forest soil treatments compared to arable soil treatments (p ¼ 0.025). In detail, variability between replicates for arable soil treatments were 5.4% (AG) and 3.3% (AY) on average, while standard deviations of 0.9% were observed for replicates of both forest soil treatments (FG and FY). The proportion of biocharderived carbon in the respiration gas was 28% (sd ¼ 7.9%) in the AG treatment and 22% (sd ¼ 24.3%) in the AY treatment. In forest soil 8% (sd ¼ 1.2%) of the respired carbon derived from biochar in the FG treatment and 12% (sd ¼ 3.6%) derived from biochar in the FY treatment. In the AG treatment, the proportion of biocharderived CO2 showed an increasing trend with time, reaching the maximum of 43% in week 20. The AY treatment showed the most inconsistent pattern in the composition of the respiration gas during incubation, varying between 0 and 53% biochar carbon in the gas without any regularity. In contrast, in the forest soil treatments the proportion of biochar carbon in the respiration gas

Fig. 1. SEM picture of (a) glucose-derived biochar and (b) yeast-derived biochar. Scale bar 10 mm.

S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

A AG AY

respiration rate in mg C d-1

60

F FG FY

60

50

50

40

40

30

30

20

20

10

10

0

1305

0 0

5

10

15

20

25

0

week after experiment start

5

10

15

20

25

week after experiment start

Fig. 3. Respiration rates for arable soil treatments (left) and forest soil treatments (right) including the respective controls during incubation. Error bars represent standard deviations between three replicates per treatment.

was constant at 8% for FG, while FY showed a decreasing trend from 19% in week 7 down to 9% in week 17 and later on.

3.3. Development of soil carbon stocks and mean residence times Measured respiration rates reflect temporary carbon losses and varied over time due to temperature and soil moisture variability. The total carbon budget was thus determined by elemental analysis from soil sub-samples before and after four months of incubation (Table 2). Total carbon content decreased in controls and all treatments over the incubation time. Despite different absolute numbers in the carbon budget due to the different initial carbon content of the two soil types, the relative amount of carbon remaining in the soils after biochar incubation only depended on the type of biochar added but did not depend on the soil type itself or any interaction between soil type and biochar type (Table 3). Thus, of the initially added 3% of charcoal carbon, both treatments with more stable glucose-derived biochar still contained 27% more carbon than the respective control, while both treatments with labile yeast-derived biochar still contained 23% more carbon than the respective control (Table 2). To quantify losses of biochar carbon and soil organic carbon we used the isotopic signature of the respiration gas. We normalized all losses to the respective initial carbon amounts of

Table 2 Carbon budget in g C and relative to the respective controls for all treatments before and after incubation; sd refers to standard deviation of replicated measurements. Treatment

Cinitial (g)

sd

Amount C relative to control (%)

Cfinal (g)

sd

Amount C relative to control (%)

A AG AY F FG FY

3.79 4.93 4.93 8.23 10.70 10.70

0.02 0.02 0.02 0.04 0.05 0.05

100 130 130 100 130 130

3.63 4.61 4.45 7.75 9.87 9.53

0.02 0.03 0.04 0.04 0.01 0.06

100 127 123 100 127 123

the treatments for better comparability (Fig. 4). Losses of soil organic carbon were generally smaller in the arable soil treatments compared to the respective forest soil treatments and biochar addition always increased the loss of carbon from the soil organic carbon pool (Table 4). In both soil types, soil organic carbon losses were largest when labile yeast-derived biochar was added (Fig. 4, Table 4). In these treatments, twice the amount of soil organic carbon was respired compared to the controls. Moreover, yeast-derived biochar seemed to be better degradable than glucose-derived biochar as indicated by larger biochar carbon losses in both soil types (Fig. 4), although the difference was significant only in forest soil (p ¼ 0.003, p ¼ 0.147 for arable soil). Most interestingly, normalized losses of soil and biochar carbon in the arable soil were almost identical (p ¼ 0.544), while in forest soil less biochar carbon than soil organic carbon was lost (p < 0.001). The mean residence times (Equation (2)) for biochar carbon were calculated from measured total carbon losses and the proportions of biochar carbon in the respiration gas (Equation (1)). In total, the controls lost 4% (A) and 6% (F) of their initial carbon content, treatments with glucose-derived biochar lost 7% (AG) and 8% (FG) carbon, and addition of yeast-derived biochar caused total carbon losses of 10% (AY) and 11% (FY), respectively. Consequently, mean residence times ranged between 4 (AG) and 29 (AY) years (Fig. 5). The 29 years were calculated for yeastderived biochar in arable soil and give just a rough estimate due to the huge uncertainty caused by the high variability in the detected proportion of biochar carbon in the respiration gas.

Table 3 Summary of analysis of variance (ANOVA) of the carbon budget relative to the respective controls for all biochar treatments after incubation. Parameter

Sum of squares

F-value

Significance

Soil Charcoal Soil  charcoal

0.80 56.77 0.01

1.07 75.52 0.01

0.332 <0.001 0.923

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S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

90

treatment A

AG

AY

F

FG

FY

80

mean residence time in years

0 -2 -4

% carbon lost

-6 -8 -10 -12 -14 -16 -18 -22

50 40 30 20

0

AG

Fig. 4. Losses of biochar carbon and soil organic carbon after 4 months of incubation given relative to the respective initial amounts in the treatments. Error bars reflect the uncertainties in the proportion of biochar carbon in the respiration gas used for calculation and were determined according to error propagation laws.

Glucose-derived biochar remained longer in forest soil (12 years) than in arable soil (p < 0.001), where it would be mineralized after 4 years, assuming a continuously ongoing decomposition as observed in the 4 months of incubation. For yeast-derived biochar it would take about 6 years to be mineralized in the forest soil.

3.4. Microbial community in the soils To get an estimate of microbial adaptation to the new carbon source the total amount of phospholipid fatty acids in the soils was determined before and after incubation in all treatments. As already found for the total carbon budget, biochar type was the driving parameter for any effects on the microbial community between the treatments. Arable soil generally contained smaller amounts of microorganisms than forest soil as well for the initial values as in every treatment after incubation (p < 0.001). Addition of glucose-derived biochar to both soil types caused a significant reduction of microbial biomass (p < 0.001) during incubation. In contrast, yeast-derived biochar addition did not change the PLFA content in the soils (p ¼ 0.39), which still was as high as before incubation in both soil types. We found no interaction between soil type and biochar type (p ¼ 0.15). The identified PLFAs were assigned to four main groups of microorganisms in soil, i.e. fungi, Gram-positive bacteria, Gramnegative bacteria and bacteria in general. The proportions of these groups in the microbial community were calculated for the initial soils and for all treatments after incubation (Table 5). The initial microbial community composition in both soil types was

Table 4 p-Values resulting from multiple comparison t-tests of soil organic carbon losses (normalized to the initial carbon content) for all treatments after incubation. Numbers smaller than 0.05 reflect significant differences between the treatments. A A AG AY F FG FY

60

10

soil organic carbon biochar carbon

-20

70

0.120 0.031

AG

AY

0.120

0.031 0.004

F

FG 0.001

0.004 0.005 0.001 0.018

FY

0.005 0.013

0.001

0.018 0.013 0.001

AY

FG

FY

treatment Fig. 5. Calculated mean residence times for the biochars in the different treatments. Error bars reflect the uncertainty caused by the variability of the proportion of biochar carbon in the respiration gas. They were determined according to error propagation laws.

quite similar (Fig. 6). Again, major effects of biochar addition were the same in both soil types and depended only on the biochar type (Fig. 6, Table 6). While the addition of glucosederived biochar rarely changed the composition of the soil microbial community, the yeast-derived biochar strongly promoted fungi in both soils (p < 0.001). The majority of present microorganisms belonged to the group of usually root associated Gram-negative bacteria and made up 42% (AI) and 44% (FI) of the microbial biomass. In both soils, 27% of the microbes belonged to the Gram-positive bacteria, 11% were assigned to bacteria in general and only 11% (FI) to 12% (AI) of the microbial community was made up of fungal biomass. The addition of glucose-derived biochar led to shifts along PC 2 in the principal component analyses (PCA) (Fig. 6), which only explained 4–11% of the variance and reflected non-systematic changes in the proportion of all microbial groups. In treatments with yeast-derived biochar, the proportion of fungal biomass increased by 16% in both soil types, while Gram-positive and Gram-negative bacteria decreased by 7–14%. The increase in fungal biomass was expressed in the large shifts along PC 1 of the PCA (p < 0.001) (Fig. 6), which explained 89% of the variance in forest soil and 94% in arable soil. The microbial community composition of the controls without biochar addition showed the same pattern after incubation as the initial soil samples (Table 5).

Table 5 Proportion of the amount of PLFAs assigned to different microbial groups, i.e. fungi, Gram-negative bacteria, Gram-positive bacteria and bacteria in general, before and after incubation; sd refers to standard deviation between three replicates. There was no replicate extracted for the controls (A, F). treatment

Fungi

sd

Gram() bacteria

sd

Gram(þ) bacteria

sd

Bacteria

sd

AI AG AY FI FG FY A F

11.9 10.8 28.0 11.0 10.7 27.6 12.0 10.9

0.1 0.3 0.9 0.2 0.2 0.8

41.9 41.8 30.7 43.6 37.7 28.9 41.9 39.0

0.1 2.1 0.4 0.5 0.3 0.3

26.9 25.0 18.8 26.8 29.9 20.3 26.9 27.3

0.1 2.4 0.5 0.4 0.4 0.7

11.5 13.0 15.7 10.8 13.8 16.8 11.6 14.5

0.1 0.3 0.2 0.0 0.1 0.1

S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

PC 2 2,5 2,0 1,5 FG

1,0 AG 0,5

-1,5

-1,0

-0,5

0,5

1,0

1,5

2,0

2,5 PC 1

FY AY

-0,5

Assuming biochar and soil organic carbon as only carbon sources for the soil microorganisms, the proportion of biochar carbon incorporated in the microbial biomass can be calculated. For instance, the observed enrichment in fungal biomarkers of 14.8& in the AY treatment would equal a utilization of 60% biochar carbon for fungal biomass production. In forest soil, fungi used 40% yeast-derived biochar carbon to build up their biomass. Bacteria in arable soil used between 10% and 15% glucose-derived biochar carbon as carbon source and the proportion of glucose-derived biochar carbon in Gram-negative bacteria in forest soil amounted to 13%. 4. Discussion

AI FI

1307

-1,0 -1,5

Fig. 6. Principal component analyses of the microbial community composition for both soil types. PC 1 explained 89% (forest soil) and 94% (arable soil) of the variance and was driven by the proportion of fungi and bacteria in both soil types. PC 2 explained 11% (forest soil) and 4% (arable soil) of the variance.

Finally, we determined compound-specific isotope ratios of the PLFAs to identify the major carbon sources of the different groups of soil microorganisms (Appendix 1). PLFA enriched in 13 C compared to the initial value indicated the uptake of biochar carbon by the respective microbial group, while unchanged d13C values prove the continuous uptake of soil organic carbon. Control treatments generally showed small shifts in all microbial groups as decomposition of soil organic carbon led to an enrichment in 13C in the remaining soil organic carbon. Although the microbial group specific enrichments somehow depended on the type of biochar added to the soils, e.g. significant enrichments of Gram-negative and Gram-positive bacteria for glucosederived biochar treatments (2.1–4.7&, 0.001 < p < 0.027) and strong yeast-derived biochar uptake by fungi in both soils (isotopic shift 9.5 and 14.8&, 0.003 < p < 0.062), several differences were observed between the soil types (Fig. 7). In contrast to arable soil, where fungi were less involved in the decomposition of glucose-derived biochar (isotopic shift ¼ 1.6&, p ¼ 0.350), in forest soil fungal biomarkers showed an average enrichment of 4.8& (p ¼ 0.417). Especially the d13C value of C18:2u6,9 increased by 8.4& (p ¼ 0.007), while other fungi remained unchanged (isotopic biomarkers (C18:1u9) shift ¼ 1.1&). Beside the obvious utilization of yeast-derived biochar by fungi in arable soil, also all bacterial groups were able to decompose this biochar to a certain extent in this soil type. Significant isotopic enrichments were measured in all bacterial biomarkers (p  0.002). In forest soil, Gram-negative bacteria were the only microbial group beside fungi that took up yeastderived biochar carbon in a significant amount (p ¼ 0.001).

Table 6 Summary of analysis of variance (ANOVA) of the principal component analyses of microbial community composition. Parameter

Sum of squares

PC 1

Soil Charcoal Soil  Charcoal

0.00 15.94 0.00

F-value 0.00 7.97 0.00

Significance 1.000 <0.001 0.741

PC 2

Soil Charcoal Soil  Charcoal

0.00 10.87 0.44

0.00 13.92 0.57

1.000 0.001 0.581

It has been observed in several studies that biochar addition to soils improved soil fertility and thus increased crop yields on agricultural lands (Marris, 2006; Chan et al., 2007). This fertilizer effect could be explained by a stimulation of soil microorganisms that consequently led to an increased recycling of nutrients trapped in biomass residues. The fertilizer function is additionally supported by an increased water retention and cation exchange capacity of the soils caused by the huge surface area of the biochars. An aspect of biochar amendments that got more attention recently is that additional photosynthetically fixed carbon is brought into the soil, where it could contribute to longer term carbon storage and thus mitigates increasing atmospheric CO2 concentrations (Schmidt and Noack, 2000; Lehmann, 2007). However, little is known about turnover times of biochars in soils and a long-term storage function contradicts the fertilizer function of biochars that requires a certain biodegradability of the biochar material. The major question to solve will be to design biochars that fulfil both functions with the best possible compromise. Biochar structure, e.g. the condensation grade, could easily be managed in production processes, but studies are necessary to check, whether the condensation grade is a tool to control the turnover of biochars in soils. In our greenhouse experiment we investigated the consequences of the addition of biochar with different condensation grades (high ¼ glucose-derived, low ¼ yeast-derived) to two soil types (arable and forest soil) for inherited carbon stocks and for soil microbial communities. Soil respiration measurements indicated a strong stimulation of soil microorganisms by yeast-derived biochar in the beginning of the incubation, whereas treatments that received glucosederived biochar showed respiration rates similar to the respective controls. After 12 weeks no differences between any treatments could be observed anymore and respiration rates had generally decreased to very low levels. As a result of the increased respiration total carbon losses were always higher in treatments that received biochar than in the controls. The type of biochar clearly showed a systematic influence on soil organic carbon losses. Yeast-derived biochar, the model compound for easily degradable biochar stimulated soil microorganisms most in both soils leading to soil organic carbon losses twice as high as in the controls, whereas glucose-derived biochar led to intermediate soil organic carbon losses in both soil types. Increasing soil organic carbon losses caused by charcoal input have been observed also in other studies (Wardle et al., 2008). The mechanism behind still has to be resolved. However, even if carbon turnover was increased by the biochar treatments in our experiment we want to point out that the total carbon content in the soil still was 27% higher in glucose-biochar treatments and 23% in yeast-biochar treatments compared to the controls at the end of our experiment regardless of the soil type. Calculated mean residence times of 4–29 years lead to the conclusion that

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S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

18

18 FG

AG

isotopic shift in ‰ (treatment - inital)

16

AY

16

FY F

A 14

14

12

12

10

10

8

8

6

6

4

4

2

2

0

0 fungi

gram(+)

gram(-)

bacteria

fungi

gram(+)

gram(-)

bacteria

Fig. 7. Isotopic shift of PLFA biomarkers (treatment after incubation – initial values) for certain microbial groups, i.e. fungi, Gram-negative bacteria, Gram-positive bacteria and bacteria in general. Error bars reflect the standard deviation in isotopic shift within a group of microorganisms.

biochars produced by hydrothermal pyrolysis would probably add to the decadal soil carbon pool. The fast decrease in soil respiration rates during incubation indicated that microbial stimulation and thus decomposition processes remarkably slowed down after 4 months. Concluding from this observation, we assume that any fertilizer effect of these biochars will be biggest directly after biochar addition to the soils and that the carbon storage function will gain importance on the longer term. Mean residence times given here represent results from the initial phase of biochar degradation and might increase with time. As has been shown for the total carbon stocks, also the reaction of soil microorganisms on biochar addition was driven by the biochar type and largely independent of the soil type. Yeast-derived biochar strongly increased the proportion of fungi in both soils, which consequently turned out as the microbial group that most utilized this type of biochar. Glucose-derived biochar was used as carbon source for the build up of bacterial biomass. Bacteria in arable soil, probably better adapted to carbon limitation events and more complex remaining soil carbon, respired more biochar carbon than bacteria in forest soil. Consequently, calculated mean residence times of glucosederived biochar in arable soil were slightly shorter than in forest soil. Microorganisms in the forest soil seemed to be less specialized on certain carbon sources. The adaptation of certain microbial groups to biochar degradation was less pronounced than in arable soil. To finally answer the questions that should be solved with our experiment:

Inherited soil microorganisms adapted to the new carbon source and utilized both types of biochar. The biochar type determined, which group of microorganisms were involved in the decomposition process. Yeast-derived biochar strongly promoted fungi, while glucose-derived biochar primarily was utilized by Gram-negative bacteria. 3) Is the stability of these biochars tuneable by varying the condensation grade and chemical composition of the biochar? Our results clearly show that the type of biochar, i.e. condensation grade and chemical structure, is the main driver for all differences observed between our treatments. All patterns observed for the biochar types were the same in both soils. We thus conclude that the condensation grade and the chemical structure of biochars produced by this method could serve as ‘‘tuning parameter’’ to design biochars that act as fertilizers but simultaneously add to the soil carbon pool on a decadal time scale. In our current experiment we manipulated the condensation grade and the nitrogen content of the biochars with promising results. Several other elements (phosphorus, sulphur, cations) could be introduced to the biochar structure helping to fill special nutrient demands of arable lands. Further studies are necessary to design the best possible soil amendments and to investigate the long-term behavior of these biochars in natural systems.

Acknowledgements 1) How stable are biochars produced by this method in different soil? Biochars produced by hydrothermal pyrolysis would add to the decadal soil carbon pool. 2) How do inherited soil microorganisms react on the addition of such biochars?

This investigation was financially supported by the Max Planck Society within the scope of the EnerChem project house. We thank Maria M. Titirici for her help with SEM measurements at the Max Planck Institute of Colloids and Interfaces in PotsdamGolm. Valerian Ciobota and Petra Roesch kindly recorded the Infrared-spectra at the Institute of Physical Chemistry of the Friedrich Schiller University in Jena.

S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

1309

Appendix 1 Amounts of identified PLFAs in mg g1 soil dw and d13C values in & in initial soils, all treatments and the controls after incubation. Standard deviations are given in parentheses. Source specific summaries can be found at the end of each section. AI (mg g1 dw)

AG (mg g1 dw)

AY (mg g1 dw)

A (mg g1 dw)

PLFA

Source

C14:0 br C14:0 C15:1 C15:0 br C15:0 br C15:0 C16:0 br C16:1 C16:0 br C16:1 C16:1 C16:1 C16:0 C17:0 br C17:1 C17:0 br C17:0 br C17:0 br C17:0 br C17:0 br C17:1 C17:1 C17:0 C18:0 br C18:0 br C18:0 br C18:2u6,9 C18:1u9 C18:1u11 C18:1 C18:0 C18:0 cyc C19:0 br C19:0 br C18:0 cyc C20:1u9 C20:0

Gram(þ) Bacteria Gram() Gram(þ) Gram(þ) Bacteria Gram(þ) Gram() Gram(þ) Gram() Gram() Gram() Bacteria Gram(þ) Gram() Gram(þ) Gram(þ) Gram(þ) Gram(þ) Gram(þ) Gram() Gram() Bacteria Gram(þ) Gram(þ) Gram(þ) Fungi Fungi Gram() Gram() Bacteria Gram() Gram(þ) Gram(þ) Gram() Gram() Bacteria

1.8 (0.1) 1.1 (0.1) 1.4 (0.1) 6.6 (0.6) 5.5 (0.5) 0.6 (0.0) 0.6 (0.1) 1.2 (0.1) 3.6 (0.4) 2.4 (0.2) 10.6 (0.9) 6.0 (0.5) 11.4 (1.2) 1.3 (0.1) 4.0 (0.4) 5.9 (0.5) 1.3 (0.1) 1.2 (0.1) 2.3 (0.2) 2.5 (0.2) 2.0 (0.2) 2.8 (0.2) 0.5 (0.1) 2.3 (0.2) 0.5 (0.0) 1.0 (0.1) 3.4 (0.3) 13.5 (1.4) 21.2 (2.1) 1.8 (0.1) 2.7 (0.3) 1.7 (0.2) 2.6 (0.3) 0.7 (0.0) 5.5 (0.6) 1.2 (0.1) 0.7 (0.0)

0.4 (0.2) 0.4 (0.1) 0.4 (0.2) 2.8 (1.2) 2.3 (0.9) 0.4 (0.1) 0.4 (0.1) 0.5 (0.2) 1.8 (0.7) 1.1 (0.3) 4.6 (1.2) 3.1 (0.6) 7.7 (1.5) 0.8 (0.2) 2.3 (0.6) 3.9 (0.7) 0.9 (0.1) 0.8 (0.1) 1.7 (0.4) 1.6 (0.3) 1.1 (0.3) 2.0 (0.3) 0.4 (0.1) 1.8 (0.9) 0.3 (0.1) 0.8 (0.3) 1.6 (0.3) 7.4 (1.3) 14.1 (2.2) 1.2 (0.1) 2.1 (0.4) 1.3 (0.2) 1.8 (0.6) 0.6 (0.1) 4.5 (0.5) 0.7 (0.2) 0.4 (0.0)

0.7 (0.2) 0.7 (0.1) 0.6 (0.1) 4.3 (0.7) 3.1 (0.5) 0.6 (0.1) 0.4 (0.1) 0.6 (0.1) 2.1 (0.5) 1.7 (0.3) 5.6 (1.1) 3.4 (0.7) 15.9 (3.3) 0.8 (0.1) 2.8 (0.6) 3.6 (0.9) 0.9 (0.1) 0.7 (0.2) 1.9 (0.3) 1.7 (0.4) 0.9 (0.2) 2.0 (0.4) 0.5 (0.1) 1.7 (0.5) 0.3 (0.1) 0.7 (0.2) 15.9 (3.3) 22.0 (4.6) 16.6 (3.9) 1.4 (0.3) 3.3 (0.8) 1.6 (0.3) 2.3 (0.7) 0.5 (0.1) 4.2 (1.0) 1.1 (0.2) 0.6 (0.1)

2.5 1.5 1.9 9.1 7.6 0.8 0.8 1.7 5.1 3.4 14.6 8.3 16.1 1.7 5.5 8.2 1.7 1.6 3.1 3.6 2.8 3.8 0.7 3.2 0.6 1.5 4.7 19.0 29.3 2.8 3.8 2.3 3.6 1.1 7.7 1.6 0.9

Sum

Gram() Gram(þ) Fungi Bacteria

61.8 39.7 16.9 16.5

36.9 22.7 9.0 11.4

42.5 25.7 37.9 21.6

85.7 55.0 23.7 23.8

d13C (&)

d13C (&)

d13C (&)

d13C (&)

26.6 (1.3) 22.6 (0.5) 23.0 (0.6) 21.7 (0.2) 19.0 (0.3) 23.0 (1.2) 22.8 (0.4) 21.4 (1.8) 22.5 (0.4) 17.1 (0.3) 21.6 (1.7) 18.7 (0.3) 17.8 (1.0)

24.6 (1.3) 24.3 (0.5) 23.6 (1.4) 21.5 (0.7) 25.9 (1.3) 25.3 (1.0) 24.5 (1.4) 25.9 (1.3) 20.8 (0.2) 24.9 (0.5) 21.3 (0.4) 23.9 (0.5)

C14:0 br C14:0 C15:1 C15:0 br C15:0 br C15:0 C16:0 br C16:1 C16:0 br C16:1 C16:1 C16:1 C16:0 C17:0 br C17:1 C17:0 br C17:0 br C17:0 br C17:0 br C17:1 C17:0 C18:0 br C18:0 br C18:0 br C18:2u6,9 C18:1u9 C18:1u11

Gram(þ) Bacteria Gram() Gram(þ) Gram(þ) Bacteria Gram(þ) Gram() Gram(þ) Gram() Gram() Gram() Bacteria Gram(þ) Gram() Gram(þ) Gram(þ) Gram(þ) Gram(þ) Gram() Bacteria Gram(þ) Gram(þ) Gram(þ) Fungi Fungi Gram()

29.4 (1.4) 28.8 (0.3) 26.6 (2.1) 25.0 (0.6) 21.2 (0.2) 27.8 (1.6) 22.5 (3.3) 27.1 (1.5) 25.2 (0.3) 21.3 (0.3) 26.1 (0.5) 20.7 (0.1) 24.8 (1.4) 27.1 (1.0) 23.9 (0.3) 18.9 (0.7) 22.3 (0.3) 22.2 (0.3) 23.5 (0.6) 24.4 (0.9) 25.5 (0.1) 21.6 (1.0) 27.3 (1.1) 31.6 (1.1) 27.1 (0.7) 24.8 (0.5)

25.0 (1.1) 19.1 (1.2)

23.7 (1.4) 19.0 (0.9) 20.5 (1.0) 18.8 (0.3) 20.8 (0.8)

24.8 (1.5) 23.0 (0.5) 17.6 (1.7) 21.1 (1.1) 20.6 (0.4) 22.4 (0.7)

24.2 (0.3)

21.2 (0.6) 21.8 (0.9) 20.2 (0.0) 20.3 (0.6) 18.7 (0.4) 20.7 (0.6) 20.6 (0.6) 24.0 (0.7)

31.0 (0.6) 24.6 (1.0) 16.7 (1.2)

23.9 (1.1) 15.4 (1.2) 13.8 (0.5) 17.6 (0.4)

26.6 (1.6) 29.7 (0.7) 27.2 (1.6) 24.7 (1.0)

22.0 (0.2) 15.4 (0.7) 22.3 (0.6) 15.9 (1.3)

26.1 (1.4)

FI (mg g1 dw) 5.1 (0.7) 1.9 (0.2) 2.4 (0.2) 10.9 (0.9) 14.8 (1.0) 0.8 (0.1) 0.9 (0.2) 1.8 (0.1) 5.4 (0.3) 4.2 (0.2) 11.8 (0.5) 8.5 (0.4) 20.5 (0.9) 2.1 (0.1) 5.5 (0.3) 11.2 (0.5) 1.9 (0.1) 1.8 (0.1) 4.2 (0.2) 4.1 (0.2) 1.5 (0.1) 5.9 (0.2) 0.7 (0.1) 3.0 (0.2) 0.7 (0.0) 1.4 (0.1) 3.5 (0.2) 25.7 (1.0) 46.7 (1.6) 2.9 (0.3) 4.8 (0.3) 3.2 (0.1) 4.8 (0.3) 1.3 (0.1) 22.9 (0.9) 2.2 (0.2) 1.0 (0.1)

FG (mg g1 dw)

FY (mg g1 dw)

F (mg g1 dw)

2.5 (0.4) 1.3 (0.2) 0.9 (0.1) 7.7 (1.2) 10.6 (1.7) 0.7 (0.1) 0.9 (0.1) 1.0 (0.2) 4.2 (0.8) 1.7 (0.3) 4.9 (0.7) 3.1 (0.4) 15.6 (2.4) 1.1 (0.1) 2.7 (0.4) 5.2 (0.9) 0.9 (0.1) 0.9 (0.1) 3.1 (0.5) 2.8 (0.4) 0.9 (0.1) 3.4 (0.5) 0.7 (0.1) 2.7 (0.5) 0.4 (0.1) 1.5 (0.3) 1.8 (0.3) 15.5 (2.6) 26.2 (3.9) 1.3 (0.1) 3.7 (0.6) 3.0 (0.4) 4.0 (0.8) 1.0 (0.1) 12.2 (2.0) 1.1 (0.2) 0.8 (0.1)

2.3 (0.1) 1.5 (0.1) 0.9 (0.0) 8.2 (0.4) 10.5 (0.6) 0.7 (0.0) 0.7 (0.0) 0.9 (0.1) 4.2 (0.2) 2.0 (0.2) 5.6 (0.4) 3.2 (0.2) 31.1 (2.9) 1.2 (0.1) 2.8 (0.2) 4.7 (0.3) 0.9 (0.1) 0.9 (0.0) 3.2 (0.2) 2.9 (0.2) 0.8 (0.0) 4.1 (0.3) 0.7 (0.1) 2.4 (0.1) 0.4 (0.0) 1.2 (0.1) 27.3 (3.4) 39.7 (4.1) 31.1 (2.7) 1.7 (0.1) 6.0 (0.5) 3.7 (0.3) 4.6 (0.3) 1.0 (0.1) 12.3 (0.9) 1.7 (0.2) 1.1 (0.1)

2.1 1.2 0.8 6.2 8.5 0.5 0.7 0.8 3.1 1.5 4.8 2.8 14.3 0.9 2.3 4.2 0.8 0.8 2.6 2.3 0.7 3.2 0.5 1.9 0.3 1.0 1.5 13.6 23.2 1.2 3.5 2.8 2.9 0.7 10.7 1.0 0.8

62.4 49.5 17.3 22.8

70.8 48.3 67.0 41.1

55.8 39.0 15.1 20.8

d13C (&)

d13C (&)

d13C (&)

d13C (&)

29.4 (0.4) 23.2 (0.9) 24.2 (0.3) 24.7 (0.3) 20.4 (0.2) 25.7 (0.5) 28.0 (1.9)

28.5 (1.5) 23.1 (0.9)

30.6 (3.4) 25.6 (1.2)

23.1 (1.0) 18.8 (0.2)

23.1 (1.2) 16.8 (0.6)

19.5 (0.8) 21.3 (0.6) 17.4 (0.9) 18.4 (0.2)

28.1 (0.3) 24.3 (0.0) 24.2 (0.2) 23.3 (0.5) 19.3 (0.3) 26.0 (0.5) 26.4 (0.9) 26.3 (0.5) 25.5 (0.1) 20.2 (0.1) 25.1 (0.3) 20.2 (0.5) 23.2 (0.2)

24.2 (1.7) 21.1 (1.1) 20.0 (1.3) 21.8 (1.3) 19.5 (0.7) 19.0 (0.4) 19.4 (0.6) 22.7 (1.2)

22.1 (0.5) 22.4 (0.6) 17.9 (1.3) 21.8 (0.4) 19.4 (0.5) 22.2 (0.5) 21.0 (0.5) 23.9 (0.6)

23.6 (2.5) 18.6 (0.2) 13.8 (0.3) 18.2 (0.4)

20.7 (1.7) 23.2 (1.0) 22.7 (0.5) 23.3 (0.2)

119.5 73.5 29.2 29.7

23.4 (0.9) 25.9 (0.5) 21.5 (0.3) 23.8 (0.1) 19.0 (1.1) 24.6 (0.4) 22.6 (0.4) 19.5 (1.3) 22.6 (0.2) 20.4 (0.2) 23.7 (0.3) 22.0 (1.6) 24.3 (0.2) 24.0 (0.3) 22.9 (1.7) 28.0 (0.5) 23.3 (0.3) 24.6 (0.2)

24.3 (1.8) 23.8 (0.9) 20.3 (0.4) 22.4 (0.7) 18.6 (1.9) 21.0 (1.1) 9.7 (0.8) 22.9 (1.6) 21.4 (1.1) 18.1 (0.1) 20.6 (1.4) 19.1 (1.1) 17.5 (1.7) 16.6 (0.8) 22.3 (1.6) 20.5 (0.6) 17.0 (2.0) 19.6 (1.3) 22.2 (0.3) 19.5 (0.5)

(continued on next page)

1310

S. Steinbeiss et al. / Soil Biology & Biochemistry 41 (2009) 1301–1310

Appendix 1 (continued ) PLFA

Source

AI (mg g1 dw)

AG (mg g1 dw)

AY (mg g1 dw)

A (mg g1 dw)

FI (mg g1 dw)

FG (mg g1 dw)

FY (mg g1 dw)

F (mg g1 dw)

C18:1 C18:0 C18:0 cyc C19:0 br C18:0 cyc C20:0

Gram() Bacteria Gram() Gram(þ) Gram() Bacteria

14.9 (0.5) 20.9 (0.7) 21.1 (0.9) 29.1 (0.8) 28.3 (0.5)

10.1 (0.8) 18.5 (0.3) 16.6 (0.4) 23.3 (1.0) 25.4 (1.0)

13.0 (2.0) 17.5 (0.3) 19.4 (0.4)

15.2 (1.3) 21.4 (1.2) 20.5 (0.6) 25.8 (0.8) 28.5 (0.8)

14.5 (1.1) 21.3 (0.5) 23.7 (0.5) 22.1 (0.9) 27.9 (0.4) 23.6 (1.0)

8.2 (2.5) 18.9 (0.5) 16.9 (0.3) 21.7 (1.4) 26.4 (0.4) 25.4 (0.1)

5.5 (1.3) 14.9 (0.3) 15.3 (0.4) 18.7 (0.2) 25.3 (0.5) 20.9 (0.6)

10.8 (1.0) 20.9 (0.4) 21.9 (0.6) 21.7 (0.9) 27.5 (0.3) 21.5 (1.0)

Average

Gram() Gram(þ) Fungi Bacteria

23.8 24.2 29.4 25.3

(4.0) (3.1) (3.2) (3.1)

17.9 (4.4) 21.4 (3.3) 27.8 (4.5) 19.7 (1.6)

(3.5) (3.2) (3.3) (1.5)

19.1 (5.1) 20.6 (4.3) 20.9 (1.8) 21.0 (3.4)

19.3 (6.2) 21.8 (3.8) 16.2 (3.4) 19.8 (3.9)

22.2 (4.4) 22.0 (3.5) 23.0 (0.4) 22.8 (2.1)

25.6 (1.2) 21.6 (1.9) 19.9 22.0 14.6 20.5

(3.3) (2.4) (1.1) (2.4)

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Plant Soil (2007) 300:9–20 DOI 10.1007/s11104-007-9391-5

MARSCHNER REVIEW

Mycorrhizal responses to biochar in soil – concepts and mechanisms Daniel D. Warnock & Johannes Lehmann & Thomas W. Kuyper & Matthias C. Rillig

Received: 19 April 2007 / Accepted: 9 August 2007 / Published online: 19 September 2007 # Springer Science + Business Media B.V. 2007

Abstract Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycorrhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycorrhizal associations are subject to management, understanding and exploiting interactions between them could be advantageous. Here we focus on biochar

Responsible Editor: Hans Lambers. D. D. Warnock : M. C. Rillig Microbial Ecology Program, Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA J. Lehmann Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853, USA T. W. Kuyper Department of Soil Quality, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands M. C. Rillig (*) Institut für Biologie, Freie Universität Berlin, Altensteinstr. 6, 14195 Berlin, Germany e-mail: [email protected]

effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreasing order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant–fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses. Keywords Biochar . Arbuscular mycorrhiza . Ectomycorrhiza . Carbon storage . Restoration . Terra preta

Introduction Pioneering studies, conducted primarily in Japan, where biochar application to soil has a long tradition (Ishii and Kadoya 1994), provided evidence that biochar can have positive effects on the abundance of mycorrhizal fungi (Table 1). Soil micro-organisms, especially arbuscular mycorrhizal fungi (AMF), in addition to ectomycorrhizal fungi (ECM) and ericoid mycorrhizal fungi (ERM), have well-recognized roles in terrestrial ecosystems (Zhu and Miller 2003; Rillig

BC Effects on AMF RC, and Spore density (S.D.) by Glomus intraradices grown in culture with Zea mays (G) ECM experiments Quantified ECM RC in different soil fractions of a Montana forest soil (F) Effect of AC on timing of mycorrhizal colonization of Quercus robur seedlings by Piloderma croceum.(G) AC effects on ability of ECM (Pisolithus tinctorus) to colonize Abies firma seedlings grown in culture (G)

BC Effects on AMF in soy bean fields (F) BC (ground vs un-ground) effects on AMF infectivity (F) BC effects on AMF (Glomus sp.) and Fusarium oxysporum RC of Asparagus officinalis roots. (G) BC effects on infectivity of indigenous AMF (G) BC effects on AMF RC of non N-fixing, and N-fixing Phaseolus vulgaris) roots. (G)

AMF experiments BC effects on AMF RC of Citrus iyo in an abandoned orchard (F) Effects of three BC types on AMF (Glomus fasciculatum) in river sand (G)

Experimental designa

H: RH Citrus Juice Sediment (C.J.) Woody: Western Spruce Bark (W.S.) ND H: RH Woody: Coconut Shell

BC: 2.0% BW

BC: 1,500 g m−2 BC: 33% BV BC : 10% and 30% BV

ND

ND

ND

ND

BC: 89.8% BV of growth substrate

BC: 2% BV

AC: 2% BW

AC: 0.3% BV

Woody: Acacia BC: Applied at a rate mangium bark of 10 l m−2 Woody: Eucalyptus BC: Applied at rates of 0, 30, 60 and 90 g BC kg−1 soil deglupta logs

H: RH

+2,900% RC, no. ECM root tips 100 cm3 soil fraction −1 RC Onset of RC +624% Onset mycorrhiza accelerated by formation 4 weeks measured in weeks ECM presence or +200% absence of host infection

RC SD in 100 ml−1 infectious propagules (IP) in 100 ml−1

Colonization by P. croceum increased drought resistance in Q. robur ND

ND

Non N-fixing: 30 g, ND 60 g: −38% 90 g: −20% N-fixing: 30 g, 60 g: NS; 90 g: +16% RC −21% SD: −5% ND IP: −38%

RC

ND

Enhanced plant pathogen resistance

ND

ND

Enhanced overall plant P nutrition

ND

+42%

Ground: +100% Un-ground: −20% 10% BC: +50% 30% BC: +69%

+300%

+540% RH +88% C.J. +75% W.S.

+610%

Vaario et al. (1999)

Herrmann et al. (2004)

Harvey et al. (1976)

Gaur and Adholeya (2000)

Yamato et al. (2006) Rondon et al. (2007)

Ezawa et al. (2002) Matsubara et al. (2002)

Saito (1990)

Ishii and Kadoya (1994) Ishii and Kadoya (1994)

Possible functions for Source ECM, ERM or AMFf

RC

RC

RC

RC

RC

RC

Type(s) of BCc or ACc applied Response variablesd Mycorrhiza responsee

BC: 800 g/m3 in 2, 4.8 m3 pits

Amouont ACb or BCb present

Table 1 Effects of biochar (BC) or activated carbon/charcoal (AC) additions on mycorrhizal fungi, separated by mycorrhizal type (arbuscular mycorrhizal fungi (AMF) ectomycorrhizal fungi (ECM), and ericoid mycorrhizal fungi (ERM), and listed in order of decreasing effect size of the mycorrhizal response variable(s)

10 Plant Soil (2007) 300:9–20

Amouont ACb or BCb present

BV, By volume; BW, By weight

G, Greenhouse; F, Field

RC

RC

Darcco G60, Fisher

+95% AC +128% AC + Glucose, or AC + Pectin

−38% in type B fungi

Presence or absence +80% of host infection by ECM fungi

ND

H: RH

Type(s) of BCc or ACc applied Response variablesd Mycorrhiza responsee

ND

ND

ND

Duclos and Fortin (1983)

Wellstedt et al. (2002)

Mori and Marjenah (1994)

Possible functions for Source ECM, ERM or AMFf

f

e

d

ND, Not determined

NS, non significant difference; effect size for response variables was calculated as ((Xtreatment −Xcontrol)/Xcontrol)×100

RC, root colonization; SD, spore density

AC is produced via one of the following activation procedures, CO2, steam, or chemical (e.g. phosphoric acid). All three processes remove remaining organic compounds and nutrients from previously pyrolyzed biomass while greatly increasing carbonyl content, yielding a porous material with an extremely high surface area and a very high sorptive capacity. Because the AC activation process begins with charred biomass, until further evidence is provided to the contrary, it is assumed that BC and AC will both act similarly as adsorbents, in the soil environment. However, AC will likely have a much greater surface area than BC (Pan and van Staden 1998). H, Herbaceous biochar; RH, Rice husk biochar

c

b

a

Effectiveness of RH BC/forest BC: 300 cm3 BC top soil mix as ECM inoculum mixed with 1 l soil. source for Shorea smithiana BC/soil mix placed in trees grown in degraded forest potting hole 25-cm deep× soil. (F) 25-cm diameter Effects of AC slurry on dissolved AC: Applied to soil as phenol concentration and Picea slurry, (250 g AC 3 l−1 water) microcosm mariana seedling growth (G) surface area=1,890 cm2 ERM experiments AC: Added to solid agar Effect of AC only, or AC and carbon source (0.5 g l−1 glucose medium at 1 g l−1 or pectin) additions on ERM RC of Vaccinium angustifolium

Experimental designa

Table 1 (continued)

Plant Soil (2007) 300:9–20 11

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2004; Read et al. 2004; Rillig and Mummey 2006). Mycorrhizal fungi are frequently included in management, since they are widely used as soil inoculum additives (Schwartz et al. 2006). With both biochar additions and mycorrhizal abundance subject to management practices, there clearly are opportunities for exploiting a potential synergism that could positively affect soil quality. While data on biochar effects on mycorrhiza are accumulating, there are several important gaps in our knowledge on these interactions. The most important gap concerns the mechanisms by which biochar might affect the abundance and functioning of mycorrhizal fungi. Therefore, the goals of this paper are to first evaluate the evidence of biochar effects on mycorrhizal associations thus far, and then to propose mechanisms for these biochar effects on mycorrhizae (primarily using examples of arbuscular mycorrhiza and ectomycorrhiza). In doing so, we also point out future research priorities (Fig. 1). To clarify the nomenclature used throughout this discussion we first provide a brief overview of biochar properties.

Fig. 1 Schematic representation of bio-char and its direct and indirect effects on mycorrhizal fungi abundance/functioning, emphasizing the hierarchical nature of effects. The numbers included in figure body correspond to mechanisms discussed in text: (1) effects on soil physio-chemical properties; (2) effects

Plant Soil (2007) 300:9–20

Biochar definition and properties Biochar is a term reserved for the plant biomassderived materials contained within the black carbon (BC) continuum. This definition includes chars and charcoal, and excludes fossil fuel products or geogenic carbon (Lehmann et al. 2006). Materials forming the BC continuum are produced by partially combusting (charring) carbonaceous source materials, e.g. plant tissues (Schmidt and Noack 2000; Preston and Schmidt 2006; Knicker 2007), and have both natural as well as anthropogenic sources. Restricting the oxygen supply during combustion can prevent complete combustion (e.g., carbon volatilization and ash production) of the source materials. When plant tissues are used as raw materials for biochar production, heat produced during combustion volatilizes a significant portion of the hydrogen and oxygen, along with some of the carbon contained within the plant’s tissues (Antal and Gronli 2003; Preston and Schmidt 2006). The remaining carbonaceous materials contain many poly-aromatic (cyclic) hydrocarbons, some of

through influences on other soil microbes; (3) interactions with plant–fungus signaling; and (4) provision of refugia from fungal grazers. Solid arrows indicate direct facilitative effects; dashed arrows indicate indirect facilitative effects

Plant Soil (2007) 300:9–20

which may contain functional groups with oxygen or hydrogen (Schmidt and Noack 2000; Preston and Schmidt 2006). Depending on the temperatures reached during combustion and the species identity of the source material, a biochar’s chemical and physical properties may vary (Keech et al. 2005; Gundale and DeLuca 2006). For example, coniferous biochars generated at lower temperatures, e.g. 350°C, can contain larger amounts of available nutrients, while having a smaller sorptive capacity for cations than biochars generated at higher temperatures, e.g. 800°C (Gundale and DeLuca 2006). Furthermore, plant species with many large diameter cells in their stem tissues can lead to greater quantities of macropores in biochar particles. Larger numbers of macropores can for example enhance the ability of biochar to adsorb larger molecules such as phenolic compounds (Keech et al. 2005). Because of its macromolecular structure dominated by aromatic C, biochar is more recalcitrant to microbial decomposition than uncharred organic matter (Baldock and Smernik, 2002). Biochar is believed to have long mean residence times in soil, ranging from 1,000 to 10,000 years, with 5,000 years being a common estimate (Skjemstad et al. 1998; Swift 2001; Krull et al. 2003). However, its recalcitrance and physical nature represent significant obstacles to the quantification of long-term stability (Lehmann 2007).

Evidence for biochar effects on mycorrhizal fungi From the experiments summarized in Table 1, it appears that the addition of biochar materials to soil often results in significant responses by both plants and mycorrhizal fungi. Tryon (1948), Matsubara et al. (2002), DeLuca et al. (2006), and Gundale and DeLuca (2006) demonstrated that biochar additions can change soil nutrient availability by affecting soil physico-chemical properties. Increases in soil nutrient availability may result in enhanced host plant performance and elevated tissue nutrient concentrations in addition to higher colonization rates of the host plant roots by AMF (Ishii and Kadoya 1994). Lastly, experiments by Matsubara et al. (2002) suggested that biochar can also increase the ability of AMF to assist their host in resisting infection by plant pathogens.

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In three of the six ECM studies and the single ERM study represented in Table 1, experiments demonstrated the effects of adding biochar in growth media on both the ability of the ECM and ERM fungi to colonize the host plant seedlings, and the overall effects on seedling growth. Additionally, the experiment conducted by Herrmann et al. (2004) showed that activated carbon (AC), which may in many cases have similar properties as biochar, affected the timing of host plant colonization by ECMF, which occurred 4 weeks earlier in the AC treatment than in the control. The other ECM related experiments evaluated the effects of biochar presence on host tree colonization rates (Harvey et al. 1976; Mori and Marjenah 1994). In these two cases, the presence of biochar corresponded with significant increases in plant root colonization by ECM. Observations made by Harvey et al. (1978, 1979) also support these results. In contrast to those experiments in Table 1 showing positive effects of biochar or AC additions on abundance of mycorrhizal fungi, a few studies observed negative effects. In these cases, it appears that the negative effects of the biochar or AC additions on AMF were largely due to nutrient effects. For example, Gaur and Adholeya (2000) found that the biochar media limited the amount of P taken up by host plants, compared to rates from plants grown in river sand or clay-brick granules, suggesting that P was less available. Additionally, Wallstedt et al. (2002) reported decreases in both bio-available organic carbon and nitrogen in their ectomycorrhizal system. An important consideration pertains to the study design of the experiments reported in Table 1. The first issue deals with the soils used in the experiments, e.g. river sand or OM-rich field soil; the other issue concerns the materials added to these soils as controls, e.g. organic matter vs biochar. Are soil biota, including mycorrhizal fungi, responding to an experimental addition of biochar simply because carbon is being added or are they responding to biochar’s unique properties? In at least two cases where data from field soils were presented, it appears that mycorrhizal fungi responded more positively to biochar additions than to additions of other types of organic material added as control (Harvey et al. 1976; Ishii and Kadoya 1994). The experiment by Matsubara et al. (2002) showed that a fresh organic amendment had fairly similar effects as biochar in increasing AMFmediated host plant resistance against Fusarium and

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that the asparagus plants reached similar mycorrhizal colonization levels with both additions. But the 9-week gap between inoculation with AMF and with Fusarium makes this aspect of the experiment somewhat difficult to evaluate. However, it is still possible that these positive responses shown by mycorrhizal fungi are determined in part by the amount of carbon in the material being added to the soil, with the expectation that the biochar is more carbon-rich than the organic matter. We may not be able to answer this question satisfactorily until experiments control for C amendment effects in the biochar treatment(s) and/or take into account the relative addition of C to soils. Work on terra preta de índio (TP) soil, the fertile Amazonian Dark Earths, has served as a major inspiration for the use of biochar as a promising soil additive promoting crop growth and carbon storage (Glaser et al. 2002; Glaser and Woods 2004; Lehmann et al. 2006; Glaser 2007). However, no published data are available on the impact of TP soils on mycorrhizal functioning. For that reason, the studies discussed above refer to short-term experiments and not to the historical, pre-Columbian Amazonian soils. TP soils are not only much richer in biochar than the surrounding soils, but also in nonpyrogenic carbon and nutrients, especially phosphorus and calcium; therefore it is likely that TP effects on mycorrhizal functioning could be beyond those of biochar addition alone.

Mechanisms At least four mechanisms could explain how biochar can lead to altered total abundance and/or activity of mycorrhizal fungi in soils and plant roots: (1) Biochar additions to soil result in altered levels of nutrient availability and/or other alterations in soil physicochemical parameters that have effects on both plants and mycorrhizal fungi. (2) Additions of biochar to soils result in alterations with effects that are beneficial or detrimental to other soil microbes, for instance mycorrhization helper bacteria (MHB) or phosphate solubilizing bacteria (PBS). (3) Biochar in soils alters plant–mycorrhizal fungi signaling processes or detoxifies allelochemicals leading to altered root colonization by mycorrhizal fungi. (4) Biochar serves as a refuge from hyphal grazers. Since a primary goal

Plant Soil (2007) 300:9–20

of this discussion is identifying mechanisms explaining the effects of biochar on mycorrhizae, with the intention of guiding attempts for developing methods to exploit them as soil management tools, and because many of the biochar effects included in Table 1 appear positive, we primarily present arguments explaining why biochar generally appears beneficial to mycorrhizae. However, as discussed previously, biochar applications do not always benefit mycorrhizal fungi (see Table 1). In these situations, one could argue that biochar, via any of our proposed mechanisms, reduces formation of mycorrhiza, e.g. by decreasing nutrient availability or creating unfavourable nutrient ratios in soils (Wallstedt et al. 2002). This negative effect could be especially prominent in cases where the biochar has a very high C/N ratio and a portion of the biochar is decomposable, leading to N-immobilization. Under such conditions, biochar could also negatively affect plant growth, e.g. as seen in Gaur and Adholeya (2000). Given the above possibilities for negative responses by both plants and mycorrhizal fungi to biochar amendments, and plants to mycorrhizal fungi (Johnson 1993), it cannot be assumed that biochar amendments will always result in a net benefit to plant productivity even though few such cases have been reported so far. A conceptual overview of the mechanisms and hypothesized pathways discussed in the following sections is provided in Fig. 1, emphasizing the hierarchical nature of contributing factors. In the following discussion it should be kept in mind that (a) mechanisms are not mutually exclusive but likely several contribute to the outcome, perhaps even with opposite effects; (b) there is little information available on which mechanism is likely the most important in any given environmental situation; and finally that (c) many mechanisms are hypothetical with most support for mechanism 1 at this time (we are presenting mechanisms below in decreasing amount of evidence). This figure therefore also serves as a roadmap for future research. Mechanism 1: Biochar changes soil nutrient availability Modifications of nutrient availability would clearly be a mechanism of primary importance for mycorrhizal fungal abundance. For example, nutrient additions might alleviate growth limitations of the fungi

Plant Soil (2007) 300:9–20

themselves in nutrient-poor soils (Treseder and Allen 2002). Additionally, altering the balance of nutrients can exert strong control over fungal root colonization, as for example known for shifts in soil N/P ratios for AMF (Miller et al. 2002). Biochar addition can result in elevated quantities of bio-available nutrients such as N, P and metal ions, in the affected soils (Tryon 1948; Lehmann et al. 2003; Gundale and DeLuca 2006; DeLuca et al. 2006), but has also been shown to lead to decreases particularly of N availability (Lehmann et al. 2003). These changes in soil nutrient availabilities, may be explained by some of the following observations. Additions of biochar to soil alters important soil chemical and physical (see below) properties such as pH (has caused both increases and decreases), and typically increase soil cation exchange capacity (CEC), and can lead to greater water holding capacity (WHC), while generally decreasing bulk density (Tryon 1948). Increases in soil pH towards neutral values (Lucas and Davis 1961), in addition to increased CEC (Glaser et al. 2002), may result in increases in bio-available P and base cations in biochar influenced soils. Additionally, Lehmann et al. (2003), Topoliantz et al. (2005), Gundale and DeLuca (2006) and Yamato et al. (2006) showed that biochar itself contained small amounts of nutrients that would be available to both soil biota (including mycorrhizal fungi) and plant roots. Lastly, DeLuca et al. (2006) showed that biochar from forest wildfire stimulated gross and net nitrification rates, most likely mediated by biochar adsorbing inhibitory phenols. This mechanism is likely specific to soils with ectomycorrhizal trees and/or ericaceous shrubs with an abundance of phenolic compounds, whereas in agricultural soils biochar may in the short term reduce ammonification and nitrification by a reduction either in N availability due to immobilization during initial decomposition of the N-poor biochar (Lehmann et al. 2006) or by a reduction in C cycling. Some of the experiments conducted to evaluate the effects of biochar upon mycorrhizae (Table 1) lend support to mechanism 1. These experiments show that additions of biochar materials generally result in the alteration of soil physico-chemical properties that may lead to increases in soil nutrient availability (measurements taken from both soil samples and plant tissues) and/or increases in root colonization by mycorrhizal fungi (Ishii and Kadoya

15

1994; Matsubara et al. 2002; Yamato et al. 2006). In a greenhouse experiment by Matsubara et al. (2002), the soil pH of treatments receiving biochar increased from 5.4 to 6.2 (10% biochar by volume) and 6.3 (30% biochar by volume). According to Lucas and Davis (1961), these pH values fall within the pH range (5.5 to 7.0) where plant nutrients are near their maximum availability in agricultural soils. Many of these alterations in soil characteristics probably occur at a micro-scale (Gundale and DeLuca 2006), and thus may only affect hyphae that are in the immediate vicinity of biochar particles. Mechanism 2: Biochar alters the activity of other micro-organisms that have effects on mycorrhizae Mycorrhization Helper Bacteria (MHB; Garbaye 1994) are capable, under specific conditions, of secreting metabolites, e.g. flavonoids (AMF) and furans (ECM), that facilitate the growth of fungal hyphae and the subsequent colonization of plant roots by ECM (Founoune et al. 2002; Duponnois and Plenchette 2003; Aspray et al. 2006; Riedlinger et al. 2006) and AM fungi (Duponnois and Plenchette 2003; Hildebrandt et al. 2002, 2006). Hildebrandt et al. (2002, 2006) have demonstrated that certain compounds (including raffinose and other unidentified metabolites) produced by strains of Paenibacillus can directly enhance the growth of AMF extraradical mycelium. Additionally, Kothamasi et al. (2006) demonstrated that other species of bacteria, such as Pseudomonas aeruginosa, can solubilize important plant nutrients, especially phosphate, making them part of a group of bacteria called phosphate solubilizing bacteria (PSB). These mineralized nutrients are then accessible to mycorrhizal fungi and eventually to the host plant. Furthermore, Xie et al. (1995) and Cohn et al. (1998) state that Rhizobium sp. and Bradyrhizobium sp. can produce compounds that induce flavonoid production in nearby plants (legumes) that may ultimately increase root colonization of plant roots by AM fungi. Biochar may serve as a source of reduced carbon compounds (either the biochar particle itself, or organic molecules adsorbed to the particle’s matrix), and/or nutrients, and as a refuge (see mechanism 4) for any biochar colonizing soil bacteria, including MHB and PSBs (Pietikäinen et al. 2000; Samonin and Elikova 2004). Increased populations of PSB and/or MHB might then indirectly benefit mycorrhizal fungi (Fig. 1).

16

Mechanism 3: Biochar alters the signaling dynamics between plants and mycorrhizal fungi or detoxifies allelochemicals The rhizosphere is a zone of intense signaling between microbes, including mycorrhizal fungi, and plant roots (Bais et al. 2004; Harrison 2005; Bais et al. 2006; Paszkowski 2006). For example, experiments conducted using both field soils and in vitro cultures show that compounds (e.g. CO2, flavonoids, sesquiterpenes and strigolactones) secreted by plant roots lead to both increased colonization of plant roots by AMF (Bécard and Piché 1989; Nair et al. 1991; Xie et al. 1995) and increased spore germination and AMF hyphal branching (Gianinazzi-Pearson et al. 1989; Akiyama et al. 2005). Additions of biochar could alter the exchange of signals in several ways, as shown in Fig. 1; however, we emphasize that most of the pertinent evidence stems from sterile in vitro culture studies with uncertain relevance to conditions in the soil. Angelini et al. (2003) demonstrated that some flavonoid signaling compounds could be either inhibitory or stimulatory to specific groups of soil biota as a function of pH. As discussed under mechanism 1, biochar additions usually increase soil pH. Hence, it is possible that these pH changes alone can lead to stimulatory effects, causing increases in fungal abundance. Sorptive properties of biochar (e.g. for hydrophobic substances), particularly higher temperature (e.g., 800°C) biochar, could also cause signaling interference in the rhizosphere: biochar could serve as signal reservoirs or as a sink, both for signaling compounds and for inhibitory compounds (allelochemicals). Recently, Akiyama et al. (2005) demonstrated that AC was capable of adsorbing AMF signaling (strigolactones) compounds from a hydroponic solution that were subsequently desorbable with acetone. Once desorbed, these compounds retained their activity and stimulate hyphal branching and growth of Gigaspora margarita. Biochar particles could adsorb signal molecules not immediately intercepted by AMF hyphae or spores, or consumed by other soil biota. Later on, these stored signal molecules could be desorbed by soil water reaching the biochar particles. After being re-dissolved into soil water, they would again be available to stimulate mycorrhizal colonization of plant roots. By functioning in this manner, biochar particles would be serving as secondary

Plant Soil (2007) 300:9–20

sources of signal molecules, acting concomitantly with MHB and plant roots. However, biochar’s capacity to adsorb signaling compounds and add as a sink could also decrease the ability of mycorrhizal fungi to colonize plant roots. If biochar permanently rather than temporarily removes signal molecules from soils, this signal sorption activity results in a net decrease in the number of signal molecules reaching mycorrhizal hyphae and spores. As a result, hyphal growth and spore germination, and ultimately fungal abundance, could actually decrease because of biochar activity. In addition to chemical signals, biochar may also adsorb compounds toxic to mycorrhizal fungi. For example, Wallstedt et al. (2002) showed that the addition of an AC slurry to an experimental soil resulted in a decreased amount of water-soluble phenols. Herrmann et al. (2004) and Vaario et al. (1999) related their results of stimulated ECM fungus colonization of roots in the presence of AC to toxin sorption. Mechanism 4: Biochar serves as a refuge for colonizing fungi and bacteria This mechanism is purely physical in nature, and therefore could function in a similar fashion for ECM, ERM, AMF and bacteria. Hyphae and bacteria that colonize biochar particles (or other porous materials) may be protected from soil predators (Saito 1990; Pietikäinen et al. 2000; Ezawa et al. 2002), which includes mites, collembola and larger (>16 μm in diameter) protozoans and nematodes. The documented physical parameters of the biochar particles themselves make this mechanism plausible. The average sizes of soil bacteria and fungal hyphae range from 1 to 4 μm and 2 to 64 μm, respectively, with many fungal hypha being smaller than 16 μm in diameter (Swift et al. 1979). Additionally, the average body-size of a soil protist is between 8 to 100 μm, while the average body size of soil micro-arthropods ranges from 100 μm to 2 mm (Swift et al. 1979). In contrast, the pore diameters in a biochar particle can often be smaller than 16 μm in diameter (Kawamoto et al. 2005; Glaser 2007; Hockaday et al. 2007). Based on the differences in the body sizes across these different organisms, it is clearly possible that many of the pores within a biochar particle are large enough to accommodate soil microorganisms, includ-

Plant Soil (2007) 300:9–20

ing most bacteria and many fungi, to the exclusion of their larger predators. Thus, the biochar would be acting as a refuge for MHB, PSB and mycorrhizal fungi. Supporting evidence for this hypothesis comes from Saito (1990), Gaur and Adholeya (2000) and Ezawa et al. (2002) who all showed that AMF readily colonize porous materials and were capable of heavily colonizing biochar particles in the soil. Lastly, Pietikäinen et al. (2000) and Samonin and Elikova (2004) showed that bacteria readily colonized biochar particles; these may include MHB and/or PSB. An important factor controlling pore size distribution is the charring temperature with higher temperatures yielding finer pores. Another major factor in determining the degree to which biochar may serve as a refuge is the anatomical structure of the biological tissues pyrolyzed to yield the biochar. Considering the effects that cell diameter alone can have on the sorptive capability of a given biochar material (Keech et al. 2005; Gundale and DeLuca 2006), it stands to reason that the cell types contained within the original plant tissues (e.g., tracheids, vessel elements or sieve cells) determine the pore sizes of the biochar. Not only the charring conditions and source material, but also subsequent interactions of biochar with soil can change porosity and pore sizes. For example, adsorption of organic matter to biochar surfaces can decrease porosity by blocking pores (Kwon and Pignatello 2005). While it seems clear that mycorrhizal fungi can use biochar as a habitat, the quantitative importance to the extraradical mycelium is not evident. This will highly depend on the biochar properties and the biochar addition rates. Nevertheless, the finer parts of the mycelium, generally the absorptive hyphae, are more vulnerable to fungal grazers (Klironomos and Kendrick 1996), and it is primarily these architectural elements that could be effectively protected within biochar particles. It would depend, then, on the extent to which these ‘protected’ fine hyphae make a substantial contribution towards nutrient uptake compared to the relatively ‘unprotected’ hyphae in the mineral and organic soil, whether this hypothesized mechanism is quantitatively important.

Conclusions and research recommendations Experimental results (Table 1) point to exciting possibilities regarding biochar and its possible syner-

17

gy with arbuscular, ericoid, and ectomycorrhizal symbioses. We have synthesized available data into several potential mechanisms of biochar effects on mycorrhizae (Fig. 1). This should serve as a springboard for testing the occurrence and relative importance of these factors/mechanisms in the soil. Based on this discussion we derive the following research recommendations: (a) Methods reporting. In many cases it is helpful to know as much detail about the experimental biochar application as possible. This should include: source material, production temperature, application rate, application method, and what material was used in the control application to account for C addition effects (and the amounts of available nutrients for both). This would facilitate comparisons among studies and help distinguish among the different mechanistic pathways; frequently these pieces of information are incomplete. (b) Management implications. None of the studies to date have examined the management context of biochar application on AMF, and this would also be an important research need, since application practices could have overriding effects on soil biota. (c) Fungal communities. Studies to date have focused on quantifying potential responses in fungal abundance measures, primarily root colonization and spore numbers (see Table 1). However, mycorrhizal fungi occur as species assemblages in ecosystems and in roots of individual plants (Johnson et al. 1992; Husband et al. 2002; Vandenkoornhuyse et al. 2003; Mummey et al. 2005). The species composition of a mycorrhizal fungal assemblage can be important to mycorrhizal functioning (e.g., van der Heijden et al. 1998). Data on this important aspect of the response of mycorrhizal fungi to biochar are not yet available, but represent an important priority for future studies. Here, we limited our discussion to mechanisms affecting abundance; however, many of the arguments presented could also be applied to explain potential shifts in mycorrhizal fungal species composition, because fungal life history strategies and responsiveness to changing soil environments vary between fungal taxa (e.g., Hart and Reader 2002; Escudero and Mendoza 2005; Drew et al. 2006). (d) Negative effects. There is a potential for negative effects on mycorrhizal fungi, as discussed above;

18

Plant Soil (2007) 300:9–20

it is therefore clearly also a research priority to define the environmental circumstances (e.g., soil nutrient content, plants species) and biochar parameters (e.g., quality and application rate) that lead to such effects. It is possible that negative or neutral effects have been under-reported. Increasing atmospheric concentrations of carbon dioxide have prompted the search for avenues of long-term sequestration of carbon, particularly in the soil (Lal 2004; Schiermeier 2006). Work on terra preta de índio soil has inspired the use of biochar as a promising soil additive promoting carbon storage (Day et al. 2005; Lehmann et al. 2006; Marris 2006; Glaser 2007). Biochar can add value to non-harvested agricultural products (Major et al. 2005; Topoliantz et al. 2005), and can promote plant growth (Lehmann et al. 2003; Oguntunde et al. 2004). Lehmann et al. (2006) estimated that a total of 9.5 billion tons of carbon could potentially be stored in soils by the year 2100 using a wide variety of biochar application programs. Once equipped with a better understanding of this potential synergism and the mechanisms that drive it, we could utilize biochar/mycorrhizae interactions for sequestration of carbon in soils to contribute to climate change mitigation. This interaction could also be harnessed for the restoration of disturbed ecosystems, the reclamation of sites contaminated by industrial pollution and mine wastes, increasing fertilizer use efficiencies (with all associated economic and environmental benefits) and the development of methods for attaining increased crop yields from sustainable agricultural activities. References Akiyama K, Matsuzaki K-I, Hayashi H (2005) Plant sesquiterpenes induce hyphal branching in arbuscular mycorrhizal fungi. Nature 435:824–827 Angelini J, Castro S, Fabra A (2003) Alterations in root colonization and nodC gene induction in the peanutrhizobia interaction under acidic conditions. Plant Physiol Biochem 41:289–294 Antal MJ Jr, Grønli M (2003) The art, science, and technology of charcoal production. Indust Engin Chem Res 42:1619–1640 Aspray TJ, Eirian Jones E, Whipps JM, Bending GD (2006) Importance of mycorrhization helper bacteria cell density and metabolite localization for the Pinus sylvestris– Lactarius rufus symbiosis. FEMS Microbiol Ecol 56:25–33 Bais HP, Park SW, Weir TL, Callaway RM, Vivanco JM (2004) How plants communicate using the underground information superhighway. Trends Plant Sci 9:26–32

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19 Krull ES, Skjemstad JO, Graetz D, Grice K, Dunning W, Cook G, Parr JF (2003) 13C-depleted charcoal from C4 grasses and the role of occluded carbon in phytoliths. Org Geochem 34:1337–1352 Kwon S, Pignatello JJ (2005) Effect of natural organic substances on the surface and adsorptive properties of environmental black carbon (char): pseudo pore blockage by model lipid components and its implications for N2probed surface properties of natural sorbents. Env Sci Technol 39:7932–7939 Lal R (2004) Soil carbon sequestration to mitigate climate change. Geoderma 123:1–22 Lehmann J (2007) Bio-energy in the black. Frontiers in Ecology and the Environment 5:381–387 Lehmann J, Da Silva JP Jr, Steiner C, Nehls T, Zech W, Glaser B (2003) Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant Soil 249:343–357 Lehmann J, Gaunt J, Rondon M (2006) Biochar sequestration in terrestrial ecosystems – a review. Mitig Adapt Strat Global Change 11:403–427 Lucas RE, Davis JF (1961) Relationships between pH values of organic soils and availabilities of 12 plant nutrients. Soil Sci 92:177–182 Major J, Steiner C, Ditommaso A, Falcão NP, Lehmann J (2005) Weed composition and cover after three years of soil fertility management in the central Brazilian Amazon: compost, fertilizer, manure and charcoal applications. Weed Biol Manag 5:69–76 Marris E (2006) Black is the new green. Nature 442:624–626 Matsubara Y-I, Hasegawa N, Fukui H (2002) Incidence of Fusarium root rot in asparagus seedlings infected with arbuscular mycorrhizal fungus as affected by several soil amendments. J Jpn Soc Hortic Sci 71:370–374 Miller RM, Miller SP, Jastrow JD, Rivetta CB (2002) Mycorrhizal mediated feedbacks influence net carbon gain and nutrient uptake in Andropogon gerardii. New Phytol 155:149–162 Mori S, Marjenah (1994) Effect of charcoaled rice husks on the growth of Dipterocarpaceae seedlings in East Kalimantan with special reference to ectomycorrhiza formation. J Jap Forestry Soc 76:462–464 Mummey DL, Rillig MC, Holben WE (2005) Neighboring plant influences on arbuscular mycorrhizal fungal community composition as assessed by T-RFLP analysis. Plant Soil 271:83–90 Nair MG, Safir GR, Siqueira JO (1991) Isolation and identification of vesicular–arbuscular mycorrhiza-stimulatory compounds from clover (Trifolium repens) roots. Appl Environ Microb 57:434–439 Oguntunde PG, Fosu M, Ajayi AE, Van De Giesen ND (2004) Effects of charcoal production on maize yield, chemical properties and texture of soil. Biol Fert Soils 39:295–299 Pan MJ, Van Staden J (1998) The use of charcoal in in-vitro culture – A review. Plant Growth Regul 26:155–163 Paszkowski U (2006) A journey through signaling in arbuscular mycorrhizal symbioses. New Phytol 172:35–46 Pietikäinen J, Kiikkilä O, Fritze H (2000) Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus. Oikos 89:231–242

20 Preston CM, Schmidt MWI (2006) Black (pyrogenic) carbon: A synthesis of current knowledge and uncertainties with special consideration of boreal regions. Biogeosciences 3:397–420 Read DJ, Leake JR, Perez-Moreno J (2004) Mycorrhizal fungi as drivers of ecosystem processes in heathland and boreal forest biomes. Can J Bot 82:1243–1263 Riedlinger J, Schrey SD, Tarkka MT, Hampp R, Kapur M, Fiedler H-P (2006) Auxofuran, a novel metabolite that stimulates the growth of fly agaric, is produced by the mycorrhiza helper bacterium Streptomyces strain AcH 505. Appl Environ Microb 72:3550–3557 Rillig MC (2004) Arbuscular mycorrhizae and terrestrial ecosystem processes. Ecol Lett 7:740–754 Rillig MC, Mummey DL (2006) Mycorrhizas and soil structure. New Phytol 171:41–53 Rondon M, Lehmann J, Ramírez J, Hurtado MP (2007) Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with biochar additions. Biol Fert Soils 43:699–708 Saito M (1990) Charcoal as a micro habitat for VA mycorrhizal fungi, and its practical application. Agric Ecosyst Environ 29:341–344 Samonin VV, Elikova EE (2004) A study of the adsorption of bacterial cells on porous materials. Microbiology 73:810–816 Schiermeier Q (2006) Putting the carbon back. Nature 442:620–623 Schmidt MWI, Noack AG (2000) Black carbon in soils and sediments: Analysis, distribution, implications and current challenges. Global Biogeochem Cy 14:777–793 Schwartz MW, Hoeksema JD, Gehring CA, Johnson NC, Klironomos JN, Abbott LK, Pringle A (2006) The promise and the potential consequences of the global transport of mycorrhizal fungal inoculum. Ecol Lett 9:501–515 Skjemstad JO, Janik LJ, Taylor JA (1998) Non-living soil organic matter: What do we know about it? Aust. J Exp Agr 38:667–680 Swift RS (2001) Sequestration of carbon by soil. Soil Sci 166:858–871

Plant Soil (2007) 300:9–20 Swift MJ, Heal OW, Anderson JW (1979) Decomposition in terrestrial ecosystems. University of California Press, Berkeley Topoliantz S, Ponge J-F, Ballof S (2005) Manioc peel and charcoal: a potential organic amendment for sustainable soil fertility in the tropics. Biol Fert Soils 41:15–21 Treseder KK, Allen MF (2002) Direct nitrogen and phosphorus limitation of arbuscular mycorrhizal fungi: a model and field test. New Phytol 155:507–515 Tryon EH (1948) Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecol Monogr 18:81–115 Vaario LM, Tanaka M, Ide Y, Gill WM, Suzuki K (1999) In vitro ectomycorrhiza formation between Abies firma and Pisolithus tinctorius. Mycorrhiza 9:177–183 Vandenkoornhuyse P, Ridgway KP, Watson IJ, Fitter AH, Young JPW (2003) Co-existing grass species have distinctive arbuscular mycorrhizal communities. Mol Ecol 12:3085–3095 Van der Heijden MG, Klironomos JN, Ursic M, Moutoglis P, Streitwolf-Engel R, Boller T, Wiemken A, Sanders IR (1998) Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity. Nature 396:69–72 Wallstedt A, Coughlan A, Munson AD, Nilsson MC, Margolis HA (2002) Mechanisms of interaction between Kalmia angustifolia cover and Picea mariana seedlings. Can J For Res 32:2022–2031 Xie Z-P, Staehelin C, Vierheilig H, Wiemken A, Jabbouri S, Broughton WJ, Vogeli-Lange R, Boller T (1995) Rhizobial nodulation factors stimulate mycorrhizal colonization of nodulating and nonnodulating soybeans. Plant Physiol 108:1519–1525 Yamato M, Okimori Y, Wibowo IF, Anshiori S, Ogawa M (2006) Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Sci Plant Nutr 52:489–495 Zhu YG, Miller RM (2003) Carbon cycling by arbuscular mycorrhizal fungi in soil–plant systems. Trends Plant Sci 8:407–409

Impact of Biological Growths (personal communication D. Day 2005)

- AM Fungi lifespan of ~3 weeks - Glomalin lifespans averages 24 years, carbon in aggregates can be shorter but still ~18 years. (300x the life of the fungi - Total Soil Organic Carbon ~1500Gt - With 7% of SOC =carbon from glomalin (CFG), = ~105Gt (Nichols) With ~32% of SOC =carbon in aggregates resulting from glomalin, = ~480Gt (Nichols) - An amount directly tied to AM Fungi and glomalin growth = ~31Gt of the carbon from glomalin and carbon resulting from glomalin (CRFG), classed as in the annual pool of flux. - CFG/CRFG probably does not rise linearly with glomalin growth but probably does increase as 50% of the total increase in AM fungi rise. - There are 93.5M km2 of biologically active land (UNEP) then ~334ton km-1 yr-1 of CFG/CRFG are in annual flux. - No till studies in the U.S. have found that soil carbon increases (mid level results) at 163 ton km-1 yr-1. - Assuming charcoal addition can provide a 200% increase in AM fungi growth (Low end of Ishii's findings) - And at 50%, doubles CFG production to 334 ton km-1 yr-1 - If 33% of the land were dedicated to energy crops and and converted to hydrogen or other fuel (7% yield @ ~2.5x107j kg-1), replacing coal (5.8x106j kg-1), and would replace 219 ton C km-1 of fossil C with C from bio-energy production. - Then 2.2 x10E6 km2 (2.0% of the earth's biologically active land) would need to be treated once every 3 yrs with a ton per hector with low temp char (or equivalent nutient enhanced charcaol) and using notill farming to create a sink to offset the 1.7Gt buildup. - A 400% AM fungi increase, then we would need to treat 1.5x10E6 km2 (1.6% of the earth biologically active land or 2.8 times the size of France). It is possible these amounts are not required annually since there is a significant carry over benefit from year to year. Ogawa (Japan) recommends only once every three years.

Environ Sci Pollut Res (2009) 16:1–9 DOI 10.1007/s11356-008-0041-0

AREA 1.2 • CHEMICALS IN SOILS/SEDIMENTS • RESEARCH ARTICLE

Reduction of nitrogen loss and Cu and Zn mobility during sludge composting with bamboo charcoal amendment Li Hua & Weixiang Wu & Yuxue Liu & Murray B. McBride & Yingxu Chen

Received: 28 December 2007 / Accepted: 10 August 2008 / Published online: 27 August 2008 # Springer-Verlag 2008

Abstract Background, aim, and scope Composting is an effective treatment process to realize sludge land application. However, nitrogen loss could result in the reduction of nutrient value of the compost products and the stabilization effect of composting on heavy metal concentration and mobility in sludge has been shown to be very limited. Materials and methods Laboratory-scale experiments were carried out to investigate the effects of bamboo charcoal (BC) on nitrogen conservation and mobility of Cu and Zn during sludge composting. Results The result indicated that the incorporation of BC into the sludge composting material could significantly reduce nitrogen loss. With 9% BC amendment, total nitrogen loss at the end of composting decreased 64.1% compared with no BC amendment (control treatment). Mobility of Cu and Zn in the sludge may also have been lessened, based on the decline in diethylenetriaminepentaacetic acid-extractable Cu and Zn contents of composted sludge by 44.4% and 19.3%, respectively, compared to metal extractability in the original material. Discussion Ammonia adsorption capability of BC might be the main reason for the retention of nitrogen in sludge composting materials. Decrease of extractable Cu2+ and

Responsible editor: Hailong Wang L. Hua : W. Wu (*) : Y. Liu : Y. Chen College of Environmental and Resource Science, Zhejiang University, Hangzhou 310029, China e-mail: [email protected] M. B. McBride Department of Crop and Soil Science, Cornell University, Ithaca, NY 14853, USA

Zn2+ in the composting material mainly resulted from the adsorption of both metals by BC. Conclusions Incorporation of BC into composting material could significantly lessen the total nitrogen loss during sludge composting. Mobility of heavy metals in the sludge composting material could also be reduced by the addition of BC. Recommendations and perspectives Bamboo charcoal could be an effective amendment for nitrogen conservation and heavy metal stabilization in sludge composts. Further research into the effect of BC-amended sludge compost material on soil properties, bioavailability of heavy metals, and nutrient turnover in soil needs to be carried out prior to the application of BC-sludge compost in agriculture. Keywords Amendment . Bamboo charcoal . Mobility of Cu and Zn . N conservation . Sludge composting Abbreviations BC Bamboo charcoal FBC Fresh bamboo charcoal CBC Composted bamboo charcoal TOM Total organic matter TOC Total organic carbon

1 Background, aim, and scope At least 15 million tons (78% water content) of municipal sewage sludge are produced annually in China. Due to the absence of sound treatment methods, large amounts of sludge have been stockpiled at temporary suburban storage sites. Many people regard land application as a costeffective method for the disposal and beneficial use of

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sludge (Sigua et al. 2005; Su et al. 2007). However, the presence of potentially toxic chemicals such as heavy metals in sludge could pose risks to the environment and human health (Illera et al. 2000; Hseu 2006). Composting is regarded as an effective treatment process to suppress pathogenic organisms and stabilize the organic material in sewage sludge (Fang and Wong 1999; Hernández et al. 2006). However, the stabilization effect of composting on heavy metal mobility in sludge has been shown to be very limited (Amir et al. 2005; Liu et al. 2007). On the other hand, nutrient loss is an unavoidable problem during the composting of organic waste. This is especially the case for nitrogen, the most essential fertilizer nutrient for crop production in many situations (Cooperband and Middleton 1996; Rao Bhamidimarri and Pandey 1996). According to previous research, total nitrogen (TN) loss during the course of composting organic waste ranged from 16% to 76% (Barrington et al. 2002; Raviv et al. 2002). Substantial loss of nitrogen results in the reduction of nutrient value of compost products. Among all practicable nitrogen conservation measures, an amendment was thought to be the most efficient method to reduce nitrogen loss during composting. For example, alum, peat, and zeolite amendments have been used to reduce ammonia volatilization during composting (Bernal et al. 1993; Kithome et al. 1999). Lime and coal fly ash have also been applied as amendments to reduce the mobility of heavy metals in composting mixtures (Fang and Wong 1999; Qiao and Ho 1997). Nevertheless, low efficiency, potentially negative influence on soil pH, and high cost are factors that have prevented these amendments from being adopted broadly in composting technology. Bamboo charcoal (BC) is one kind of manufactured biocharcoal, a plentiful residual byproduct of the bamboo processing industry. BC has a highly microporous physical structure. The porosity is about five times greater and the absorption efficiency ten times higher than that of wood charcoal (Zhang 2001). Bamboo charcoal may be an ideal amendment for nutrient conservation and heavy metal stabilization due to its excellent adsorption capability. Recent research found that biocharcoals could act as soil

fertilizers or conditioners to increase crop yield and plant growth by supplying and retaining nutrients (Glaser et al. 2000; Major et al. 2005; Steiner et al. 2007). However, there has been no research to date on the potential application of bamboo charcoal in nutrient conservation and heavy metal stabilization during sludge composting. The main objectives of this study, therefore, are to investigate the potential capability of BC to stabilize heavy metals and retain nitrogen during sludge composting and to clarify the possible mechanisms related to these functions. We assume that the results of this study will provide practical information to guide the exploitation of a novel compost amendment in agricultural applications.

2 Materials and methods The sewage sludge was collected from Fuyang wastewater treatment plant located in a suburb of Hangzhou city, China. It treats more than 100,000 m3 of wastewater annually and produces about 90 tons day−1 of sludge (80% water content). The bamboo charcoal particles used in this study were purchased from the Yaoshi CharcoalProduction Company located in Hangzhou. Rapeseed marc was purchased from a local farm, which was used as a bulking agent in sludge composting due to its higher bulk density and lower moisture content. Characteristics of sludge, bamboo charcoal, and rapeseed marc are listed in Table 1. Cu and Zn were chosen as sludge metals for study, because they are quantitatively prevalent metals in sludges and are known to have higher bioavailability than less soluble metals such as Pb and Cr according to previous studies (Oliveira et al. 2007; Dai et al. 2007). 2.1 Composting and sampling Composting was carried out in a tank with dimensions of 1.0×0.4×1.0 m and a volume of approximately 0.4 m3. There were six different treatments. The stock material consisted of 180-kg sewage sludge and 20-kg rapeseed

Table 1 Characteristics of sludge, rapeseed marc, and bamboo charcoal Sludge Total nitrogen (%) Organic matter (%) Total phosphorus (%) pH Water content (%) Total Zn (mg kg−1) Total Cu (mg kg−1) C/N

ND No detection

Rapeseed marc 2.31±0.15 34.32±2.26 1.5±0.10 7.41±0.15 78.72±2.2 1,530±56 270±15 16±1

Total nitrogen (%) Organic matter (%) Total phosphorus (%) pH Water content (%) Total Zn (mg kg−1) Total Cu (mg kg−1) C/N

Bamboo charcoal 1.01±0.05 73.62±4.22 0.45±0.02 8.23±3.55 8.30±4.24 ND ND 129±5

Pyrolysis temperature (°C) Density (g cm−3) Specific surface (m2 g−1) pH Water content (%) Total Zn (mg kg−1) Total Cu (mg kg−1) C/N

600 0.75±0.04 330±24 7.32±0.1 10±1 0.45±0.03 ND 356±10

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marc with 0%, 1%, 3%, 5%, 7%, 9% (w/w) of BC incorporated into the stock material. These BC treatments are labeled as control, 1% BC, 3% BC, 5% BC, 7% BC, and 9% BC. Aeration was ensured by forced ventilation during the first 3 weeks of composting and by turning the pile over manually during the remaining incubation time. Temperature of the composting pile was recorded daily using temperature sensors. Each sampling was carried out in triplicate. All together, six times of samplings were performed. 2.2 Chemical analyses Total nitrogen was measured by the Kjeldahl digestion method (Hernández et al. 2006). Total organic matter was determined by potassium dichromate (K2Cr2O7) and sulfuric acid (H2SO4) oxidation (Dai et al. 2007). Pile mass was based on the total mass of all the composting material including sludge, bamboo charcoal, and rapeseed marc at the initial and the final composting stages. Based on the N concentration and the total pile mass before and after composting, the actual N loss could be obtained. The actual N amount was calculated by multiplying the N concentration and the total pile mass of the composting material. The actual N loss was the difference between the initial N amount and the final N amount in the composting materials. Boehm titration (Boehm 1994) was used to quantify various surface functional groups on the fresh BC (FBC) particle and composted BC (CBC; separated from mixed final composting materials) particle. A solar Thermo MkII6 atomic absorption spectrometer with deuterium background corrector was used to determine the contents of heavy metal in compost samples. To determine the total concentration of heavy metals, 0.5 g of sample was digested in a 20-mL mixture of nitric, hydrochloric, and hydrofluoric acid (in the ratio 1:1:2; Scancara et al. 2000). Diethylenetriaminepentaacetic acid (DTPA)-extractable metal contents were obtained by mechanically shaking the compost samples at a 1:5 solid to extractant ratio (w/v) for 2 h with 0.005 M DTPA+0.1 M triethanolamine solution buffered at pH 7.3 (Page et al. 1982). 2.3 Cu2+, Zn2+, and NH4+ adsorption by fresh BC and composted BC Twenty milliliters of Cu2+, Zn2+ solutions with the concentrations of 200–2,000 mg L−1, or NH4+ solutions with concentrations of 2–10 mg L–1 were added to 0.2 g of FBC/ CBC in order to find out if the change of surface characteristic would result in the change of retaining capability of bamboo charcoal to these ions. Copper sulphate pentahydrate (CuSO4·5H2O), zinc sulphate heptahydrate (ZnSO4·7H2O), and ammonium chloride (NH4Cl)

3

were used as stock chemicals in the BC adsorption experiments and the concentrations were dependent on the actual concentration in sludge of these ions. The solutions with BC particle were then kept in a thermostatic shaker at 250 rpm and 25°C for 48 h to achieve equilibrium. Afterwards, each sample was filtered to separate the FBC/ CBC particles from solution. These particles were analyzed to determine amounts of Cu Zn and ammonium adsorbed and used for desorption tests. For the desorption experiment, the residual FBC or CBC samples collected from the adsorption experiment were extracted by 0.05 M DTPA solution to measure the strength of Cu2+ and Zn2+ retention on FBC/CBC. The detection process was the same as described in the adsorption experiment. The heavy metal retention capability was expressed as the percent of the total Cu and Zn in BC that was retained after extracting by DTPA. The FBC/CBC particles which had already reached ammonium adsorption equilibrium were extracted with 30 mL of 0.01 M CaCl2 (Nishantha Fernando et al. 2005) using the same conditions as described for adsorption. The ammonium retention capability was expressed by the same approach described for metals. In the adsorption–desorption test, triplicated sampling were implemented for the analysis of the bamboo charcoal in initial composting material and final composting material. 2.4 Data analysis All data were expressed as means and standard deviations compared statistically by Tukey’s t test at the 5% level with SPSS11.5 (SPSS for windows, version 11.5, USA). Any differences between values with p>0.05 are not considered to be statistically significant.

3 Results 3.1 Chemical changes of material during composting Temporal trends of the temperature within the composting materials were quite similar regardless of the level of BC amendment (Fig. 1). The compost temperature rose to 55°C within 5 days and remained above 55°C for around 7 days. Afterwards, the compost temperature gradually declined and reached ambient temperature in 30 days. Finally, the compost went into maturation stage until composting was completed. Total organic matter of the composting materials experienced a relatively fast decline at the early stage of composting and then decreased steadily over time. There were no significant differences in total organic matter of the composting materials among different treatments except in the early stage. By the end of the experiment, about 30% of the initial total organic matter had mineralized (Fig. 2). In

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Fig. 1 Change of temperature during the course of composting

contrast, trends in the change of TN in composting materials over the composting process varied with treatment. TN concentrations in the composting material with lower BC amendment (<3%) decreased during the thermophilic phase and then increased afterwards. When the BC amendment rose to more than 5%, TN concentrations in the composting material increased over the entire composting process (Fig. 3). A first-order kinetic equation was used to calculate the potentially mineralizable C (C0):
Cm ¼ C0 1
e
kt where Cm (mg C/kg) is the organic C mineralized at any specific time, t (days), and k is the first-order rate constant. Similarly, the increase of N with time could be expressed as a first-order kinetics equation. Overall, the TN loss (based on mass balance) in the composting material

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Fig. 3 Change of total nitrogen concentration during the course of composting

decreased with an increasing amount of BC amendment. The highest TN loss (674 g) was found in composting material with no BC amendment, whereas TN loss in the treatment with 9% BC amendment was only 240 g, a difference of more than 64% (Table 2). Boehm titration is one of the most widely used methods to quantify acidic groups in charcoal. Based on this method, the amount of total acid groups of BC underwent a significant change during the course of composting, which increased quickly in the first 4 weeks and became stable after 28 days of composting. Among all acidic groups, the amount of carboxylic groups increased most. As shown in Table 3, the amount of carboxylic groups of BC increased up to 0.69 mmol g−1 at the end of composting, which was about 2.4 times higher than that of the original value (0.29 mmol g−1). However, the amounts of phenolic and lactonic groups on BC surface increased only about 50% compared with those of the original values. 3.2 Changes of DTPA-extractable Cu and Zn contents in the composting material

Fig. 2 Change of total organic matter during the course of composting

Sewage sludge contains various kinds of heavy metals. However, Cu and Zn are quantitatively primary heavy metals in sludge of China, as well as in sludge of other countries (Udom and Mbagwu 2004; Dai et al. 2007). Relative percentages of total Cu and Zn in the composting material that were DTPA-extractable during the composting process are shown in Figs. 4 and 5. In general, DTPAextractable contents of Cu and Zn in the composting material decreased with composting time. The decrease of DTPA-extractable Cu in the composting materials was greater than that of DTPA-extractable Zn content during the composting process. By the end of composting, DTPAextractable Cu and Zn contents in the composting material

Environ Sci Pollut Res (2009) 16:1–9

5

Table 2 Mass balances and losses of nitrogen during composting of sludge Treatment

Control 1% BC 3% BC 5% BC 7% BC 9% BC

Initial material

Finished material

Pile mass (kg)

Content (g kg−1)

N mass (g)

Pile mass (kg)

Content (g kg−1)

N mass (g)

200 202 206 210 214 218

8.3 8.21 8.07 7.94 7.82 7.63

1,660.0 1,658.4 1,662.6 1,667.4 1,673.5 1,663.3

105. 106 109 113 117 120

9.30 9.63 10.36 10.83 11.32 11.87

983.6 1,022.76 1,127.2 1,219.5 1,327.8 1,423.2

without BC amendment had decreased 29.2% and 12.0%, respectively, compared with the initial value before composting began. Furthermore, significant effects of BC amendment on the reduction of DTPA-extractable Cu and Zn in composting material were observed during composting, with the effects differing considerably depending on the BC amendment level. For DTPA-extractable Cu, a significant difference between the BC amendments and the non-BC control was detected when the addition of BC was higher than 3%. For DTPA-extractable Zn, a difference between the BC amendments and the non-BC control was found only when the BC amendment was larger than 5%. Compared with the original value before composting, the DTPA-extractable Cu and Zn in the treatment with 9% BC amendment decreased 44.4% and 19.3%, respectively, over the course of composting. Overall, in contrast to the nonBC control, DTPA-extractable Cu and Zn contents in composting materials could be further reduced by 27.5% and 8.2%, respectively, with 9% BC amendment. 3.3 Cu2+, Zn2+, and NH4+ adsorption by BC before and after composting As shown in Table 4, the amount of Cu adsorbed onto BC was much higher than that of Zn, which was consistent with the fact that DTPA-extractable content of Cu decreased more

N loss (g)

N loss rate (%)

676.4 635.6 535.4 447.9 345.7 240.1

40.7 38.3 32.2 26.7 20.4 14.6

than that of Zn. For example, in solutions with 2,000 mg L−1 of Cu2+ and Zn2+, the amounts of Cu2+ adsorbed on FBC was 36.0 mmol g−1, whereas Zn2+ adsorbed on FBC was only 14.2 mmol g−1. Results in Table 4 also indicate that the retention of Cu2+ and Zn2+ by FBC and CBC decreased as initial adsorption of these two metals increased. The Cu2+ retention against DTPA extraction on FBC and CBC decreased from 88.0% to 74.0% and 88.2% to 75.0%, respectively. Retention of Zn2+ on FBC and CBC decreased from 69.8% to 53.5% and 70.0% to 52.1%, respectively. However, according to the result of Tukey’s t test, no difference was observed between the retention capability of FBC and CBC for Cu2+ and Zn2+. According to Nishantha Fernando et al. (2005), the retaining of NH4+ against Ca2+ exchange can express the retaining capacity of absorbent to NH4+; therefore, CaCl2 was adopted as extracting solvent in desorption test to determinate the retaining rate of BC to NH4+. In this research, the retention of NH4+ against Ca2+ exchange on FBC decreased with increasing adsorption on BC (Table 5), a pattern of behavior similar to that of Cu2+ and Zn2+. However, the retention of NH4+ on CBC did not decrease significantly with an increase of adsorption. A significantly greater retention of NH4+ was observed by CBC compared to FBC, which indicated that composting has a significantly positive effect on the adsorption capability of BC for NH4+.

Table 3 Amount of surface functional groups determined by Boehm titration (p<0.05) Sample

Original BC BC after 7 days composting BC after 14 days composting BC after 21 days composting BC after 28 days composting BC after 35 days composting BC after 42 days composting

Carboxylic groups (mmol g–1)

Phenolic and lactonic groups (mmol g–1)

Total acidic functional groups (mmol g–1)

0.29e±0.03 0.36de±0.04 0.46cd±0.05 0.55bc±0.04 0.62ab±0.03 0.67a±0.05 0.69a±0.06

0.84c±0.03 0.88c±0.07 1.02b±0.06 1.10b±0.04 1.24a±0.05 1.26a±0.07 1.27a±0.08

1.17d±0.05 1.26d±0.07 1.48c±0.04 1.66b±0.05 1.86a±0.03 1.94a±0.03 1.95a±0.02

Amount values of surface functional groups followed by different small letters within the same vertical column are different significantly at 5% level

6

Fig. 4 Change of DTPA-extractable Cu content during the course of composting

4 Discussion Bamboo charcoal amendment has little effect on the microbial activity and organic matter mineralization during sludge composting, based on the measured temporal changes in temperature and organic matter content. However, TN loss in the composting material varied depending on the amount of BC amendment. Overall, nitrogen loss decreased as the amount of BC incorporated into the composting materials increased. It is generally known that surface area and pore size distribution, as well as heteroatoms and compounds affecting surface properties, affect the adsorption capacity (Tennant and Mazyck 2007). As shown in Table 1, the specific surface and bulk density of BC were 330 m2 g−1 and 0.75 g cm−3, indicating that BC has a substantial adsorption capability. It is probably this high adsorption capability resulted in the considerable reduction of TN loss with the BC amendment during and after sludge composting. Specifically, ammonia adsorption

Fig. 5 Change of DTPA-extractable Zn content during the course of composting

Environ Sci Pollut Res (2009) 16:1–9

capability of BC might be the main reason for the retention of nitrogen in sludge composting materials, as 47–77% of nitrogen loss has been reported as resulting from ammonia volatilization during composting (Martins 1992). The reductions of TN content in composting materials with lower amount of BC amendment during the thermophilic period were probably attributable to an insufficient concentration of BC particles to adsorb ammonia emitted rapidly by the degradation of proteins and amino acids (Pagans et al. 2006). However, ammonia binding to complex organic materials involved in the humification process has a role in preventing ammonia release and volatilization at the maturation stage (Paredes et al. 2002; Baddi et al. 2004). As a result, the TN concentration recovered to higher values in the composting materials as weight loss due to the mineralization of organic matter continued in the maturation phase. According to adsorption theory, the adsorbate occupies sites where it is more exchangeable or labile first by a fast reaction and then migrates to sites where it is less exchangeable over time. Therefore, after the sites with nonexchangeable adsorbate are filled, additional adsorbate will remain exchangeable, suggesting that adsorbate would be released more easily as greater loading occurs on the adsorbent. In this study, the NH4+ retention rate of FBC decreased as the amount of adsorption increased, indicating the lower stability of adsorption at higher levels. The saturation of strong binding sites at high adsorption amounts could explain the phenomenon. However, results for the CBC desorption test showed that there were no significant differences in NH4+ retention rate regardless of amount of NH4+ adsorbed, which indicated that composting could improve the nitrogen conservation capacity of BC. As the results of Boehm titration have shown, the amount of total acidic groups, especially carboxylic groups, which would retain NH4+ through ionic bonding, increased substantially during the course of composting. As is well known, ionic bonding is more energetic than simple physical adsorption. This could explain the high retention rate of NH4+ on CBC, even for treatments with higher added NH4+. Therefore, we conclude that the bio-oxidation of BC during sludge composting could increase NH4+ conservation, with this increase mainly attributed to the increased acid groups on the BC surface. Nishantha Fernando et al. (2005) stated that the carboxylic groups may deprotonate and therefore form complexes with NH4+, and phenolic constituents could react with NH4+ to form stable complexes. Some authors had also reported the nitrogen retention properties of other biocharcoals. For example, Oya and Iu (2002) and Iyobe et al. (2004) found black charcoal in soil could efficiently adsorb ammonia and act as a buffer for ammonia in soil, suggesting that it has the potential to decrease ammonia volatilization from

Environ Sci Pollut Res (2009) 16:1–9

7

Table 4 Results of adsorption–desorption tests of Cu and Zn on fresh bamboo charcoal and composted bamboo charcoal (p<0.05) Concentration of solution for adsorption test (mg L−1)

Cu

Sorption value (mmol g−1)

Retention rate (%)

Sorption value (mmol g−1)

Retention rate (%)

Sorption value (mmol g−1)

Retention rate (%)

Sorption value (mmol g−1)

Retention rate (%)

200 400 800 1,200 1,600 2,000

6.14e±0.15 15.01d±0.25 27.49c±0.84 31.54b±1.68 34.48a±1.37 35.99a±2.04

87.99a±2.32A 87.25a±2.54A 81.57b±2.23A 80.81b±2.10A 74.58c±2.47A 74.02c±3.18A

6.01e±0.29 14.23d±0.28 25.82c±0.76 29.80b±0.60 33.89a±0.28 34.61a±0.56

88.18a±3.25A 86.58a±3.11A 82.68b±2.15A 79.95b±1.20A 75.18c±2.16A 74.96c±3.12A

4.94e±0.41 6.40d±0.15 8.97c±0.81 10.63b±0.31 13.23a±1.15 14.22a±0.73

69.78a±2.11A 68.76a±2.35A 63.64b±1.46A 64.54b±1.96A 59.96c±2.38A 53.53d±2.24A

4.33d±0.29 6.49c±0.23 8.81b±0.6 9.67b±0.17 12.30a±0.21 13.25a±0.86

70.0a±2.15A 68.85a±2.55A 63.36b±2.02A 63.17b±2.50A 58.87c±2.29A 52.10d±2.10A

Zn

FBC

CBC

FBC

CBC

Sorption values followed by different small letters within the same vertical column are different significantly at 5% level. Retention rate followed by different capital letter of BC and CBC transversely are different significantly at 5% level

agricultural fields. However, there have been no studies prior to this research about the effect of biocharcoal and especially BC on nitrogen conservation during the course of composting. DTPA-extractable content of heavy metals can estimate the mobility of heavy metals in most cases (Hseu 2006; Fang and Wong 1999). In comparison with the original values before composting, DTPA-extractable contents of Cu2+ and Zn2+ in treatment with 9% BC decreased by 44.4% and 19.3%, respectively, over the course of composting. In contrast to the non-BC control, DTPAextractable contents of Cu2+ and Zn2+ in composting material could be further decreased by 27.5% and 8.2%, respectively, with the 9% BC amendment. This additional decrease of extractable Cu2+ and Zn2+ in the composting material mainly resulted from the adsorption of both metals by BC. The findings of Hiller and Brümmer (1997) that charcoal particles tended to accumulate heavy metals support this hypothesis. In addition, the results of this study indicated that BC played a more efficient role in stabilization of Cu2+ than Zn2+. This stabilization discrepancy might result from the different adsorption stability of BC to Cu2+ and Zn2+, which may correlate with the greater

tendency for covalent bonding (higher electronegativity) of Cu. In addition, the results of adsorption–desorption tests showed that the retention of Cu2+ and Zn2+ on FBC and CBC decreased with increasing adsorbate loading. According to the adsorption theory mentioned above, this decrease could be explained by saturation of the strong binding sites on the absorbent. Moreover, there was no significant difference in Cu2+ and Zn2+ retention by FBC compared to CBC, thus suggesting that BC oxidation during composting had no evident effect on the adsorption of Cu2+ and Zn2+ by BC.

5 Conclusions Incorporation of BC into composting material could significantly lessen the total nitrogen loss during sludge composting. TN loss decreased with an increasing amount of BC amendment. In comparison to the non-BC control, the amendment of 9% BC reduced TN loss from the sludge composting material by 64.1% after composting. This reduction of TN loss mainly resulted from the high adsorption capacity of BC and the bio-oxidation of BC

Table 5 Results of adsorption–desorption tests of ammonium on fresh bamboo charcoal and composted bamboo charcoal (p<0.05) Concentration of solution for adsorption test (mg L−1)

2 4 6 8 10

FBC

CBC

Sorption value (mmol g−1)

Retention rate (%)

Sorption value (mmol g−1)

Retention rate (%)

0.53d±0.02 0.81c±0.04 1.05b±0.04 1.17a±0.03 1.20a±0.02

84.4a±3.08A 83.8a±3.14B 76.6b±2.26B 75.1b±2.85B 70.9c±2.56B

0.56c±0.02 0.92b±0.05 1.15a±0.05 1.22a±0.03 1.23a±0.05

88.2a±2.30A 88.8a±2.82A 87.7a±3.29A 87.7a±3.45A 88.1a±2.44A

Sorption values followed by different small letters within the same vertical column are different significantly at 5% level. Retention rate followed by different capital letters of BC and CBC transversely are different significantly at 5% level

8

particles during composting, which significantly increased the amount of surface acid groups, especially carboxylic groups. Mobility of heavy metals in the sludge composting could also be reduced by the addition of BC. However, the stabilization effect of BC was different for Cu2+ and Zn2+. DTPA-extractable contents of Cu2+ and Zn2+ in sludge composting material with 9% BC amendment dropped 27.5% and 8.2%, respectively, at the end of composting as compared with that of the non-BC control. There was no significant difference in the ability of FBC compared to CBC to retain either Cu2+ or Zn2+, indicating that composting had little effect on the adsorption capacity of BC for these heavy metals.

6 Recommendations and perspectives According to the results of the study, it is concluded that BC could be an effective amendment for nitrogen conservation and heavy metal stabilization in sludge composts. However, further research into the effect of BC-amended sludge compost material on soil properties, bioavailability of heavy metals, and nutrient turnover in soil needs to be carried out prior to the application of BC-sludge compost in agriculture. Acknowledgements This study was partially supported by China National Natural Science Fund (40432004), Project of Science and Technology Department of Zhejiang Province (2006C13066 and 2007C03002), and Program for New Century Excellent Talents in University.

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9 Su JJ, Wan HL, Kimberley MO, Beecroft K, Magesan GN, Hu CX (2007) Fractionation and mobility of phosphorus in a sandy forest soil amended with biosolids. Environ Sci Pollut Res 14(7):529–535 Tennant MF, Mazyck DW (2007) The role of surface acidity and pore size distribution in the adsorption of 2-methylisoborneol via powdered activated carbon. Carbon 45:858–864 Udom BE, Mbagwu JSC (2004) Distribution of Zn, Cu, Cd, and Pb in a tropical ultisol after long-term disposal of sewage sludge. Environ Int 4(2):467–470 Zhang QS (2001) Prospect and utilization of bamboo resources in China, mechanism and science of bamboo charcoal and bamboo vinegar (in Chinese). China Forestry, Beijing

BIOCHAR VOLATILE MATTER CONTENT EFFECTS ON PLANT GROWTH AND NITROGEN TRANSFORMATIONS IN A TROPICAL SOIL Jonathan L. Deenik, A.T. McClellan and G. Uehara Department of Tropical Plant and Soil Sciences, University of Hawaii, Honolulu, HI

ABSTRACT Biochars made from modern pyrolysis methods have attracted widespread attention as potential soil amendments with agronomic value. A series of greenhouse experiments and laboratory incubations were conducted to assess the effects of biochar volatile matter (VM) content on plant growth, nitrogen (N) transformations, and microbial activities in an acid tropical soil. High VM biochar inhibited plant growth and reduced N uptake with and without the addition of fertilizers. Low VM charcoal supplemented with fertilizers improved plant growth compared with the fertilizer alone. The laboratory experiments showed that high VM biochar increased soil respiration and immobilized considerable quantities of inorganic N. This research shows that biochar with high VM content may not be a suitable soil amendment in the short-term. INTRODUCTION The use of biochar as a soil amendment is modeled on the C-rich anthropogenic soils known as “Terra Preta do Indio” (Indian black earth) found in Amazonia and associated with habitation sites of pre-contact Amerindian populations dating as far back as 7,000 cal yr BP (Glaser, 2007). The defining characteristic of Terra Preta soils is the presence of large quantities of charcoal in the soil organic matter to depths of 1 m or greater (Glaser et al., 2000; Sombroek et al., 1993). These soils are remarkable because they have remained fertile and enriched in soil C compared with adjacent forest soils despite centuries of cultivation. Recent efforts to replicate the “Terra Preta” phenomenon using biochars created from modern pyrolysis techniques show that charcoal additions can have an ameliorating effect on highly weathered, infertile tropical soils by increasing CEC and plant nutrient supply, reducing soil acidity and aluminum toxicity, and improving fertilizer efficiency due to reduced nutrient leaching (Glaser at al., 2002; Lehmann et al., 2003). Plant growth response to charcoal amended soils has been variable with both negative and positive results reported in the scientific literature (Glaser at al., 2002). Several studies have reported that plant growth responses are largest when charcoal and fertilizers are combined suggesting a synergistic relationship (Chan et al., 2007; Lehmann et al., 2003; Steiner et al., 2007). Gundale and Deluca (2007) observed that laboratory produced charcoal from ponderosa pine and Douglas-fir had a negative effect on plant growth whereas the same charcoal created from wildfires showed a positive effect on plant growth. The authors speculated that the low temperature charring method used to create the charcoal in the laboratory either created toxic compounds that inhibited plant growth or acted as a source of labile carbon (C) stimulating microbial growth and N immobilization. The objectives of the present research were to determine the effects of charcoal volatile matter content on plant growth and N transformations in a tropical acid soil. We hypothesized that biochar created at low temperatures with high VM would increase microbial activity resulting in a decrease in plant available N due to immobilization.

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MATERIALS AND METHODS Two greenhouse bioassays and two laboratory incubations were conducted to test the effects of biochar VM content on plant growth and N transformations. The soil was an infertile, acid Leilehua series (very-fine, ferruginous, isothermic, ustic kanhaplohumults) collected from the 30-80 cm depth at the Waiawa Correctional Facility, Mililani, Oahu Island (N21°26’53”, W157° 57’ 52”). The charcoal feedstock used in our experiments was macadamia nut shells. The charcoal was made using a flash carbonization process developed at the Natural Energy Institute at the University of Hawaii (Antal et al., 2003). Selected chemical properties of the soil and biochars used in the different experiments are presented in Table 1. Total C and N content of the biochars were determined by dry combustion on a LECO CN-2000. Biochar pH was measure in 1:1 slurry of charcoal to deionized water. Base cations were extracted with 1M ammonium acetate at pH 7 and Al+++ was extracted with 1M KCl and measured in solution by inductive coupled plasma spectrophotometer. The effective cation exchange capacity (ECEC) of the biochars and soil was determined by summing the exchangeable cations. Table 1. Selected chemical properties of the Leilehua soil, and the biochars used in the greenhouse and laboratory experiments (LVM = low VM content and HVM = high VM content). VM

Ash

OC

TN

pH

Soil Leilehua Charcoal LVM MacNut HVM MacNut

P

K

Ca

mg kg-1

% 4.28

0.12

4.70

2.22

Mg

Na

cmolc kg

Al

ECEC

-1

0.09

0.72

0.52

0.29

1.61

3.22

6.30

4.18

88.7

0.45

8.16

17.2

1.25

3.7

0.31

0.011

22.5

22.5

3.33

85.2

0.45

5.72

18.5

0.74

0.7

0.15

0.032

20.2

In the first greenhouse bioassay we imposed five treatments consisting of a control (unamended soil), soil+lime, soil+biochar, soil+lime+NPK and soil+biochar+lime+NPK arranged in randomized block design with four replications. The biochar contained 22.5 % VM and was considered a high VM biochar. Biochar was applied to achieve 10% (w/w), lime to achieve 2 T ha-1, N as NH4NO3 at a rate of 200 mg N kg-1, P as Ca(H2PO4)2 to achieve a rate of 750 mg P kg-1, K and Mg were added in solution at a rate equivalent to 200 and 100 kg ha-1 respectively, and the micronutrients Cu, Mn, and Zn were added in solution at a rate of 10 kg ha1 . We used corn (Zea mays, var super sweet #9) as the test crop. Eight corn seeds were planted into each pot and thinned to four plants after emergence. The second greenhouse bioassay consisted of five treatments (unamended soil, soil+lime+NPK, soil + high VM biochar, soil + low VM biochar, soil + low VM biochar + NPK) installed in a complete randomized block design with four replicates. Lime and fertilizers were applied at the same rates as in the first experiment and corn was the test crop. At harvest time, above-ground biomass was cut at the soil surface dried at 70°C for 72 hours, weighed and tissue analyzed for nutrient content according to standard procedures (Hue et al., 2000). We conducted two laboratory studies to evaluate the effect of biochar VM content on net N mineralization rates and on CO2 respiration. Both experiments consisted of three treatments, a control (untreated Leilehua soil) and the Leilehua soil amended with high and low VM macadamia nut biochar applied at the same rate as in the greenhouse experiment. For the N

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study, the biochar was mixed thoroughly with 50 g (oven dry equivalent) of soil followed by the addition of the appropriate volume of deionized water required to bring the soil to 75% of water holding capacity. The soils were placed in 100 mL beakers, weighed at the outset of the incubation, covered with perforated parafilm, and incubated at constant temperature (28°C) and moisture. Soils were sampled and analyzed for inorganic N, protease activity, and K2SO4 extractable organic C and TN after 2, 7, and 14 days. The soluble C fraction of the biochar was determined by shaking 3 g of biochar in 30 mL deionized water for 1 hour and filtering through a 45 μm nylon membrane. For the CO2 respiration study, we used the alkali adsorption method where 50 g of treated and untreated soils and 50 ml of 0.05 M NaOH were sealed in airtight 1 L mason jars and incubated at 28°C for 14 days (Alef, 1995). The beaker containing the NaOH solution was removed from the mason jar at 48 hour intervals and titrated with 0.05 M HCl following the addition of 0.5 M BaCl2. Four mason jars with the 0.05 M NaOH solution, but without soil were used as controls.

Shoot Biomass ( g pot-1)

RESULTS AND DISCUSSION The high VM biochar used in the first greenhouse bioassay had a significant negative effect on corn growth compared to the control (Fig. 1). Amending the soil with conventional inorganic fertilizers (lime+NPK) produced significant 5 increases in corn growth, but the beneficial a effects of the fertilizer was erased when 4 combined with charcoal. Indeed, by combining charcoal with the fertilizer there 3 was an approximately 50% decline in corn b growth compared with the fertilized soil. 2 Corn plants growing in the control soil showed very low N, P and K concentrations c 1 c in the tissue (data not shown). Tissue N and d K concentrations remained low after the 0 addition of charcoal, but P concentrations L L L S C F+ F+ S+ S+ S+ C+ increased significantly. Applying NPK S+ fertilizers significantly increased tissue N, P, Figure 1. Treatment effects on above ground corn dry and K concentrations and the accompanying matter production in an infertile Leilehua soil amended significant rise in dry matter production with high VM biochar and fertilizer (S = soil, S+C = indicated that the Leilehua soil was severely soil + biochar, S+L = soil + lime, S+F+L = soil + NPK deficient in N, P, and K. The biochar in + lime, S+C+F = soil + biochar + NPK). combination with fertilizers, however, significantly decreased tissue N, P, and K concentrations compared to the fertilizer control treatment. Our observations were in disagreement with a recent greenhouse experiment reporting that biochar significantly improved N fertilizer use efficiency by radish plants (Chan et al., 2007). We speculated that the relatively high VM content of the biochar used in this experiment may have played a role in inhibiting corn growth.

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NH4-N (mg kg )

Shoot Biomass (g pot-1)

The results of the second greenhouse experiment showed that biochar VM content had significant effects on plant growth. High VM biochar significantly reduced shoot dry matter compared with the control whereas low VM biochar had no significant effect on dry matter production (Fig. 2). Corn growth was significantly better in the low VM 0.4 b a charcoal treatment than in the high VM charcoal treatment. The low VM biochar 0.3 combined with fertilizer showed a a significant increase in dry matter production compared with the fertilizer 0.2 alone treatment. The high VM biochar reduced N uptake by 50% compared with the control. On the other hand, the low b 0.1 b VM biochar did not reduce N uptake in c either biochar alone treatment or the biochar augmented with fertilizer 0.0 L K S VM VM PK+ +NP treatment. Although the low VM biochar S+L S+H VM S+N S+L with fertilizer treatment did not show as high an increase in plant growth nor a Figure 2. Treatment effects on above ground corn dry significant increase in N uptake compared matter production in an infertile Leilehua soil amended with high and low VM biochar and fertilizer (S = soil, HVM = with the fertilizer treatment as in the high VM biochar, LVM = low VM biochar). results reported by Chan and his group (2007), our results provide evidence that the VM content of the biochar is an important factor affecting its agronomic value as a soil amendment. We suspected that high VM charcoal is a source of labile C for soil microorganisms, and the high C:N ratio of the C source stimulated immobilization of the plant available N in the soil causing N deficiency in the 50 growing plants. A recent experiment reported similar results showing that 40 charcoal produced at low temperature (350°C) had a negative effect on plant growth (Gundale and DeLuca, 2007), 30 and the researchers speculated that the Soil decline in plant growth was caused by 20 Soil+HVM Soil+LVM N immobilization due to high concentrations of soluble and total 10 phenols in the charcoal, which served as a high C:N carbon source for soil 0 microorganisms. 0 2 4 6 8 10 12 14 16 Results from the two incubation Days experiments confirmed that biochar VM exerts a strong influence on N + mineralization and microbial Figure 3. Biochar effects on soil NH4 -N in a 14 - day incubation. respiration. The untreated soil showed an initial drop in soil NH4+-N after two days from 39.4 to 31.7 mg kg-1 followed by a slow increase to 45.3 and 43.4 mg kg-1 after seven

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Respiration (mg CO2 kg 48hr )

and fourteen days respectively (Fig. 3). The soil amended with high VM biochar, however, showed a dramatic decline in soil NH4+-N that persisted throughout the fourteen day incubation. The low VM biochar had a much smaller effect on soil NH4+-N decreasing it to around 30 mg kg-1. In the CO2 respiration study, the high VM biochar amendment caused a steep increase in respiration reaching a peak at four days followed by a gradual decline through the 12th day (Fig. 4). At day 2 and day 6 the high VM 400 biochar treatment showed a respiration Soil rate threefold higher than the control, Soil+HVM Soil+LVM which remained at least twice as high as 300 the control throughout the remainder of the incubation period. The low VM treatment showed an initial spike in 200 respiration at day 2 followed by a rapid decline matching the control values by the eighth day. The relatively high CO2 100 respiration rate combined with the dramatic decline in soil NH4+-N 0 concentration observed in the high VM 0 2 4 6 8 10 12 biochar treatment is strong evidence that Days N immobilization by the microbial biomass was an important factor Figure 4. Biochar effects on CO2 respiration in a 12-day explaining the observed decline in plant incubation. growth and N uptake in the high VM biochar treatments. The high water extractable C content of the high VM biochar (265 mg C kg1 ) compared with the low VM biochar (53 mg kg-1) provided a labile source of C fueling the observed stimulation of microbial activity in the high VM treatment. With the high C:N ratio of the biochar, the microbial biomass was forced to scavenge soil N inducing N deficiency in the growing plants. SUMMARY This research shows that biochar VM content, or the degree of carbonization, can play a critical role in determining its agronomic value as a soil amendment. Our results provide clear evidence that biochars that are high in VM content (i.e., a typical barbecue charcoal) would not be good soil amendments because they can stimulate microbial activity and immobilize plant available N in the short-term. On the other hand, more fully carbonized biochars with lower VM content containing a smaller labile C component have a smaller effect on soil microbial activity and N immobilization. While our research provides one explanation for why some biochars have a negative effect on plant growth, it still remains unclear why low VM biochars in combination with fertilizer appear to have a beneficial effect on plant growth. Despite our findings elucidating the role of VM content in inhibiting N mineralization, research at the field scale is required to truly assess the agronomic value of biochars as soil amendments. REFERENCES Alef, K. 1995. Soil Respiration, p. 214-216, In K. Alef and P. Nannipieri, eds. Methods in applied soil microbiology and biochemistry. Academic Press, London.

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Antal, M.J., K. Mochidzuki, and L.S. Paredes. 2003. Flash carbonization of biomass. Industrial & Engineering Chemistry Research 42:3690-3699. Chan, K.Y., L. Van Zwieten, I. Meszaros, A. Downie, and S. Joseph. 2007. Agronomic values of greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45:629-634. Glaser, B. 2007. Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century. Philosophical Transactions of the Royal Society BBiological Sciences 362:187-196. Glaser, B., E. Balashov, L. Haumaier, G. Guggenberger, and W. Zech. 2000. Black carbon in density fractions of anthropogenic soils of the Brazilian Amazon region. Organic Geochemistry 31:669-678. Glaser, B., J. Lehmann, and W. Zech. 2002. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal - a review. Biology and Fertility of Soils 35:219-230. Gundale, M.J., and T.H. DeLuca. 2007. Charcoal effects on soil solution chemistry and growth of Koeleria macrantha in the ponderosa pine/Douglas-fir ecosystem. Biology and Fertility of Soils 43:303-311. Hue, N.V., R. Uchida, and M.C. Ho. 2000. Sampling and analysis of soils and plant tissues. pp. 23-30, In J. A. S. a. R. S. Uchida, ed. Plant Nutrient Management in Hawaii Soils. College of Tropical Agriculture and Human Resources, University of Hawaii, Honolulu. Lehmann, J., J.P. da Silva, C. Steiner, T. Nehls, W. Zech, and B. Glaser. 2003. Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant and Soil 249:343-357. Sombroek, W.G., F.O. Nachtergaele, and A. Hebel. 1993. Amounts, dynamics and sequestering of carbon in tropical and subtropical soils. Ambio 22:417-426. Steiner, C., W. Teixeira, J. Lehmann, T. Nehls, J. de Macêdo, W. Blum, and W. Zech. 2007. Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant and Soil 291:275-290. ACKNOWLEDGEMENTS We thank Dr. Michael Antal for providing biochar samples along with proximate analysis data and Yudai Tsumiyoshi and Jocelyn Liu for assistance with laboratory analysis. Funding for this research came in part from USDA HATCH project 863H.

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Copyeditor: Maria Timothy Santiago

TECHNICAL ARTICLE

Impact of Biochar Amendment on Fertility of a Southeastern Coastal Plain Soil Jeffrey M. Novak,1 Warren J. Busscher,1 David L. Laird,2 Mohamed Ahmedna,3 Don W. Watts,1 and Mohamed A. S. Niandou3

Abstract: Agricultural soils in the southeastern U.S. Coastal Plain region have meager soil fertility characteristics because of their sandy textures, acidic pH values, kaolinitic clays, low cation exchange capacities, and diminutive soil organic carbon contents. We hypothesized that biochar additions will help ameliorate some of these fertility problems. The study objectives were to determine the impact of pecan shellYbased biochar additions on soil fertility characteristics and water leachate chemistry for a Norfolk loamy sand (fine-loamy, kaolinitic, thermic typic Kandiudults). Soil columns containing 0, 0.5, 1.0, and 2.0% (wt/wt) biochar were incubated at 10% (wt/wt) moisture for 67 days. On days 25 and 67, the columns were leached with 1.2 to 1.4 pore volumes of deionized H2O, and the leachate chemical composition determined. On days 0 and 67, soil samples were collected and analyzed for fertility. The biochar had a pH of 7.6, contained 834.2 and 3.41 g kgj1 of C and N, respectively, and was dominated by aromatic C (58%). After 67 days and two leaching events, biochar additions to the Norfolk soil increased soil pH, soil organic carbon, Ca, K, Mn, and P and decreased exchangeable acidity, S, and Zn. Biochar additions did not significantly increase soil cation exchange capacity. Leachates contained increasing electrical conductivity and K and Na concentrations, but decreasing levels of Ca, P, Mn, and Zn. These effects reflect the addition of elements and the higher sorption capacity of biochar for selective nutrients (especially Ca, P, Zn, and Mn). Biochar additions to the Norfolk soil caused significant fertility improvements. Key words: Biochar, coastal plain soil, fertility, GRACEnet, leachate (Soil Sci 2009;174: 00Y00)

F

or more than 150 years, sandy soils of the southeastern U.S. Coastal Plain region have been cultivated for row crops, particularly corn and cotton (Gray, 1933; Trimble, 1974). Most of these agricultural soils are Ultisols (Buol, 1973; Gardner, 1981) formed in fluvial and marine sediments (Daniels et al., 1999) deposited 0.5 to 5 million years before present during the Pliocene to early Pleistocene periods (Daniels et al., 1970; 1978). The warm, humid climate and long time for pedogenesis have created distinct soil profile, mineralogical, and chemical characteristics. Extensive clay eluviation has created shallow A horizons (0Y0.20 m thick); well-developed E horizons (0.2Y1 m

1

USDA-ARSYCoastal Plain Soil, Water and Plant Research Center, Florence, SC. Dr. Novak is corresponding author. E-mail: [email protected] USDA-ARSYNational Soil Tilth Laboratory, Ames, IA. 3 Interdisciplinary Energy and Environment Program, North Carolina A&T University, 171 Carver Hall, Greensboro, NC. Received August 19, 2008, and in revised form November 30, 2008. Accepted for publication December 2, 2008. Manuscript accepted for publication to Soil Science on: September 24, 2008. Mention of a specific product or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture or imply its approval to the exclusion of other products that may be suitable. Copyright * 2009 by Lippincott Williams & Wilkins ISSN: 0038-075X DOI: 10.1097/SS.0b013e3181981d9a 2

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thick) that have sand, loamy sand, or sandy loam textures; and relatively thick Bt horizons (1.0Y3.0 m thick) with sandy clay to clay textures (Daniels et al., 1970; Shaw et al., 2004). Intensive leaching of bases has resulted in low soil pH values, extensive clay mineral weathering, low cation exchange capacity (CEC) values (2Y8 cmolc kgj1), and high levels of exchangeable Al (Gamble and Daniels, 1974; Daniels et al., 1978). These soil characteristics severely limit soil fertility and agricultural management options. For instance, sandy soils exhibit high N leaching after fertilizer or manure application (Trindale et al., 1997; Ritter et al., 1998; Zotarelli et al., 2007). Moreover, Ultisols in the Coastal Plain region have low soil organic carbon (SOC) contents in the surface 0- to 15-cm depth (6.3Y9.2 g kgj1; Hunt et al., 1996; Novak et al., 2007a) because of rapid residue oxidation, which is further accelerated by inversion tillage for row crop production (Bauer et al., 2006). The physical and chemical problems discussed above severely limit soil fertility and hence crop productivity on the Ultisols of the southeastern U.S. Coastal Plain. Fertility problems associated with southeastern Coastal Plain Ultisols are similar to those of Oxisols in intertropical regions (Eswaran and Tavernier, 1980), which also have low pH, SOC, and CEC values (Tiessen et al., 1994; Lehmann et al., 2003). Poor soil fertility raises concerns about the sustainability of agriculture in regions dominated by Oxisols and has spurred the development of management practices to restore or improve their fertility status (Glaser et al., 2002). Applications of mulches, composts, and manures increase soil fertility; however, under tropical conditions, the increase is short term because the added organic matter is quickly oxidized and added bases are rapidly leached (Tiessen et al., 1994). On the other hand, application of biochar (charcoal produced by pyrolysis of biomass feedstock) to infertile Oxisols has been shown to provide longer-lasting improvements in soil fertility (Glaser et al., 2002; Lehmann et al., 2003; Steiner et al., 2007). Biochar composed primarily of single and condensed ring aromatic C (Lehmann, 2007) has both a high surface area per unit mass and a high charge density. Because of these properties, biochar is both more recalcitrant in tropical soils and contributes a higher capacity to sorb cations per unit mass than does biogenic soil organic matter (Sombroek et al., 2003; Liang et al., 2006). Biochar application to soils is not a new concept (Mann, 2005). For example, in the Amazon basin, anthropogenic dark earth soils (referred to as Terra Preta) contain large amounts of charred materials most likely added by pre-Columbian farmers who practiced a form of slash and char agriculture (Sombroek et al., 2003) along with disposal of charcoal remains from hearths (Glaser et al., 2002). In these soils, the biochar acts as a soil conditioner, improving soil physical properties and nutrient use efficiency, thereby increasing plant growth. Today, 500 years after cessation of the practices that created these soils, the Terra Preta soils are highly valued for agricultural and horticultural use in the Amazon basin (Glaser et al., 2002; Lehmann and Rondon, 2006).

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To predict the reactivity as well as stability of biochar when used as a soil amendment, it is important to know the biochars organic structural composition. Biochar from Terra Preta soils analyzed using solid-state nuclear magnetic resonance (NMR) analysis was shown to be composed of a highly heterogeneous mixture of organic structures (Novotny et al., 2007). The structural form of C in biochar depends on the biogeochemistry of the biomass feedstock and the conditions under which it was pyrolyzed (Kramer et al., 2004; Lehmann, 2007). Biochars composed primarily of condensed aromatic C are known to persist in soil environments for millennia, whereas biochars with higher levels of single-ring aromatic and aliphatic C will mineralize more rapidly (Lehmann, 2007; Novotny et al., 2007). Surface area and surface charge density of biochar will have a large influence on soil CEC and the ability of biochar additions to ameliorate soil fertility problems. We hypothesize that biochar additions to the sandy, Coastal Plain soils of the southeastern United States would increase the SOC content and CEC and improve the fertility status. The specific objectives of this investigation were to determine the 1) chemistry of biochar derived from pyrolysis of pecan shells, a locally abundant source of feedstock; 2) effects of biochar additions on fertility characteristics of a Norfolk soil; and 3) effects of biochar additions on the chemical composition of leachate collected from a Norfolk soil.

MATERIALS AND METHODS Production and Characterization of Pecan ShellYBased Biochar

AQ1

Pecan shells were obtained from a supplier in Lumberton, NC. They were ground using a Retsch Mixer Mill (SR-2000; Cole-Palmer, Vernon Hills, IL) to pass through a 2-mm sieve. Per each pyrolysis batch, approximately 1000 to 2000 g of shells were placed into a crucible (25 cm wide ! 10 cm deep) and were inserted into a Lindberg box programmable furnace equipped with an airtight retort (model 5116HR; Lindberg, Watertown, WI). The furnace retort atmosphere was purged with N2 using a flow rate of 0.1 m3 hj1. The furnace was controlled with a multiple-step pyrolysis temperature program. The furnace was initially heated to 40 -C; temperature was ramped to 170 -C at 5 -C minj1 and was maintained at this temperature for 30 min. The temperature was then ramped to 700- C at 5 -C minj1, and the pecan shells were subjected to pyrolysis for 1 h. The biochar was cooled in the oven under the N2 atmosphere overnight. After cooling, the biochar was ground to pass through a 0.25-mm sieve. The sieved biochar moisture percent (wt/wt) content was measured by oven drying a 2-g portion overnight at 80 -C. Biochar pH was measured according to Ahmedna et al. (1998). The method consisted of preparing a 1% (wt/wt) suspension of biochar in deionized water. The suspension was heated to about 90 -C and stirred for 20 min to allow dissolution of the soluble biochar components. After cooling to room temperature, the pH of the biochar suspension was measured using a Corning pH meter (Acton, MA). The biochar percent ash content (wt/wt) was determined by dry combustion at 760 -C in air for 6 h using an Isotemp laboratory muffle furnace (Fisher Scientific). Biochar percent moisture was 1.4%, pH was 7.5, and ash content was 3.8% (wt/wt). A sample of the biochar was analyzed for total C, H, N, S, and O (by difference) determination using ASTM D 3176 method (ASTM, 2006). For total elemental analyses, the biochar was redried and then digested using the EPA method 3052 microwave-assisted acid digestion method (USEPA, 2008). The

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elemental concentrations (Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Si, and Zn expressed on a dry, wt/wt, ash-free basis) in the biochar digests were measured using an Elan DRC-II (PerkinElmer, Shelton, CT) inductively coupled plasma mass spectrometer. Analytical operating conditions and element detection limits are available at EBG-SWES-UA (2008). Solid-state cross-polarization magic angle-spinning totalsideband suppression 13C NMR spectral pattern of the biochar was obtained using a Bruker DSX-300 spectrometer (Karlsruhe, Germany) operated at a 13C frequency of 75.5 MHz. Additional technical parameters to acquire the spectra have been described by Wang et al. (2007). The chemical shift region assignments were as follows: 0 to 50 ppm, aliphatic C; 50 to 109 ppm, O-alkyl C; 109 to 163 ppm, aromatic C; and 163 to 190 ppm, carboxylic C. The percent C distribution was determined by estimating the area in these chemical shift regions as a percentage of the total area under the spectral curve.

Norfolk Soil Collection and Analyses A bulk sample of a Norfolk soil from the Ap horizon (0Y15 cm deep) was collected from a field contiguous to the USDA-ARSYCoastal Plain Research Center, Florence, SC. The field is nearly level (1Y2% slopes) and has a 30-year history of row crop production (Sojka et al., 1984). The soil was collected using a shovel in mid-April, approximately 1 week after fertilization with 49 kg N haj1 of 28-0-0 UAN (urea + NH4NO3) for an upcoming corn crop. The soil was air dried and 2-mm sieved. The Ap horizon is a loamy sand with a particle size distribution of 730, 250, and 20 g kgj1, respectively, of sand, silt, and clay (sedimentation method; Soil Characterization Lab, Ohio State University, Columbus, OH). X-ray diffraction analysis of the clay fraction revealed a preponderance of kaolinite, with minor amounts of hydroxy (Fe and Al) interlayered chlorite (X-ray diffraction method; Soil Characterization Lab, Ohio State University). The pH of the untreated Norfolk Ap soil was 4.8, as measured in a 1:1 soil-to-deionized water mixture (Novak et al., 2007a). The total C and total combustible nitrogen (TCN) contents were determined using a LECO TruSpec CN analyzer (LECO Corp., St Joseph, MI). Soil C was assumed to be organic in nature because the low soil pH precluded carbonates.

Biochar Incubation in Norfolk Ap Soil The biochar incubation experiment was conducted in opentop, 10-cm-diameter, 17-cm-tall schedule-40 PVC columns. Column bottoms were sealed using a nylon mesh fabric to support the soil bed and minimize soil loss. Sufficient amounts of 0.25-mm sieved biochar was mixed into 750-g of air-dried, 2-mm-sieved Ap horizon soil to create 0, 0.5, 1.0, and 2.0% (wt/wt) biochar treatments. These biochar rates equated to field applications of approximately 0, 10, 20, and 40 metric tons haj1. Each treatment was set up in triplicate. Deionized H2O was then mixed into each treatment to obtain a soil-moisture content of 10% (wt/wt), representing the upper range (between 5 and 10%) of field capacity for a typical Norfolk Ap soil horizon. The moist soil treatments were then placed into columns, and they were tamped down by hand to obtain a bulk density of 1.2 g cm3. This created a headspace above the soil of 8 to 10 cm for adding water. The columns were laboratory incubated for 67 days at 10% soil moisture. The laboratory room temperature and percent relative humidity, respectively, throughout the incubation ranged between 17 and 27 -C and 23 and 61%. On days 25 and 67, each column was leached with 1.2 to 1.4 pore volumes of deionized water; the leachate was collected and weighed. The leachates were analyzed for total organic carbon (TOC) concentrations using a Shimadzu TOC-Vcs (Shimadzu * 2009 Lippincott Williams & Wilkins

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Biochar in Coastal Plain Soil

FIGURE 1. 13C NMR spectral pattern for pecan shellYbased biochar (%C distribution for structural groups determined as described by Wang et al. (2007).

Corp., Columbia, MD), and for Ca, Cu, Fe, K, Mg, Mn, Na, P, S, and Zn concentrations with a Varian ICP-OES (Varian Inc., Palo Alto, CA). The ICP detection limit for this suite of 11 elements was a conservative 0.05 mg Lj1. The leachate pH and electrical conductivity (EC) were measured using a standard pH and a conductivity meter. Samples of the biochar-treated Norfolk Ap soil were collected on incubation days 0 and 67 for analysis of plant available nutrients using Mehlich 1 (diluted HCl and H2SO4) extractant. Measurements of Mehlich 1Yextractable Ca, Cu, Fe, K, Mg, Mn, Na, P, S, and Zn and exchangeable acidity values were conducted by the Clemson University Soil Testing Laboratory using ICP. The pH and EC of the biochar-treated Norfolk Ap soil were measured using the methods of Novak et al. (2007a).

structures of the biochar. This speculation has merit because the high pyrolysis temperature explains the lack of alkyl C (0Y50 ppm) as volatile material such as oils, fatty acids, and alkyl alcohols would be lost (Antal and GrLnli, 2003). Carboxylcontaining structures were present in the NMR spectra possibly because of their structural decomposition resistance during pyrolysis. Alternatively, their presence could be due to water sorption during handling and grinding. The biochar percent moisture after grinding and before total elemental analyses was less than 2% and 4%, respectively. Consequently, single-ring aromatic and some heterocyclic compounds could have been reoxidized, forming carboxylic and acetyl OH groups as evident

Statistics

TABLE 1. Total elemental analyses of pecan shellYbased biochar and Norfolk Ap soil† (data sorted into macroelement, microelement pools)

The mean values of SOC and TCN contents between the treatments, sorted by incubation day, were tested using a oneway analysis of variance (ANOVA) with a P G 0.05 level of significance. The soil fertility characteristics and chemical composition of the deionized water leachates were sorted and tested in a similar manner. All statistical tests were performed using SigmaStat v. 3.5 software (SSPS Corp., Chicago, IL).

RESULTS AND DISCUSSION Biochar and Soil Compositional Analyses

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The 13C NMR spectral pattern of the pecan biochar (Fig. 1) revealed two prominent peaks at 120 and 187 ppm and a shoulder near 90 ppm. These peaks indicate that most of this biochar is distributed in aromatic structures (58%), with less amounts of C having single bonds to O (29%) and in carboxyl (13%) groups. The lack of a distinct peak near 75 ppm suggests little carbohydrate C; rather, the shoulder near 90 ppm is more characteristic of acetal C (Wershaw, 1985). The pecan shells used as feedstock for preparation of the biochar are composed primarily of lignin and cellulose (47%, acid-detergent lignin; Ramirez et al., 1986). Charring of lignin and cellulose at temperatures of 500 -C was reported to cause loss of their aliphatic components along with a conversion of ring structures into aromatic compounds (Rutherford et al., 2004). During pyrolysis at 700 -C in this study, it was suspected that a similar decomposition of cellulose and lignin and structural rearrangement of ring compounds to form condensed and single-ring aromatic

Biochar

Norfolk Ap soil

Macroelement (g kgj1) Al 0.22 C 834.2 Ca 3.64 Fe 0.07 H 10.3 K 4.15 N 3.41 O 19.8 Si 104.9 Microelements (mg kgj1) Cu 14 Cr 0.31 Mg 698 Mn 78 Na 218 Ni 0.5 P 263 S 95 Zn 7 †

5.1 16.8 0.49 2.91 V 0.38 1.26 V 424.8 4.6 23 445 55 951 2 185 2 43

Determined on biochar and soil using EPA 3052 method (HNO3 + HF).

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TABLE 2. SOC and TCN contents of Norfolk Ap soil and soil + percent biochar mixtures on 0- and 67-day incubations Norfolk Ap soil + % biochar

SOC (g kgj1)† 0d

67 d a

0 0.5 1.0 2.0

TCN (g kgj1)

17.0 18.1a 22.2b 31.2c

0d

a

67 d a

17.4 18.3a 21.9b 29.2c

a

1.26 1.14a 1.25a 1.49b

1.24 1.28a 1.09b 1.21a

† Means compared within a column followed by a different letter are significantly different at P G 0.05 using a one-way ANOVA (multiple comparisons vs. Norfolk Ap soil + 0% biochar as a control).

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in the 13C NMR spectra (Fig. 1). The NMR spectra indicate that this pecan shellYbased biochar is composed of a mixture of organic structural groups reflecting the chemistry of the feedstock and reactions occurring during both pyrolysis and after pyrolysis on exposure of the biochar to oxygen and water. These findings are similar to reports for black C isolated from dark earth soils (Schmidt and Noack, 2000; Novotny et al., 2007). The total elemental analyses of the pecan shell biochar and the Norfolk Ap soil were quite dissimilar (Table 1). The biochar was enriched in C, Ca, K, Mg, N, and Si compared with soil, whereas the Norfolk Ap soil was enriched in Al, Fe, Na, and Si. Pyrolysis of organic feedstock’s from 400 to 700 -C results in a concentration of C but a reduction of O and H due to evaporation of sorbed H2O and driving off of jOH functional groups (Antal and GrLnli, 2003). The N-containing structures in the biochar, such as amino acids, amines, and amino sugars during the hightemperature pyrolysis (700 -C) process were probably condensed to form N-heterocyclic aromatic structures (Koutcheiko et al., 2007). Thus, much of the residual N in the biochar (Table 1) was likely present as recalcitrant heterocyclic N rather than the more bioavailable amine N. The elemental composition (C, H, O, N, and S) of biochar was similar to values reported for other carbonized charcoals (Antal and GrLnli, 2003). The Norfolk Ap soil elemental composition was Al-, Fe-, and Si-enriched; these elements are predominant in the chemical structure of aluminosilicates in the

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sand-size fraction (Smith et al., 1976), and Fe-oxides and hydroxides in the clay-size fraction (Shaw et al., 2004).

Changes in Soil Organic Carbon Content and Fertility Characteristics The Norfolk Ap soil treatments with 1 and 2% biochar addition on day 0 had significantly greater mean SOC contents than the control (Table 2); mean SOC content was increased between 5.1 and 14.2 g kgj1. Similar SOC concentrations were present in the soil after 67 days of incubation, indicating no significant loss of biochar C during the incubation. The biochar contained some N (3.41 mg kgj1; Table 1); however, mixing 0.5 to 1.0% biochar had no detectable effect on TCN of the Norfolk Ap horizon. Adding 2% biochar significantly increased the soil mean TCN content, but only by 0.23 g kgj1. This trend was not observed after 67 days of incubation. Mean TCN contents in treatments after 67 days of incubation (except 1.0% biochar) were similar to the control (0% biochar). The C:N ratio of the pecan biochar is 244:1. Nitrogen immobilization typically occurs when organic residues possessing a C:N ratio of greater than 32:1 are added to soils (Alexander, 1977; Thompson and Troeh, 1978). The wide C:N ratio, in association with its aromaticity, will cause slow biochar decomposition (Lehmann, 2007). Although biochars/soil black carbon will undergo slow chemical and microbial decomposition (Schmidt and Noack, 2000), the rate of decomposition is so slow that even large additions of biochar to soil will probably not significantly immobilize N. The high stability of biochar in soil environments is beneficial with respect to C sequestration because C added to the soil as biochar will be removed from the atmosphere for 1000 years or more. German (2003) reported that biochar in soils is stable and resistant to microbial attack; one site in the Amazonian Black Earth region had biochar dated to 6850 years old. In comparison, the mean residence time of soil organic matter has been estimated as between 250 and 3280 years (Stevenson, 1994). In hind sight, we suggest that the SOC dated in those presented in Stevenson (1994) likely contained significant amounts of black C, which would make the average age of the total SOC pool much older than the age of the biogenic SOC fraction. Laird et al. (2008) physically separated biogenic humic material from black C from an Iowa Mollisol and reported modern radio C dates for

TABLE 3. Fertility characteristics of Norfolk Ap soil + percent biochar mixtures on 0- and 67-day incubations (Mehlich 1 extractant)† Fertility characteristics‡ Norfolk Ap soil + % biochar 0 0.5 1.0 2.0 0 0.5 1.0 2.0

Incubation day 0 0 0 0 67 67 67 67

§

pH

CEC

Exch. acid j1

- - - - - -cmolc kg a

4.8 5.1b 5.5c 6.3d 5.2a 5.6b 5.9c 6.4d

a

5.7 5.3a 5.4a 5.9a 5.2a 5.4a 5.6a 5.9a

------a

2.4 2.0a 1.9a 1.2b 2.4a 2.1a 2.0a 1.5b

Ca

Cu

K

Mg

Mn

Na

P

S

Zn

j1

- - - - - - - - - - - - - - - - - - - - - - mg kg a

437 470b 516c 720d 392a 462b 537c 692d

a

0.6 0.7a 0.7a 0.8a 0.6a 0.7a 0.7a 0.8a

a

35 49b 66c 111d 26a 47b 49c 69d

a

117 98b 90c 91d 93a 91a 92a 89a

a

12 7b 15c 10d 7a 6a 16b 10c

---------------------5a 5a 6a 7b 3a 5b 4a 4a

30.5a 30.8a 31.2a 35.2b 28.7a 31.7b 31.7c 33.3d

8.67a 7.67a 7.83a 8.50a 6.33a 5.16a 4.00b 3.17c

13a 12a 11a 11a 12a 11b 11b 10c

†

Extracted with H2SO4 + HCl. Mean values sorted by incubation day were compared using a one-way ANOVA for multiple-comparisons tests vs. a control (Norfolk Ap soil + 0% biochar). § Means followed by a different letter are significantly different at P G 0.05. ‡

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the biogenic humic material and much older dates for the black C fraction. Therefore, soil applied biochar has the potential to increase the recalcitrant pool of soil C and will persist in soil environments much longer than C added in the form of residues or biogenic soil organic matter. Biochar additions to soils are reported to improve soil fertility by raising soil CEC (Liang et al., 2006). Soil CEC increases are due to carboxylate groups on the surfaces of the biochar itself and to exposed carboxylate groups of organic acids sorbed by the biochar, both of which contribute negative surface charge to biochar particles (Liang et al., 2006). Biochar in this experiment contained some carboxyl characteristics (13%; Fig. 1); yet, the ability of biochar additions to increase the soil CEC even at 2% biochar addition was negligible (Table 3). One might expect after a 67-day incubation that additional carboxylate groups would form because of oxidation of the biochar surfaces (Schmidt and Noack, 2000). However, differences in Norfolk Ap CEC values for the day-0 and day-67 samples were negligible (Table 3). The high pyrolysis temperature (700 -C) may have contributed to the relatively low level of surface oxidation of the pecan shell biochar and hence the lack of a significant impact of biochar additions on the CEC of the Norfolk Ap horizon soil. Higher pyrolysis temperatures generally cause greater condensation of aromatic structures and even the formation of graphitic cores (Antal and GrLnli, 2003). Such highly condensed aromatic C has less surface area and fewer oxidizable surface functional groups than more open (less condensed) aromatic C structures. High-temperature biochars are also more resistant to chemical oxidation and microbial degradation and hence have a longer half-life in soil environments than soil organic matter. The recalcitrant characteristics of high-temperature biochar, however, would be a desirable property if the primary goal was to remove atmospheric CO2 and sequester C in soil for millennia (Laird, 2008). On the other hand, if the primary goal was to increase soil CEC values, then the addition of biochar prepared by pyrolysis of feedstocks at lower temperatures (400Y500 -C) or under different moisture and pressures conditions (Antal and GrLnli, 2003) may be more desirable. Low-temperature biochars will most likely also increase soil C sequestration, but they will probably more rapidly change soil fertility characteristics when compared with using high-temperature biochars. Some microbial oxidizable compounds such as anhydrocellulose (dehydrated forms of cellulose), polysaccharides, alcohols, and so on, should exist in biochars prepared by pyrolysis of feedstocks at lower temperatures (Antal and GrLnli, 2003). Baldock and Smernik (2002) and Hamer et al. (2004) both reported a relationship between biochar pyrolysis temperature and resistance to soil microbial decomposition. Hamer et al. (2004) found that biochars produced from maize and rye at 350 -C were more prone to soil microbial degradation than biochar made from oak wood pyrolyzed at 800 -C. The authors attributed differences in biochar decomposition because of their C:N ratios; higher pyrolysis temperatures caused wider C:N ratios in the oak wood biochar because of loss of N and concentration of C (Hamer et al., 2004). Upon decomposition and oxidation by soil microbial communities, these organic carbon structures should produce byproducts containing a higher density of carboxylate and other O-containing functional groups (i.e., jOH, jOR, etc.) capable of serving as sites for cation exchange (Stevenson, 1994). Therefore, when creating biochars for use as a soil fertility amendment, the biomass pyrolysis conditions could be designed to carbonize the material under moist conditions and at lower temperatures. Research has shown that soil pH is more influenced by monomeric Al species on exchange sites than by H+1 (Sparks,

Biochar in Coastal Plain Soil

1995). Aqueous monomeric hexahydronium [Al(H2O)6]+3 species act as pH buffers because they can undergo rapid and reversible hydrolysis reactions influencing solution pH values by liberating or accepting H+1 (Sparks, 1995). For soil pH to change, the biochar itself or a cation in the biochar must react with the soluble monomeric Al species or displace it from exchange surfaces on clays or soil organic matter. At pH 4.8, the Norfolk soil with no biochar had 42% (2.4 cmolc exchangeable acidity kgj1 " 5.7 cmolc CEC kgj1 ! 100; Table 3) of the total soil CEC sites occupied by [Al(H2O)5]+2. This would be the dominant monomeric Al species in the Norfolk Ap soil + 0% biochar at pH 4.8 (Sparks, 1995). Additions of 0.5 and 1% biochar to the Norfolk soil did not significantly modify the exchangeable acidity values, although soil pH values significantly increased by 0.7 U (Table 3). With the addition of 2% biochar, the pH increased from 4.8 to 6.3, and exchangeable acidity was reduced by 50% ($1.2 cmolc kgj1; Table 3). Thus, biochar was an effective liming agent, neutralizing solution pH and reducing exchangeable acidity values. However, substantial additions of biochar (2% or 40 metric tons haj1) were required to obtain increases in pH and reductions in exchangeable acidity. During pyrolysis, cations (primarily K, Ca, Si, and Mg) present in the pecan shells formed metal oxides (e.g., ash) that were admixed with the biochar. Once in the soil environment, these oxides can react with H+1 and monomeric Al species, modifying soil pH and exchangeable acidity values. Because the biochar contained a high Ca concentration (3.64 mg kgj1; Table 1), Reaction (1) involving CaO exemplifies the liming ability of the ash associated with the biochar: 2Al # soil þ 3CaO þ 3H2O Y 3Ca # soil þ 2A1ðOHÞ3

ð1Þ

During this reaction, Ca replaces the monomeric Al species on soil mineral or soil organic matter CEC sites. Accompanying this reaction is an increase in soil solution pH caused by the depletion of the readily hydrolysable monomeric Al and the formation of the more neutral [Al(OH)3]0 species (Sparks, 1995). This general reaction explains the decline in exchangeable acidity for the Norfolk Ap soil and the increase in solution pH and Ca on CEC sites (Table 3). The pH increase and exchangeable acidity decrease were similar for the day-0 and day-67 samples. This suggests that the liming effect of biochar occurred rapidly and was sustainable on equilibration. The biochar significantly increased some important plant macronutrients. Mehlich 1Yextractable Ca, K, and P all increased with the level of biochar additions (Table 3). However, the P increase was significant only at the highest level of biochar addition. By contrast, Mehlich 1Yextractable Mg decreased with increasing biochar addition at day 0, suggesting that the Mg was strongly retained by the biochar. Extractable S and Zn concentrations also decreased slightly with increasing biochar additions, but the trend was significant only for the day-67 samples. Copper concentrations were not significantly affected by biochar additions, and Mn concentrations were variable. The observed variations in Mehlich 1Yextractable plant nutrient concentrations, at days 0 and 67, reflected the combined effects of fertilization (nutrients added with the biochar), leaching of nutrients, and nutrient adsorption by the soil and added biochar. No plants were grown in these soils, and hence, plant uptake was not a variable in this study. In general, biochar additions increased the levels of plant macronutrients and had little effect on micronutrients.

Chemical Composition of the Water Leachates It is important to examine the chemical composition of a deionized water extract of an amended soil; in some cases, the amendment can release elements that may cause plant growth

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TABLE 4. Chemical composition of deionized water leachates from Norfolk Ap soil + percent biochar mixtures after 25- and 67-day incubation† Leachate chemical composition‡ Norfolk Ap soil + % biochar 0 0.5 1.0 2.0 0 0.5 1.0 2.0

Incubation day 25 25 25 25 67 67 67 67

pH

§

EC j1

KS cm 5.7a 6.0a 6.0a 6.0a 5.8a 5.9a 5.7a 6.0a

364a 382a 439a 559a 364a 387a 502a 571a

TOC

Ca

Cu

K

Mg

Mn

Na j1

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - mg L 76a 65b 70a 82a 45a 38a 48a 68a

189a 175a 136b 99c 31a 32a 37a 46a

32a 58b 72c 99d 9a 17a 25b 52c

V V V V V V V V

113a 82b 63c 34d 18.6a 17.1a 17.1a 15.9a

5.4a 1.1b 0.3c 0.2d 0.1 V 0.1 V

P

S

Zn

------------------------8.2a 11.0b 11.9c 14.0d 2.80a 3.02a 4.02a 5.90b

2.0a 1.4b 1.5c 1.2d 2.20a 1.26b 1.40c 1.42d

25a 22a 23a 26a 9.5a 8.9a 10a 11a

1.3a 0.7a 0.4a 0.1b 0.27a 0.12b 0.13c 0.06d

A dash line indicates mean value was below detection limit (0.05 mg Lj1). Mean values sorted by incubation day were compared using a one-way ANOVA for multiple comparisons vs. a control (Norfolk Ap soil + 0% biochar, significant digits varied because of low mean element concentrations on day 67). § Means followed by a different letter are significantly different at P G 0.05. † ‡

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issues (Novak et al., 2007b). For the 25- and 67-day leachates, pH, EC values, and TOC concentrations (except 0.5% on day 25) were similar for the biochar-treated soils and control soils (Table 4). The cation concentrations in the 25- and 67-day leachates seem to be influenced by cation valency. For instance, the monovalent cation (K and Na) concentrations in both the 25- and 67-day leachates increase with the level of biochar addition to the Norfolk Ap soil, whereas concentrations of multivalent cations (Ca, Mg, Mn, and Zn) all decreased for the day-27 leachates and either decreased or were not significantly different for the day-67 leachates with increasing levels of biochar addition. The strength of cation retention or repulsion from negatively charged surfaces increases with increasing ion charge and with distance between the charged surface and either the source of charge or the soluble ion (basis of diffuse double layer theory; Bohn et al., 1979). Consequently, multivalent cations were preferentially adsorbed over monovalent cations on exchange sites, and hence, the monovalent K and Na cations would be more available for movement with the leachate. The decrease in concentration of multivalent cations in the leachates with increasing levels of biochar addition (Table 4) is particularity interesting in light of the fact that substantial amounts of Ca and Mg and less amounts of Mn and Zn were present in the biochar (Table 1). Much of the Ca added with the biochar probably replaced monomeric Al species on clays and/or soil organic matter exchange sites [see Reaction (1)]. This hypothesis is supported by increasing levels of Mehlich 1Yextractable Ca with higher levels of biochar addition (Table 3). An explanation for the decrease in Mg, Mn, and Zn concentrations in day-27 leachates is a bit more complex, because their Mehlich 1Yextractable concentrations of these elements either decreased or did not show substantial changes with increasing biochar additions. These observations suggest that the Mg, Mn, and Zn were either specifically adsorbed or very highly selectively adsorbed by exchange sites associated with the biochar. The P concentrations generally decreased with increasing biochar application in both 25- and 67-day leachates by approximately 40% (0 vs. 2% biochar addition; Table 4). The field from which the Norfolk soil was collected has a long history of row crop production; past P fertilizer applications were the likely source of much P in the soil. The declines in leachate P concentrations with increasing biochar additions are probably due to a

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combination of reactions such as retention of o-PO4j3 through ligand exchange reactions involving O-containing functional groups on the biochar surface, adsorption of o-PO4j3 by Fe and Al oxides and hydroxides, and by adsorption and precipitation by Ca, Mg-phosphates (Bohn et al., 1979). Regardless of sorption mechanisms, these results suggest that biochar has the potential to ameliorate P leaching in soils with sandy textures, a common problem in fields containing excess soil P concentrations as a result of overapplication of swine manure (Novak et al., 2000).

Net Norfolk Ap Soil Fertility Changes The net soil fertility change to the biochar-treated Norfolk Ap soil is presented in Table 5. The results after adding 2% biochar were presented because this treatment caused the most significant soil fertility variations compared with the untreated soil. The treated Norfolk Ap soil pH was more basic after TABLE 5. Changes in Norfolk Ap soil fertility characteristics with and without 2% biochar (after 67-day incubation and two deionized water leaching events) Characteristic pH CEC Exchange acidity C Ca Cu K Mg Mn N Na P S Zn

Unit

0% 2% Net Relative Biochar Biochar change %†

V cmolc kgj1 cmolc kgj1

4.8 5.7 2.4

6.4 5.9 1.5

+1.6 +0.2 j0.9

+33 +3.5 +38

g kgj1 mg kgj1 mg kgj1 mg kgj1 mg kgj1 mg kgj1 g kgj1 mg kgj1 mg kgj1 mg kgj1 mg kgj1

17.4 437 0.6 35 117 12 1.24 5 31 9 13

29.2 692 0.8 69 89 10 1.21 4 34 4 10

+11.8 +255 +0.2 +37 j28 j2 j0.03 j1 +3 j5 j3

+68 +58 +33 +106 j24 j17 j2.4 j20 +10 j56 j23

†

Percent change based on values in Norfolk Ap soil + 0% biochar.

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biochar addition through a 38% reduction in monomeric Al species on exchange sites (lower exchangeable acidity values). Soil Ca and K concentrations had marked increases (+58 and + 106%, respectively) implying that biochar additions can increase these important plant macronutrients. The Norfolk Ap horizon had an 11.8 g C kgj1 increase after mixing in 2% biochar, and there was no detectable loss of SOC during the 67-day incubation, suggesting that biochar additions may be an effective means of sequestering C; longer-term studies need to be quantified in terms of C sequestration. Two percent biochar application to field soil is approximately 40 tons biochar haj1. This is a large amount of biochar to apply to soil, but the benefits of long-term C sequestration coupled with additions of several plant nutrients, neutralizing soil acidity, and reduced nutrient leaching should not be overlooked. Although we observed decreased leaching of several plant nutrients with increasing biochar additions, we did not observe significant increases in CEC or EC for the Norfolk Ap soil. The influence of biochar additions on Mehlich 1Yextractable micronutrient concentrations was minimal.

CONCLUSIONS Biochar has been used as a fertility amendment in soils of tropical regions for thousands of years, although scientific investigations of the effects on soil fertility are few. This same technology may improve fertility-poor soils in the southeastern U.S. Coastal Plain region. A laboratory study was conducted where a pecan shellYbased biochar was incubated in a sandy, acidic Norfolk Ap soil. Biochar additions increased the SOC content but did not significantly improve the soil N status. Biochar additions seem to potentially be an effective means of sequestering C in soils as no detectable loss of SOC occurred during the 67-day incubation. A goal of this study was to increase the Norfolk Ap soil CEC by adding biochar. For soil CEC to increase, surfaces of the biochar must be oxidized to produce negatively charged carboxylate groups. No increase in soil CEC after 67 days was obtained, implying that this hightemperature biochar was not suited for that purpose within the time frame of this study. Soil pH and three major plant nutrients (Ca, K, and P) concentrations, however, increased after applying this biochar. Most soil micronutrient concentrations were not influenced by the biochar additions. Water leaching of biochartreated Norfolk Ap soil showed K enrichment but net sorption of P and most multivalent cations. This biochar was highly recalcitrant because the pecan shells were pyrolyzed at a high temperature forming primarily condensed aromatic C structures. On one hand, the recalcitrant nature of biochar may be important if the key goal is to sequester C in the highly stable SOC pool. On the other hand, if the goals are to improve soil fertility and also increase C sequestration, then a biochar having more readily oxidizable structural groups and a low C:N ratio may be more appropriate. Eventually, the biochar will oxidize and soil pH will decrease and CEC increase. The conditions under which feedstocks are pyrolyzed can potentially be designed to produce biochars with single or dual targeted characteristics either as a C-sequestration amendment, a soil fertility correction, or both. ACKNOWLEDGMENTS This publication is based on work supported by the US Department of AgricultureYAgricultural Research Service under the ARS-GRACEnet project. The authors thank Ms. Sheeneka Green, Mr. Dean Evans, Dr. Baoshan Xing, and Ms. Mary Kay Amistadi for laboratory analyses.

Biochar in Coastal Plain Soil

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Novak, J. M., P. J. Bauer, and P. G. Hunt. 2007a. Carbon dynamics under long-term conservation and disk tillage management in a Norfolk loamy sand. Soil Sci. Soc. Am. J. 71:453Y456. Novak, J. M., A. A. Szogi, D. W. Watts, and W. J. Busscher. 2007b. Water treatment residuals amended soils release Mn, Na, S and C. Soil Sci. 172:992Y1000. Novotny, E. H., E. R. Deazevedo, T. J. Bonagamba, T. J. Cunha, B. E. Madari, V. D. Benites, and M. H. Hayes. 2007. Studies on the compositions of humic acids from dark earth soils. Environ. Sci. Technol. 41:400Y405. Ramirez, R. G., H. E. Kiesling, M. L. Galyean, and D. R. Miller. 1986. Influence of pecan shells and hulls as a roughage source on milk production, rumen fermentation, and digestion in ruminants. J. Dairy Sci. 69:1355Y1365. Ritter, W. F., R. W. Scarborough, and A. E. M. Chirnside. 1998. Winter cover crops as best management practice for reducing nitrogen leaching. J. Contam. Hydrol. 34:1Y15. Rutherford, D. W., R. L. Wershaw, and L. G. Cox. 2004. Changes in composition and porosity during the thermal degradation of wood and wood components. USGS Sci. Invest. Rep. 2004Y5292. Available at http://pubs.usgs.gov/sir/5292 (verified November 6, 2008). Schmidt, M. W., and A. G. Noack. 2000. Black carbon in soils and sedi-

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Tiessen, H., E. Cuevas, and P. Chacon. 1994. The role of soil organic matter is sustaining soil fertility. Nature 371:587Y615. Trindale, H., J. Coutinho, M. L. van Beusichem, D. Schofield, and N. Moreira. 1997. Nitrate leaching from sandy loam soils under a doublecropping forage system estimated from suction-probe measurements. Plant Soil 195:247Y256. Trimble, S. W. 1974. Man-Induced Soil Erosion on the Southern Piedmont, 1700-1970. Soil Conserv. Soc. Am., Ankeny, IA. USEPA. 2008. Microwave assisted acid digestion of siliceous and organically based matrices. In Test Methods for Evaluating Solid Waste, Physical/Chemical Methods. SW-846. USEPA, Washington, DC. Available at http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3052.pdf (verified November 28, 2008). Wang, X., R. Cook, S. Tao, and B. Xing. 2007. Sorption of organic contaminants by biopolymers: Role of polarity, structure and domain spatial arrangement. Chemosphere 66:1476Y1484. Wershaw, R. L. 1985. Application of nuclear magnetic resonance spectroscopy for determining functionality of humic substances. In: G. R. Aiken, et al (eds.). Humic Substances in Soil, Sediment, and Water. John Wiley & Sons, New York, NY, pp. 561Y582. Zotarelli, L., J. M. Scholberg, M. D. Dukes, and R. Mun˜oz-Carpena. 2007. Monitoring of nitrate leaching in sandy soils. J. Environ. Qual. 36: 953Y962.

* 2009 Lippincott Williams & Wilkins

Copyright @ 2009 by Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

Poster identificat ion card

Black carbon from rice residues as soil amendment and for carbon sequestration 1Haefele

SM, 2Konboon Y, 3Knoblauch C, 4Koyama S, 1Gummert M, 1Ladha JK

1 International

INTERNATIONAL RICE RESEARCH INSTITUTE

Rice Research Institute, 2 Ubon Ratchathani Rice Research Center, 3 University of Hamburg, 4 Japan International Cooperation Agency Tsukuba,

IRRI

1 Background and objectives

3. The effect of carbonized rice husks in greenhouse and field experiments

On highly weathered soils in tropical and subtropical climates, maintenance of soil organic matter is essential to sustain system productivity and avoid rapid soil degradation. But climatic conditions as well as soil characteristics favor the rapid decomposition of organic matter. However, several recent studies indicated that carbonized plant residues (black carbon), the product of incomplete combustion of organic material, could combine characteristics highly beneficial for soil nutrient dynamics with high stability against chemical and microbial breakdown. Our project investigates i) past and present uses of carbonized rice residues, ii) the agronomic and environmental effects of carbonized rice residues in rice-based systems, iii) the bio-degradability of carbonized residues in rice soils, and iv) the possibilities to integrate residue use into the rice production process.

To investigate the effect of carbonized residue application, we conducted greenhouse studies and established field experiments in different rice production systems (irrigated and rainfed). Preliminary results indicate beneficial agronomic effects on poor soils only. Analysis of the effect on soil characteristics has not yet been completed. Greenhouse experiment

a

ab b

ab b

b

2. Past and current use of carbonized rice residues Carbonized rice husk are traditionally used in Japan. In and outside of Japan they are mainly used in seed beds, in hydroponics and for the cultivation of ornamental plants. Kuntan production in provided by A. Kubota)

Japan

In Japan, carbonized rice husk (Kuntan) has been produced and used in agriculture since a long time. Several books on the utilization of Kuntan in agriculture were already published in the 1910’s in Japan. In and outside of Japan, Kuntan was and is used to cover and protect rice nurseries, as an additive to the culture medium for ornamental plants, and as a component of growth media for seedlings and hydroponics. It was also reported to function as absorptive for moisture and gas and as water purifier.

(photo

Siniloan, Philippines

Los Banos, Philippines

Because of the known use and production of carbonized rice husk in Japan, the same material and procedure for our experiments was used. Weight loss due to carbonization was 68%, but the bulk density did not change (128 g per liter). Data of the chemical analysis is given below. Note that these results depend highly on the temperature and duration of the carbonization process.

Kuntan production at IRRI

C Plain rice husk Carbonized husk 1 Carbonized husk 2 Charcoal (wood)

Fe

Zn

-----------------------------------g kg-1--------------------------------362 6.9 1.4 4.5 0.6 0.8 95 0.9 398 19.7 7.8 13.4 1.4 3.7 187 1.2 398 4.9 1.1 7.2 1.6 1.2 220 5.6 805 9.4 1.2 11.2 11.8 1.3 1 0.4

N

P

K

Ca

Mg

Si

ppm 17 63 36 21

4. Bio-degradability of carbonized rice husks in incubation experiments

Husks constitute about 20% of the paddy weight. Using a newly developed rice hull furnace, they could substitute fossil fuels in the paddy drying process, supply a material for soil improvement and contribute to carbon sequestration in the soil. Carbonized rice husk can also be the end product of rice hull furnaces used by small commercial rice mills to dry the paddy. A new semi-automatic down-draft rice husk furnace, developed by IRRI, Hohenheim University (Germany) and Nong Lam University (Vietnam) has an adjustable feed mechanism for setting the retention time of the rice husk inside the burning chamber.

Fig 1: Experimental setup. Anoxic incubations (left panel) were done with field fresh soil in sealed glass flasks. CH4 and CO2concentrations were measured repeatedly and gas production rates calculated. Oxic carbon turnover was studied in soil samples incubated in gas tight glass flasks under ambient air (right panel). A NaOH trap was used to precipitate CO2 produced. After the incubation period (24-48 h) CO2 production was quantified by titration with HCl.

Oxic

Anoxic

sandy Fluvisol

No rice husk added

Carboni zed rice husk added

Untreat ed rice husk added

No rice husk added

Carboni zed rice husk added

Untreat ed rice husk added

Fig 2: Production of CH4 and CO2 in two temperate Fluvisols. Upper panels show CH4 (black) and CO2 (grey) production under anoxic incubation conditions, lower panels CO2production under oxic conditions. Error bars indicate standard deviation of quadruplicate incubations, the diamond the content of Corg in the different treatments. Preliminary results: If dried rice husks were added, the initial CO2 and CH4 production rates increased by a factor of 3 to 7. In case of the addition of carbonized material, no effect could be measured. These results indicate the strong resistance of carbonized organic matter towards microbial breakdown.

Preliminary results: greenhouse experiments did indicate small biomass and yield increases due to the application of carbonized rice husks. Even high application rates did not result in increased leaching of organic carbon. Results of the field trials did not show any significant agronomic effect (biomass or grain yield) in irrigated systems with medium soil fertility (Los Baños, Modipuram), but considerable yield increases were observed in rainfed systems with poor soil fertility. Particularly interesting at these sites and in the greenhouse experiments was that the addition of carbonized husks did increase the fertilizer use efficiency. Analysis of soil related results is still ongoing.

5. Integrated use of rice residues (husks)

The decomposition of carbonized organic matter in soils was evaluated under oxic and anoxic conditions by measuring the carbon dioxide and methane production. Under both conditions, carbonized rice husks were inert and not decomposed.

loamy Fluvisol

Greenhouse experiments were conducted at IRRI and URRRC (NE Thailand), comparing treatments without, with plain and with carbonized husk application. Fertilizer treatments (none and medium NPK rate) were superimposed. Four field trials with identical treatments were established in irrigated systems in the Philippines and India (Los Baños, Modipuram), in a rainfed upland system in the Philippines (Siniloan), and in a rainfed lowland system in NE Thailand (Ubon).

At high feed rates the husks are incompletely burned resulting in a higher ash recovery, i.e. the furnace produces a high percentage of carbonized rice husk without loosing much efficiency. Hence, rice husks could simultaneously substitute fossil fuels (CO2 emission neutral) during the paddy drying process, supply a material for soil improvement and contribute to carbon sequestration in the soil.

Conclusions: Carbonized crop residues could contribute to increase soil carbon storage (carbon sequestration), reduce climate-relevant gas emissions and improve the natural soil resource in ricebased production systems.

Presented by SM Haefele, IRRI ([email protected])

Climate Change: Global Risks, Challenges and Decisions IOP Conf. Series: Earth and Environmental Science 6 (2009) 372052

IOP Publishing doi:10.1088/1755-1307/6/7/372052

P37.45 Biochar as a soil amendment positively interacts with nitrogen fertiliser to improve barley yields in the UK Alfred Gathorne-Hardy, J Knight, J Woods Imperial College, Centre for Energy Policy and Technology (ICEPT), London, UK Introduction: Soil organic carbon (SOC) is vital for sustainable yields, retaining water and nutrients, providing a habitat for soil biota and improving soil structure (Lorenz 2007). SOC is also a major carbon store, containing over twice the total carbon present in the atmosphere. Land Use Change and arable farming practises have already led to a marked reduction in SOC, and with the increased temperatures expected with climate change SOC is likely to fall further (Raich, Potter et al. 2002). Its loss reduces soil fertility and further exacerbates climate change. Biochar, the use of charcoal as a soil amendment, has been proposed to increase both SOC levels and soil fertility. Biochar has two key properties: 1. a high affinity to nutrients and water, reducing onsite nutrient loss and offsite pollution from nutrient leaching 2. a long residence time. Unlike soil amendments such as compost/manure biochar has a half life of up to several centuries (Lehmann, Gaunt et al. 2006) The long residence time has lead to biochar’s promotion for carbon sequestration, as it solves the lack of permanence problem that plagues most other (non-geological) carbon capture and storage programmes, for example afforestation. But before biochar can be widely taken up it is essential that its impacts on arable cropping are understood. To date there has been almost no work looking at the use of biochar in temperate agriculture. Aim: To investigate the impacts of different rates of biochar on cereal growth within temperate agriculture, and specifically the interaction of biochar and nitrogen fertiliser. Methods: In 2008 a semi-randomised block design was established using spring barley on light land with five levels of biochar (0, 5 10, 20 and 50 t/ha) and 5 levels of N (ammonium nitrate) fertiliser (0, 25, 50, 70 and 100 kgN/ha). Each biochar level was tested against each N level, giving 25 treatments. Each treatment was repeated 5 times. Other nutrients were supersaturated on all plots. Results were analysed using ANOVA in R. Results and Conclusions: Interestingly the results showed no significant effect of yield for biochar alone, but do show a significant interaction (p = 0.055) between biochar and N fertiliser. Biochar appears to increase the nitrogen use efficiency. In this site the addition of 50t/ha of biochar increased the total yield by c. 30% when high levels of N were used. A likely explanation for the lack of effect from biochar alone on yield is that one of the most important attributes of biochar – its ability to retain water – was not tested as the 2008 growing season was exceptionally wet, so water was unlikely to have been a limiting factor.

c 2009 IOP Publishing Ltd 

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Climate Change: Global Risks, Challenges and Decisions IOP Conf. Series: Earth and Environmental Science 6 (2009) 372052

IOP Publishing doi:10.1088/1755-1307/6/7/372052

Barley yield (g/250cm2)

250 200 0 N kg/ha

150

10 N kg/ha 100

20 N kg/ha 80 N kg/ha

50

100 N kg/ha

0 0

5

10

20

50

Biochar application rate (t/ha)

Figure 1. The effect of different levels of biochar, N fertiliser, and their interactions on barley yield

In addition to the onsite experiment, an economic model is being developed to see which price mechanisms, if any, are required to encourage farmers to use biochar as a regular soil amendment. Conclusion: These results demonstrate that biochar can have an important role in addressing climate change through carbon sequestration and increased nitrogen use efficiency, and at the same time improving yields and food security. It is hoped that through its high affinity to nutrients and water biochar can help to buffer climatic variability and reduce the need for fertiliser inputs. Thus biochar could both adapt agriculture to, and mitigate it from, climate change. List of References Lehmann, J., J. Gaunt, et al. (2006). "Bio-Char Sequestration in Terrestrial Ecosystems – a Review." Mitigation and Adaptation Strategies for Global Change 11: 25. Lorenz, K. (2007). "Strengthening the soil organic carbon pool by increasing contributions from recalcitrant aliphatic bio(macro)molecules." Geoderma 142(1-2): 1-10. Raich, J. W., C. S. Potter, et al. (2002). Interannual variability in global soil respiration, 1980-94. 8: 800-812.

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African Journal of Agricultural Research Vol. 3 (11), pp. 759-774, November, 2008 Available online at http://www.academicjournals.org/AJAR ISSN 1991-637X © 2008 Academic Journals

Full Length Research Paper

Preliminary evaluation of the effects of carbonized chicken manure, refuse derived fuel and K fertilizer application on the growth, nodulation, yield, N and P contents of soybean and cowpea in the greenhouse Seth O. Tagoe, T. Horiuchi and T. Matsui United Graduate School of Agricultural Science, Gifu University, Yanagido 1-1 Gifu, 501-1193, Japan. Accepted 3 November, 2008

Carbonized organic materials have not traditionally been applied to grain legumes such as soybean (Glycine max L. Merrill) and cowpea (Vigna unguiculata L. Walp) although the potential for favourable agronomic responses exist because of their high contents of available P. We explored the effects of carbonized chicken manure and carbonized refuse derived fuel (RDF) from municipal organic waste with or without inorganic K fertilization on the growth, nodulation, seed yield, N and P contents of soybean and cowpea in a vinyl house pot experiment. Growth, nodulation, plant total N and P contents were evaluated at peak flowering stage of legume growth. The application of carbonized chicken manure only increased seed yield by 41 and 146% for soybean and cowpea respectively while the carbonized chicken manure with inorganic K fertilizer increased seed yield by 53 and 185% for soybean and cowpea respectively relative to the un-amended control. The application of carbonized RDF only increased seed yield by 20 and 59% for soybean and cowpea respectively while the application of carbonized RDF with inorganic K fertilizer increased seed yield by 45 and 126% for soybean and cowpea respectively relative to the absolute control. The application of both carbonized organic materials with inorganic K fertilizer increased number of nodules more than their sole application. Results suggested that the application of carbonized chicken manure and carbonized RDF improved the growth, nodulation, seed yield, N and P contents of both grain legumes due to their high content of P. The application of the carbonized organic materials with inorganic K fertilizer further increased seed yields of both grain legumes suggesting that K was limiting the response to P from the organic materials in the experimental soil. Key words: Carbonization, chicken manure, grain legumes, refuse derived fuel, seed yield. INTRODUCTION Soybean (Glycine max (L) Merrill) and Cowpea (Vigna unguiculata (L) Walp) are important grain legumes grown in the tropics and sub-tropics. Cowpea is particularly important in West Africa where it occupies 6 million hectares of agricultural land (Bationo et al., 1990) with over 9.3 million metric tons of annual production (Ortiz, 1998). The main limiting nutrients for legume production

*Corresponding author. E-mail:[email protected]; Tel: +81-90-1822-9702. Fax: +81-58-293-2846.

in West Africa are N and P (Fox and Kang, 1977). The high cost and scarcity of inorganic fertilizers had renewed interest in the use of unorthodox organic soil amendment materials such as carbonized organic materials (Shinogi et al., 2003) and bio-char (Ishii and Kadoya, 1994) for cultivation of crops. Carbonization has been proposed as a management tool for agricultural and municipal wastes producing fertilizer, renewable energy and bio-char. Carbonization is achieved through pyrolysis of organic wastes at temperao tures ranging between 300 and 500 C and eliminates the bad smell, reduces the volume and weight of organic wastes (Popov et al., 2004). During carbonization, some

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amount of N is lost in the form of ammonia gas but the resulting carbonized material is higher in available P by up to 5 times compared to the original waste (Shinogi et al., 2003; Tagoe et al., 2008). Carbonized organic wastes can be used as soil amendments to supply plant nutrients especially N and P. The application of carbonized organic wastes to soil improve the physical properties of the soil, improve soil fertility and nutrient retention (Sombroek et al., 1993; Lehmann and Rondon., 2005), stimulate microbial activities in soil (Tejada et al., 2006), increase mycorrhizal abundance and/or functioning (Warnock et al., 2007), increase nodule abundance in soybean (Tagoe et al., 2008) as well as improve biological N2 fixation in common beans (Rondon et al., 2007). No work has been reported in the scientific literature on the use of carbonized refuse derived fuel (CRDF) as soil amendment for legume growth while only one work had been reported on the use of carbonized chicken manure as soil amendment for soybean growth (Tagoe et al., 2008). In this study, we assess the effects of two carbonized organic soil amendment materials (chicken manure and RDF) on the growth, nodulation, yield, N and P concentrations of two grain legumes (soybean and cowpea) with or without inorganic K fertilizer. We hypothesized that the application of carbonized organic materials will improve the growth, nodulation, seed yield, N and P concentrations of grain legumes more with K fertilizer than without K fertilizer because K could limit the response of grain legumes to P from carbonized organic materials in low P status soils (Carsky, 2003) and also because of the low K content of the experimental soil. Our major objectives are to elucidate the effect of carbonized chicken manure and carbonized RDF on 1) the growth, nodulation and seed yield and 2) plant and seed concentrations of N and P of both crops. MATERIALS AND METHODS Plant culture Experiments were conducted from May to October, 2007 at the greenhouse of Gifu University Experiment Farm (35o 27’ N, 136o 46’ E). Wagner pots (1/2000a) were filled with sandy loam soil with the following characteristics: pH; 5.62, EC; 0.28 mS cm-1, total N; 0.100%, total C; 0.88%, available P; 1.16 mg 100 g-1, available K; 13.3 mg 100 g-1, available Ca; 90.0 mg 100 g-1, and available Mg; 31.0 mg 100 g-1. The nutrient concentrations, pH and EC of the carbonized chicken manure and RDF used in the experiment are shown in Table 1. Carbonized chicken manure was obtained from Tokyo Yougyou Kabushiki Kaisha, Tajimi City, Gifu Prefecture, Japan. Carbonized chicken manure was produced from pelleted, dried chicken manure through pyrolysis at a temperature of 450oC for one hour in a furnace. Carbonized RDF was obtained from Kurimoto Tekkosho, In a City, Gifu Prefecture, Japan. Carbonized RDF was prepared from municipal organic waste through pyrolysis at a temperature of 500oC for 2 h in a kiln after drying the waste in a furnace for 10 h. The amounts of the carbonized organic materials applied per pot for the various treatments are shown in Table 2. Carbonized organic amendments were applied to the appropriate

treatments three weeks before sowing. Potassium fertilizer was applied as Muriate of Potash (KCl) at a rate of 83 kg K ha-1 to the appropriate treatments at sowing. No chemical pesticides were used in this experiment. Five seeds of soybean (Glycine max (L) Merrill cv Akishirome) and cowpea (V. unguiculata (L) Walp cv Tsurushi sasage) were sown per pot on 7th June, 2007. After emergence, seedlings were thinned to two per pot. Plants were watered as when necessary. All pots were kept completely free of weeds within the duration of the experiment by hand-picking when they appear. Experimental design The experiment was set up using two grain legumes (soybean and cowpea), two carbonized organic materials (carbonized chicken manure and carbonized RDF) with two rates of inorganic K fertilizer with or without K, 83 kg K ha-1 and 0 kg K ha-1 respectively in a factorial combination giving a total of 48 treatments (2 x 2 x 2 x 6) arranged in completely randomized design (CRD) of six replications. All data collected from the study were analyzed by using Duncan’s Multiple Range Test (DMRT) (Excel Statistical Package Version 6.0) and mean separations were done by the same method. Measurements Plant height and relative chlorophyll content (SPAD) were measured twice within the duration of the experiment. For both parameters, the first (pre-flowering) and second (post-flowering) samplings were done on 16th July and 31st July respectively. SPAD was measured with a chlorophyll meter model SPAD-502 (Minolta Co. Ltd., Japan). SPAD readings were taken from 12 randomly selected youngest and fully expanded leaves of plants in each pot. Each SPAD reading was taken on one side of the mid-rib of the leaf blade, midway between the leaf blade and tip. Sampling for leaf area, dry matter weight, and number of nodules was done on 26th July for cowpea and 1st August for soybean when the plants were at peak flowering stage. Shoots were harvested by cutting the plants in each pot at the soil level. Roots were harvested by lifting the soil in each pot and washing off the soil under running water from a tap. The harvested shoots were separated into leaves, stems (including petioles), flowers etc. The roots were washed clean of soil and root nodules were separated and counted. The leaves were used to estimate leaf area by the core borer method after oven-drying harvested samples at 80oC for 72 h. The dried samples were then weighed to determine dry weights of leaves, stems, roots and nodules and finally total dry matter weight. The total dry material was milled to pass 0.5 mm mesh sieve using a wonder blender (Model WB-1). The milled plant samples were used for total N and total P analyses and determination. Total N was determined with an automatic high sensitive NC analyzer (Sumigraph NC-95A, Shimadzu Co. Ltd., Japan). Total P was determined colorimetrically (HITACHI-U-1800) according to Bray and Kurtz (1945) and Murphy and Riley (1962). Residual experimental soil exchangeable cations (K+, Ca2+, and Mg2+) were measured with a Polarized Zeeman Atomic Absorption Spectrophotometer (HITACHI-180-60) after extraction of samples with 1.0N Ammonium acetate solution (pH 7.0).

RESULTS Plant growth At the pre-flowering sampling of the relative chlorophyll

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Table 1. Nutrient composition of carbonized organic materials used in the experiment after pyrolysis. Property pH † EC (µS cm-1) Total N (g kg-1) NO3-N (mg kg-1) Total C (g kg-1) C/N ratio Na (g kg-1) P (g kg-1) K (g kg-1) Ca (g kg-1) Mg (g kg-1)

Carbonized chicken Manure 9.93 3.64 44,0 1.90 497.5 11.31 2.37 24.6 37.00 7.67 1.93

Carbonized refuse derived fuel 7.76 65.03 20.2 500.9 25.00 3.38 5.22 3.45 30.28 2.10

† The pH and EC were measured in the extracts of carbonized organic materials in distilled water [ 1:20 (w/v)] on dry weight basis.

Table 2. Treatment details showing amounts of carbonized organic materials and inorganic K fertilizer applied per pot and treatment abbreviations. Treatment

No carbonized organic material (Control) No carbonized organic material (Control) Carbonized chicken manure Carbonized chicken manure Carbonized refuse derived fuel Carbonized refuse derived fuel

Amount of carbonized organic material applied (g) 0 0 11.40 11.40 24.75 24.75

content (SPAD) leaves of soybean plants treated with carbonized chicken manure were the greenest. Leaves of soybean plants treated with carbonized RDF were of intermediate greenness while those of the control were the least green with or without K fertilizer. Generally, leaves of soybean plants without K fertilizer were greener than those with K fertilizer (Figure 1). The observed differences were significant according to DMRT at p< 0.05. At the post-flowering sampling of SPAD, a similar trend was observed for the control and carbonized RDF treatments with or without K fertilizer. However, leaves of soybean plants treated with carbonized chicken manure were the greenest with or without K fertilizer (Figure 1). At the pre-flowering sampling of SPAD of cowpea, leaves of plants treated with carbonized chicken manure with or without K fertilizer were the greenest. Cowpea leaves of plants treated with carbonized RDF with or without K fertilizer were of intermediate greenness. Leaves of cowpea plants without any organic amendment (control) with or without K fertilizer were least green (Figure 2). For cowpea leaves of plants treated with carbonized chicken manure and carbonized RDF, no difference in greenness were observed for treatments with and without K fertilizer.

Amount of K fertilizer applied as muriate of potash (KCl) (mg) 0 830.0 0 410.0 0 740.0

Abbreviation

Control (Without K) Control (With K) CCM (Without K) CCM (With K) CRDF (Without K) CRDF (With K)

Leaves of control cowpea plants that received K fertilizer were greener than those that did not (Figure 2). At the post-flowering sampling of SPAD for cowpea, a similar trend to the pre-flowering SPAD was observed except that leaves of control cowpea plants without K fertilizer were greener than those with K fertilizer (Figure 2). The observed differences among treatments for both preflowering and post-flowering were significant at p<0.05 according to DMRT. Total dry weight was significantly highest according to DMRT at p<0.05 in soybean plants treated with carbonized chicken manure followed by those treated with carbonized RDF. Control soybean plants were least heavy in total dry weight (Table 3). For all treatments, soybean plants with K fertilization produced heavier dry matter than the corresponding treatments without K fertilization (Table 3). There was a strong and significant positive relationship between total dry weight and plant 2 total N content of soybean (R = 0.79 **, Figure 3a). A strong and significant positive relationship was observed between soybean total dry weight and plant total P 2 content (R = 0.90 **, Figure 3b). Total dry weight of cowpea followed a similar trend as that of soybean. Cowpea plants treated with carbonized

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Figure 1. Effects of carbonized organic materials supply on the pre-flowering and post-flowering SPAD values of soybean. Data show the means ± SD of three independent replications.

Figure 2. Effects of carbonized organic materials supply on the pre-flowering and post-flowering SPAD values of cowpea. Data show the means ± SD of three independent replications.

chicken manure produced significantly the highest dry matter followed by those treated with carbonized RDF according to DMRT at p<0.05. Control cowpea plants

produced the least dry matter (Table 4). For all treatments, cowpea plants that received K fertilizer produced heavier dry matter than those that did not

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Table 3. Growth, nodulation, total N and P contents of soybean as affected by the application of carbonized organic materials. Treatment

K fertilizer

Total dry weight (g)

Number of nodules

Control

Without K With K Without K With K Without K With K

38.0 a 49.3 b 64.2 c 81.8 d 54.1 b 69.2 c

380.7 a 428.3 b 529.3 c 611.0 d 437.3 b 567.0 c

CCM CRDF

Plant total N content (g kg-1) 27.8 a 27.2 a 31.9 c 33.0 d 30.4 b 30.8 b

Seed total N content (g kg-1) 66.1 a 66.8 a 72.8 d 73.8 e 70.8 b 71.8 c

Plant total P content (g kg-1) 0.35 a 0.38 b 0.44 d 0.47 f 0.43 c 0.45 e

Seed total P content (g kg-1) 0.09 a 0.11 b 0.27 c 0.34 e 0.26 c 0.31 d

Within each column, means having a common letter(s) are not significantly different according to DMRT at p < 0.05. Table 4. Total dry weight, number of nodules, total N and P contents of cowpea as affected by the application of carbonized organic materials. Treatment

K fertilizer

Total dry weight (g)

Number of nodules

Control

Without K With K Without K With K Without K With K

17.5 a 31.7 bc 34.8 c 38.3 d 29.3 b 37.7 d

103.3 a 140.0 b 122.0 ab 215.0 d 113.0 a 189.0 c

CCM CRDF

Plant total N content (g kg-1) 23.1 a 22.9 a 27.3 c 31.9 d 24.9 b 28.0 c

Seed total N content (g kg-1) 40.3 a 41.3 b 46.6 e 47.9 f 43.5 c 44.9 d

Plant total P content (g kg-1) 0.54 a 0.56 b 0.64 d 0.67 e 0.62 c 0.64 d

Seed total P content (g kg-1) 0.12 a 0.14 b 0.18 d 0.21 f 0.16 c 0.19 e

Within each column, means having a common letter(s) are not significantly different according to DMRT at p < 0.05.

(Table 4).There was a significant positive relationship between total dry weight and plant total N content of 2 cowpea (R = 0.56 *, Figure 4a). A strong and significant positive relationship was observed between total dry 2 weight and plant total P content of cowpea (R = 0.70 **, Figure 4b). Number of nodules of soybean was significantly highest in soybean plants treated with carbonized chicken manure followed by those treated with carbonized RDF according to DMRT at p<0.05. Control soybean plants produced the least number of nodules. For each carbonized organic amendment treatment, soybean plants that received K fertilizer produced more nodules than those that did not (Table 3). There was a strong and significant positive relationship between number of 2 nodules and plant total N content of soybean (R = 0.75**, Figure 5a). Also, a strong and significant positive relationship was observed between number of nodules 2 and plant total P content of soybean (R = 0.83**, Figure 5b). Cowpea plants of both carbonized organic amendment treatments without K fertilization produced similar number of nodules. However, cowpea plants treated with carbonized chicken manure and K fertilizer produced significantly the greatest number of nodules followed by cowpea plants treated with carbonized RDF and K fertilizer according to DMRT at p<0.05. Control cowpea plants with K fertilizer produced the least number of

nodules (Table 4). There was a significant positive relationship between number of nodules and plant total N 2 content of cowpea (R = 0.68 *, Figure 6a). No significant positive relationship was observed between number of 2 nodules and plant total P content of cowpea (R = 0.43 ns, Figure 6b). Yield and yield components Dry pod yield and seed yield of soybean followed a similar trend. Soybean seed yield was heaviest in treatments amended with carbonized chicken manure with or without K fertilizer followed by carbonized RDF amended treatments with or without K fertilizer. Soybean seed yield was least in control treatments with or without K fertilizer (Table 5). Generally, carbonized organic amendment treatments that received K fertilizer produced better dry pod and seed yields than those without K fertilizer. The application of carbonized chicken manure only increased soybean seed yield by 41% while the application of carbonized RDF only increased soybean seed yield by 20%. The application of carbonized chicken manure and K fertilizer increased soybean seed yield by 53% while the application of carbonized RDF and K fertilizer increased soybean seed yield by 45%. Dry pod yield and seed yield of cowpea followed a similar trend. Cowpea plants treated with carbonized

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= Without K fertilizer;

= with K fertilizer; ** = significant at 1%.

= Without K fertilizer;

= with K fertilizer; ** = significant at 1%.

Figure 3. Relationship between total dry weight, plant total N content and plant total P content of soybean at peak flowering. 3a. Relationship between total dry weight and plant total N content of soybean at peak flowering stag 3b. Relationship between total dry weight and plant total P content of soybean at peak flowering stage

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= Without K fertilizer;

= Without K fertilizer;

= with K fertilizer; ** = significant at 1%.

= with K fertilizer; * = significant at 5%.

Figure 4. Relationship between total dry weight, plant total N content and plant total P content of cowpea at peak flowering. 4a. Relationship between total dry weight and plant total N content of cowpea at peak flowering stage. 4b. Relationship between total dry weight and plant total P content of cowpea at peak flowering stage.

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= Without K fertilizer;

= Without K fertilizer;

= with K fertilizer; ** = significant at 1%.

= with K fertilizer; ** = significant at 1%.

Figure 5. Relationship between number of nodules, plant total N content and plant total P content of soybean at peak flowering. 5a. Relationship between number of nodules and plant total N content of soybean at peak flowering stage. 5b. Relationship between number of nodules and plant total P content of soybean at peak flowering stage.

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= Without K fertilizer;

= with K fertilizer;

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= significant at 5% .

(6a)

= Without K fertilizer;

= with K fertilizer; ns = not significant .

6b) Figure 6. Relationship between number of nodules, plant total N content and plant total P content of cowpea at peak flowering. 6a. Relationship between number of nodules and plant total N content of cowpea at peak flowering stage. 6b. Relationship between number of nodules and plant total P content of cowpea at peak flowering stage.

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Table 5. Yield and yield components of soybean as affected by the application of carbonized organic materials. Treatment

K fertilizer

Dry pod yield (g)

Seed yield (g)

Control

Without K With K Without K With K Without K With K

49.5 a 68.7 c 69.8 c 71.9 cd 59.7 b 75.8 d

38.1 a 52.9 c 53.7 c 58.4 d 45.9 b 55.4 cd

CCM CRDF

No. of pods plant-1 50.4 a 108.7 c 79.0 c 137.5 d 68.9 b 103.7 d

No. of seeds pod-1 1.8 a 1.8 a 1.9 b 2.0 c 1.9 b 1.9 b

100 seed wt (g)

Harvest index

26.4 a 28.0 b 28.9 c 29.9 e 27.8 b 29.6 d

0.54 ab 0.63 e 0.57 bc 0.59 bc 0.67 e 0.52 a

Table 6. Yield and yield components of cowpea as affected by the application of carbonized organic materials. Treatment

K fertilizer

Control

Without K With K Without K With K Without K With K

CCM CRDF

Dry pod yield (g) 26.1 a 40.6 c 47,9 d 54.9 e 35.6 b 47.1 d

Seed yield (g) 14.2 a 27.6 c 34.9 e 40.5 f 22.6 b 32.1 d

chicken manure with or without K fertilizer produced the heaviest seed yield followed by those treated with carbonized RDF. Control cowpea plants with or without K fertilizer produced the least heavy seed yield. Generally, cowpea plants that received K fertilizer produced heavier seed yield than those that did not receive K fertilizer (Table 6). Cowpea seed yield increased 146% by the application of carbonized chicken manure only while it increased by 49% as a result of the application of carbonized RDF only. The application of carbonized chicken manure and K fertilizer increased cowpea seed yield by 185% while the application of carbonized RDF and K fertilizer increased it by 126%. Number of pods/plant of soybean followed a similar pattern to dry pod and seed yields of soybean. In all treatments, number of pods/plant of soybean was better for treatments that received K fertilizer than for those without K fertilizer (Table 5). Number of pods/plant was highest in cowpea plants that received K fertilizer than those that did not for all treatments. Number of pods/plant was significantly highest in cowpea plants treated with carbonized chicken manure followed by carbonized RDF. Number of pods/plant was least in control cowpea plants. Number of seeds per pod was only slightly increased by K fertilizer in soybean plants treated with carbonized chicken manure (Table 5). Number of seeds/pod of cowpea was neither affected by carbonized organic amendment material supply nor K fertilizer application (Table 6). 100 seed weight of soybean was increased by K fertilizer

No. of pods plant-1 9.4 a 12.0 bc 11.9 b 14.9 d 11.4 b 13.0 c

No. of seeds pod-1 11.7 ab 11.3 ab 12.0 b 12.3 b 10.7 a 11.3 ab

100 seed wt (g) 17.4 a 17.3 a 19.8 b 20.2 b 18.1 a 19.6 b

Harvest index 0.66 d 0.60 ab 0.61 bc 0.63 c 0.59 ab 0.58 a

in all organic amendment treatments. 100 seed weight was significantly heaviest in carbonized chicken manure treated plants according to DMRT at p< 0.05 followed by carbonized RDF treated plants. 100 seed weight was least heavy in control soybean plants (Table 5). 100 seed weight of cowpea was not affected by K fertilizer application in control and carbonized chicken manure treated plants but was increased slightly in carbonized RDF treated plants. 100 seed weight of cowpea was highest in plants treated with carbonized chicken manure with or without K fertilizer and similar to plants treated with carbonized RDF and K fertilizer (Table 6). Harvest index was increased by K fertilizer application in control soybean plants and reduced in carbonized RDF treated soybean plants. K fertilizer application did not affect harvest index in carbonized chicken manure treated soybean plants (Table 5). Harvest index of cowpea did not follow any particular trend but was highest in control cowpea plants without K fertilizer and lowest in carbonized RDF treated plants with K fertilizer (Table 6).

N contents Plant total N content of soybean was highest in carbonized chicken manure amended plants followed by carbonized RDF amended plants. Control soybean plants were least in plant total N content (Table 3). K fertilizer

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only slightly increased plant total N content of carbonized chicken manure amended soybean plants while it had no effect on plant total N content of carbonized RDF amended soybean plants (Table 3). Seed total N content of soybean followed a similar trend as plant total N content of soybean. The only difference is that K fertilizer application increased seed total N content of carbonized chicken manure and carbonized RDF amended soybean plants while it had no effect on seed total N content of control soybean plants (Table 3). There was a significant positive relationship between seed total N content and 2 seed yield of soybean (R = 0.50*, Figure 7). Plant total N content of cowpea was highest in plants treated with carbonized chicken manure with or without K fertilizer followed by plants treated with carbonized RDF with or without K fertilizer. Control cowpea plants were lowest in plant total N content with or without K fertilizer (Table 4). K fertilizer application increased plant total N content in carbonized chicken manure and carbonized RDF amended cowpea plants but not in control cowpea plants (Table 4). Seed total N content of cowpea followed a similar trend (Table 4). However, K fertilizer application increased cowpea seed total N content in all treatments (Table 4). There was a strong positive relationship between plant total N content and seed yield of cowpea 2 (R = 0.72**) as well as between seed total N content and 2 seed yield of cowpea (R = 0.81**, Figure 8). P contents Plant total P content of soybean was affected by both carbonized organic amendment supply and K fertilizer application. Plant total P content of soybean was highest in plants amended with carbonized chicken manure with or without K fertilizer followed by carbonized RDF treated plants with or without K fertilizer. Control soybean plants were lowest in plant total P content (Table 3). K fertilizer application increased plant total P contents of all treatments (Table 3). Seed total P content of soybean followed a similar trend as plant total P content of soybean (Table 3). There was a positive relationship between plant total P content and seed yield of soybean 2 (R = 0.62*, Figure 9). Plant total P content of cowpea was affected by both carbonized organic amendment and K fertilizer application. Plant total P content of cowpea was highest in carbonized chicken manure amended cowpea plants with or without K fertilizer followed by carbonized RDF amended plants with or without K fertilizer. Plant total P content was lowest in control cowpea plants (Table 4). K fertilizer application increased plant total P contents of cowpea in all treatments. Seed total P content of cowpea followed a similar trend as plant total P content of cowpea (Table 4). There was a strong positive relationship between plant total P content and seed yield of cowpea 2 (R = 0.71**, Figure 10). There was a strong positive relationship between seed total P content and seed yield

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of cowpea (R = 0.83**, Figure 10). DISCUSSION The effects of two carbonized organic materials that is, chicken manure and refuse derived fuel (RDF) with or without inorganic K fertilizer on the growth, nodulation, yield, N and P contents of two grain legumes i.e. soybean and cowpea were explored in this greenhouse trial. The application of carbonized chicken manure only increased seed yield by 41 and 146% in soybean and cowpea respectively while the application of carbonized chicken manure and inorganic K fertilizer increased seed yield by 53 and 185% in soybean and cowpea respectively. The application of carbonized RDF only increased seed yield by 20 and 59% in soybean and cowpea respectively while the application of carbonized RDF and inorganic K fertilizer increased seed yield by 45 and 126% in soybean and cowpea respectively. The trends for dry pod yield and total dry weight of both grain legumes were similar to that of their respective seed yields. This result is consistent with that reported by Rondon et al. (2007) who observed a 46% increase in common bean yield over the control in response to bio-char application. Chan et al. (2007) observed in their work that in the absence of N fertilizer, green-waste bio-char application to soil did not increase radish yield even at higher rates but reported significant bio-char and N fertilizer interaction highlighting the role of bio-char in improving N fertilizer use efficiency of the plant. Although few works are available for comparison with the results of this study, our results are consistent with previous works done using ordinary un-carbonized chicken manure. Garcia and Blancaver (1983) reported that the application of poultry manure increased soybean seed yield by 62% over the control. Schmidt et al. (2001) found that soybean seed yield increased linearly with increasing swine manure rate. Several researchers have reported soybean seed yield increases with applied commercial N fertilizer (Lamb et al., 1990; Wesley et al., 1998). The higher seed yields of both grain legumes in response to the application of carbonized organic materials especially carbonized chicken manure suggest that both N and P are important nutrients that influence the growth and yield of soybean and cowpea. Carbonized chicken manure and carbonized RDF contain high levels of macro-nutrients especially N and P as well as micronutrients that would be available to plant roots and soil biota. Hariston et al. (1990) and Schmidt et al. (2001) observed that soybean not only requires a considerable amount of N to produce a crop, but also a constant supply of available P to maintain rapid growth and development. Carbonized chicken manure and carbonized RDF are particularly rich in both total and available P and their application to soil at high rates can supply a considerable amount of available P for plant uptake. Again, carbonized organic materials such as

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= Without K fertilizer;

= with K fertilizer;

= significant at 5%.

Figure 7. Relationship between seed total N content and seed yield of soybean.

Figure 8. Relationship between plant total N content, seed total N content and seed yield of cowpea.

carbonized chicken manure, carbonized RDF and biochar can act as soil conditioners to enhance plant growth by supplying macro and micro-nutrient elements,

retaining nutrients and improving soil physical and biological properties (Glaser et al., 2002; Lehmann and Randon, 2005). Abdelhamid et al. (2004) found increased

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= Without K fertilizer;

= with K fertilizer; * = significant at 5%.

Figure 9. Relationship between plant total P content at peak flowering and seed yield of soybean.

Figure 10. Relationship between plant total P content, seed total P content and seed yield of cowpea.

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dry weight of faba bean as a result of chicken manure supply. Cowpea responded positively to the application of carbonized chicken manure and CRDF in this study in terms of growth parameters and seed yield. This response underscores the importance of P as a critical nutrient element influencing the performance of cowpea and soybean. Several researchers have reported significant responses of cowpea and soybean to P application (Tenebe et al., 1995; Ankomah et al., 1995; Okeleye and Okelana, 1997). They observed significant increases in total dry matter yield, number of flowers, pod and seeds per plant, seed yield and nodulation as a result of P application. Rondon et al. (2007) reported a 39% increase in biomass production of common bean in response to bio-char application which they attributed to greater availability of K, Ca and P. Chan et al. (2007) observed additional increase in dry matter of radish in the presence of N fertilizer varied from 95% in the control to 266% in the 100 t/ha bio-char amended soils. Carsky (2003) working on the response of cowpea and soybean to P and K on terre de barre soils in southern Benin, reported that soybean and cowpea grain yield increased by 147% and 95% respectively in response to P application. Number of nodules of soybean and cowpea increased with the application of carbonized organic materials. This observation is consistent with that of Tagoe et al. (2008) who reported increased nodule abundance of soybean as a result of carbonized chicken manure application and attributed it to the high available P content of carbonized chicken manure. The application of carbonized chicken manure increased nodule abundance of both grain legumes more than carbonized RDF. This observation can be attributed to the high P content of carbonized chicken manure relative to carbonized RDF. Rondon et al. (2007) also observed that biological N2 fixation of common bean increased with bio-char application. They reported that the proportion of fixed N increased from 50% without bio-char addition to 72% with 90 g kg-1 biochar added and attributed this observation to greater availability of B, and Mo and to a lesser extent K, Ca and P availability. The application of the carbonized organic materials plus K fertilizer further increased the number of nodules of both legumes thus confirming the hypothesis that K could limit the response of P from the carbonized organic materials in low P status soils (Carsky, 2003). P fertilization has been shown to increase number of nodules and their weight in soybean (Cassman et al., 1993; Jones et al., 1977) and in cowpea (Wan Othman et al., 1991). This is because P is known to initiate nodule formation, increases the number of nodule primordia and is essential for the development and functioning of formed nodules (Waluyo et al., 2004). Nodules are known to be a strong sink for P and P concentration in nodules can be three times higher than in other plant organs with a minimum effect from P deficiency (Vadez et al., 1999). Several researchers have reported that the supply of P

plays important roles in establishment, growth and function of nodules (Israel, 1987; Beck and Munns, 1984; Leung and Bottomley, 1987) and growth of host plants (Munns et al., 1981). Number of nodules is important because a positive correlation has been reported between nodule number and total nitrogenase activity of soybean (Singleton and Bohlool, 1984) and alfalfa (Porter, 1983). According to Gates and Muller (1979) the application of fertilizer containing N, P and S to soybean contributed to forming a stronger symbiotic mechanism and more active N2-fixation. Since the carbonized organic materials used in this experiment especially carbonized chicken manure contain N, P and S (Sharpley et al., 1993) their application to soybean and cowpea could be beneficial to the symbiotic N2-fixing mechanism. Low P availability is especially problematic for leguminous crops because legume nodules responsible for N2-fixation have high P requirement (Vance, 2001). P is essential for plant growth, nodulation and N2-fixation (Pereira and Bliss, 1989). Nodule number as well as nodule dry weight is greatly reduced by P deficiency (Ribet and Drevon, 1995) and nitrogenase activity varies with P availability (Israel, 1987). Acute P deficiency is known to prevent nodulation of grain legumes. P deficiency is more likely to affect N2fixation legumes than other species because symbiotic N2-fixation is an energetically expensive process which requires more P than does plant growth (Olivera et al., 2004). The strong positive relationship between number of nodules and plant total P content of soybean confirms the importance of P in legume nodulation. Total N and total P contents of plant and seed of soybean and cowpea increased with the application of carbonized organic materials with or without inorganic K fertilizer. This observation is consistent with that reported by Jassen (1998) that nutrient uptake requires N, P and K in balance to reach maximum values. Adeli (2005) observed increased N concentration in the above ground biomass of soybean in response to poultry manure application. The application of chicken manure to faba bean increased total N contents in roots, shoots and the whole plant (Abdelhamid et al., 2004). Belle (2006) reported significant increases in the uptake of N and P in common bean as a result of the application of N and P fertilizers. Barker and Sawyer (2005) observed that N concentration in plant dry matter of soybean was increased significantly with applied N. Studies with several legumes have consistently shown a positive response to P application; whole plant N concentration and plant dry matter were found to increase in response to phosphate in the growth media (Pereira and Bliss, 1987). P application has been reported to influence the contents of other nutrients in cowpea leaves (Kang and Nangju, 1983), shoots (Bagayoko et al., 2000) and seed (Omueti and Oyenuga, 1970). Seed total N content of soybean was positively correlated with seed yield. Also plant total N and seed total N contents of cowpea were

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correlated with seed yield of cowpea. These observations suggest the importance of N in the seed yields of these grain legumes due to the high protein contents of their seeds especially soybean. Plant total P content of soybean was positively correlated with soybean seed yield. Also, plant total P and seed total P contents were positively correlated with seed yield in cowpea. These observations underscore the importance of not only N, but P as well in increasing the growth and seed yield of these grain legumes. Bio-char addition can result in elevated quantities of bio-available nutrients such as N, P and metal ions, in the soil (Tryon, 1948; Lehmann et al., 2003; Gundale and DeLuca, 2006; DeLuca et al., 2006). Addition of bio-char to soil alters important soil physical and chemical properties such as pH (Lucas and Davis, 1961) and typically increase soil cation exchange capacity (CEC) (Glaser et al., 2002), and can lead to greater water holding capacity (WHC) while generally decreasing bulk density (Tryon, 1948) as well as increase bio-available P and cations in soils. Improvement in physical properties of the soil as a result of the addition of carbonized chicken manure and carbonized RDF to a lesser extent, may have contributed to the increased growth and yield of the grain legumes. Conclusion The growth, nodulation, seed yield, total N and P contents of plant and seed of soybean and cowpea all increased with the supply of carbonized chicken manure and carbonized RDF due to their high available P contents. The application of carbonized organic materials and inorganic K fertilizer increased grain yield and other parameters in both crops more than the sole application of the carbonized organic materials thus suggesting that it is a good potential option to be evaluated for use in the field and home garden for grain legume production. ACKNOWLEDGEMENT The authors would like to express their profound gratitude to the Ministry of Education, Culture, Sports, Science and Technology, Japan for financial support without which this research would not have been possible. REFERENCES Abdelhamid M, Horiuchi T, Shinya O (2004). Nitrogen uptake by faba bean from 15N labeled oilseed-rape residue and chicken manure with ryegrass as a reference crop. Plant Prod Sci 7:371-376. Adeli A, Sistani KR, Rowe DE, Tewolde H (2005). Effects of broiler litter on soybean production and soil nitrogen and phosphorus concentrations. Agron. J. 97:314-321. Ankomah AB, Zapata F, Hardarson G, Danso SKO (1995). Yield, nodulation and N2-fixation by cowpea cultivars at different phosphorus levels Biol. Fertil. Soil 22: 10-15.

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Sombroek W, Nachtergaele FO, Hebel A (1993). Amounts, dynamics and sequestering of carbon in tropical and subtropical soils. Ambio. 22: 517-426. Tagoe SO, Horiuchi T, Matsui T (2008). Effects of carbonized and dried chicken manures on the growth, yield and N content of soybean. Plant Soil 306: 211-220. Tejada M, Hernandez MT, Garcia C (2006). Application of two organic amendments on soil restoration: effects on the soil biological properties. J. Environ. Qual. 35: 1010-1017. Tenebe VA, Yusufu Y, Kaigama BK, Aseime IOE (1995). Effects of sources and levels of phosphorus on the growth and yield of cowpea variety. Trop. Sci. 35: 223-228. Tryon EH (1948). Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecol. Monogr. 18: 81-115. Vadez V, Lasso JH, Beck DP, Drevon JJ (1999). Variability of N2-fixation in common beans (Phaseolus vulgaris L.) under P deficiency is related to P use efficiency. Euphytica 106: 231-242. Vance CP (2001). Symbiotic nitrogen fixation and phosphorus acquisition: Plant nutrition in a world of declining renewable resources. Plant Physiol. 127: 390-397. Waluyo SH, Lie TA, Mannetje L (2004). Effect of phosphate on nodule primordia of soybean (Glycine max) in acid soils in rhizotron experiments Indonesian J. Agric. Sci. 5:27-44. Wan Othman WM, Lie TA, Mannetje L, Wassink GY (1991). Low level phosphorus supply affecting nodulation, N2-fixation and growth of cowpea (Vigna unguiculata L. Walp). Plant Soil 135: 67-74. Warnock DD, Lehmann J, Kuyper TW, Rillig MC (2007). Mycorrhizal responses to bio-char in soil- concepts and mechanisms. Plant Soil 300: 9-20. Wesley TL, Lamond RE, Martin VL, Duncan SR (1998). Effects of lateseason nitrogen fixation on irrigated soybean yield and composition. J. Prod. Agric. 11: 331-336.

Soil Science and Plant Nutrition (2006) 52, 489–495

doi: 10.1111/j.1747-0765.2006.00065.x

ORIGINAL ARTICLE Effect M. Yamato of charcoal et al. application on crop yield Blackwell Publishing, Ltd.

Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia Masahide YAMATO1, Yasuyuki OKIMORI1, Irhas Fredy WIBOWO2, Saifuddin ANSHORI2 and Makoto OGAWA3 1

Biological Environment Institute, Research and Development Department, The General Environmental Technos Company, Kyoto 611-0021, 3Osaka Institute of Technology, Osaka 535-8585, Japan; and 2Research and Development, PT Musi Hutan Persada, Jl. Residen H. Abdul Rozak 99, Palembang 30114 South Sumatra, Indonesia

Abstract Charred bark of Acacia mangium (bark charcoal), which is made of wood waste from pulp production, was applied as soil amendment for the cultivation of maize, cowpea and peanut to examine its effects on crop yield and soil chemical properties in South Sumatra, Indonesia. The yields of maize and peanut significantly increased after the application of bark charcoal under a fertilized condition in an infertile soil environment. In addition, increases in the root amount and colonization rate of arbuscular mycorrhizal (AM) fungi after bark charcoal application were also observed in maize. In general, the application of bark charcoal induced changes in soil chemical properties by increasing the pH value, total N and available P2O5 contents, cation exchange capacity, amounts of exchangeable cations and base saturation, and by decreasing the content of exchangeable Al3+. The amelioration of the soil chemical properties could be effective in highly weathered infertile tropical soils. The application of charcoal in agriculture is expected to lead to the formation of a carbon sink in soil and to increase crop yield because it has been suggested that charcoal is highly resistant to abiotic and biotic degradation, even in a soil environment. Key words: Arachis hypogaea L., arbuscular mycorrhizal fungi, bark charcoal, Vigna unguiculata L., Zea mays L.

INTRODUCTION It is widely recognized that charcoal can be used as soil amendment in agriculture (Ogawa 1994). The effect of charcoal application on yield increases in soybean, pea, moong (Iswaran et al. 1980), sugarcane (Uddin et al. 1994, 1995) and sweet potato (Islam et al. 2000) has been reported. Igarashi (2002) reported that rice husk charcoal application increased the yield of maize, soybean and peanut in Indonesia. Glaser et al. (2002) pointed out that the effects of charcoal can be attributed to increases in soil pH and the contents of available nutrients, improvement of nutrient retention by increased Correspondence: M. YAMATO, Biological Environment Institute, Research and Development Department, The General Environmental Technos Company, 8-4 Ujimatafuri, Uji, Kyoto 611-0021, Japan. Email: [email protected] Received 3 April 2006. Accepted for publication 14 March 2006. © 2006 Japanese Society of Soil Science and Plant Nutrition

cation exchange capacity (CEC), and amelioration of soil physical properties such as soil water retention and aggregation. In South-East Asia, industrial plantations of the fastgrowing tree, Acacia mangium, have been promoted for pulp production, and a large amount of wood waste, mainly bark, is being discharged from pulp mills. To effectively use the wood waste, Ogawa (1997) proposed a scheme to utilize charred wood waste as soil amendment in agriculture. Ogawa (1997) designated this scheme the “Carbon Sequestration by Forestation and Carbonization (CFC)” because a carbon sink could be formed in the soil and the wood waste could be used effectively. The feasibility of CFC has been examined by Okimori et al. (2003) in cooperation with PT Musi Hutan Persada (MHP), an industrial plantation company, and PT Tanjungenim Lestari Pulp and Paper (TELPP), a pulp production company, in South Sumatra, Indonesia. To implement the CFC project, it would be necessary to promote the utilization of bark

490 M. Yamato et al.

charcoal. Although bark composts have been used as soil amendment in agriculture and horticulture, there are few studies examining the application of bark charcoal. The purpose of the present study was to investigate the effects of the application of bark charcoal of A. mangium on the yield of maize, cowpea and peanut and its effect on the soil chemical properties. For maize, the effects on the root dry weight and colonization rate of arbuscular mycorrhizal (AM) fungi were also examined. In addition, the role of charcoal application in the formation of a carbon sink was considered.

MATERIALS AND METHODS Experimental site For the experiment examining the application of bark charcoal and agricultural crops, three types of farmland, Sites A, B and C, were selected near the boundary of the tree plantation of MHP. Site A was located in a garden of a farmhouse. Site B was located in a garden reclaimed from a chicken farm. Site C was located in a farmland reclaimed from grassland. All the sites had been newly reclaimed for the current experiment and no fertilizers had been applied previously.

Charcoal Bark charcoal of A. mangium was produced in flat kilns built near the pulp mill. A flat kiln is a built-up brick furnace with an open top for the continuous addition of materials (Okimori et al. 2003). This method is often adopted to char powdered or granular materials such as bark and sawdust. The charring temperature was low, ranging from 260 to 360°C. The air-dried charcoal sample was mixed with distilled water or 1 N 1 mol L−1 KCl at a ratio of 1:5 to determine the pH (H2O) and pH (KCl), respectively. The contents of total C and N were determined by the dry combustion method using an NCanalyzer 1000, Sumigraph (Shimadzu A-6000, Kyoto, Japan). The sample, oven-dried at 105°C, was analyzed to determine the chemical properties as follows. The dried sample was subjected to extraction with 0.1 N 0.1 mol L−1 HCl and 0.03 N 0.03 mol L−1 ammonium fluoride to determine the amount of available P2O5 (Bray 1), with 1 N 1 mol L−1 ammonia acetate to determine the CEC and amounts of exchangeable cations (K+, Na+, Ca2+ and Mg2+), and with 1 N 1 mol L−1 KCl to determine the exchangeable acidity (Al3+ and H+). All analyses, except for the total N and C contents, were carried out at the Soil Research Institute, Bogor, Indonesia.

Experimental design The experiments were done twice in two different years, 2003 (Experiment 1) and 2004 (Experiment 2).

Experiment 1: Effect on crop yield In this experiment, the effect of bark charcoal application on the yield of maize (Zea mays L.), cowpea (Vigna unguiculata [L.] Walp.) and peanut (Arachis hypogaea L.) was examined at Sites A and B. Three treatments, no application (Con), application of chemical fertilizer 1515-15 (BASF, Aktiengesellschaft, Germany) at 50 g m−2 (NPK), and application of the fertilizer at 50 g m−2 and bark charcoal at 10 L m−2 (Char-NPK), were conducted for each crop. The amount of applied chemical fertilizer, 50 g m−2, which was equivalent to 75 kg ha−1 of each component, was determined in a preliminary experiment because this amount was found to be effective in the growth and production of cowpea under charcoal application. For each treatment, three ridges measuring 1 m × 2 m in size were prepared and the applied chemical fertilizer and bark charcoal were mixed with topsoil at a depth of approximately 10 cm. For the experiment on maize, nine seed sowing positions were prepared in the ridge at an inter-row spacing of 30 cm and an intra-row spacing of 50 cm. For each position, four seeds were sown, which were thinned to two plants each after 2 weeks. Thus, 18 plants were grown in total in each ridge. For the experiment on cowpea, six seed sowing positions were prepared in each ridge at an inter-row spacing of 60 cm and an intra-row spacing of 60 cm. For each position, five seeds were sown, which were thinned to two plants each after 2 weeks. Thus, 12 plants were grown in total in each ridge. For the experiment on peanut, 28 seed sowing positions were prepared in each ridge at an inter-row spacing of 20 cm and an intra-row spacing of 20 cm. For each position, three seeds were sown, which were thinned to one plant each after 2 weeks. Thus, 28 plants were grown in total in each ridge. The seeds were sown on 19 September 2003 at Site A and on 1 October 2003 at Site B. For cowpea, seedpods longer than 40 cm were harvested every 3 days for 1 month from day 60 after seed sowing. After 3 months, pieces of corn with cob were harvested for maize, and seedpods were harvested for peanut. The total fresh weight of the harvested crops was measured in each ridge for each crop.

Experiment 2: Effects on yield, root amount and colonization rate of AM fungi in maize The effects of bark charcoal application on yield, root amount and colonization rate of AM fungi in maize at Site C were examined. Four treatments, no application (Con), application of chemical fertilizer at 50 g m−2 (NPK), application of bark charcoal at 10 L m−2 (Char), and application of fertilizer at 50 g m −2 and bark charcoal at 10 L m−2 (Char-NPK), were conducted. For © 2006 Japanese Society of Soil Science and Plant Nutrition

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each treatment, three ridges measuring 1 m × 2 m in size were prepared and the applied chemical fertilizer and bark charcoal were mixed with topsoil at a depth of approximately 10 cm. The number and size of the prepared ridges for each treatment, the method of application of the chemical fertilizer and bark charcoal, the seed sowing position and the number of plants were the same as those described for maize in Experiment 1. The seeds were sown on 12 September 2004. The total fresh weight of harvested corn with cobs was measured in each ridge at 3 months after seed sowing. At harvest, roots were collected from four samples of core topsoil (5 cm in diameter and 10 cm in depth) collected around the center of each ridge. The root samples in each ridge were gathered to determine the dry weight and colonization rate of AM fungi. The colonization rate of the AM fungi was determined for the randomly collected fine roots using the grid-line intercept method (Giovannetti and Mosse 1980) after staining with a 0.05% Trypan blue solution.

ridge after harvest, which were mixed together at each experimental site or in each treatment. For each of the collected soil samples, the chemical properties, pH (H2O), pH (KCl), amount of available P2O5 (Bray 1), CEC, amounts of exchangeable cations (K +, Na +, Ca 2+ and Mg 2+) and exchangeable acidity (Al3+ and H+) were determined. The analytical methods were the same as those described above for the charcoal sample. For the determination of the total N content (Kjeldahl), the samples, oven-dried at 105°C, were decomposed in heated sulfuric acid and then distilled ammonia was collected. All the analyses were carried out at the Soil Research Institute, Bogor, Indonesia.

Soil analyses

RESULTS AND DISCUSSION

Topsoil samples, 10 cm in depth, were randomly collected from 10 spots at each experimental site, Sites A, B and C, before the experiments and from three spots in each

The yield of maize, cowpea and peanut at Sites A and B is shown in Fig. 1. The yield of maize and peanut was significantly higher after the application of bark charcoal

Figure 1 Effect of the application of chemical fertilizer 15-15-15 at 50 g m−2 (NPK) and bark charcoal at 10 L m−2 (Char) on the fresh weight (FW) of harvested maize, cowpea and peanut crops. Control (Con): no application. Values are means ± standard error (n = 3). Columns with the same letter (a, b and c) are not significantly different (P < 0.05). © 2006 Japanese Society of Soil Science and Plant Nutrition

Statistical analysis For the results on crop yield, root dry weight and colonization rate of AM fungi, one-way anovas were carried out to evaluate the difference between the treatments.

492 M. Yamato et al.

Figure 2 Effects of the application of chemical fertilizer 15-15-15 at 50 g m−2 (NPK) and bark charcoal at 10 L m−2 (Char) on the fresh weight (FW) of harvested maize, root dry weight and the colonization rate of arbuscular mycorrhizal (AM) fungi in maize. Control (Con): no application. Values are means ± standard error (n = 3). Columns with the same letter (a, b and c) are not significantly different (P < 0.05).

Table 1 Properties of the applied bark charcoal

pH (H2O) 7.4

pH (KCl)

Total C (kg kg−1)

Total N (g kg−1)

Available P2O 5 (mg kg−1)

7.1

0.398

10.4

63.1

Exchangeable acidity (cmolc kg−1)

CEO (cmolc kg−1)

Ca2+

Mg2+

K+

Na+

Al3+

H+

Bulk density (g cm−3)

37.14

48.82

2.78

4.03

1.85

0.01

0.08

0.37

and fertilizer (Char-NPK) than after the application of fertilizer only (NPK) at Site A. Particularly for maize, an approximate twofold increase in yield was obtained by bark charcoal application. At Site B, the average yield of cowpea and peanut in the different treatments showed the same tendency as that at Site A, namely, Con < NPK < Char-NPK, although no significant difference (P < 0.05) was observed. The yield of maize at Site C is shown in Fig. 2. The yield increased significantly after Char-NPK application. It was observed that the standard errors for the means of yield among the replicates were smaller in the Char-NPK application than in the application of other materials. This suggests that the yield after Char-NPK application was more stable than that after a single application of NPK or Char. As the amount of applied chemical fertilizer, 50 g m−2, which was equivalent to 75 kg ha−1 of each component, was approximately half of that of the standard fertilizer application in the region, it was expected that the amount of fertilizer applied could be reduced by the application of bark charcoal.

Exchangeable cations

The applied bark charcoal displayed a neutral pH, high carbon content, high CEC and high content of exchangeable cations, particularly Ca2+ (Table 1). The amount of Ca 2+ was higher than the CEC, which indicates that free Ca2+ was included in bark charcoal. Glaser et al. (2000) suggested that the high CEC of charcoal resulted from slow oxidation on the edges of the aromatic backbone of charcoal for the formation of carboxylic groups. Based on the contents of total N and available P in charcoal (Table 1), charcoal application, 10 L m−2, was equivalent to a total N dose of 38.5 g m−2 and an available P dose of 0.23 g m−2, respectively. A large amount of total N, approximately fivefold as high as that applied using chemical fertilizer, was supplied by charcoal application. The results of the soil analysis are shown in Table 2. Before the experiments, the amounts of available P2O5 (Bray 1) and exchangeable cations and base saturation were higher at Site B than at Sites A or C. The previous chicken farming activities probably influenced the fertility of the soil at Site B. Soil analysis at harvest revealed © 2006 Japanese Society of Soil Science and Plant Nutrition

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Table 2 Soil chemical properties before the experiment and at harvest

Site and Treatments Site A Before experiment At harvest Maize Con NPK Char-NPK Cowpea Con NPK Char-NPK Peanut Con NPK Char-NPK Site B Before experiment At harvest Maize Con NPK Char-NPK Cowpea Con NPK Char-NPK Peanut Con NPK Char-NPK Site C Before experiment At harvest Maize Con NPK Char Char-NPK

Exchangeable Available cations (cmolc kg−1) P2O 5 pH pH Total N CEC (H2O) (KCl) (g kg−1) (mg kg−1) (cmolc kg−1) Ca2+ Mg2+ K+ Na+

Exchangeable Base acidity (cmolc kg−1) saturation (%) Al3+ H+

3.9

3.9

1.7

47.8

10.12

1.21 0.30 0.15 0.25

18.9

2.67

0.26

4.0 4.0 5.1

3.8 3.8 4.5

1.7 1.9 2.4

22.0 44.5 80.2

9.87 10.23 12.72

0.80 0.20 0.12 0.22 0.79 0.18 0.12 0.07 6.21 0.45 0.25 0.13

13.6 11.3 55.3

2.93 2.97 0.12

0.20 0.22 0.12

4.2 4.1 5.3

3.9 3.9 4.8

1.2 1.8 1.6

25.4 44.0 91.8

10.81 10.66 16.42

1.30 0.24 0.08 0.08 1.01 0.28 0.12 0.02 7.80 0.43 0.29 0.14

15.7 13.4 52.7

2.49 2.81 0.02

0.15 0.15 0.12

4.2 4.0 5.1

3.9 3.9 4.6

1.9 1.8 2.5

55.3 137.5 176.0

10.21 10.01 12.66

1.27 0.29 0.08 0.07 0.91 0.22 0.10 0.03 5.98 0.37 0.18 0.07

16.7 12.6 52.1

2.41 2.77 0.15

0.15 0.20 0.10

4.7

4.1

2.0

210.1

11.77

4.05 1.04 0.40 0.25

48.8

0.48

0.20

4.4 4.4 5.6

3.9 3.9 5.1

1.7 2.1 2.4

23.4 113.2 126.6

11.64 12.76 15.42

2.97 0.81 0.22 0.09 3.11 0.73 0.22 0.13 9.32 0.82 0.31 0.13

35.1 32.8 68.6

1.64 1.44 0.00

0.18 0.19 0.02

5.2 4.6 5.8

4.6 4.1 5.3

1.9 1.8 2.4

75.3 151.2 188.2

11.93 11.23 15.11

3.77 1.35 0.41 0.13 5.22 1.48 0.22 0.13 9.30 1.10 0.53 0.13

47.4 62.8 73.2

0.04 0.44 0.00

0.11 0.09 0.02

4.6 4.5 5.5

4.1 4.0 5.0

2.0 2.0 2.8

302.9 298.7 355.6

12.31 13.21 17.18

4.56 1.39 0.59 0.13 4.51 1.19 0.53 0.10 9.73 1.25 0.65 0.20

54.2 47.9 68.9

0.26 0.40 0.00

0.15 0.16 0.05

4.1

3.9

1.4

94.2

8.54

0.64 0.21 0.07 0.06

11.5

2.35

0.35

4.5 4.4 5.4 5.3

3.9 3.8 4.5 4.4

1.3 1.3 2.1 2.1

108.1 144.5 84.3 148.7

8.85 8.60 12.38 13.04

0.79 0.79 5.86 6.06

13.4 14.3 54.2 51.8

2.31 2.10 0.11 0.23

0.31 0.33 0.21 0.17

that the pH, contents of total N and available P2O5, CEC, contents of exchangeable cations and base saturation were generally higher after the application of bark charcoal and fertilizer (Char-NPK) than after the application of fertilizer only (NPK). The high level of available P2O5 after Char-NPK application indicated that the application of bark charcoal led to a high retention of nutrients. The increase in base saturation as well as CEC showed that a large amount of exchangeable cations was introduced by bark charcoal application. These effects of charcoal application on soil chemical properties were also reported © 2006 Japanese Society of Soil Science and Plant Nutrition

0.27 0.25 0.55 0.45

0.07 0.14 0.21 0.18

0.06 0.05 0.09 0.06

by Tryon (1948). In contrast, the amount of exchangeable Al3+ markedly decreased after the application of bark charcoal. Low pH, low base saturation, high Al3+ content and low fertility, which are typical characteristics of soils in the tropical region, lead to a low productivity of crops in this region. Therefore, amelioration of the soil properties by bark charcoal application could be effective in increasing crop yield particularly in the tropical region. The effect of bark charcoal application on crop yield was not significant at Site B, which indicates that the effect would not be appreciable on fertile soils.

494 M. Yamato et al.

The effects on the root dry weight and colonization rate of AM fungi of maize at Site C are shown in Fig. 2. The root amount significantly increased after the application of bark charcoal. Ishii and Kadoya (1994) also reported an increase in the root amount after the application of charcoal. Because it has been shown that charcoal application increases soil water retention (Piccolo et al. 1996) and the gaseous phase (Ezawa et al. 2002), such amelioration of the soil physical and chemical properties could be effective in enhancing root growth. The enhancement of root growth may account for the stable crop production, as evidenced by the lower standard error in the application of bark charcoal (Figs 1,2), because enhanced root growth may reduce the effect of uneven soil conditions. The colonization rate of AM fungi was highest in the case of bark charcoal application without fertilizer (Fig. 2). A large number of studies on the effect of charcoal application on the enhancement of AM fungal colonization have been conducted (Ezawa et al. 2002; Ishii and Kadoya 1994; Ogawa 1989; Saito 1990). Ogawa (1989, 1994) suggested that the porous structure of charcoal may create a favorable habitat for symbiotic microorganisms. Further studies on the microenvironment should be carried out to clarify the relationship between charcoal application and such symbiosis. Based on calculations using the bulk density (0.37 g cm−3) and the carbon content (39.8%) of applied bark charcoal, the application at 10 L m−2 was found to be equivalent to a carbon dose of 1.47 kg m−2 (14.7 Mg ha−1). The aromatic structure of charcoal is highly resistant to abiotic and biotic degradation (Glaser et al. 2002; Schmidt et al. 1999). Shindo (1991) showed that charred plant residues applied to volcanic ash soil were hardly decomposed by microorganisms even after 40 weeks. In the Brazilian Amazon region, patchy distribution of black soil containing large amounts of charred carbon, the so-called Terra Preta, was found. The soil environment is assumed to be anthropogenic probably because of charcoal production in hearths by pre-Columbian Indios (Glaser et al. 2002). The long persistence of charcoal carbon in soil environments was suggested by the presence of black carbon for 1000–2000 years in Terra Preta, as indicated by 14C dating (Glaser et al. 2000, 2002). In the present study, it was shown that bark charcoal application is effective in increasing the yield of crops through the amelioration of the soil chemical properties and the creation of an appropriate environment for root growth and AM fungal colonization. Considering the long persistence of charcoal carbon in the soil environment, charcoal application in agriculture could contribute to the formation of a carbon sink in farmlands.

ACKNOWLEDGMENTS This study was financially supported by The Kansai Electric Power Company. We thank Mr Minoru Sugai for the instructions for charcoal making and Mr Naohiro Matsui for his help in the analysis of charcoal carbon.

REFERENCES Ezawa T, Yamamoto K, Yoshida S 2002: Enhancement of the effectiveness of indigenous arbuscular mycorrhizal fungi by inorganic soil amendments. Soil Sci. Plant Nutr., 48, 897 – 900. Giovannetti M, Mosse B 1980: An evaluation of techniques for measuring vesicular-arbuscular mycorrhizal infection in roots. New Phytol., 84, 489 – 500. Glaser B, Balashov E, Haumaier L, Guggenberger G, Zech W 2000: Black carbon in density fractions of anthropogenic soils of the Brazilian Amazon region. Org. Geochem., 31, 669 – 678. Glaser B, Lehmann J, Zech W 2002: Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review. Biol. Fertil. Soils, 35, 219 – 230. Igarashi T 2002: Effectiveness of soil amendments like rice husk charcoal. In Handbook for soil amendment of tropical soil., Ed. Association for International Cooperation of Agriculture and Forestry., 127 –134, Sozosha, Tokyo (in Japanese). Ishii T, Kadoya K 1994: Effect of charcoal as a soil conditioner on citrus growth and vesicular-arbuscular mycorrhizal development. J. Jpn. Soc. Hort. Sci., 63, 529 – 535. Islam AFMS, Kitaya Y, Hirai H, Yanase M, Mori G, Kiyota M 2000: Effect of volume of rice husk charcoal masses inside soil ridges on growth of sweet potato in a wet lowland. J. Agric. Meteorol., 56, 1– 9. Iswaran V, Jauhri KS, Sen A 1980: Effect of charcoal, coal and peat on the yield of moong, soybean and pea. Soil Biol. Biochem., 12, 191–192. Ogawa M 1989: Inoculation methods of VAM fungi: charcoal ball method and rice hull method. In Recent Advances in Microbial Ecology, Eds T Hattori, Y Ishida, Y Maruyama, R Morita, A Uchida, pp. 247–252, Japan Scientific Societies Press, Tokyo. Ogawa M 1994: Symbiosis of people and nature in the tropics. Farming Japan, 28, 10 – 34. Ogawa M 1997: Charcoal-utilization of fixed carbon and its return to environment. In Annual Research Report in 1998 on Carbon-Sink Project Development, pp. 177 – 184, Japan International Forestry Promotion and Cooperation Center (in Japanese). Okimori Y, Ogawa M, Takahashi F 2003: Potential of CO2 emission reductions by carbonizing biomass waste from industrial tree plantation in South Sumatra, Indonesia. Mitiga. Adapta. Strate. Global Change, 8, 261– 280. Piccolo A, Pietramellara G, Mbagwu JSC 1996: Effects of coal-derived humic substances on water retention and structural stability of Mediterranean soils. Soil Use Manage, 12, 209 – 213. © 2006 Japanese Society of Soil Science and Plant Nutrition

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Saito M 1990: Charcoal as a micro-habitat for VA mycorrhizal fungi, and its practical implication. Agric. Ecosyst. Environ., 29, 341– 344. Schmidt MWI, Skjemstad JO, Gehrt E, Kögel-Knabner I 1999: Charred organic carbon in German chernozemic soils. Euro. J. Soil Sci., 50, 351– 365. Shindo H 1991: Elementary composition, humus composition, and decomposition in soil of charred grassland plants. Soil Sci. Plant Nutr., 37, 651– 657. Tryon EH 1948: Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecol. Monogr., 18, 81–115.

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Uddin SMM, Murayama S, Ishimine Y, Tsuzuki E 1994: Studies on sugarcane cultivation. 1. Effect of the mixture of charcoal with pyroligneous acid on cane and sugar yield of spring and ratoon crops of sugarcane (Saccharum officinarum L.). Jpn. J. Trop. Agr., 38, 281– 285. Uddin SMM, Murayama S, Ishimine Y, Tsuzuki E, Harada J 1995: Studies on sugar cane cultivation II. Effect of the mixture of charcoal with pyroligneous acid on dry matter production and root growth of summer planted sugarcane (Saccharum officinarum L.) Jpn. J. Crop Sci., 64, 747 – 753.

PRODUCT RESEARCH - 06/07

Effects of Carbon-Based Soil Amendment (CSA) on Crop Yield of Irish Potato, Sweet Corn, Tomato and Bell Pepper By Ronald Morse, Ph.D. Professor Emeritus, Vegetable Crops Department of Horticulture, VA Tech Blacksburg, VA 24061-0327

Paul Stevens—Graduate Student Department of Horticulture, VA Tech Blacksburg, VA 24061-0327

Summary This research evaluated preplant in-row application of CSA on crop yield of Irish potato, sweet corn, tomato and bell pepper at the Kentland Agricultural Research Farm, located near Blacksburg, VA. Overall, our data are encouraging, indicating that beneficial microorganisms (microbes) in CSA granules improved productivity of sweet corn (2006 and 2007) and tomato (2007). Based on limited data and observations, enhanced mineralization in the rhizosphere of CSA-treated sweet corn and tomato plants is at least partially responsible for increased uptake of nitrogen and improved crop yield. Apparently, placement in near proximity to sweet corn and tomato seed stimulated rapid rhizosphere development of microbial biomass and improved effectiveness of CSA. Crop yield of Irish potato and bell pepper was not affected by CSA. Distant placement of CSA (3-4 inches above the seed pieces in 2007) possibly accounted for lack of crop yield response with Irish potato. Reasons for lack of yield response of CSA to bell pepper are not know, since tomato and pepper transplants were treated the same throughout these experiments. Materials and Methods Description of field soil and treatments. In 2006 and 2007, all field plots were grown in an organic transition high-quality silt loam soil having a pH of 6.4, with medium to high levels of phosphorus, potassium, calcium and magnesium. Irish potato and sweet corn. The research field plots both years were divided into four replications (424 ft long and 24 ft wide), consisting of four raised beds (6 ft center to center, and 6 inches high). The top of each bed was approximately 42 inches wide, and the alleyways between beds (bed shoulders and bottoms) were 30 inches. In September preceding each year, two beds in each replication were seeded with forage radish (Raphanus sativus) and two beds to crimson clover (Trifolium incarnatum). Alleyways in all plots were seeded with cereal rye (Secale cereale). Forage radish was frost killed at approximately 20 F and crimson clover and rye over-wintered. In mid April, bed tops were flail mowed and the residues were shallow incorporated (2-3 inches deep) with a rototiller (Table 1). Biomass produced (and thus mineralizable nitrogen, N) of both cover crops was considerably less in 2006/2007 than 2005/2006. Although actual amounts of cover crop biomass and

mineralizable N were not measured, the estimated quantity of plant-available N would be approximately 30 and 15 lb N/acre in 2006, compared to 10 and 5 lb N/acre in 2007, from crimson clover and forage radish, respectively. Because nitrogen availability was a major limiting factor both years, especially in 2007, these relatively small amounts of plant-available N would have contributed relatively little to improved crop yield. In mid April of 2006 (but not in 2007), before seeding Irish potato or sweet corn, all beds were fertilized using 800 lb/acre of Renaissance 8N-1P-5K organic fertilizer (composed of feather meal, bone meal, soybean and potassium sulfate). The organic fertilizer was precision placed in-row and incorporated to a depth of 5-6 inches deep in grow zones located 20-inches apart on top of the raised beds. Grow zones are the designated row areas on raised beds where vegetables were seeded. Growing Irish potato. Whole seed potatoes (Chieftain in 2006 and Kueka Gold in 2007) were cut into 2-oz seed pieces, treated with Oxidate for 5 minutes, stored for 1-2 weeks and planted by hand in 2006 and using a potato seeder in 2007 (Table 1). Seed pieces were set 10-12 inches apart and 5-6 inches deep in the two grow zones on each bed (212 ft long). In 2006, CSA granules (30 lb/acre) were applied before planting the seed pieces. CSA granules were hand applied to subplots (two beds, 76 ft long) in the grow zones and incorporated to a depth of 3-5 inches with a wheel hoe. In 2007, CSA granules (20 lb/acre) were applied (after planting potato seed pieces with the seed planter) in the grow zones and shallow incorporated (only 1-2 inches deep) with a hand hoe. Each year, the remaining row area (136 ft long) of each row was left untreated, of which the middle 60 ft was designated as a buffer zone separating the CSA-treated (+CSA, 76 ft) from the untreated (no CSA, 76 ft). Plots were irrigated and hand weeded as needed throughout the growing season. Stand counts were made and potato tubers were harvested in late September using a two-row potato digger. In 2007, each subplot was further divided into two equal sub-subplots (one 6-ft bed, 76 ft long, received 2 gallon of fish concentrate/acre and a second adjacent bed received no fish concentrate—i.e., control). Each sub-subplot was further divided into two equal sub-sub-subplots (one bed, 38 ft long) (one-half of each sub-subplot received 80 lb N/acre as a sidedress fertilizer and the other half received no sidedress fertilizer—i.e., control). Growing sweet corn. Sweet corn seed (Spring Treat in 2006 and Sugar Queen in 2007) was hand planted with and Earthway Seeder in the two grow zones (212 ft long and 20 inches apart) of the raised beds. Immediately before seeding in both years, CSA granules were applied to subplot inrow grow zones (76 ft long) of each bed. In 2006, CSA granules (20 lb/acre) were hand applied and incorporated to 1-2 deep with a wheel hoe. In 2007, CSA granules (30 lb/acre) were hand applied using the Earthway Seeder to a depth of 1-2 inches. The remaining area (136 ft) of each bed was left untreated, of which the middle 60 ft was designated as a buffer zone, separating the CSA-treated (+CSA, 76 ft) and the untreated (no CSA, 76 ft) sections. Plots were irrigated and hand weeded as needed throughout the growing season. Stand counts were made and sweet corn ears were harvested by hand (Table 1). In 2007, subplots were further divided into sub-subplots and sub-sub-subplots, as described above for Irish potato. Nitrogen sidedressing (2006). Two weeks after immergence, potato plants in untreated subplots (no CSA) were sidedressed by hand at the rate of 60 lb N/acre (20 lb N from sodium nitrate and 40 lb N from feather meal). Plants in the CSA-treated (+CSA) were not sidedressed. Five weeks after planting, sweet corn plants of both +CSA and no-CSA subplots were divided into three subsubplots (25 ft long) and were sidedressed by hand at three rates of nitrogen fertilizer (0, 50 and 100 lb N/acre, from a mixture of sodium nitrate and feather meal).

Tomato and bell pepper (2007). In two separate experiments, tomato (Mountain Fresh) and bell pepper (Aristotle) were grown on small plastic covered plots (24 ft wide and 72 ft long). The experimental design was a randomized split block, with four replications. Main plots were transplant-growing mixes: McEnroe Lite (ML—an organic potting mix) and Metro Mix 360 (MM—an inorganic potting mix). Subplots were addition of CSA granules to the growing mixes (1 cup CSA granules/5 gallons of growing mix): untreated control (no CSA) and CSA-treated (+CSA—granules were thoroughly blended in the growing mixes). Seeds of tomato or bell pepper were placed into 72-cell trays containing either untreated or CSA-treated ML or MM growing mixes, and grown to maturity (about 7 weeks for tomato and 9 weeks for bell pepper). At maturity, the tomato and bell pepper transplants were set by hand in previously established raised beds covered with black plastic mulch. A starter solution consisting of hydrolyzed fish concentrate (2 gallons/acre) was applied with water (200 gallon/acre) as a liquid drench around the base of each transplant in all treatments. To avoid contamination, untreated (no CSA) and CSA-treated subplots were separated by 150 ft. A cereal rye/hairy vetch (R/HV) cover crop biculture was seeded in the tomato/bell pepper field site in early October of 2006. Before laying off raised beds and applying black plastic mulch, the R/HV cover crop was flail mowed and incorporated using a disk plow. No fertilizer was applied at planting or during the growing season for either tomato or bell pepper; however, the incorporated R/HV residues would have provided approximately 40-60 lb N/acre. Results and Discussion Effects of CSA on marketable crop yield. Marketable crop yield was highest in CSA-treated plots for sweet corn (2006 and 2007) and tomato (2007). Application of CSA had no crop yield effects for Irish potato and bell pepper (Table 2). Why different yield responses to CSA occurred for tomato (17% increased fruit yield) and bell pepper (no response) is unknown, since both crops were treated identically throughout the duration of the experiments. In-row placement of CSA granules was distinctly different for Irish potato and sweet corn and could possibly account for different yield responses to application of CSA. Granules of CSA were placed in close proximity to sweet corn seed in both 2006 and 2007; however, in 2007, shallow incorporation of CSA granules and deep placement of potato seed pieces (5-6 inches below the soil surface) resulted in relatively reduced CSA-seed contact with potato, compared to sweet corn. In 2006, CSA-seed contact was adequate; however, yield response to application of CSA granules was confounded, because the untreated control (no CSA) potato plants were sidedressed with 60 lb N/acre, while the CSA-treated plants were not sidedressed. How (what mechanisms) CSA improves crop yield is mere speculation. Perhaps, CSA microbes (at proper concentration, placement and timing) can improve absorption of plant-available soil moisture, and/or improve rate of mineralization (release of plant-available N). Drip irrigation was applied uniformly across all plots both years; hence, we have no evidence that improved water absorption contributed to improved crop yield in CSA-treated plots. On the other hand, enhanced mineralization could have accounted for the increase crop yields, as evidence by the potato data for 2006. Potato tuber yield in 2006 was nearly identical in CSA-treated and untreated (no CSA) plots, although the untreated plants received 60 lb N/acre as a fertilizer sidedressing, while CSA-treated plants were not sidedressed. Since the soils in our experimental sites were nitrogen deficient, these data indicate that more plant-available N was released (mineralized) in CSA-treated than untreated plots.

Effect of growing mixes and CSA on marketable fruit yield of tomato. An interaction occurred between potting mixes used for growing tomato transplants and application of CSA granules. Tomato transplants grown in the inorganic Metro Mix 360 (MM) out yielded plants grown in the organic McEnroe Lite (ML) by 6%; however, when CSA granules were added to the potting mixes, tomato transplants grown in MM out yielded ML by 16% (Table 3). Apparently, proliferation of beneficial microbes was uninhibited in the more “sterile” CSAtreated MM, while microbial competition possibly reduced buildup of beneficial microbes in CSA-treated ML. The result was a 22% tomato yield increase in CSA-treated MM (vs. untreated), compared to only a 12% yield increase in CSA-treated ML (Table 3). Effect of CSA on growth of tomato and bell pepper transplants. Application of CSA granules to MM and ML potting mixes (priming) enhanced growth rate and size of both tomato and bell pepper. Although not measured, transplant size at time of field setting was approximately 1525% larger. Enhancement in growth response to CSA priming appeared to be greater for tomato than bell pepper. The potential of CSA priming to shorten the time required to produce marketable transplants and subsequent increased marketable fruit yield merits further research. (Refer to the 2006 report). Effect of cover crops on marketable yield of Irish potato and sweet corn. There was no yield response to cover crops in 2007 (data not shown). No yield response is highly predictable, since growth of cover crops was severely curtailed because of delayed seeding, drought and poor plant stands. Refer to the 2006 report for discussion of the cover crop effects on crop yield in 2006, when growth of cover crops was excellent. Effect of N sidedressing and liquid fish concentrate on marketable yield of Irish potato and sweet corn in 2007. In accordance with the agreed-upon protocol, no preplant fertilizer was applied in 2007. Therefore, since the soil at the research sites is relatively low in plant-available N and little cover crop biomass was produced, these unfertilized plots showed a dramatic yield response to N sidedressing (80 lb N/acre) for both Irish potato and sweet corn (Table 4), and even showed a slight response to in-row application of liquid fish concentrate for Irish potato (Table 5). Table 1. Dates of important cultural practices. Cultural practice

2006

2007

Seeded cover crops

Sept. 6 (05)

Sept. 18 (06)

Applied preplant fertilizer

Mid April

------

Planted Irish potato

April 19

May 9

Planted Sweet corn

June 13

May 31

Transplanted tomato and bell pepper

------

June 11

Applied nitrogen sidedressing—Irish potato*

May 24

June 13

Applied nitrogen sidedressing—sweet corn July 18 July 2 *Only untreated (no CSA) potato plants were sidedressed (60 lb N/acre) in 2006.

Table 2. Effect of application of CSA on marketable organic crop yield. 2006 2007 Vegetable Yield (cwt/acre) Yield (cwt/acre) Crop No CSA CSA Sign. No CSA CSA

Sign.

Irish potato

189*

183

ns

88

82

ns

Sweet corn

93

107

.05

61

67

.10

Tomato

----

----

----

634

740

.10

Bell pepper ---------352 357 ns *In 2006, untreated (no CSA) potato plots received 60 lb N/acre as a sidedressing; CSA-treated potato plots were not sidedressed. Cwt = hundred weight units (100 lb); ns = not statistically significant at p = .10

Table 3. Effect of priming growing mixes with CSA on marketable organic crop yield, 2007. Growing mix

Yield (cwt/acre) No CSA CSA Avg. Tomato

Difference (cwt/acre) CSA- no CSA (%)

ML = McEnroe Lite

615

687

651

+72

+12

MM = Metro Mix 360

653

794

724

+141

+22

634

740

----

+106

+17

MM-ML

+38

+107

+73

----

----

(%)

+6

+16

+11

----

----

Avg. Difference:

Bell Pepper ML = McEnroe Lite

366

368

367

+2

0

MM =Metro Mix 360

339

346

342

+7

+2

352

357

----

+5

+1

-27

-22

-25

----

----

Avg. Difference:

MM-ML

(%) -7 -6 -6 ------CSA = Carbon Based Soil Amendment; cwt = hundred weight units (100 lb); Avg. = average; CSA-no CSA = CSA minus no CSA; MM-ML = MM minus ML.

Table 4. Effect of nitrogen fertilizer sidedressing on marketable organic crop yield of Irish potato and sweet corn. 2006

2007

Vegetable Crop

N rate (lb/acre)

Yield (cwt/acre)

N rate (lb/acre)

Yield (cwt/acre)

Irish potato

-----

-----

0

73

-----

-----

80 Sign.

98 .001

0

102

0

31

50

98

80

96

Sweet corn

100 100 Sign. .001 Sign. ns Cwt = hundred weight units (100 lb); ns = not statistically significant at p = .05.

Table 5. Effect of liquid fish concentrate applied in row at planting on marketable organic crop yield of Irish potato and sweet corn, 2007. Liquid fish (Gallons/acre)

Yield (cwt/acre) Irish potato

Sweet corn

0

80

61

2

91

66

Significance .05 ns Cwt = hundredweight units (100 lb); ns = not statistically significant at p = .05.

Biochar, climate change and soil: A review to guide future research Saran Sohi1, Elisa Lopez-Capel2, Evelyn Krull3 and Roland Bol4 Corresponding author and editor: Evelyn Krull CSIRO Land and Water Science Report 05/09 February 2009

CSIRO Land and Water Science Report series ISSN: 1834-6618

Copyright and Disclaimer © 2008 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. Important Disclaimer: CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. Citation: Sohi, S1.Loez-Capel, E2., Krull, E3., Bol, R4., 2009. Biochar's roles in soil and climate change: A review of research needs. CSIRO Land and Water Science Report 05/09, 64 pp.. 1

Centre for Bioenergy and Climate Change, Rothamsted Research, Harpenden, AL5 2JQ, UK; now at UK Biochar Research Centre, School of Geosciences, University of Edinburgh, UK, Email: [email protected]

2

School of Civil Engineering and Geosciences, University of Newcastle, Newcastle uponTyne, NE1 7RU, UK, Email: [email protected]

3

CSIRO Land and Water, PMB2, Glen Osmond SA 5064, Australia, Email: [email protected]

4

Biogeochemistry of Soils and Water group, North Wyke Research, UK, Okehampton, EX20 2SB, UK, Email: [email protected]

Cover Photographs: Cover photo 1 Fragments of biochar 0.2-0.5mm diameter comprising willow stems carbonised at 600 C. Source: Saran Sohi Cover photo 2 Scanning electron micrograph of biochar formed from rubber tree stems at 800 C in a 200kW gasification plant in rural Cambodia. Source: Simon Shackley and Erik Middelink © 2008 CSIRO

ACKNOWLEDGEMENTS The preparation of this report was funded by the CSIRO Land and Water Opportunity Development Fund. Rothamsted Research and North Wyke Research received grant-aided support from the Biotechnology and Biological Sciences Research Council (BBSRC) in the UK. Rothamsted Research is an Institute of the UK Biotechnology and Biological Sciences Research Council. Newcastle University receives grant-aided support from the Engineering and Physical Sciences Research Council (EPSRC) in the UK. Keith Goulding (Manager of the Cross-Institute Programme for Sustainable Soil Function Department of Soil Science, Rothamsted Research), Peter Hairsine (Leader, Science Development CSIRO Land and Water) and Mike Grundy (Theme Leader, Managing Australia’s Soil & Landscape Assets. CSIRO Land and Water) provided helpful reviews and comments that improved the final version of the report.

iii

EXECUTIVE SUMMARY Biochar is the charred by-product of biomass pyrolysis, the heating of plant-derived material in the absence of oxygen in order to capture combustible gases. The objective of this report was to review and evaluate published studies with regard to what evidence and arguments currently exist that assess the application of biochar to soil to a) sequester carbon and b) produce secondary agronomic benefits. Current analyses suggest that there is global potential for annual sequestration of atmospheric CO2 at the billion-tonne scale (109 t yr-1) within 30 years. So far, however, the underlying published evidence arises mainly from small-scale studies that do not currently support generalisation to all locations and all types of biochar. From the available published and peer-reviewed literature the following general findings can be made for eight key questions. It is noted that for each of these key questions there remains major research questions that require the attention of researchers. This summary provides these outstanding research issues along side the major findings. 1.

Is all biochar the same? Key chemical and physical properties of biochar are greatly affected both by choice of feedstock (crop waste, energy crop, wood chip, municipal waste, manure, etc.) and process conditions (mainly temperature and time). These properties affect the interactions biochar has within the environment of its application as well as its fate. A rapid screening technique that provides the means for biochar products to be compared or matched to a particular use does not currently exist.

2.

How stable is it? Studies of charcoal from natural fire and ancient anthropogenic activity indicate millennial-scale stability. However, it is difficult to establish the half-life of modern biochar products using short experiments due to the presence of small amounts of labile components, partial oxidation and biotic or abiotic surface reactions. At the moment there is no established method to artificially-age biochar and assess likely long-term trajectories.

3.

Is it safe to use? Analysis of a limited number of biochar samples has indicated concentrations of toxic combustion products such as polycyclic aromatic hydrocarbons that are not at environmental risk level. However, a more systematic evaluation for a more complete range of other potentially harmful chemical contaminants associated with combustion, as well as toxic substances within feedstocks, has not been made. An environmental risk assessment that includes the impacts of these on terrestrial or aquatic ecosystems is outstanding. Given the stability of biochar, safe rates of applications need to be determined for individual soil types to avoid possible detrimental effects due to overapplication (e.g. reduction in soil productivity).

4.

What are the agronomic benefits? Currently, a large number of studies have been conducted where biochar application has shown significant agronomic benefits with a minor number of studies showing no significant effects of biochar application on crop productivity and some studies reporting adverse effects. This suggests that the extent of the effect of biochar on crop productivity is variable, due to the different bio-physical interactions and processes that occur when biochar is applied to soil, which are not yet fully understood.. There is a need for models to allow extrapolation of location-specific findings by accounting for mechanistic effects of geographic variations in soil type, climate, cropping and pyrolysis feedstock.

5.

Is it economically viable? The economic value of sequestered carbon will be determined within complex carbon markets that are influenced by energy supplies and demand, the supply and demand for

iv

low emissions technologies, the availability of alternative carbon sequestration technologies and global policy responses to climate change. The growing price of waste disposal is likely to make the production and application of biochar for electricity and waste management economically viable. Carbon offsets will have a greater role once biochar is certified under the Clean Development Mechanism (CDM) of the Kyoto Protocol. Uncertainty over market interventions may risk the investment in energy facilities that are able to produce biochar. 6.

What are the environmental and societal benefits? Models exist for viable agronomic use of biochar (without energy capture) in subsistence agriculture. However, relevant technological innovation is required to deal with environmental issues such as smoke production from traditional char production and associated health risks. Socio-economic constraints are not adequately researched. Higher crop yields resulting from biochar applications would be expected to mitigate pressures on land and would also have relevance to land restoration and remediation. Other environmental benefits of biochar application may lie in its application to rehabilitate contaminated wetlands and as a means to assist in managing (avoiding) algal blooms in aquatic ecosystems through adsorption of nutrients.

7.

Are the benefits of biochar in mitigating greenhouse gases widely accepted? It is generally accepted that biochar is a highly stable form of carbon and as such has the potential to form an effective C sink, therefore sequestering atmospheric CO2. Several projects are currently underway assessing/monitoring greenhouse gas emissions in fields amended with biochar in USA, Colombia, Kenya and Australia (). While biochar surpasses other biological forms of C with regard to its stability, estimates on the mean turnover time of biochar in soil vary from hundreds to thousands to tens of thousands of years. The mitigation potential of biochar with regard to other greenhouse gases, such as N2O and CH4, through its application to soil is less well established and requires further research.

8.

What are the research gaps and future challenges? Biochar performance Currently, the predictive capacity for biochar ‘performance’ does not exist and how to best optimise the multiple useful characteristics as a function of feedstock has not been assessed. This is currently inhibiting the realisation and application of this technology. Interaction of biochar with soil microbial communities and plants The physical, biological and chemical processes that biochar may exert on microbial communities and their symbiotic interaction with plants, and possibly enhanced nutrient use efficiency, are not yet understood. The apparent contradiction between the high stability of biochar, soil organic matter accumulation and apparent enhancement of soil microbial activity needs to be resolved. Research in Japan and in Germany has indicated that biochar can complex the carbon from dead micro-organisms. Further research work is required to determine under what conditions this complexation takes place. Cation exchange capacity (CEC) While the CEC of fresh char itself is not very high, biochar that has resided in soil for hundreds of years has been shown to have much higher CECs, comparable to those of zeolites. However, several studies have reported an increase in soil CEC after the application of fresh biochar. Thus, the processes that are instrumental in developing CEC over time as well as the effects that lead to an increase in CEC by addition of fresh (low CEC) biochar require detailed understanding.

v

Water holding capacity and aggregate stability While some studies report positive effects of biochar application on water-holding capacity, the specific mechanism that biochar exerts on water retention, macroaggregation and soil stability are poorly understood – yet should be of critical importance in climate change adaptation, where mitigating drought, nutrient loss and erosion are critical. Erosion, transport and fate The loss of biochar through vertical or lateral flow is not quantified, and only recently have studies been initiated to examine movement through soil profiles and into waterways. These processes complicate the task of confining the range of current estimates (from hundreds of years to millennia) of the mean residence time of biochar in soil. Long-term monitoring research stations (analogous to the Waite permanent rotation trial in Australia or the Rothamsted long-term experiments in the UK) are required to adequately assess the long-term stability and dynamics of biochar in soil. Decreased emissions of non-CO2 greenhouse gases (e.g. N2O and CH4) The currently available data on the effect of biochar additions on trace gas emission is very limited, but has a potentially great impact on the net benefit of biochar application. Development of cost effective means of measuring decreased emissions will ensure this potentially large greenhouse saving can be compliant with emissions trading schemes. Soil carbon modelling Modelling of the linked carbon and nitrogen cycles in soil with and without application of biochar is essential to understanding the fundamental mechanisms referred to above and the impact on soil-based emissions of greenhouse gases. Project specific Life Cycle Assessment (LCA) The total environmental life-cycle assessment has been conducted for some biochar case studies. Greenhouse balances, for example, are very project specific and hence there is opportunity to assess the benefits over a large range of feedstock, process and biochar application scenarios.

vi

CONTENTS 1.

Introduction ......................................................................................................... 1

2.

Biochar ................................................................................................................. 2 2.1.

What is biochar? ....................................................................................................... 2 2.1.1. 2.1.2. 2.1.3. 2.1.3.1. 2.1.3.2. 2.1.3.3. 2.1.3.4. 2.1.3.5. 2.1.3.6.

2.2.

Biogeochemical characterisation of biochar ........................................................... 10 2.2.1. 2.2.2. 2.2.3. 2.2.4.

3.

The purpose of biogeochemical characterisation ................................................10 Physical and chemical characterisation...............................................................11 Quantification of biochar and char .......................................................................13 Background and biochar history: from terra preta to terra nova...........................14

Biochar application in Agriculture................................................................... 16 3.1.

Biochar and climate change ................................................................................... 16 3.1.1. 3.1.2. 3.1.3. 3.1.4. 3.1.5. 3.1.5.1. 3.1.5.2. 3.1.5.3. 3.1.5.4. 3.1.5.5. 3.1.6. 3.1.6.1. 3.1.6.2. 3.1.6.3. 3.1.6.4. 3.1.6.5. 3.1.7. 3.1.8.

3.2.

Soil organic matter and climate change...............................................................17 Carbon stabilisation and sequestration using biochar .........................................19 Combined bioenergy and biochar production ......................................................20 Evaluation of biochar systems .............................................................................21 Stability of biochar in soil .....................................................................................21 Stability of biochar in natural systems .................................................................22 Influence of biochar feedstock on stability ...........................................................23 Climatic effects on biochar mineralisation ...........................................................23 Soil biological activity and the stability of biochar ................................................24 Effects of biochar on ease of tillage and mechanical disturbance .......................24 Indirect impacts of biochar on CO2-equivalent emissions....................................25 Indirect effects of yield benefits and nutrient requirement ...................................25 Impact of biochar on nitrous oxide emission from soil .........................................26 Impact of biochar on methane emission from soil................................................27 Biological activity and stabilisation of soil organic matter ....................................27 Effects of biochar on tillage and irrigation requirements ......................................28 Biochar scenarios for agriculture .........................................................................28 Notes on the natural cycling of char in soil ..........................................................31

Biochar, crop productivity and resource management ........................................... 32 3.2.1. 3.2.2. 3.2.3. 3.2.4. 3.2.5. 3.2.6.

4.

Why and how is biochar made?.............................................................................3 Biochar feedstocks ................................................................................................5 Biochar production systems ..................................................................................6 Slow pyrolysis........................................................................................................7 Fast pyrolysis.........................................................................................................8 Intermediate pyrolysis............................................................................................9 Carbonisation ........................................................................................................9 Gasification............................................................................................................9 Production of ammonia during pyrolysis ..............................................................10

Soil fertility ...........................................................................................................32 Crop yield ............................................................................................................33 Soil moisture retention.........................................................................................35 Nutrient retention and use-efficiency ...................................................................35 Use of biochar to manage water quality ..............................................................37 Potential risks to soil and water from use of biochar............................................37

Policy context and Analysis ............................................................................. 38 4.1. 4.2. 4.3. 4.4. 4.5.

A framework to evaluate applications of biochar .................................................... 38 Scenarios for the uptake of biochar for use in soil.................................................. 38 Market intervention and carbon trading .................................................................. 39 Market acceptability issues..................................................................................... 40 Research................................................................................................................. 41

vii

5.

Research Priorities and Future Challenges .................................................... 41 5.1. 5.2. 5.3. 5.4. 5.5.

Fundamental mechanisms...................................................................................... 42 Properties, qualities and environmental risk assessment....................................... 43 Carbon cycle modelling .......................................................................................... 44 Beneficiaries ........................................................................................................... 44 Commentary on likely barriers to the adoption of a large scale enterprises utilising Biochar.................................................................................................................... 45

References .................................................................................................................. 46

TABLE OF FIGURES Figure 1.

Biochar as a C sequestration tool

Figure 2.

Summary of pyrolysis processes

Figure 3.

Illustrative slow pyrolysis process

Figure 4.

Schematic process diagram for fast pyrolysis

Figure 5.

Simplified flow chart of how biomass releases energy as it captures CO2 as ammonium carbonate

Figure 6.

Scanning electron microscope image of biochar from pelletised peanut shell

Figure 7.

Components of black carbon assessed by available quantification methods

Figure 8.

Comparison of profiles of terra preta and adjacent soils

Figure 9.

The key physical (purple arrows), natural (orange arrows) and anthropogenic (red arrows) interactions of biochar in the environment

Figure 10. Scenario for multi-feedstock production of biochar, and multi-application use, emphasising the spatial context

TABLE OF TABLES Table 1.

Fate of initial feedstock mass between products of pyrolysis processes

Table 2.

Reported elemental composition for a range of bio-oil and biochar products

Table 3.

Properties of biochar from bagasse carbonisation

Table 4.

Physico-chemical properties of terra preta and adjacent soils

Table 5.

Summary of experiments assessing the impact of biochar addition on crop yield

viii

1.

INTRODUCTION

Periodic fire across Australian landscapes results in a natural process of carbon (C) sequestration from atmosphere to soil by the conversion of biomass to charcoal. The extent of this process has recently been quantified for Australia (Lehmann, 2009). There are increasing calls to mirror and enhance this process by the concerted use of ‘biochar’, a form of charcoal produced with the simultaneous production and capture of bio-energy which is then applied to the soil. A measure of the need and interest for a concerted effort in this area has been the evolution of an organised consortium, known as the International Biochar Initiative (IBI) (<www.biochar-international.org>). The inspiration for the supplementation of soil with charcoal stems from observations made in the ancient agricultural management practices that created terra preta, deep black soils. These soils, found throughout the Brazilian Amazon, are characterised by high levels of soil fertility compared with soils where no organic C addition occurred (Harder, 2006; Marris, 2006; Lehmann, 2007a; Renner, 2007). The evident value of the terra preta led to the suggestion that investment into biochar and application to agricultural soil may be both economically viable and beneficial. Rising fossil fuel prices, the need to raise yields in light of the global food crisis, and the emergence of a significant global market for trading carbon appear to promise added economic incentives in the future. At the same time the need to protect soils under an increasingly uncertain climate makes the apparent ability of biochar to increase the capacity for soil to absorb and store water vitally important. It also appears that adding biochar to soil may be one of the only ways by which the fundamental capacity of soils to store and sequester organic matter could be increased. There are a number of detailed reviews describing charcoal formation (Knicker, 2007) and associated C dynamics (Preston et al., 2006; Czimczik et al., 2007), including its role in the global carbon cycle (Schmidt et al., 2000). Forthcoming is a compendium of review articles (“Biochar for Environmental Management: Science and Technology”), which will place existing studies in the context of pyrolysis bioenergy (Lehmann and Joseph, 2009b ). A number of studies have now highlighted the net benefit of using biochar in terms of mitigating global warming and as an active strategy to manage soil health and productivity (Figure 1) (Lehmann, 2007a; Lehmann, 2007b; Lehman et al., 2005; Ogawa et al., 2006; Laird, 2008; Mathews, 2008; Woolf, 2008). However, relatively few studies exist that make a quantitative assessment of biochar-based soil management scenarios with regard to greenhouse gas, energy, and economic perspectives (Fowles, 2007; Gaunt et al., 2008). Nonetheless, the concept and value of biochar production and application is gradually incorporated by policy makers and governments (Winsley, 2007). Current studies are in many cases conceptually or geographically limited, and are often constrained by limited experimental data. In particular, mechanistic descriptions of the characteristics of biochar and its function in the soil and experimentation relevant to widescale applications of biochar are currently limited. In this report we examine existing published research within a framework constrained by a policy context. Thereby, we aim to identify gaps where new research should be focused in a way that will enable biochar to engage with climate change mitigation and to maintain soil productivity.

1

Fossil fuel

Bioenergy

Bioenergy with biochar to soil

atmospheric carbon dioxide

combustion

combustion

soil carbon fossil carbon 2.

pyrolysis

biochar

Figure 1. Biochar can result in a net removal of carbon from the atmosphere, especially with enhanced net primary productivity

BIOCHAR

2.1. What is biochar? Biochar is a fine-grained and porous substance, similar in its appearance to charcoal produced by natural burning. Biochar is produced by the combustion of biomass under oxygen-limited conditions. The definition adopted by the International Biochar Initiative (IBI) furthermore specifies the need for purposeful application of the material to soil for agricultural and environmental gain. The term biochar was originally associated with a specific type of production, known as ‘slow pyrolysis’. In this type of pyrolysis, oxygen is absent, heating rates are relatively slow, and peak temperatures relatively low (Section 2.1.3.1). However, the term biochar has since been extended to products of short duration pyrolysis at higher temperatures known as ‘fast pyrolysis’ (Section 2.1.3.2) and novel techniques such as microwave conversion. It is important to note that there is a wide variety of char products produced industrially. For applications such as activated carbon, char may be produced at high temperature, under long heating times and with controlled supply of oxygen. In contrast, basic techniques for manufacture of charcoal (such as clay kilns) tend to function at a lower temperature, and reaction does not proceed under tightly controlled conditions. Traditional charcoal production should be more accurately described as 'carbonisation' (Section 2.1.3.4), which involves smothering of biomass with soil prior to ignition or combustion of biomass whilst wet. Drying and roasting biomass at even lower temperatures is known as ‘torrefaction’ (Arias et al., 2008). A charred material is also formed during 'gasification' of biomass, which involves thermal conversion at very high temperature (800°C) and in the partial presence of oxygen (Section 2.1.3.5). This process is designed to maximise the production of synthesis gas (‘syngas’). Materials produced by torrefaction and gasification differ from biochar in physico-chemical properties, such as particle pore size and heating value (Prins et al., 2006) and have industrial applications, such as production of chemicals (methanol, ammonia, urea) rather than agricultural applications. In order to differentiate biochar from charcoal formed in natural fire, activated carbon, and other black carbon materials, the following list of terms aims to better define the different products. The differences, however, are relatively subtle since all products are obtained from the heating of carbon-rich material.

2

•

Char: the solid product arising from thermal decomposition of any natural or synthetic organic material. Examples are char from forest fire and soot resulting from the incomplete combustion of fossil hydrocarbon.

•

Charcoal: produced from the thermal decomposition of wood and related organic materials, mainly for use as an urban fuel for heating and cooking, but also traditional uses as soil amendment or control of odour (Okimori et al., 2003). Temperatures in traditional kilns approach 450-500°C, which is similar to that of industrial pyrolysis but with lower yields: conversion of feedstock dry mass may be as low as 10 % compared to 35% using more formal production technology. Also, all heat as well as gaseous and liquid co-products are lost during the combustion process.

•

Activated carbon: manufactured by heating carbonaceous material at a high temperature (above 500°C) and over long (>10 hours) periods of time. The resulting material is characterised by a very high adsorptive capacity. It is not used as a soil amendment but has been applied for cleansing processes, such as water filtration and adsorption of gas, liquid or solid contaminants (Tomaszewski et al., 2007).

•

Black carbon: a general term that encompasses diverse and ubiquitous forms of refractory organic matter that originate from incomplete combustion (Baldock et al., 2002). The diversity of burning conditions results in black carbon occupying a continuum of material. The review by Schmidt (1999) provides a thorough account of the ‘black carbon’ continuum, its constituents and definitions.

Biochar from pyrolysis and conventional charcoal and char share key characteristics which are related to carbon sequestration (long residence time) and soil fertility (soil conditioning effect). This is important since there is currently a much greater amount of research for char (Glaser et al., 2002) than for biochar. Biochar produced in association with bioenergy generation may be more applicable in some countries than others, depending on economic circumstance, political priorities, technology and infrastructure. The central quality of biochar and char that makes it attractive as a soil amendment is its highly porous structure, potentially responsible for improved water retention and increased soil surface area. Addition of biochar to soil has also been associated with increased nutrient use efficiency, either through nutrients contained in biochar or through physico-chemical processes that allow better utilisation of soil-inherent or fertiliser-derived nutrients. Importantly, it is the apparent biological and chemical stability that allows biochar to both act as a carbon sink, as well as provide benefits to soil that are long-lived. Using pyrolysis to turn sustainably produced biomass into a recalcitrant substance that is decomposed at a much slower rate, constitutes both a tool for carbon sequestration and avoided emission. It is argued that sequestration of carbon in biochar allows for a much longer storage time compared with other terrestrial sequestration strategies, such as afforestation (Schulze et al., 2000). The stability and carbon sequestration potential of biochar in soil is examined in Section 3.1.2.

2.1.1. Why and how is biochar made? Modern industrial bioenergy systems involve pyrolysis and gasification, the heating of a biomass feedstock under controlled conditions to produce combustible synthesis gas (‘syngas’), and oil (‘bio-oil’) that can be burnt to produce heat, power, or combined heat and power. Biochar, the third combustible product produced in pyrolysis, is the solid charred and carbon-rich residue. The balance in energy release and biochar formation can be optimised. Effectively, it is a ‘combustion’ process that may be curtailed at a point where any desired ratio in these products has been achieved. This ratio can then be adjusted and re-optimised to satisfy changing objectives. Whereas simple combustion of a feedstock maximises energy yield per unit mass, combusting syngas from pyrolysis gives – where optimised for biochar – a much greater energy yield per unit of carbon release.

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If incorporating biochar into soil can reliably deliver the environmental benefits outlined in 3.1.2, the carbon-equivalent saving resulting from conversion of biomass using pyrolysis can be increased further, relative to the production of energy only (i.e. combustion). Globally, there is an estimated 15x109 ha of cropland (Ramankutty et al., 2008). On the basis of calculations by Gaunt (2008), the application of biochar once every ten years to this land area would result in a CO2 -equivalent gain of 0.65 GtC yr-1.

FEEDSTOCKS Biomass energy crops (corn, cereals, wood pellets, palm oil, oilseed rape) Bioenergy residues “cake” Agricultural waste (wheat straw, hazelnut and peanut shells, waste wood, etc) Compost (green waste) Manure/ animal waste (chicken) Kitchen waste plastic, food, etc Sewage sludge

PROCESS

PRODUCT

USES and APPLICATIONS

Fast pyrolysis (anhydrous)

Synthesis gas Bio-oil liquid Biochar solid

- Heat - Fuel (combusted to generate electricity or converted to syngas) - High value biochemicals used as food additives or pharmaceuticals - Soil conditioners / fertilisers

Slow pyrolysis (low temp. 450450-free, 550°C, O2-free, sometimes some-times steam) steam) Slow pyrolysis (high temp.600900°C, O2-free) Gasification (high temp., fast heating rate.,OO2 present) rate,

Syngas Biochar Activated Biochar Combustible ethane, methane Biochar

Fermentation, anaerobic digestion and mechanical bio-treatment Carbonisation (‘brown’ at 300°C, ‘black’ at 380°C)

ethanol Ethanol Methane and sludge Charcoal

- Soil amendment (neutral / alkaline pH, porosity retains water, cation exchange capacity: robust benefits to plant growth compared to high-temp high-temp char) char) --Fuel Fuel(cooking (cookingand andheat) heat) - Extreme porosity and surface area - Water filtration and adsorption of contaminants (gas, liquid or solid) - Fuel (low yield, high reactivity) - Contamination of some feedstocks (e.g. metal and plastic in kitchen waste) may preclude use of sludge / char in soil - Fuel (for electricity or cooking) - Bi-products By-products(wood (woodspirits, spirits,wood woodtar) tar) - Substitute for coal coal-derived -derived coke cokeinin metal smelting

Figure 2. Summary of pyrolysis processes in relation to their common feedstocks, typical products, and the applications and uses of these products Pyrolysis has a requirement for initial energy, in the same way as in straight combustion some heat in the flame is used to initiate combustion of new feedstock. But the relative requirements must be carefully compared, together with any difference between pyrolysis and alternative bioenergy technologies in the energy requirement of feedstock transportation and drying. The potential advantage of pyrolysis-derived bioenergy over other bioenergy strategies in terms of greenhouse gas emissions results not only solely from the retention of up to 50% of the feedstock carbon in stable biochar, but from indirect savings that may result from the use of biochar in agriculture, specifically the soil (Gaunt et al., 2008). Biomass pyrolysis and gasification are well established technologies for the production of biofuels and syngas. However, commercial exploitation of biochar by-products as a soil amendments is still in its infancy. In Japan, which has the largest market for such products, approximately 15 000 t yr-1 is traded annually for soil use (Okimori et al., 2003). More usually biochar products are gasified for extraction of residual energy, or used in production of high value products such as activated carbon (Demirbas et al., 2006b). The pyrolysis process greatly affects the qualities of biochar and its potential value to agriculture in terms of agronomic performance or in carbon sequestration. The process and process parameters, principally temperature and furnace residence time, are particularly important; however, the process and process conditions also interact with feedstock type in determining the nature of the product.

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These variables together are key influences on the chemical, biological and physical properties, which limit the potential use for biochar products. A summary of feedstock, production processes and products is illustrated in Figure 2. The assignment of feedstock to process in Figure 2 is based on examples from the literature and does not indicate that they should be an exclusive classification. Each category of pyrolysis process is characterised by a contrasting balance between biochar, bio-oil and syngas (Table 1). The precise ratio in these products may vary between plants, and may be optimised at a particular installation; however, it is critical that maximising the production of biochar relative to mass of initial feedstock (Demirbas, 2006), is always at the expense of usable energy in the liquid or gaseous form. Although a greenhouse gas mitigation strategy may favour maximising the biochar product (Gaunt et al., 2008), the balance that is realised is a function of market and engineering constraints. In a generalised analysis, the economic cost of maximising the retention of carbon in biochar using slow pyrolysis has been assessed against the possible net gain in CO2 –equivalent emissions from using the product in soil, after accounting for the additional fossil-carbon offset that could be obtained through complete combustion of the feedstock (Gaunt et al., 2008). The net carbon gain over fossil fuel scenarios was 2–19 t CO2 ha-1 y-1, encompassing figures 2–5 times higher than those for strategies based on biomass combustion. The eligible portion of this added saving would have to attract CO2 -offset at a value sufficient to cover the USD 47 t-1 value of residual energy in biochar. A more detailed description of this analysis and discussion of the competing processes associated with energy and char production is discussed in detail in Chapter 3. Table 1. Fate of initial feedstock mass between products of pyrolysis processes (IEA, 2007) Process

Liquid (bio-oil)

Solid (biochar)

Gas (syngas)

FAST PYROLYSIS Moderate temperature (~500 °C) Short hot vapour residence time (<2s)

75% (25% water)

12%

13%

INTERMEDIATE PYROLYSIS Low-moderate temperature, Moderate hot vapour residence time

50% (50% water)

25%

25%

SLOW PYROLYSIS Low-moderate temperature, Long residence time

30% (70% water)

35%

35%

GASIFICATION high temperature (>800 °C) Long vapour residence time

5% tar 5% water

10%

85%

2.1.2. Biochar feedstocks Although current results suggest that the type of feedstock used for pyrolysis is more important where biochar is to be applied as a soil conditioner (Section 3.2.) there is little consensus as to what constitutes optimal feedstock for energy production. This is mainly due to the fact that the number of existing commercial plants is small, and that these plants are dedicated to specific waste streams, giving little incentive to experiment with this parameter. However, some research-scale pyrolysis plants have conducted experiments with a wider range of feedstocks (Day et al., 2005; Das et al., 2008; Gaunt et al., 2008). Feedstocks currently used at a commercial-scale or in research facilities include wood chip and wood pellets, tree bark, crop residues (including straw, nut shells and rice hulls), switch grass, organic wastes including distillers grain, bagasse from the sugarcane industry and 5

olive waste (Yaman, 2004), chicken litter (Das et al., 2008), dairy manure, sewage sludge (Shinogi et al., 2002) and paper sludge. The elemental ratios of carbon, oxygen and hydrogen are key feedstock parameters in commercial use and the quality of fuel products (Friedl et al., 2005). The feedstocks which are favoured for bio-oil and fuel-gas are those that have low mineral and N content. These include wood and biomass from energy crops, including short-rotation woody plants (such as willow), high productivity grasses (such as Miscanthus spp.), and a range of other herbaceous plants. They may also include abundant, available and low-cost agricultural byproducts, including cereal straw. The proportions of hemi-cellulose, cellulose and lignin content determine the ratios of volatile carbon (in bio-oil and gas) and stabilised carbon (biochar) in pyrolysis products. Feedstocks with high lignin content produce the highest biochar yields when pyrolysed at moderate temperatures (approx. 500 °C) (Fushimi et al., 2003; Demirbas, 2006). In the future, selection of feedstock may be dictated by the desired balance between pyrolysis products (gas, oil and biochar), and whether the production process is slow pyrolysis, or a related process. Charring of agricultural waste products such as nut shells and rice hulls for energy production may be advantageous compared to disposal as waste by some other means (Demirbas, 2006; Demirbas et al., 2006a). Alternative use for such materials includes composting and mulching. However, it is important to recognise that continuous removal of crop residues from the same land compromises soil cover and diminishes soil nutrient supply. This is further discussed in Chapter 3.

2.1.3. Biochar production systems Biochar is a multi-process product whose qualities are dependent on each process and also the material to which the process is applied. Since the technology is still in a period of development and not yet optimised to producing a product for use in soil, it is useful to review the various technologies currently in use. The processes of slow- and fast-pyrolysis are exemplified in Figure 3 and 4 and discussed in the subsequent sections.

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Figure 3. Illustrative slow pyrolysis process (Source: BEST Energies)

Char separation

Gas

Pyrolysis Biomass

Drying

Grinding

to < 10% water

to < 3mm

Fluid bed CFB Transported bed Rotating cone Entrained flow Ablative Etc.

Bio-oil cool and collect

Char

Figure 4. Schematic process diagram for fast pyrolysis (modified from Bridgewater (2006))

2.1.3.1. Slow pyrolysis Slow pyrolysis is the thermal conversion of biomass by slow heating at low to medium temperatures (450 to 650°C) in the absence of oxygen, with the simultaneous capture of syngas. Feedstocks in the form of dried biomass pellets or chips of various particle sizes are fed into a heated furnace and exposed to uniform heating, generally through the use of internal or external heating as retort furnace or kilns, respectively. Conventional production conditions have been summarised by Peacocke and Joseph in : • • • • •

residence times: >5 seconds for the production of syngas; minutes, hours or days for biochar production relatively low reactor temperatures (450-650°C) reactor operating at atmospheric pressure very low heating rates, ranging from 0.01–2.0°C s-1 very short thermal quenching rate for pyrolysis products: minutes to hours. 7

Several commercial facilities generate syngas and biochar using a continuous flow system in which feedstock passes slowly through a kiln in an auger feed, with combustible syngas continuously drawn away. Biochar, bio-oil and syngas are formed in approximately equal proportions due to the slow speed of the combustion process, which promotes extensive secondary reactions within biochar particles and in the gas and vapour phases, leading to condensation. The pyrolysis reaction itself is mildly endothermic, with the bulk of energy capture being in the form of the syngas and bio-oil condensates. The biochar has a residual energy content of about 30–35MJ kg-1 (Ryu, 2007), and conventionally this is extracted within the plant by burning or gasification, providing heat to drive the primary pyrolysis (Demirbas, 2006), or to dry incoming feedstocks. The syngas product may be combusted on site to generate heat or electricity (via gas or steam turbine), or both. A variant of slow pyrolysis includes a steam gasification step, a technology developed by Eprida in collaboration with the University of Georgia (). Adding steam to the pyrolysis reaction liberates additional syngas from the biochar product, mainly in the form of hydrogen. The biochar that remains after this ‘secondary’ pyrolysis displays rather different properties from the primary product, differing in pore size and carbon to oxygen ratio (Demirbas, 2004). Syngas can be purified through a sequence of operations to yield pure streams of the constituent gases: hydrogen (50% of gas yield), carbon dioxide (30%), nitrogen (15%), methane (5%), and lower molecular weight hydrocarbons, as well as some carbon monoxide (Day et al., 2005). There is a small energy penalty associated with these steps. Slow pyrolysis research plants currently process feedstock at a rate of 28–300 kg hr-1 on a dry mass basis, and commercial plants operate at 48–96 t d-1. Comparing the efficiency of pyrolysis plants is complex since the mix and use of products vary, and the composition and heat value of syngas differs. Feedstock quality and moisture content is also variable, and there is a conversion loss in the generation of electrical power through steam or gas turbines.

2.1.3.2. Fast pyrolysis Very rapid feedstock heating leads to a much greater proportion of bio-oil and less biochar (Table 1). It was with the objective of achieving this high yield of liquid fuel that fast pyrolysis technology was developed. The time taken to reach peak temperature of the endothermic process (the ‘resistance time’) is approximately one or two seconds, rather than minutes or hours as is the case with slow pyrolysis. The lower operating temperature also enhances the overall conversion efficiency of the process relative to slow pyrolysis. Maintaining a low feedstock moisture content of around 10% and using a fine particle size of <2mm permits rapid transference of energy despite relatively moderate peak temperatures of around 450°C (and in the range 350 to 500°C). In many systems the transfer is further increased by mechanically enhancing feedstock contact with the heat source or maximising heat source surface area. Various technologies have been used and proposed or tested including: fixed beds, augers, ablative methods, rotating cones, fluidized beds and circulating fluidized beds. Surface charring must be continuously removed during reaction to prevent pyrolysis of particle interiors being inhibited by its insulating effect. Bio-oil is condensed from the syngas stream under rapid cooling, with the combustion of syngas providing the pyrolysis process heat. The bio-oil is a low grade product with a calorific value, on a volume basis, approximately 55% that of regular diesel fuel. It is unsuitable as a mainstream liquid transport fuel even after refining, and is most suitable as a fuel-oil substitute. It is considered to have an advantage over typical fuel oils in zero SOx and low NOx emission on combustion (Bridgewater, 2004). In addition to combustion for electricity generation, bio-oil may be converted to syngas for production of clean fuels (gasification).

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Bio-oil also contains high value bio-chemicals of relevance to food and pharmaceutical industries. The biochar product of fast pyrolysis is granular and displays a lower calorific value (23– 32 MJ kg-1) than that of slow pyrolysis (Demirbas, 2001). However, there are currently no published studies to assess the effects of biochar from fast pyrolysis when it is applied to soil. It is highly likely that condensed volatiles will be present in the product and that this will affect its performance and desirability.

2.1.3.3. Intermediate pyrolysis This term describes a hybrid technology under evaluation at Aston University, UK, designed to produce bio-oil with very low tar content, with perceived potential for use as a motor fuel. The process has been tested with woody and non-woody feedstocks, and produces biochar in greater quantity and of contrasting quality as compared to fast pyrolysis.

2.1.3.4. Carbonisation Carbonisation describes a number of pyrolysis processes that most closely resemble traditional, basic methods of charcoal manufacture, and which produce biochar of the highest carbon content. The auto-thermal carbonisation process is the small-scale method widely used in rural communities around the world (FAO, 1987). The second requires fossil fuel to provide an external heat source, and is associated with industrial, mass production of charcoal (FAO, 1985). The process is optimised for the solid products of pyrolysis, but condensed gases provide an industrial product known as ‘wood vinegar’, which as well as providing the basis for food flavouring ingredients, is considered to have a fertiliser value to plants. The auto-thermal process as the most realistic option has been proposed for the participation of local communities in using biochar to build soil fertility, especially in developing countries. It is lower cost, and easier and simpler than pyrolysis systems where ratios of solid, liquid and syngas products have to be optimised. A comparison of three alternative options has recently been investigated for the carbonisation of biomass wastes from tree plantations: a drum kiln, a Hume pipe kiln, and a brick kiln (Okimori et al., 2003; Ogawa et al., 2006). For wood, 24% of wood mass was converted to biochar of 76% carbon content at 400 to 500°C, but carbonisation at 600°C gave 28% biochar with a higher carbon content of 89%. The 50% of feedstock carbon stabilised in each case was similar to the maximum yield obtained in slow pyrolysis. Brazil has the largest concentration of industrial charcoal manufacture. This is associated with the pig-iron (smelting) industry, where substitution of charcoal for fossil-derived coke has been achieved in a number of very large projects under the Clean Development Mechanism, and associated with large-scale plantations of eucalypt.

2.1.3.5. Gasification Gasification is the process by which any carbonaceous material (coal and petroleum as well as biomass) is substantially converted into a stream of carbon monoxide and hydrogen in a high temperature reaction and controlled-oxygen environment, sometimes at high pressures of 15–50 bars (Bridgewater, 2006). The gas mixture is the key energy output and the gasification process has an application as a clean waste disposal technique (Bapat et al., 1998). In slow pyrolysis facilities, gasification is often used to generate further syngas from biochar ‘waste’. Syngas may be used for electricity generation via gas or steam turbines (or both), used to manufacture chemicals and fertilisers, or further cleaned for use as liquid fuel. Since conversion of feedstock to syngas is often the main objective, the process is maximised for gas production and so the biochar yield from gasification tends to be very low (Table 1). However, this also carries the risk of higher levels of metals and minerals that may be

9

concentrated in biochar, with potential safety implications with regard to application to soil (Fernandes et al., 2003a). Although biochar from gasification has a high calorific value (Demirbas, 2006; Demirbas et al., 2006a), it has high value use as the basis for activated carbon production. Its potential to act as the carrier in a slow nutrient release fertiliser product has also been noted (Ueno, 2007). Worldwide, gasification has been used on a commercial scale worldwide for more than 50 years, mainly in the refining, fertiliser, and chemical industries, and for more than 35 years in the electric power industry. There are more than 140 gasification plants currently in operation, with worldwide gasification capacity projected to grow 70% by 2015, with 80% of this growth occurring in Asia (Anon, 2008). The majority of gasification plants produce chemicals, mainly methanol or ammonia and urea, and use coal or refuse-derived feedstocks (Kedco, 2008). However, biomass feedstocks are also used, for example wood pellets, wood chips or paper and sugar cane bagasse (Ueno et al., 2007), and rural gasification projects are expanding.

2.1.3.6. Production of ammonia during pyrolysis In the Haber-Bosch process, a fossil hydrogen source (usually methane) is used to fix atmospheric nitrogen and create ammonia for manufacture of fertiliser. Hydrogen in syngas streams from pyrolysis (7-8% of slow pyrolysis syngas) can substitute methane and be used, potentially not only to create ammonia but, if conducted on the same site as the pyrolysis, fix ammonia to a biochar co-product. This offers the prospect of a crop fertiliser that simultaneously adds stabilised carbon to soil, possibly with slow release characteristics. This could offer greater net benefit in terms of CO2 -equivalents than using syngas to, for example, generate electricity. The process of fixing ammonia from the hydrogen syngas stream at atmospheric pressure and ambient temperature has been demonstrated (Day et al., 2005) and is illustrated diagrammatically in Figure 5. However, agronomic evaluation of the product has not been published and the concept has not yet been commercialised.

Figure 5. Simplified flow chart of how biomass releases energy as it captures CO2 as ammonium carbonate (modified from Day et al., 2005 )

2.2. Biogeochemical characterisation of biochar 2.2.1. The purpose of biogeochemical characterisation Although commercial biochar products are being developed for use in soil, credit for carbon storage will require predictable levels of stability and the ability to verify actual rates of degradation through quantitative soil analysis (Ogawa et al., 2006; Matthews, 2008). Identifying the characteristics that determine the stability of biochar will enable its properties to be optimised and standardised in production. Techniques to unambiguously detect and

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measure its abundance in soil are necessary to verify its application and to trace the fate of particular biochar products. Biogeochemical characterisation techniques may also help understand the function of biochar products in soil at the process level. With specific knowledge of the nature of biochar-driven processes in the soil, predictive capacity for the longevity and reactions of biochar in soil that will determine its value as a soil carbon sink and soil conditioner are possible. From a practical point of view it is important that the methods devised enable biochar characteristics to be determined sufficiently rapidly and inexpensively to permit widespread application and use.

2.2.2. Physical and chemical characterisation Kuwagaki (1990) proposed that seven properties should be measured for a quality assessment for agronomically-used biochar: pH, volatile compound content, ash content, water holding capacity, bulk density, pore volume, and specific surface area. Feedstock is a primary factor governing the chemical and physical properties of biochar. The elemental composition reported for a range of bio-oil and biochar products from various feedstocks are compared in Table 2. Table 2. Reported elemental composition for a range of bio-oil and biochar products (% dry ash-free mass) Elemental composition (%) Product

C

H

N

O

HHV* (MJ/kg)

Beech-trunk bark biochar

87.9

2.9

0.6

10.6

33.2

Beech-trunk bark bio-oil

68.8

8.9

0.8

21.5

34.6

Rapeseed cake biochar

66.6

2.5

6.1

24.3

30.7

Rapeseed cake bio-oil

73.9

10.8

4.7

10.6

36.5

Wood bark biochar

85.0

2.8

–

12.2

30.8

Wood bark bio-oil

64.0

7.6

–

28.4

31.0

Cotton stalk biochar

72.2

1.2

–

26.6

21.4

Cotton stalk bio-oil

59.7

7.8

1.8

30.6

26.0

Bio-char from hazelnut shell

95.6

1.3

–

3.1

32.0

Sunflower bio-oil

72.1

9.8

5.2

12.9

36.2

*HHV= higher heating value (enthalpy of complete combustion of a fuel including the condensation enthalpy of former water); Demirbas et al.,(2004)

In general, the carbon content of biochar is inversely related to biochar yield. Increasing pyrolysis temperature from 300 to 800°C decreased the yield of biochar from 67 to 26% and increased the carbon content from 56 to 93% (Tanaka, 1963). Beyond a certain threshold, the mass of biochar may decrease without any affect on the amount of carbon retained within it; but as mass is lost, the ash content of biochar increases. In one study, the proportion of biochar comprised of ash increased from 0.67 to 1.26% between 300°C and 800°C (Kuwagaki and Tamura, 1990). For a particular feedstock, the elemental composition of the pyrolysis products can still be greatly affected by the processing temperature and pyrolysis residence time. The effect of temperature on the composition of biochar from sugarcane bagasse is listed in Table 3. 11

There was a corresponding impact on the pH of the biochar from 7.6 at 310°C to 9.7 at 850°C (Kuwagaki and Tamura, 1990). Table 3. Properties of biochar from bagasse carbonisation (Ueno et al., 2007) Parameter or property o

Biochar

Feedstock

Preset temperature ( C)

500

600

700

800

Average temperature (oC)

490

690

740

830

Specific surface area (m2/g)

Nd

270

322

273

Nd

EC (mS m )

7.78

7.15

6.95

7.83

Nd

pH

7.46

7.59

7.68

7.89

Nd

TN (%)

0.58

0.45

0.32

0.44

0.19

70.5

71.0

65.2

73.9

46.1

3361

4601

5359

4363

841

-1

TC (%) -1

Minerals (mg 100g )

nd=not determined There are inevitable accompanying differences in the physical and other chemical properties of biochar. Scanning electron microscopy (SEM) is often used to describe the physical structure of biochar, and the architecture of cellulosic plant material is clearly retained (Figure 6). It has been suggested that the porous structure of biochar can explain its impact on soil water holding and adsorption capacity (Day et al., 2005; Ogawa et al., 2006; Yu et al., 2006).

Figure 6. Scanning electron microscope (SEM) image of biochar produced at 400°C from pelletised peanut shell (Jason Nadler, Eprida, Day et al., 2005) 12

Process temperature greatly affects the surface area of pyrolysis products. In one study, surface area was shown to increase from 120 m2g-1 at 400°C to 460 m2g-1 at 900°C (Day et al., 2005). This effect of temperature has led to suggestions that biochar created at low temperature may be suitable for controlling the release of fertiliser nutrients (Day et al., 2005), whilst high temperature biochars would be more suitable for use as activated carbon (Ogawa et al., 2006). The surfaces of low temperature biochar are, however, hydrophobic and this may limit the capacity to store water in soil. The form and size of the feedstock and pyrolysis product may affect the quality and potential uses for the biochar product. Initially, the ratio of exposed to total-surface-area of biochar is affected by its particle size. However, although low temperature biochar is stronger than high temperature products, it is brittle and prone to abrade into fine fractions once incorporated. Thus, over the long term, surface area, i.e. of weathered biochar, may not be greatly affected by this parameter. Biochar comprises part of a continuum of materials described as ‘black carbon’ (Schmidt et al., 2001), which are difficult to quantify. Techniques that have been used to characterise this wider class of materials – which includes soot, charcoal, and char from vegetation fire – may be applied to detect the presence of biochar in soil, sediments and air. These methods include extractive techniques analogous to those applied to soil organic matter, solid state 13C nuclear magnetic resonance (NMR) spectroscopy (with crosspolarization, CP, or Bloch decay, combined with magic angle spinning, MAS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy (Baldock et al., 2002; Fernandes et al., 2003b; Lehmann et al., 2005b). Biochar occurs naturally in soil as a consequence of wildfire (see Section 3.1.5.1.) and is considered to be a distinct soil carbon pool (Krull et al., 2003). Research to quantify and characterise this material has highlighted the limitations of various analytical techniques when applied to soil and separation procedures to physically separate char from other soil organic matter. A key problem is the interference that the mineral matrix poses, particularly with its associations with highly stabilised soil organic matter, which chemically resembles char. This has been successfully addressed through the use of high energy ultraviolet photooxidation, which oxidises most non-char carbon (Smernik and Oades, 2000; Smernik et al., 2000). Thermal oxidation to remove lignin (De la Rosa et al., 2008) and chemical oxidation using hydrofluoric acid to remove mineral interferences (Simpson and Hatcher, 2004a) have also been used.

2.2.3. Quantification of biochar and char The categorisation of organic carbon in soil is in general a major challenge. Quantifying different components of black carbon is particularly difficult, on account of its chemical complexity and its inherently un-reactive nature. To compare the efficacy of candidate methods depicted in Figure 7, a ring trial was recently undertaken using a selection of 12 materials of contrasting origin and source (Hammes et al., 2007). Methods included in the trial included approaches based on biomarkers, particularly benzene polycarboxylic acids (BPCA). Chemical oxidative treatments using acid dichromate or sodium chlorite were represented; other oxidative approaches used ultra-violet treatment (photooxidation) with correction for non-black aromatic carbon through 13C NMR analysis of oxidised residues. A chemo-thermal oxidation method used a temperature threshold of 375°C, also with 13C NMR and elemental analysis of residues. A purely thermal (gravimetric) analysis was represented using a helium gas flow containing 20% oxygen. Purely spectroscopic methods included thermal or optical laser transmittance and reflectance, and mid-infrared. Additional methods assessed were matrix assisted laser desorption ionisation (MALDI –TOF) and hydrogen pyrolysis. The most promising reference techniques for determination of biochar in soils were UV or chemical oxidation with elemental analysis and 13C NMR analysis of residues (Skjemstad et

13

al., 1999; Smernik et al., 2002), thermal analysis (De la Rosa et al., 2008; Hammes et al., 2007) and hydrogen pyrolysis (Ascough et al., 2008). Mid-infrared spectroscopy shows promise as a means to rapidly estimate black carbon (Janik et al., 2007) and has been applied to large sample sets (Lehmann et al., 2008). This is a correlative technique calibrated against a reference method.

S lig h tly c h a rre d b io m a s s

Char

C h a rc o a l

m m a n d la rg e r p a rtic le s

Soot GBC

m m to s u b m ic ro n

s u b m ic ro n

h ig h ly re a c tiv e

in e rt

U V O X ID A T IO N –

13C

NM R

u ltra -h ig h re s o lu tio n m a s s s p e c tro m e try th e rm o -c h e m ic a l m e th o d s

v is u a l / m ic ro s c o p ic

c h e m ic al m e th o d s BCPAs o th e r m o le c u la r m a rk e rs

Figure 7. Components of black carbon assessed by available quantification methods across a continuum of recalcitrance increasing from left to right (Hammes et al., 2007)

2.2.4. Background and biochar history: from terra preta to terra nova The terra preta of the Brazilian Amazon are anthropogenic dark earths, characterised by enhanced levels of soil fertility and popular locally for growing cash crops such as papaya and mango. These crops are said to grow three times faster than on surrounding land, a landscape characterised by soils of generally low fertility. Although the terra preta occur in small patches averaging 20 ha, sites as large as 350 ha have been reported (Smith, 1999). Similar soils have not only been identified elsewhere within the region, namely Ecuador and Peru, but also beyond, in West Africa (Benin, Liberia), and the savanna of South Africa (Lehmann et al., 2003). The terra preta display high levels of soil organic matter (SOM) and nutrients such as nitrogen, phosphorus, potassium and calcium (Table 4). These characteristics and their high fertility is attributed in part to a high char content (Glaser et al., 2001), which is the main reason why the terra preta tend to be much darker in colour than adjacent soils (Figure 8). The source of the large amounts of char is considered to have been incompletely combusted biomass carbon, such as wood from kitchen fires or in-field burning, conducted by relatively large and settled communities in the distant past.

14

The terra preta phenomenon has widespread public appeal and has attracted extensive coverage in popular science publications, TV and film, and a plethora of websites. The potential relevance of the terra preta as a model for modern day variants using by-products of bioenergy is now well established and recognised in popular science (Lehmann, 2007b; Baskin, 2006) as well as high impact scientific journals (Marris, 2006; Lehmann, 2007a). From this, the idea of terra nova has emerged: soils whose properties would be enhanced by modern variants of the management practices that created terra preta,

Figure 8. Comparison of profiles of terra preta and adjacent soils (Source: IBI website)

Table 4. Physico-chemical properties of terra preta and adjacent soils (data from Solomon et al., 2007; Liang et al., 2006)

Site

Soil type

Depth range (cm)

Age (yr)

terra preta

43-69

Adjacent soil

Organic carbon (mg g-1 soil)

Total soil nitrogen (mg g-1 soil)

C:N ratio

Clay content (% soil)

pH

600-1000

27.0

6.4

22.0

1.0

23

0-10

600-1000

35.9

4.6

21.8

1.6

14

terra preta

0-16

900-1100

22.6

5.9

31.5

1.8

18

Adjacent soil

0-8

900-1100

26.7

4.2

17.5

1.3

14

terra preta

48-83

2000-3000

10.4

5.6

15.7

1.0

16

Adjacent soil

0-30

2000-3000

8.5

4.7

15.4

0.8

20

terra preta

190-210

6700-8700

0.3

5.0

16.5

1.1

15

Adjacent soil

0-12

6700-8701

0.3

3.9

10.2

0.4

27

Hatahara

Lago Grande

Acutuba

Dona Stella

15

3.

BIOCHAR APPLICATION IN AGRICULTURE

In the context of this report, carbon sequestration is the primary driver for considering the application of biochar to soil. Policy makers charged with meeting greenhouse gas emission targets and addressing public concern over increasingly evident climate change may recognise the potential for biochar-based strategies. The land-owner or farmer is likely to have a more practical or financial perspective. A particular combination of feedstock, pyrolysis technology, energy conversion and byproduct usage can comprise a biochar-based system. Alternative systems have different greenhouse gas balances. In Section 3.1.4, economically and politically conceivable systems for different regions of the world are considered. The future price of carbon and the inclusion of biochar in carbon-trading schemes is a key factor. The likely additional benefits of biochar to agricultural production are reviewed in Section 3.2. These factors are critical since they dictate whether relevant practices are adopted on a large scale through their effect on the decision making of individual farmers. From a global and policy perspective the potentially negative impacts of biomass use on climate forcing must be considered. These include the effects of soot and trace gases that are emitted into the atmosphere during combustion. Airborne transport and deposition of soot has been implicated in the acceleration of polar ice melt, but conversely in facilitating cloud formation and ‘global dimming’ (McConnell et al., 2007; Ramanathan et al., 2008). Currently biomass burning accounts for 10% of global CH4 emissions and 1% of N2O (Crutzen et al., 1990). Although current charcoal production activity could account for a component of these emissions (Woolf, 2008), a general shift to pyrolysis-based systems would decrease, if not eliminate, them. However, the net result with great expansion of alternative bioenergy systems has not been assessed. As is apparent in the terra preta, the addition of biochar can dramatically darken the colour of soil, especially in soils that are low in organic matter. A relationship between soil colour and low temperature fire occurrence has been demonstrated (Ketterings et al., 2000). Oguntunde (2008) found soil at charcoal manufacturing sites to have 8% greater hue, and 20% higher value and chroma. Since dark soils absorb more solar energy they may, depending on water content and plant cover, display higher soil temperatures (Krull et al., 2004). This will affect rate processes, enhancing the cycling of nutrients and potentially extending the growing season in seasonal climates. In Japan it is a traditional farming practice to apply charcoal to accelerate snow melt. Anecdotal evidence suggests more rapid crop establishment in temperate soils enriched in char, but to date no quantitative relationships between biochar application rate and these parameters have been reported. The study of Oguntunde (2008) showed a one-third reduction in soil albedo in soils enriched in char. On a large spatial scale, the application of biochar could affect the albedo of the Earth’s surface. Increasing surface albedo has been proposed as a possible mitigation measure for climate forcing (Crutzen, 2006). The frequency with which potentially toxic compounds materialise in biochar and their concentration is inadequately researched. Two classes of compounds are of generic concern, since they can potentially from in the pyrolysis of any feedstock: polycyclic aromatic hydrocarbons (PAH) and dioxins. These compounds and available evidence for their presence in biochar is examined in Section 3.2.6.

3.1. Biochar and climate change The natural carbon cycle includes natural char production from wildfires, the ensuing transport of char from the soil to watercourses and the ultimate burial in marine or estuarine sediments. Since routine and universally acceptable methods for black carbon and specifically charcoal are still outstanding, the precise magnitude of the rates and processes, and the relative size and stability of char in the soil and sediment pools are still uncertain 16

(Schmidt, 2004; Simpson and Hatcher, 2004b). However, the potential to enhance the contribution that char makes to the natural carbon cycle through the addition of biochar in soil is a topic of much public discussion and a rising profile in influential policy circles, for example, in Australia (Garnaut, 2008). The contribution that such strategies can have on climate change mitigation depends on attaining a much more extensive research base and detailed economic analyses. It is useful to consider a biochar-based strategy against more established approaches to increase the organic carbon stored in soil, such as the use of manures and composts. The longevity of biochar in the soil is an important element when comparing pyrolysis bioenergy and biochar production with conventional bioenergy strategies, in mitigating climate change. However, it is also vital to assess any indirect reduction in net greenhouse gas emissions from agriculture through the use of biochar. There may be additional benefits arising from the contribution of biochar to facilitating agricultural development and improving the socioeconomic circumstances of farmers in developing countries. Figure 9 captures the complexity of potentially beneficial interactions of biochar in the context of natural cycles and anthropogenic interventions.

3.1.1. Soil organic matter and climate change In order to understand the potential significance of carbon in soil in the form of biochar, its characteristics and dynamics should be compared to those of the remaining soil organic matter, which accounts for most of the carbon that exists in soil (the exception being calcareous soils which contain stocks of inorganic carbon in carbonate minerals). Depending on land-use and climate, most soils contain up to approximately 100 t ha-1 carbon as organic matter. Peat soils, though, comprise mainly organic matter and contain much more carbon on a per unit area basis. It is increasingly recognised, however, that a greater proportion of the total carbon may comprise an accumulated store of the products of burning or fire (Skjemstad et al., 2004a), and that this has implications for the response of the wider soil carbon pool to climate change (Skjemstad et al., 1999; Lehmann et al., 2008). Modelling indicates that about 90% of the organic matter present in soils turns over on decadal to centennial timescales (Coleman et al., 1996; McGill, 1996). Most organic matter in soil is derived from plant roots, plant debris and microbially re-worked substances. The presence of soil organic matter is important for a range of useful soil properties, which has been comprehensively reviewed by Krull (2004). The process of microbial energy acquisition (and concomitant CO2 release) from substrate is accompanied by a release of various nutrient elements, which may be conserved in the soil in microbial biomass or the particulate residues of substrate decomposition. A portion of certain nutrients may also be released in soluble form, and a fraction may be lost from the soil through leaching or run-off; which is essential to crop nutrition. This is particularly the case where external nutrient provision (from fertiliser or manure) is limited or absent. Overall, a balance slowly develops between the rate of carbon addition and the emission of CO2, which are specific to the land-use and environmental conditions. The amount of organic matter maintained once this balance is reached, depends on its average rate of turnover. To date there have been few means proposed that permit manipulation of this rate, so that soil carbon can be permanently increased. Beyond simply increasing the amount of external organic matter inputs (Smith et al., 2000), the main strategies are to disturb the soil less by using less intensive tillage or zero tillage (Lal, 1997; Smith et al., 1998), or by selecting particularly recalcitrant, lignin-rich amendments (Palm et al., 2001). Although conversion to no-till soil management has been widely promoted as an approach to enhance soil organic matter as well as to control erosion and conserve water, the main effect appears to be a vertical re-distribution of organic matter, and an increase toward the surface more or less matched by a corresponding depletion at depth (Bhogal et al., 2007; BlancoCanqui et al., 2008). Nonetheless, the Chicago Climate Exchange includes a specification for ‘conservation tillage’ amongst its Carbon Financial Instruments for carbon sequestration and thus a precedent for the active engagement of farming in the carbon market

17

(). Managing decomposition in soil by manipulating the quality of inputs has been explored extensively in tropical environments where decay is rapid (Palm, 2001). But simply altering the composition of soil inputs has only a relatively minor impact on the composition and long-term fate of the small portion that is stabilised, with incorporation and repeated decomposition inside the dominant, slow turnover pool. Thus the main emphasis in the sequestration debate has been focused on increasing soil carbon by increasing organic matter additions in the form of straw or other crop residues, and from external sources such as manures and a range of organic wastes: sewage sludge, municipal compost, paper waste, and so on. Although there is a large amount of such material available, the quantity is relatively small compared with the total flux through soil, particularly the size of the global soil carbon pool. When a soil is at an equilibrium, only about 10% of the carbon added to soil is stabilised for more than one year. During a transition, progress to new equilibrium is slow, with the annual increase being small relative to the carbon invested. As equilibrium is approached the annual rate of accumulation decreases, and once reached, the new level of input has to be sustained simply to maintain it. Furthermore, the capacity to store organic matter is ultimately limited (with the capacity varying with soil type, water regime and climatic factors); thus the improvement in carbon storage that is possible for each incremental increase in input (Stewart et al., 2007; Gulde et al., 2008). As well as added carbon being rapidly re-emitted into the atmosphere, carbon is lost in the formation of soil organic matter through digestion in the animal gut or oxidation in conversion to compost. The level of carbon sequestration or offset that could be realised through an alternative use of these materials, including fossil fuel substitution, must be considered when assessing the efficacy of these strategies from the perspective of climate mitigation alone (Schlesinger, 2000). For example, the carbon cost of producing N fertiliser is relevant when proposing to increase soil carbon storage indirectly through enhanced plant growth (Schlesinger, 2000).

CO2

SOIL organic matter

MANAGE climate change

CROP productivity

water

PLANT biomass

ENERGY capture

N supply

N2O effect

soot charcoal biochar

AGRICULTURAL development

Figure 9. The key physical (purple arrows), natural (orange arrows) and anthropogenic (red arrows) interactions of biochar in the environment 18

In the context of the interventions generically referred to as ‘management options’, important soil physical benefits may be gained by accumulating soil organic matter (Janzen, 2006). However, these must be balanced against the opportunity costs, the forgone benefits that might arise from its breakdown and turnover, most importantly the release of crop nutrients (Janzen, 2006). In general, however, any form of organic matter added to the soil degrades resulting relatively quickly in CO2 emission. Thus adding degradable organic matter into the soil is inefficient in terms of climate change mitigation, with the energy contained being captured and dissipated by soil microbes rather than in power plants where it can offset fossil fuel use (Woolf, 2008).

3.1.2. Carbon stabilisation and sequestration using biochar Turning biologically-derived organic matter into a highly stabilised form can decrease CO2 emission from soil by considerably lowering its rate of decomposition. Whether stabilisation by conversion to biochar represents a net carbon saving depends on the time horizon for the comparison. However, the immediate CO2 emission from syngas released by pyrolysis would, within a few months, be exceeded by the CO2 emitted in decomposition if the same material had been added to soil directly (Lehmann et al., 2005a). Also, although there is a CO2 emission associated with provision of heat for the pyrolysis process, the calculations of Gaunt (2008) indicate that it is relatively small; in an example where pyrolysis consumed 40% of the carbon in the feedstock (in producing syngas), the CO2 resulting from provision of process heat for that process would equate to only a further 10%. Even in temperate environments where decomposition in soil is relatively slow, it is calculated that within two to five years, the effective emission in the pyrolysis scenario is already less than that which would have accrued from the soil (Gaunt et al., 2008). Over a period of the one to five decades relevant to mitigation of climate change, the net saving is therefore considerable. Even within the first few years, however, the higher initial loss of CO2 may be offset by the effects of biochar on other soil processes, in particular prevention of N2O and CH4 release from soil. Natural emissions of N2O from soil are a function of soil moisture status and possibly tillage (Pekrun et al., 2003). Because biochar in soil may modify the moisture regime and physical location of water within the soil matrix, it may mitigate the enhanced emission of N2O that may occur in no-till systems. Methane emissions produced from agricultural soils, mainly under paddy rice agriculture, account for 12% of the global methane emission from all sources. Some studies have suggested that addition of biochar may partially suppress methane emissions. The evidence for these effects is examined in Section 3.1.6.2. There may be additional, potentially important offsets of other indirect emissions. These could include avoided emission of CO2 if the fertiliser required to produce a tonne of product is decreased via a positive effect of biochar on crop use efficiency. This extends to avoided emissions of N2O during the manufacture of the fertiliser as well as from the soil upon application – it is estimated that a carbon-equivalent emission of 1.8 tC is associated with production and use of 1000 kg of fertiliser nitrogen (Mortimer, 2003). Any effect of biochar on increased crop yield could significantly ease pressure on natural lands if implemented on a large scale. Since the conversion of forest or savannah to agriculture can result in an emission as high as 100 tC ha-1 (from above- and below-ground carbon stocks) this could be important (Searchinger et al., 2008). It has been suggested from visual observation of the terra preta that biochar could also lead to a net stabilisation of other organic matter (Sohi et al., 2006; Lehmann and Sohi, 2008). If this is the case, this could be another factor benefiting the overall net carbon gain from biochar-based soil management strategies. This is a particularly intriguing prospect since the capacity for soils to store biochar, not relying on protective capacity of a limited clay surface area, is not finite in the way that it appears to be for other soil organic matter. Thus in addition to representing a carbon store of its own, it is possible that biochar can enhance the intrinsic soil organic carbon storage capacity of soil by affecting the turnover of indigenous carbon. However, apparently contradictory data have been published, which seems to suggest an accelerated decomposition of leaf litter in soil amended with biochar (Wardle et 19

al., 2008). The mechanisms and predictive description are, however, still to be determined and defined. A carbon balance for a pyrolysis scenario that appears positive with respect to the atmosphere in the short term (i.e. a net emission) may be rendered negative if the feedstock for biochar production comprises a new, additional and sustainably supplied resource. This resource could derive from a managed increase in the above-ground productivity of existing crops, or by maintaining vegetation in a state of high net primary productivity through growth continuous cropping. Maintaining high net primary productivity above ground also promotes higher productivity below ground, with an associated increase in root exudation and root turnover. Plant and root productivity can also be enhanced by the use of fertiliser; noting, however, the overall carbon balance of a strategy based on increasing soil carbon through increased use of fertiliser. In assessing the carbon balance of a biochar strategy, it is important to include the carbon cost of transporting feedstock and biochar between field and pyrolysis facility and vice versa. In the scenario where there is no energy capture from pyrolysis of organic matter, gains will depend on positive impacts on crop yield and soil health.

3.1.3. Combined bioenergy and biochar production Greatest overall impact on greenhouse gas emissions are likely to be realised where gases produced during pyrolysis are captured and utilised in a manner that offsets fossil fuel energy. In comparing a strategy that involves biochar production and its use in soil, it can be argued that the reference scenario should be the use of the same feedstock in some other form of bioenergy capture, such as simple combustion or, alternatively, pyrolysis with gasification or combustion of the biochar by-product. Bioenergy in general is often described as carbon neutral, since the carbon emitted in the use of the energy approximates to the amount removed from the atmosphere to create the feedstock in photosynthesis. For a biochar-based strategy to be carbon-negative, the avoided carbon emission – or rather CO2 -equivalent emissions (since other greenhouse gases have to be considered) – from use of 1t carbon in feedstock must exceed 1tC (Renner, 2007). If it is assumed that the feedstock would otherwise decompose and return to the atmosphere as CO2, as is the case for organic material added to soil, the carbon emission from producing biochar and adding the stabilised residue to soil may alone, over a few years, be close to one unit. Thus, with any net energy capture through use of gases (or oils) produced during pyrolysis, the technology may be considered carbon negative (Lehmann, 2007). The indirect effects on carbon emissions resulting from a positive impact on agricultural productivity, plus an effect of biochar or the emission of non-CO2 greenhouse gases from soil, may enhance this. However, the carbon-negative status of the technology has been questioned by Bruun (2008), who considered the additional fossil fuel offset that could be obtained if biochar was used for non-energy purposes. Furthermore, biomass pyrolysis itself did not extract more energy from a feedstock when compared to another bioenergy use. Bruun (2008) also pointed out that over longer timescales, an increasing proportion of the carbon initially sequestered in biochar would be slowly returned to the atmosphere through its slow degradation back to CO2. In terms of energy captured per unit of CO2 released it may be correct that biochar production is not associated with less carbon emission than other forms of bioenergy. However, when expressed in terms of energy captured per unit of carbon in the feedstock, this is not the case. During pyrolysis the majority of energy embodied in feedstock (about 70%) is converted into combustible syngas, but with the liberation of only half of the feedstock carbon (Lehmann et al., 2005a). This is because energy rich but less carbonaceous functional groups are liberated first. In the pyrolysis of organic wastes and crop residues, the emission avoided in preventing its natural decomposition in soil, composting or landfill (for example) is an important part of the overall CO2 -equivalent savings. In the utilisation of non-waste feedstocks, such as biomass 20

crops, there is no such avoided emission. Indirect CO2-equivalent savings resulting from use of biochar in soil must then exceed the energy embodied in the biochar and allowance made for the implications of land use.

3.1.4. Evaluation of biochar systems Since pyrolysis is a more carbon-efficient way to capture bioenergy compared with other bioenergy systems (in terms of CO2 MJ-1), manufacture and storage of biochar would add significant benefits for climate change mitigation alone. From this perspective, storage of biochar does not need to be in the soil, and it had been proposed that entire valleys could be used as storage facilities for biochar (Seifritz, 1993). However, applying biochar to agricultural soils is currently the most widely proposed path, since it is more likely to overcome the opportunity cost in energy production (the recoverable energy forgone in the biochar). If biochar can provide reliable agronomic benefit it may command a value in crop production in addition to a potential carbon credit. However, whilst the potential for management of the terrestrial carbon cycle is the reason for the current interest in biochar, to be workable a biochar-based scenario must: (1) assess the monetary value of direct and indirect emission savings arising from the use of biochar against the opportunity cost of biochar combustion or alternative use, (2) provide certainty, verification and possibly evidence for carbon-equivalent savings and (3) consider the indirect costs and benefits to land users and upstream food processors from the use of biochar in soil. The latter might include the cost of biochar application, weighed against the marketing benefits gained through carbon-neutral food products. In short, a full life-cycle analysis of alternative scenarios is required. However, greater certainty is required on the following in order to fully assess biochar-based soil management for specific applications: (a) the stability of biochar carbon in soil, (b) the indirect impacts of biochar on carbon-equivalent emissions and (c) the security, reliability and constancy of price for pyrolysis feedstocks. These are reviewed in more detail in the next sections. The potential for technological developments in pyrolysis to enhance flexibility and overall efficiency is a separate topic, and will be facilitated by its expansion and forums such as IBI, and national networks such as the Network of Australian and New Zealand Biochar Researchers, and the UK Biochar Research Centre. It should be highlighted, however, that from the perspective of the economics of energy capture, the value of biochar and the overall outcome of the analysis is sensitive to the price of heat and power generated from other fuels. It is also affected by any subsidy for renewable energy, which may have the effect of inflating the monetary value of the energy in biochar (Woolf, 2008).

3.1.5. Stability of biochar in soil Its extraordinary stability means that charcoal particles in soil have been used as a tool for dating and paleo-environmental reconstruction as well as evaluation of cropping practices over centennial and millennial timescales (Ferrio et al., 2006, Scott et al 2000). Studies of the age of the carbon in terra preta of Brazil, as well as similar black carbon accumulations in the soils of other natural ecosystems that have resulted from natural fire events, provide considerable reassurance for the general long-term stability of at least some significant component of biochar. However, laboratory-based studies using freshly-made char tend to show some mass loss – sometimes large – in a period of days to years. The paradox of apparent long-term stability against measurable short-term decomposition suggests that biochar comprises both stable and degradable components. At the moment there is insufficient data in the literature to compare the responses between short- and longterm stability under different climates and in different soils, which could enable the relative size of these fractions to be assessed. Combustion conditions during pyrolysis as well as the type of feedstock are probably influential in determining the proportion of relatively labile components in biochar products. Measuring the influence is essential for the optimisation of pyrolysis for maximum net carbon 21

stability. In optimising biochar production against energy capture to address climate change most effectively, a consistent level of stability in biochar is the aim. Maximising retention of carbon into biochar is counter-productive however, in both carbon and economic terms, if the additional material is in fact associated with short- or medium-term loss to the atmosphere. The chemical composition of biochar provides the principal explanation for its generally high level of stability and is reflected in broad terms by its elemental composition: highly aromatic and with a very high carbon content. It is likely that its stability is strongly modified by its physical properties and structure, however. If the biotic and abiotic processes determining the fate of biochar are the same as those for other soil organic matter, higher soil temperature, moisture availability, lower clay content and intensive tillage will accelerate decomposition rate. The soil system has a remarkable propensity to degrade organic substrates introduced into it. As a substrate generally very low in the concentration of key crop nutrients, the rate at which biochar degrades in situ may also be influenced by the exudation of labile, nutrient rich substances in the rhizosphere. This, in turn, is affected by cropping pattern.

3.1.5.1. Stability of biochar in natural systems Soils that contain large amounts of char are those that have experienced relatively frequent natural fires over a period of millennia (Lehmann et al., 2008). Converting a fraction of standing plant biomass to black carbon in soil constitutes net removal of CO2 from the atmosphere (Forbes et al., 2006). A relatively minor under-estimation in our estimates for the percentage converted could explain up to one-fifth of the so-called missing carbon sink, that is the imbalance between carbon eliminated from forest and fossil fuels, against observed atmospheric CO2 (Kuhlbusch, 1998). In natural systems it is not possible to determine the exact amount of biochar added to a soil over the long-term history and the biochar in these soils will be of disparate age. However, a loss rate constant can be derived mathematically by assuming that current and historic levels of standing biomass are representative (Graetz et al., 2003; Mouillot et al., 2005; Forbes et al., 2006), and a simple factor applied to capture the rate of conversion of biomass to charcoal in burning episodes. This approach has yielded the best estimates for long-term mean residence times, which are in excess of 1000 years (Lehmann et al., 2009). Direct monitoring of archived soils from medium-term experiments seems to support such stability (Skjemstad et al., 2001). A portion of black carbon in soils globally also comprises condensed aromatic carbon in the form of soot particles. This, in turn, can be confused with soot similarly formed in fossil fuel combustion. Such black carbon is considered to lie at the most stable end of a black carbon continuum (Masiello, 2004). Over extended timescales the physical transport of this material through the soil and into water and sediment is inevitable and is seen in its accumulation in marine sediment (Masiello et al., 1998). This observation highlights the potential to confuse physical transport of biochar from a trial site for oxidative loss. It also indicates the importance of such processes to the sequestration of carbon in the natural carbon cycle (Smittenberg et al., 2006). Although char from wildfire offers opportunities to study the long-term dynamics of pyrolysed biomass, the fire and low rate of biomass conversion to char suggests probable differences in composition and function. Simple charcoal manufacture probably began with the discovery of fire; therefore, it is not surprising that sites of ancient habitation are associated with soils enriched in char. Whilst the terra preta provide a neat and convincing example for the deliberate use of biochar in agriculture, there is circumstantial evidence for its informal use in other regions, not only in the distant past but in recent centuries (Young, 1804) and in the current day (Lehmann and Joseph, 2009a).

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3.1.5.2. Influence of biochar feedstock on stability In soils where charcoal has been known to be abundant, it is associated mainly with the very fine, sub-50 µm soil fraction (Brodowski et al., 2006). This suggests that through some abrasive physical process or the destructive physical impacts of freeze-thaw and shrinkswell, the initial size of brittle biochar particles may be relatively unimportant to its long term interactions in soil. Ponomarenko (2001) found biochar evenly distributed across particle size and biochar particles to become increasingly rounded over time at a rate dependent upon the abrasiveness of the soil. Ponomarenko (2001) also found the concentration of clay-sized mineral particles embedded in biochar pores to increase with time and noted that this would inhibit their isolation using density-based techniques. Brodowski (2006) found a small proportion of biochar particles in soil to be associated with micro-aggregates, but for this biochar to account for a rather large proportion of the carbon that is present in such structures i.e. compared to other particulate organic matter. The authors used this as evidence for physical protection of biochar against degradation and also noted that biochar might act as a binding agent for organic matter in aggregate formation. Although they did not specify whether the latter would be a purely physical interaction or a consequence of biological activity, Watts (2005) previously found no effect of charcoal on aggregation at low temperatures designed to preclude biological activity. In an earlier publication Glaser (2000) found a large proportion of biochar in terra preta to be present in unprotected fractions. Obtaining similar results, Murage (2007) noted that the misleading impression might be gained that active soil fractions turn over more slowly in soils that are enriched in biochar. Currently there is no published information to demonstrate whether the physical diminution of biochar in soil is accompanied by oxidative loss of carbon. However, X-ray photoelectron spectroscopy showed abiotic oxidation (with proliferation of carboxyl groups) to occur in the porous interior of biochar, whilst biotic oxidation affected external surfaces only (Cheng et al., 2006). Biotic oxidation might therefore be enhanced as particle size decreases, although in the study of Cheng (2006) it was also quantitatively less important. These findings have been further validated (Lehmann et al., 2005b) using synchrotron-based techniques (near-edge Xray absorption fine structure spectroscopy). At the macro-scale biochar products range from powdery to brittle, depending upon the physical microstructure of the material from which they are derived. Those produced from woody feedstock display a predominantly xylemic structure that is coarse and strong. These also display the highest carbon contents, in excess of 70% C and up to 90% C, and are low in trace elements. Those produced from rye grass, maize and digested feedstocks i.e. manures are powdery, lower in C (over 60%), and enriched in minerals and nutrients. Thus the latter are not only less physically recalcitrant, they are also a more attractive microbial substrate.

3.1.5.3. Climatic effects on biochar mineralisation Climate determines soil temperature, which affects the rate at which both biotic process and abiotic reactions occur in the soil. However, in the absence of water the effect of temperature is irrelevant, as water is essential for biological cell function, and solution phase reactions proceed by definition only where water is present. Thus synchrony in a conducive environment of rainfall and temperature and rainfall conditions is required in order to maximise overall soil activity. Biochar should modify not only the soil water holding capacity of the bulk soil, but also the physical location of water within the soil matrix, since the smallest pores become water-filled first and remain moist the longest (Gaskin et al 2007). The size of these pores makes them relevant to microbial populations as a physical niche. There is also evidence that mean soil temperature and diurnal temperature fluctuations are impacted by the effect of biochar on soil colour (Krull et al., 2004; Oguntunde et al., 2008).

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The effect of climate on biochar oxidation has been evaluated in a transect study spanning several climatic zones. Sites along the transect had each received inputs of biochar during a brief and defined period in industrial history 130 ybp, but received greatly contrasting mean annual temperatures (Cheng et al., 2008). The accumulation of cation exchange capacity was correlated to mean temperature and the extent of oxidation was seven times higher on the external surfaces of biochar particles than in the interior. The potential consequence of a warmer global climate releasing CO2 through accelerated mineralisation of black carbon was first scoped by Druffel (2004) who indicated potential emission rates of 2 to 7 GtC y-1 by 2100. However, if a larger proportion of the global soil carbon stock comprises recalcitrant black carbon than is assumed in current models, the more active pools must be smaller and the overall response to warming significantly slowed (Lehmann et al., 2008). General arguments concerning the relative response of recalcitrant carbon and more active carbon pools to changing temperature has not been resolved (Fang et al., 2006).

3.1.5.4. Soil biological activity and the stability of biochar A number of relatively short-term laboratory incubation experiments have been conducted using soil mixed with biochar, with or without added substrate, to assess the biological and chemical degradation of biochar to CO2. Early studies found that even graphitic carbon could significantly be mineralised biologically (Schneur, 1966). Laboratory studies where loss routes can be controlled have generally found some measurable initial loss of carbon from biochar (Cheng et al., 2006); however, a few studies have found a much larger loss (Hamer et al., 2004). In the Hamer (2004) study, not only was charcoal substantially degraded within 60 days, but the mineralisation of simultaneously added glucose solution was also enhanced, suggesting a priming effect. Combined products comprising labile nitrogen and stable carbon have been proposed (Day et al., 2005). However, the evidence (Hamer et al., 2004) suggests that the addition of nitrogen could impact on the stability of biochar and its value in carbon sequestration. This has not, however, been experimentally assessed to date. Further studies seem to indicate that biochar may prime the decomposition of native soil organic matter. After nine years in the field, Wardle et al. (2008) measured mass loss greater in a charcoal-litter mixture, than for the sum loss in a charcoal-only plus litter-only. However, the mesh bags in which the samples were contained had been buried in a forest litter layer, and thus separated from mineral soil. Although the loss could have been from the priming of litter decomposition, it was also possible that the loss could result from priming of charcoal loss (Lehmann and Sohi, 2008). If the level of organic matter input to the soil by plants is steady for a particular ecosystem, enhanced microbial activity over the long term is not consistent with a net accumulation of non-black organic matter (as well as charcoal) that is observed in terra preta, compared to their adjacent soils. But in fact these observations need not be contradictory if carbon that is mobilised in the litter layer is, once transported to the mineral soil, rapidly stabilised. The latter effect could directly involve biochar surfaces or minerals in subsoil, as well as mineral material in the surface horizon (Lehmann and Sohi, 2008).

3.1.5.5. Effects of biochar on ease of tillage and mechanical disturbance If, as proposed, natural soil movement influences the breakdown of biochar through its reduction in size, then the rate of breakdown would be expected to be further accelerated by tillage. This is important to consider since tillage is perhaps envisaged as the primary means to incorporate biochar into soil. Quénéa (2006) reported a 60% decrease in both the soot and charcoal content of sandy soil under temperate forest during 22 years after conversion to intensive agriculture with annual tillage. The loss of total soil carbon over the same period was 30%, suggesting that biochar and charcoal were relatively less resistant to degradation than bulk soil organic matter after 24

disturbance. However, the analysis of the charcoal data was based on larger hand-picked fragments and it seems likely that particles broken down into very fine fractions might have led to an overestimate of the loss. The initial soot content was very low. In contrast, 50 years of cropping and cultivation had no measurable change in the aromatic aryl carbon, taken to reflect charcoal, whilst other fractions declined rather rapidly (Skjemstad et al., 2001). More research may enable likely rates of breakdown to be predicted. If, for example, tillage was a key factor, maximum longevity of biochar targeted by application on land where minimum tillage is practised. In no-till systems, biochar could be sequestered into soil through a one-time addition at the time of conversion from a tilled system.

3.1.6. Indirect impacts of biochar on CO2-equivalent emissions The net carbon gain resulting from stabilisation of carbon into biochar, and its storage in soil, needs to be refined. There is even less information available for the impact of biochar in soil on the emission of greenhouse gases other than CO2. The contribution of nitrous oxide (N2O) and methane (CH4) are major contributors to climate forcing and have significant agricultural sources, including soils. There is evidence that biochar may suppress the emission of these gases from soil. There may be additional indirect benefits in terms of greenhouse gas emissions, resulting from improved crop production through use of biochar. Although the global possibilities are currently hypothetical, in an era of falling global grain stocks, the value of biochar could extend beyond a purely financial consideration for land users and become increasingly relevant politically and economically. Growing concerns around both energy and food security may accelerate the development and application of biochar technology and associated Governmental or inter-Governmental market interventions to support it.

3.1.6.1. Indirect effects of yield benefits and nutrient requirement The direct impacts of biochar on crop yield are reviewed in Section 3.2.2. Where economically optimal fertiliser rates are currently applied, biochar has the potential to deliver the same crop yield with a lower application rate – with potentially significant greenhouse benefits. In more detailed assessments for the overall carbon balance of a biochar strategy (Gaunt et al., 2008), an assumed 10% reduction in the fertiliser required to maintain current crop yield was found to be a particularly important component of the net carbon benefit. This reflected the energy intensive nature of nitrogen fertiliser production and the N2O emissions that result from fertiliser application and use. The purpose of biochar application might not simply be to attain a greater yield, however, but possibly to achieve predictability in yield through a lower susceptibility to climatic events such as floods and drought. Also, the economic optimum after biochar application could be gained through a gain in crop yield at the same current or possibly higher rate of application, in which case the net result would be higher per hectare yields. Furthermore, biochar could increase, maintain or at least limit gradual decreases in crop yield on land where soil fertility and productivity is currently in decline. Under changing climate the benefit of biochar in response to increasingly erratic or intense rainfall events could be more acute, and/or enable plants to better exploit higher CO2 concentrations. This suggests a potential role for biochar to assist in adaptation to climate and environmental change. These factors would benefit global carbon balance in several very important ways. Firstly it could reduce the degradation of existing agricultural land, and thus alleviate pressure on natural systems, which usually represent a significant store of carbon as well as biodiversity. Maintaining or enhancing productivity of existing land may also make relatively more land available for bioenergy or other alternative crop production systems.

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Modelling of these possibilities, at this stage, may not be possible due to too many uncertainties (economic as well scientific). However, if we view biochar as a technology with the potential to be practised on a very large scale, they have to be assessed in the long term. Importantly, they highlight the complexity of the biochar topic and the need to think carefully about the system boundaries drawn in assessing benefits and impacts.

3.1.6.2. Impact of biochar on nitrous oxide emission from soil The global warming potential (GWP) of a gas reflects two aspects: the efficiency of the molecule in absorbing incoming solar radiation and its rate of chemical breakdown in the atmosphere. By definition the global warming potential (GWP) of CO2 is 1.0; by comparison the GWP of nitrous oxide is 310. Under anaerobic conditions N2O is emitted from soil through denitrification, a process in which specialised microbes that obtain energy from the reduction of nitrate (NO3-), or intermediate gases, to dinitrogen (N2). However, it appears that nitrifying bacteria generally involved in conversion of N2 to ammonium (NH4+), i.e. nitrification, may simultaneously denitrify (Bateman, 2005). The availability of NH4+ is generally controlled by organic matter mineralisation, which is climate driven, but its concentration is greatly enhanced by the application of nitrogen fertiliser or, in livestock and gazed grassland systems, from dung or slurry application. Regardless of the setting or source, the majority of soil nitrogen is in organic form and N2O emanates from the utilisation of a relatively small and dynamic nitrogen pool. Life cycle assessments quantifying the benefits of biochar-based strategies for energy depend quite heavily on a decrease in the emission of N2O that frequently follows the addition of mineral nitrogen fertiliser. Accounting for this effect makes a great difference to the overall analysis of how a biochar to soil strategy impacts on net greenhouse gas balance (Gaunt et al., 2008). The expectation for this effect relates to the general impact of biochar on retention of N in the soil in a way that also enhances crop nutrition (see Section 3.1.6.1.). If the latter effect is surface-mediated, it seems unlikely that biochar confines N to a physical location – such as very small pores – where it is inaccessible to denitrifying bacteria. It may be that, instead, biochar inhibits the process by sequestering dissolved mineral N. Published data demonstrating the effect of biochar on suppression of N2O remains very limited. In the most widely cited study to date (Yanai et al., 2007) ‘bio-waste’ charcoal was applied during a re-wetting of a former grassland soil, high in organic matter, in laboratory incubation (25°). Nine-tenths of N2O was suppressed in five-day emission episodes after wetting of soils to 73% and 78% water filled pore space. At a slightly higher water filled pore space (83%), charcoal had the opposite effect, increasing N2O emission. The rate of biochar addition used in the study equated to a relatively high application rate of 180 t ha-1 in topsoil. However, the authors were able to exclude the possibility that the alkalinity of their charcoal, or its nutrient content, were significant factors in their observations. In an arable soil with much lower C content (2.2 %C), Sohi (2008) has studied the effect of willow charcoal at a much lower rate of 10 t C ha-1 which were assessed during 20°C incubation of wet (70% water holding capacity) and re-wetted (from 20% water holding capacity) soils, with and without simultaneous addition of small amounts of inorganic N (equivalent 75 kg N ha-1). A more modest suppression of 15% was proportionally similar for all treatments where there was any response at all (the already-wet soil did not emit significant N2O). After six months, available soil N would have been largely consumed and the soils thoroughly equilibrated. A second inorganic N addition (without new charcoal) at this time showed no difference in N2O emissions between amended and control soils. If any correspondence exists between the two studies it appears that not only is effect of biochar on N2O likely to be non-linear with respect to rate of application (and significant but not large at realistic rates) but – as authors of both papers conclude – the effects are likely to reflect the impacts of biochar on soil physical properties, particularly modification of pore-size distribution (of which water holding capacity is not a sensitive measure). In particular the effect may only be seen during re-wetting, and not when soils are maintained wet. Whether the benefit upon re-wetting is repeatable remains to be established. 26

Measurements of N2O emission in the field environment are difficult due to the transient and spatially variable nature of denitrification. Like the studies described in Chapter 3, the availability of sample biochar in the quantities required to assess its many effects in true randomised plot designs presents a major challenge. Biochar field experiments with periodic measurement of N2O in cover boxes is currently in a third year in upstate New York (). In tropical environments field experiments have been established in Columbia and in Kenya. Results from the Columbian trials indicate 80% suppression of N2O emissions (Renner, 2007).

3.1.6.3. Impact of biochar on methane emission from soil Methane has a relatively low GWP of 21, but is six times more abundant in the atmosphere than N2O (1.8 ppm compared to 0.3 ppm for methane), and has an annual flux approximately 50 times higher. Aside from industrial emissions, including natural gas exploitation and distribution (accounting for about 20%), methane emanates primarily from the soil of natural habitats and thus, uniquely for the main greenhouse gases, increasing rates of emission have begun to stabilise. Within agriculture, paddy cultivation of rice and the guts of the growing ruminant population (primarily grazing domestic animals) are key methane sources (IPCC-2001, ) Specialised methanotrophic bacteria make most aerobic soils a net sink for methane, however, and the relatively rapid consumption of methane explains to a large extent its relatively low GWP. The link between methane consumption and aerobicity is important in the context of reduced tillage, however. These practices have been widely promoted for their sequestration of carbon. Whilst higher topsoil organic matter is liable to improve both water infiltration and holding capacity, increased moisture status is likely to result in a relative increase of methane emissions (e.g. Castro et al., 1995). Field experimentation with biochar in Columbia showed the elimination of CH4 emission (Renner, 2007). A number of studies are currently assessing the impact of biochar on the emission of methane from paddy soils. At this time there are no results published in the scientific literature.

3.1.6.4. Biological activity and stabilisation of soil organic matter The stability of biochar and the biological activity that results from its application are intrinsically linked, as are soil properties such as clay content, pH and cation exchange capacity (CEC) and climatic variables. The ancient terra preta are higher in organic matter compared with adjacent soils that do not contain black carbon (Lehmann et al., 2003). This has lead to the hypothesis that black carbon in soil leads to increased stabilisation and hence accumulation of other carbon. This may provide one of the few mechanisms by which the intrinsic capacity of a soil to store organic matter can be modified from a management perspective, and if correct, increases the net carbon gain from the use of biochar. However, some studies have reported increased microbial activity in soils enriched in biochar (Steiner et al., 2003; Steiner et al., 2008). Upon addition of biochar to soil for the first time, mineralisation may be stimulated by the presence of an active fraction and associated soluble nutrients or labile carbon fractions. It has also been noted that the physical structure of typical biochar products provides a secure environment for microbial colonies (Ogawa, 1994). However, it should be noted that experiments must be designed such that the system is correctly monitored, e.g. all soil layers, gaseous losses and plant growth. Currently, findings to date should be viewed as provisional. Microbial biomass is not a measure of microbial activity but the abundance of microbial cells. Thus whilst an increased microbial population associated with increased soil organic matter

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without any obvious increase in substrate supply may seem paradoxical, it might suggest a decrease in microbial efficiency, possibly associated with a change in the balance between different groups of microbes. A simultaneous increase in CO2 emission, however, would indicate enhanced plant growth and higher inputs of labile carbon via the plant roots. In soils where char is present naturally in higher concentrations as a result of natural forest fire or prescribed burning, the microbial community may include specialised species with a capacity to degrade a relatively scarce and challenging substrate. This may explain the distinct communities observed in terra preta, but is not clear whether these species are truly ubiquitous to other soils (if scarce), or whether the capacity for soils to degrade such materials is acquired over relatively long periods.

3.1.6.5. Effects of biochar on tillage and irrigation requirements Lower bulk density and/or higher organic matter reduce the fuel requirement for mechanical tillage, which can be managed in few other ways. It may also facilitate the process of reducing the tillage used in agricultural systems. Soils with higher organic matter content also tend to display higher water-holding capacity. Thus a further saving in energy costs can come from reduced irrigation frequency or intensity. Surprisingly little information has been collected on the impact of biochar on such parameters. However, in Ghana, kiln sites showed topsoil bulk density approximately 10% lower than in adjacent soils (Oguntunde, 2008).

3.1.7. Biochar scenarios for agriculture In addition to the price of biochar, land-users will incur the direct costs of applying biochar to the soil. There are also potential non-monetary costs associated with the collection of straw from their land as a pyrolysis feedstock, which affects the readiness of land owners to engage in the market. In ‘closed’ systems where biochar is returned to the same land that the feedstock originated, there may be opportunity costs. Currently, no socio-economic studies exist that would address questions on these matters. However, one key advantage of a biochar strategy is that, assuming that the provision of key functions is limited only by the longevity of the biochar, its stability would dictate that annual or even regular applications would be unnecessary to obtain benefits. Widespread use of non-waste feedstocks for energy and biochar (or only biochar) could impact not only commodity prices but, in a manner analogous to that seen with large-scale bio-ethanol production in the USA, impact on the economics of continued energy production through feedbacks on land and input prices. This raises complex socio-economic issues that must be considered (The Royal Society, 2008) and modelled (Rokityanskiy et al., 2007). Also, as for any assessment of bioenergy systems, it is essential to define boundaries that spatially allow all possible land-use effects to be assessed, in the context of the overall net greenhouse gas benefit (Searchinger et al., 2008). The proximity of a pyrolysis facility to an adequate catchment for feedstock must be economically and logistically viable, and can potentially affect the CO2 -equivalent savings. This is the case for biomass and bioenergy facilities generally. However, for biochar the proximity of suitable locations for biochar application to soil is important as well. If the gathering of feedstock and distribution of biochar occur over the same area, the logistical and cost impacts may not be greatly affected. However, it is important to think about biochar scenarios in a spatial context (Figure 10).

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Figure 10. Scenario for multi-feedstock production of biochar, and multi-application use, emphasising the spatial context Possible off-farm resources include municipal green waste from gardens and parks, composted or compostable urban waste, digested sewage sludge and mixed municipal waste. In addition, in the future, by-products of other bioenergy or bio-fuel systems may be available. Utilisation of off-farm wastes for biochar production holds the attraction of potential cost savings from avoiding landfill or other disposal charges. In addition, compared to typical or existing disposal methods, there may be a lower emission of CH4 and N2O greenhouse gases than that emanating from direct placement in soil, enhancing the net gain in carbon equivalents through avoided emissions of high GWP gases. However, many such wastes have a high water content which will incur increased emissions (and cost) associated with higher requirement for process energy in pyrolysis. In a ‘closed loop’ scenario, biochar is incorporated into the same land, or at least the same enterprise or groups of enterprises, from which the pyrolysis feedstock originates. A typical scenario would involve utilisation of cereal crop straw that in intensive arable areas is often, effectively, a waste product. Although there is no published laboratory work to support the use of biochar produced from wheat straw, there is limited existing information on the relative stability of biochar from rice husk, sugarcane bagasse and straw from maize. In industrial agriculture crop straw may constitute 2 t C ha-1. Putting this scenario in the context of the UK

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example, with approximately 4 M ha of cereal crops grown, annual total fossil fuel CO2 emissions amount to 170 M t. Theoretical comparisons have been made for the carbon-equivalent gain offered by the pyrolysis of maize straw versus use of a dedicated biomass crop (Gaunt et al., 2008). Utilising biomass crops for energy on a large scale has a potential impact on the land available for food production and may exert new pressure on non-agricultural land use. Biochar produced from the pyrolysis of biomass crops might be incorporated into different agricultural land from where the biomass feedstock was grown. This could be for greater agronomic gain, to apply the product in rotation over a wider area to maximise benefits, or to deal with the cumulative quantity of product. In the combined energy and bio-oil coproduction case study considered by Ogawa (2006), the biochar by-product was also returned to adjacent arable land. Most scenarios considered to date have focused on conventionally managed arable land, where biochar could be added to soil as part of an existing tillage regime. Biochar could be incorporated during conversion of land to no-till, but a strategy of integration into no-till and grazed grassland systems has not yet been considered.

3.1.7.4 Forestry Ogawa (2006) outlined a scheme for carbon sequestration by forestation and carbonisation. This scheme revolved around fast growing plantation tree species fixing atmospheric CO2, with the products comprising not only conventional timber, wood chip, and pulp, but diversion of wastes and residues to a carbonisation procedure and re-application of this stabilised carbon back to the plantation soil. This approach has been formally proposed under the Clean Development Mechanism for a scheme in Sumatra, Indonesia. In the state of Minas Gervais, Brazil, an existing commercial project claims, under CDM, a carbon credit for substitution of coal-derived coke for smelting of iron by pyrolysed plantation eucalypt. The project produces 300,000 t y-1 charcoal. The charcoal ‘fines’ that account for about 5% of the product are utilised for briquette manufacture rather than application into soils. In Australia, the potential for integration of oil production from oil mallee trees with processing of wood waste for production of biochar for use in crop production has been examined (McHenry, 2009). Seifritz (1993) evaluated the size and cost of the carbon gain that could be realised by straight conversion of plantation forest biomass to stockpiled biochar. The scenario included no capture of energy in the conversion, highlighting instead the net primary productivity that is maintained by cropping, and the long lifetime of charcoal compared to the nature and fate of traditional timber products. In the tropical context, ‘slash and char’ scenarios have been discussed, where one-off inputs of biochar are made during conversion of land from forest to agriculture (Steiner, 2006), or perhaps ‘crop and char’, with cycle of positive feedback between one-off, occasional or rotational inputs of biochar and increasing biomass productivity and feedstock resource. In both cases, pyrolysis would be performed using the most basic (and perhaps relatively inefficient) technology such as simple pits of clay kilns. However, as examples of viable, village-scale bioenergy based on gasification technology in developing countries increase, it is conceivable that technological development in tandem with increased income from ‘crop and char’ practices might ultimately realise combined biochar production and energy capture at the same scale. In the absence of adequate technological development, charring and manufacture of charcoal may not offer the same benefits to human health as, for example, the substitution of existing biomass burning practices for basic but cleaner and more efficient combustion technology (Wang et al., 1999). Conventional charcoal production may also release methane and other trace greenhouse gases (Edwards et al., 2003). Sub-micron soot particles produced by condensation reactions in gas streams from combustion comprise the most recalcitrant forms (Figure 7) of black carbon but, despite the relatively small quantities of 30

carbon involved, may be having an important impact on the albedo of both the global atmosphere and ice caps, altering the radiative balance and exacerbating climate change (Ramanathan et al., 2008). Currently the global emission of soot is predicted to decline as rural users of biomass in developing countries switch to clean burning fossil sources (Streets et al., 2004). Charcoal manufacture produces less soot than open burning, but despite the possible scale of future biochar production, its future contributions to the global soot inventory has not been formally examined.

3.1.8. Notes on the natural cycling of char in soil Observation shows that wildfires are a routine natural and indeed often essential feature of many natural grassland, forest and woodland ecosystems, and fire is gradually being incorporated into global ecosystem models (Thonicke et al., 2001). Fire frequency does not appear to decrease soil C by affecting plant productivity (Ansley et al., 2006) and may increase it (Czimczik et al., 2005; Ansley et al., 2006); fire does not destabilize black carbon already present (Ansley et al., 2006) or only partially in organic boreal soils (Czimczik et al., 2005). Studies using remote sensing have attempted to quantify the pattern and frequency of burnings (Seiler et al., 1980) and most estimates suggest approximately 1-5% of standing biomass is converted to black C (Schmidt et al., 2000; Forbes et al., 2006). This figure is much lower than the figure previously proposed by Kuhlbusch (1996), who suggested sequestration into black C during the relatively recent era of forest clearance could explain up to 20% of the so-called missing carbon sink. A detailed analysis in Australia has suggested that natural fire might provide a sink equivalent to 8.3 MtC yr-1 (Graetz et al., 2003). In fired-affected systems standing biomass remains in equilibrium, viewed over the long term. However, a modest rate of stable charcoal formation during burning means that the net result of natural fire is that the carbon content of the wider system, including the soil, should gradually increase. However, this is a slow process and difficult to measure in the field with repeated experimental burning (Dai et al., 2005). Given that the net primary productivity of biomass (60 GtC yr-1) is quite large relative to the soil C pool (1500 Gt) the black C pool should become dominant in the soil over geological time if this fraction did not degrade at all, even with occasional fire and a low charcoal conversion rate (Graetz and Skjemstad, 2003). Thus the fact that soil carbon dynamics can be modelled by postulating a relatively small inert- or very slow-turnover pool (Falloon and Smith, 2000; Smith et al., 2000) is an indication that biochar must degrade, at some slow rate, even once transport into water and estuarine sediments is considered (Schmidt, 2004; Simpson and Hatcher, 2004b; Smittenberg et al., 2006) and accounted for (Masiello et al., 1998). The Roth-C soil carbon model explicitly incorporates char as one of its pools (Falloon and Smith, 2000). The inert pool in the Roth-C soil carbon model represents more than simply char, but also exceptionally degraded, highly stabilised organic matter (Falloon and Smith, 2000). Radiocarbon dating can be used to experimentally refine the site-specific size of the inert pool to model total soil carbon. However, estimates for a range of sites where such data are available has suggested only a general relationship with soil texture (Falloon et al., 1998). It is likely, however, that long-term field experiments of duration useful in parameterisation of soil C models will provide the data needed to improve on the char pool in the model. It may be significant that one experimental site where the model does not simulate field measurements well is the site of the Waite plots in Australia, where there is a documented history of burning (Coleman et al., 1997). Also in Australia, Skjemstad (2004b) demonstrated that by re-allocating carbon between soil pools according to a direct measurement of char, the Roth-C model may simulate the trajectory of carbon for a range of soils with similar burning history. In addition, new techniques for quantifying char experimentally (see Section 2.2.3.) reveal that, when applied to a wider variety of sites, observed levels of char were considerably higher than accommodated by the modelled inert pool (Schmidt et al., 1999; Preston et al., 31

2006). The implications of this finding for our prediction of climate change feedbacks from enhanced decomposition will become important, as soil models are increasingly linked into global climate modelling (Lehmann and Joseph, 2009b). Unfortunately the most reliable and direct techniques for quantifying char are currently not sufficiently practical for application at the scale useful to assessing the carbon stock that it represents, at the relevant (global) scales. However, the development of new spectral analysis techniques using mid-infrared wavelengths (Section 2.2.3) may lead to an approach that is both rapid and low cost (Janik et al., 2007).

3.2. Biochar, crop productivity and resource management Conceptually three main mechanisms have been proposed (described in detail below) to explain how biochar might benefit crop production: (i.) direct modification of soil chemistry through its intrinsic elemental and compositional make up, (ii.) providing chemically active surfaces that modify the dynamics of soil nutrients or otherwise catalyse useful soil reactions, (iii.) modifying physical character of the soil in a way that benefits root growth and/or nutrient and water retention and acquisition. The first mechanism may result in a temporary change in crop productivity, the size and duration of which will be dictated by the natural process of biochar weathering and the effects of crop off-take. This could occur where the biochar has significant mineral nutrient content, or conversely increase in CEC over time as the biochar weathers. If biochar releases these elements, then establishing the fate of biochar carbon during this release is extremely important in the context of the underlying rationale for biochar production and application in soil. Benefits provided through the second and third mechanisms depend on the long-term physical persistence of biochar and may thus also be finite, although over a much longer timeframe. This would include the impact of porous biochar on water retention or lowering soil bulk density. The magnitude and the relative importance of the three mechanisms in a particular setting will evolve over time as the slow process of chemical and physical modification results in a gradually increasing concentration of smaller, partially-oxidised particles. Evidence for the general resistance of biochar to chemical and biological oxidation is addressed in an earlier section (3.1.5.). Quantitative evidence for the stability of biochar does not equate to constancy in functional characteristics, since the chemical properties of biochar itself have been shown to develop over time, with implications for functional interactions in the soil environment. In a key multiparameter study Cheng (2008) showed that properties that become enhanced over time are CEC and pH, as a result of gradual surface oxidation (Section 3.1.5.). The size of biochar particles is relatively rapidly decreased, concentrating in size fractions <5µm diameter (Sections 3.1.5.1. and 3.1.5.5.). In assessing the agronomic performance of biochar, comparisons should be made against the properties of both the same feedstock un-pyrolysed and alternative biochar produced from other feedstocks. If the feedstock is produced from the same land to which the material is returned (e.g. cereal straw), biochar would not normally substitute all deliberate returns of organic matter to a soil, but rather a one-time or occasional amendment. This is important since as previously noted (Section 3.1.1.) soil fertility depends on degradation of organic matter, and the recycling of plant nutrients. Biochar should be viewed as a mechanism to enhance that process through its moderation, and not its termination. In any case, the material potentially used in pyrolysis, is roughly matched by the amount of labile organic matter exuded into the soil by the plant roots.

3.2.1. Soil fertility

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Expectation of increased soil fertility benefits arise from studies of the terra preta that contains high proportions of black carbon (Haumaier et al., 1995; Glaser et al., 2002; Lehmann et al., 2003; Lehmann and Rondon, 2006). The evident fertility of the terra preta is generally attributed to high soil organic matter content – organic matter assists in the retention of water, soil solution and cations – and the retentive capacity of aged biochar itself for nutrients and water (Section 3.2.3 and 3.2.4), The black carbon present in terra preta is thought to originate from partially-combusted biomass residues derived from a range of anthropogenic activities, including kitchen fires and field burning. A particularly striking characteristic is a stronger relationship between soil carbon content and soil CEC in these soils relative to adjacent land, indicating that biochar comprises a greater proportion of soil carbon (Liang et al., 2006). Since CEC is indicative of the capacity to retain key nutrient cations in the soil in plant-available form and minimise leaching losses (Section 3.2.4), this is cited as a key factor where differences in crop productivity are observed. High rates of biochar addition in the tropical environment have been associated with increased plant uptake of P, K, Ca, Zn and Cu (Lehmann and Rondon., 2006). In contrast to mainstream chemical fertilizer, biochar also contains bioavailable elements such as selenium that have potential to assist in enhancing crop growth. There has been much speculation concerning the potential effects of biochar on microbial activity in soil, which in the context of terra preta has been reviewed in detail by Steiner (Steiner et al., 2003). Assuming that plant inputs and hence microbial substrate remain unchanged, enhanced microbial activity alone would diminish soil organic matter. However, this is contrary to the observation in terra preta, where soil organic matter is generally higher than in similar surrounding soil (Liang,2006). However, a change in the balance of microbial activity between different functional groups could benefit crop nutrition, specifically enhancement of mycorrhizal fungi (Ishii et al., 1994), and this could feed back into higher net primary productivity and carbon input. There is relatively extensive literature documenting stimulation of indigenous arbuscular mycorrhizal fungi by biochar, and this has been reflected in plant growth e.g. Rondon (2007), Nishio (1996). This literature has been reviewed in some detail by Warnock (2007), who proposed four mechanistic explanations, of which a combined nutrient, water and CEC effect was considered most probable.

3.2.2. Crop yield The majority of currently published studies assessing the effect of biochar on crop yield are generally small scale, almost all short term, and sometimes conducted in pots where environmental fluctuation is removed. These limitations are compounded by a lack of methodological consistency in nutrient management and pH control, biochar type and origin. Studies in a wide range of climates, soils and crops have been conducted. It is not therefore possible at this stage to draw any quantitative conclusion, certainly not to project or compare the impact of a particular one-time addition of biochar on long-term crop yield. Nonetheless, evidence suggests that at least for some crop and soil combinations, moderate additions of biochar are usually beneficial, and in very few cases negative. Glaser (2001) reviewed a number of early studies conducted during the 1980s and 1990s. These tended to show marked impacts of low charcoal additions (0.5 t ha-1) on various plant species. Higher rates seemed to inhibit plant growth. In later experiments, combination of higher biochar application rates alongside NPK fertiliser increased crop yield on tropical Amazonian soils (Steiner et al., 2007) and semi-arid soils in Australia (Ogawa, 2006). Due to the year to year variation in climate and its impact on short-term dynamics, results from a number of field experiments recently set up are, whilst generating data, not yet published. The nature and mechanistic basis for interactions between crop, soil type, biochar feedstock, production method and application rate will have to be understood to gain predictive capacity for the performance of biochar in soil, and open the possibility for large scale deployment.

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Table 5. Summary of experiments assessing the impact of biochar addition on crop yield Authors

Study outline

Results summary

Iswaran et al (1980)* Iswaran et al (1980) * Kishimoto & Sugiura (1985) *

Pea, India

Kishimoto & Sugiura (1985) *

Sugi trees on clay loam, Japan

Chidumayo, (1994}* Glaser (2002)

Bauhinia trees on alfisol/ultisol Cowpea on xanthic ferralsol

0.5 Mgha-1 char increased biomass 160% 0.5 Mgha-1 char increased biomass 122% 0.5 Mgha-1 char increased yield 151% 5 Mgha-1 char decreased yield to 63% 15 Mgha-1 char decreased yield to 29% 0.5 Mgha-1 wood charcoal increased biomass 249% 0.5 Mgha-1 bark charcoal increased biomass 324% 0.5 Mgha-1 activated charcoal increased biomass 244% Charcoal increased biomass by 13% and height by 24% 67 Mgha-1 char increased biomass 150% 135 Mgha-1 char increased biomass 200%

Lehmann (2003)

Soil fertility and nutrient retention. Cowpea was planted in pots and rice crops in lysimeters at the Embrapa Amazonia Ocidental, Manaus, Brazil Comparison of maize yields between disused charcoal production sites and adjacent fields. Kotokosu watershed, Ghana Maize, cowpea and peanut trial in area of low soil fertility

Oguntunde (2004)

Yamato (2006)

Mung bean, India Soybean on volcanic ash loam, Japan

Chan (2007)

Pot trial on radish yield in heavy soil using commercial greenwaste biochar (three rates) with and without N

Rondon (2007)

Enhanced biological N-2 fixation (BNF) by common beans through bio- char additions. Colombia

Steiner (2007)

Four cropping cycles with rice (Oryza sativa L.) and sorghum (Sorghum bicolor L.)

Mitigation of soil degradation with biochar. Comparison of maize yields in degradation gradient cultivated soils in Kenya. *source of selected references (Woolf 2008) Kimetu et al. (2008)

Bio-char additions significantly increased biomass production by 38 to 45% (no yield reported) Grain yield 91% higher and biomass yield 44% higher on charcoal site than control.

Acacia bark charcoal plus fertiliser increased maize and peanut yields (but not cowpea) 100 t ha-1 increased yield x3; linear increase 10 to 50 t ha-1 - but no effect without added N Bean yield increased by 46% and biomass production by 39% over the control at 90 and 60 g kg(-1) biochar, respectively. Charcoal amended with chicken manure amendments resulted in the highest cumulative crop yield (12.4 Mgha-1) doubling of crop yield in the highly degraded soils from about 3 to about 6 tons/ha maize grain yield

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3.2.3. Soil moisture retention In soil science the following principles are widely accepted and published (summarised in Krull et al. 2004): The mineral and organic components of soil both contribute to soil water holding capacity, but only the latter can be actively managed. Water is held more tightly in small pores, so clayey soils retain more water. The lower soil bulk density generally associated with higher soil organic matter is a partial indication of how organic matter modifies soil structure and pore size distribution. Many studies where the effect of biochar on crop yield has been assessed have cited moisture retention as a key factor in the results. Given that the pore size of biochar is relatively fixed, whereas that of the mineral soil is determined primarily by texture, it may be expected that charcoal increases available moisture in sandy soil, has a neutral effect in medium textured soils, and decreases available moisture in clayey soil. Any effect of biochar particle size may be short-lived, as it appears to physically break down into fine fractions relatively quickly (Section 3.1.5) Experimentally, the usual technique for assessing pore size characteristics is the moisture release curve, which indicates how quickly soil moisture is drawn from a soil under increasing tension. The method is well suited to discriminating differences between soils of contrasting texture, but its sensitivity may be less satisfactory for discriminating the effect of contrasting management at one specific location: high levels of replication may be necessary to show a significant impact of a management intervention of realistic magnitude. In a more recent study (Gaskin, 2007), moisture release curves were determined using samples of loamy sand soil from a field experiment where biochar had been added at rates up to 88 t ha-1. For soils where biochar was added at rates up to 22 t ha-1 there was no difference compared to non-amended soil, but at the highest rate the difference was significant at water potentials in the range 0.01–0.20 MPa. At the highest potential the mean volumetric water content impact was doubled by the biochar addition. Soil temperature, soil cover, evaporation and evapotranspiration affect available water in soil. Comparison of actual volumetric water content between biochar-amended and control soils in field experiments may therefore be confounded by any indirect effect of biochar on plant growth and soil thermal properties. Soil organic matter increases soil water holding capacity and in the biochar-enriched terra preta with their associated higher levels of soil organic matter, Glaser (2002) reported a water retention capacity that was 18% higher than in adjacent soils in which charcoal was low or absent. This was likely a combined effect of the char itself and the higher levels of organic matter that this promotes (Section 3.1.6.4).

3.2.4. Nutrient retention and use-efficiency There are several reasons to expect that biochar might decrease the possibility of nutrient leaching in soils, and enhanced nutrient cycling has been cited in various field studies for positive impacts on yield. However, very few studies have demonstrated the effect or attempted quantitative description of the mechanism. In general, the mineral and organic fractions of soil can both contribute to overall CEC, which affects the ability for soils to buffer periodic flushes of ammonium that result from application of chemical fertilisers or manures, or bursts of organic matter mineralisation during favourable, seasonal conditions. The adsorption of ammonium ions is a relatively loose association that does not necessarily prevent plant acquisition, yet greatly mitigates the potential for leaching loss and the diffuse pollution issues of drinking water quality and eutrophication of riverine and estuarine water bodies. Since considerable fossil energy is

35

required to fix nitrogen into fertiliser (Section 2.1.3.6), a low ratio of fertiliser nitrogen application to crop nitrogen uptake can impact the overall carbon balance of agricultural activities (see Section 3.1.6.1). Higher fertiliser use efficiency should lead to a lower fertiliser requirement per unit yield and usually lower nitrous oxide emission (Section 3.1.6.2). Only certain mineral constituents of soil contribute to CEC on account of abundance, and hence surface area, and mineralogy, with certain types of clay being most important. On a mass basis the exchange capacity of soil organic matter may be greater than for any clay (and up to 50 times greater), but it is a relatively small proportion of soil mass in most agricultural situations, particularly under tropical conditions. Given these factors, heavy textured soils under climates that favour higher levels of organic matter show the highest contributions of organic matter – about one-third – to total soil CEC (Stevenson, 1982). Since mineralisation of organic matter is a major source of ammonium release in soil, attempts to raise soil organic matter by increasing rates of input may not decrease – and can potentially increase – leaching losses. In addition to the chemical stabilisation of nutrients, the physical structure of soil determines its capacity to hold water, and hence soil nutrients in solution (Section 3.2.3 above). There are several reasons to expect that biochar might modify leaching potential in soils. Available evidence suggests that on a mass basis, the intrinsic CEC of biochar is consistently higher than that of whole soil, clays or soil organic matter. An analogy may be drawn to the extreme CEC of activated carbon, which is relevant to its function as a sorption medium for decolourisation and decontamination. Since secondary thermal treatment of charcoal is one means of carbon activation, it is not surprising that the process parameters impact the CEC of primary biochar products with temperature increasing this property (Gaskin, 2007). This is a function of both enhanced specific surface area and the abundance of carboxyl carbon groups that they display. The indirect affect of biochar that may result from its modification of soil pH has not yet been included in most studies by, for example, applying lime to the control soil. Whilst determination of CEC and water release curves in homogeneous materials such as biochar should be straightforward, it is more complex to quantitatively determine the contribution of biochar once added to soil. Furthermore, the observation that CEC of biochar may develop over time through both abiotic and biotic modification of its surfaces (Cheng et al., 2006) implies that in order to develop a predictive, quantitative understanding, methods to recover aged biochar from soil is required. Information on the CEC of pyrolysis products is limited mainly by the availability of materials produced from a sufficiently diverse range of feedstock under different production conditions. Information on the CEC of char naturally present in soils is limited by isolation methods, so available studies tend to rely on a comparison of whole soils amended and non-amended with biochar (Lehmann, 2003; Liang, 2006). The second mechanism for mitigation of leaching relates to the physical retention of soil water, which may be enhanced by biochar in coarse-textured soils and any indirect effect of biochar on the accumulation of soil organic matter (see previous, Section 3.2.3). The inherent stability of biochar confers a distinction between the CEC benefits that are possible compared to other soil organic matter; importantly there is no immediate constraint to the level that can be attained by repeated addition, so in principal this capacity could be incrementally enhanced. Provided that biochar is biologically stable (Section 3.1.5), the benefit of higher CEC may be obtained without the risk of contributing to seasonal flushes of nitrate. The possible contribution of modified soil water dynamics and CEC to the apparent effects of biochar on nitrous oxide emission were discussed in Section 3.1.6.2. In addition to mitigating greenhouse gas emissions, limiting gaseous nitrogen loss can be relevant to crop fertiliser requirement. A beneficial impact of biochar on the plant-available phosphorus has been observed in soils enriched with biochar, which in contrast to ammonium, is not a characteristic generally

36

associated with soil organic matter (Lehmann, 2007b; Steiner et al., 2007). In the context of nutrient availability, the impact of biochar addition on pH may be important.

3.2.5. Use of biochar to manage water quality Biochar may offer benefits in reducing diffuse pollution originating from agriculture through deployment in soils from which polluting elements arise. It may also be possible to utilise its sorptive capacity to remove contamination in the water treatment process. Studies that demonstrate the capacity for biochar to remove nitrate (Mizuta, 2004) and phosphate (Beaton, 1960) in this context have been cited, and in by-passing the complexity of the soil system, controllability is achieved. However, whilst biochar may loosely hold nutrient elements in a plant-available form, the by-product of water treatment could also be contamination by toxic organic compounds in wastewater; biochar also has an affinity for organic compounds (Kookana, 2006). This could confound use of the post-treatment biochar product on land; the economic and overall carbon and environmental gain to be achieved from centralised versus diffuse deployment for management of water quality have yet to be assessed. The precedent for a centralised approach is the current use of activated carbon for the removal of chlorine and organic chemicals such as phenols, polychlorinated biphenyls, trihalomethanes, pesticides and halogenated hydrocarbons, heavy metals, and organic contaminants (Boateng 2007). It is not clear whether the higher surface area and sorptive capacity resulting from activation of biochar from agricultural crop wastes (Zanzi, 2001) results in significant differences compared to biochar.

3.2.6. Potential risks to soil and water from use of biochar Charcoal production and use appears engrained in many cultures and the apparent success and longevity of the civilisation that created the terra preta provides some reassurance as to the long-term safety of biochar incorporation to soil. Currently in Japan, a strong tradition in the use of charcoal as an authorised soil improver for horticultural and agricultural applications means that 15,000 t of carbonized material is annually applied to soil (Okimori et al., 2003). Nonetheless, a critical and non-prescriptive experimental analysis of risks that might arise from the deployment of biochar has not been undertaken according to modern criteria, taking into account all risks associated with production, distribution and physical application of biochar, as well as its impacts in the soil. The analysis must also be based around products of slow and fast pyrolysis, rather than simply biomass carbonisation. This assessment is critical for three reasons: the irretrievability of biochar once added to soil, the apparent general permanency of biochar once in the soil and the scale and speed at which the strategy needs to be implemented to contribute to climate change mitigation. In addition, the issue of responsibility and liability with respect to large scale application to land is an impediment for companies seeking to invest in the production of biochar or the sale of food products from treated land, as well as being a moral and political issue for Government and regulatory bodies. To date, available information is focused on the two classes of toxic compounds that are associated most often with combustion processes, namely PAHs and dioxins. Dioxins predominantly form at temperatures in excess of 1000°C and there are no published studies to confirm their absence in biochar products (Garcia-Perez, 2008). The proliferation of PAH in secondary pyrolytic reactions above 700°C is well established (Ledesma et al., 2002), but smaller quantities may form in the temperature range of pyrolysis reactors (Garcia-Perez, 2008). Unpublished analyses of several biochar samples also found a PAH content no greater than that of bulk soil (Manning, pers. comm.); a single published study examined the full PAH profile (40 individual PAH compounds) in a number of synthetic char samples manufactured at relatively high heating rate concentrations (Brown, 2006). Total PAH concentration was 3–16 μg g-1, depending on peak temperature, compared to 28 μg g-1 in char from a prescribed burn in pine forest. Information contained in PAH may 37

provide a measure of thermal history (Brown 2006), but empirical relationships to relate them to process parameters have not been defined. The above analyses determine principally the total initial content. It is not clear over what timescale these compounds are altered in the soil, and most importantly, the bio-available component in soil is not known. However, it has been stated by Ahmed (1989) that whilst biochar should contain systems of PAH, existing evidence indicates that no leachable PAH is present. No results of bio-assays using biochar in soil have been reported, nor have the appropriate biochar concentrations been defined in the context of the accumulations that might occur in water and marine sediments.

4.

POLICY CONTEXT AND ANALYSIS

4.1. A framework to evaluate applications of biochar The strategies for the use of biochar considered here are those that result in biochar being applied to soil on a significant scale. The strategies take a broad geographic perspective and look to avoid significant practical, regulatory or economic obstacles. They therefore are those situations where the benefits exceed the price of the biochar product; benefits may apply to the economy as a whole, arise from economic benefits for the individual enterprise or provide other non-monetary benefits from the use of biochar in soil. Non-monetary benefits include the opportunity cost to a biochar producer of not utilising the pyrolysis residue in combustion to realise its residual energy content. However, the application of biochar to land must also be in accordance with regulatory frameworks and law and until relevant standards are defined, the direct costs to individual users in addressing these controls may be prohibitive. Although scenarios might involve large scale bioenergy and industrial agriculture, the same framework should be used to evaluate its potential contribution to subsistence or slash-and-burn agriculture. However, although these practices contrast quite starkly, like soil and climatic factors, farming practices occur over a continuum of different scales, and these examples sit at opposite extreme ends. As such, it will be highly advantageous to define a single framework for assessment and comparison of different biochar scenarios for their net carbon benefit and socio-economic impacts. Separate evaluations should be made for the economic and environmental sustainability of alternative biochar scenarios. If the assured carbon-equivalent gain available using biochar is positive but the economic analysis for mainstream agriculture negative, then utilisation of economic instruments – most likely carbon trading or a subsidy that ensures biochar is used in soil rather than for combustion – is essential. The introduction, expansion or revision of such instruments that place a monetary value on the utilisation or disposal of organic waste, maintenance of soil quality and support for renewable and bioenergy as a whole may then be considered. For any biochar scenario it is possible that the agronomic value for biochar is sufficient to render the economic evaluation positive, without resorting to carbon markets or Government incentives. Then concerted research effort will be sufficient to establish certainty around the extent and realisation of such benefits.

4.2. Scenarios for the uptake of biochar for use in soil Even pending further research, biochar may be attractive to producers of high value crops, where certain characteristics of biochar (such as water storage) have high economic value. In these markets the price of biochar may be acceptable even in the absence of subsidy or payment. Some additional brand value may be derived from the carbon balance of the production system but would not be the driver of the system. Biochar could also be profitably

38

employed on recreational land or on sports turf. Such applications may increase recognition, but will not provide the extent of use required to contribute to climate change mitigation. Currently, uncertainty around the expected benefits and potential returns at current prices is likely to limit widespread use in mainstream agriculture. This uncertainty stems from inadequate understanding or quantitative description of the underlying processes and the multiplicity of potential benefits and interactions. Key biochar characteristics will vary according to the nature of the agricultural management system, soil and climate, and may not be static over time. The number of useful biochar properties and their relative importance will vary accordingly, but at the moment the understanding necessary to produce biochar optimised to deliver a particular balance of properties – especially in tandem with viable energy capture – does not yet exist. The complexity and diversity of decision making on farms, and the susceptibility of soil management strategies to commodity prices and external economic forces is important too. To date, assessments of the benefits to be derived from applying biochar to soil have been made on the basis of very limited experimental evidence, and are often scoping studies based on generalised situations. The sensitivity of proposed scenarios to the spatial dimension presented by climate is improving but still inadequate in predictive terms. Comprehensive, whole-system life-cycle analyses (LCA) with full accounting are required in order to avoid unintended negative consequences. In such analysis it will be recognised that deliberate accentuation of one biochar characteristic may impact on the delivery of others, for example porosity versus nutrient value. Thus not only does the predictive capacity for biochar ‘performance’ not currently exist, but the feasibility of optimising multiple useful characteristics is not known. This is inhibiting realisation of other benefits to the wider system. In the financial evaluation of biochar technologies it is important to consider not only current prices, which are known or can be determined, but also their likely future value. Given the current trajectory of global greenhouse gas emissions, the price of emissions as a tradable commodity will be increasingly important. The future price of fossil fuel and subsidy levels for renewable energy are difficult to predict. However, the indirect gains from the use of biochar will probably increase with the future price of fossil energy, reflecting the generally energyintensive nature of the key inputs associated in mechanised agriculture, and possibly with finite supply of water (irrigation costs). There will be a corresponding increase in value of the residual energy in biochar as fossil energy prices rise. The price of bioenergy may also be enhanced by Government subsides designed to improve energy security and promote environmental goals. In many industrialised countries the opportunity cost associated with using biochar in soil is artificially enhanced by renewable energy subsidies. The future price of grains and other commodities is difficult to predict, but changing diet, a growing global population, and increasingly limited supply of new agricultural land is likely to increase demand relative to supply.

4.3. Market intervention and carbon trading Markets for the sale of pyrolysis feedstocks are not currently accessible, and markets for potential feedstocks are ill-developed. A market for credits relating to ‘avoided emissions’ in which land managers could engage does not yet exist. In general, there also remains a lack of knowledge and awareness of bioenergy and carbon markets, how to access these markets, and particularly a way to accurately evaluate costs and benefits associated with the use of biochar in soil. In the absence of research to support the optimisation of biochar and its agronomic evaluation, the viability of biochar-based soil management based on carbon-offsets alone is important. However, no framework exists within which the carbon sequestered in biochar can be certified as a tradable commodity. This barrier extends beyond carbon trading under the UN Clean Development Mechanism (CDM) to the voluntary carbon markets. To date the methodology required to recognise the stabilisation of degradable organic matter as an

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‘avoided emission’ of CO2 has not been presented, although this is a current activity within the International Biochar Initiative. Additional evidence for the portion of biochar that can be considered stable over the long term is required. Furthermore, research is required to determine whether the carbonequivalent benefits of biochar application to soil extend beyond direct carbon sequestration or the avoidance of other greenhouse gas emissions. At the moment these effects are not fully understood or proven in the predictive sense, nor have the timescales over which they mainly occur been established (Section 3.1.5.). However, the existence of a current methodology for stabilisation of organic matter in avoidance of methane emission represents an important precedent (UNFCCC). Various national Governments have implemented carbon trading schemes in order to meet emission reduction commitments under the Kyoto protocol. This has resulted in the European Union Greenhouse Gas Emission Trading Scheme and subsidiary schemes such as the UK Emissions Trading Scheme. More recently, Australia has announced plans for a Carbon Pollution Reduction Scheme (Anon, 2007c). In these countries, their regional neighbours and in the USA there is a strong market for voluntary carbon trading carbon. Individuals or organisations engage outside of Government requirements in a market currently valued in excess of USD 30 billion yr-1. Offsets traded in the voluntary market are unregulated, and their credentials have been questioned. Biocharbased schemes should offer the opportunity to trade a more demonstrable offset (by virtue of the visibility and durability of biochar in soil), that has community as well as climate benefits through its impact on agriculture. However, there is an expectation within some NGOs that the inclusion of biochar into any carbon trading scheme will ultimately lead to large projects based around dedicated biomass crops that will not benefit agriculture and put additional pressure on rural livelihoods in developing countries as a consequence of land acquisition. Other major NGOs have not yet adopted a specific position on biochar. Alongside the IBI, pressure groups such as the US-based Clean Air Task Force have been promoting biochar based offsets alongside other bioenergy schemes for trading in all carbon markets (Baum et al., 2006).

4.4. Market acceptability issues There are significant organisational and institutional obstacles to the use of biochar in soil. Since biochar could be used on a wide scale and cannot be removed from soil once applied, there is a need to carefully assess any potential negatives in occupational health (possible inhalation risks from physical application to soil), environmental pollution (particulates travelling into water or air), water quality (impacts on aquatic life and water treatment) and food safety (surface and systemic contamination of food products). Since several sectors are involved – broadly water, waste and food safety – it requires a concerted effort to evaluate potential products, and ideally define product standards. Support for the use of biochar in meeting policy objectives will draw upon life-cycle analysis with full greenhouse accounting, backed by a body of experimental data. Where biochar is designated as a regulated waste material, land-users in many countries may be subject to a complex and expensive approval process pending defined standards. However, the political and economic case for using food crops as feedstock for liquid biofuel production (bioethanol), or devoting large land areas to biomass production for bioenergy, is increasingly challenged in the context of rising commodity prices and increasing land pressure. Strategies based around pyrolysis with the use of biochar in soil are distinct from these, since productivity and sustainability of land is potentially enhanced. Globally, rising prices favour cash-crop farming, and the economic case for applying biochar to land is likely to improve. The lack of mechanistic understanding as to the function of biochar and its interaction with already complex soil processes, mean predicting the return to an investment in biochar between locations in terms of extent, predictability and durability of benefits does not yet 40

exist. Providing a measure of certainty to the many possible benefits is a key challenge to be addressed by further research.

4.5. Research To date there are a limited number of examples of large-scale publicly funded research initiatives that assess the use and optimisation of biochar for use in soil. In New Zealand the Massey University has a Biochar Research Initiative. In the UK the Engineering and Physical Sciences Research Council supports two established projects, one building capacity in technology for fast pyrolysis (as part of a wider bioenergy initiative, SUPERGEN) and testing by-products in soil, and the other developing Carbon Sequestration and Capture technology. Brazil has funded second and third tier levels within ‘macro-programs’ defined by the research organisation, EMBRAPA. These will extend field experimentation to create new terra preta (terra preta nova). At Federal Government level, the US has created the Farm Bill that supports ‘biochar research development and demonstration’ which seeks to enhance agricultural energy programs (Anon, 2007b). Biochar was specifically mentioned in the Garnaut Climate Change Review in Australia (Garnaut, 2008) and has been raised in Environment Select Committee discussions in the UK. Currently much of our understanding of the long-term dynamics of biochar is based on studies of charcoal from natural fire, new charcoal produced using traditional methods or analogous procedures undertaken in the laboratory. Studies in Brazil use charcoal fines (waste) from industrially produced charcoal. However, only a small number of comprehensive studies using the products of commercial bioenergy plants currently exist, and although the conditions used to produce these products has been guided by preliminary studies, those conditions may not have been optimised for the soil into which they have been incorporated. The only full-scale field trials using biochar from slow pyrolysis energy plants are being conducted in NY, USA (). .

5.

RESEARCH PRIORITIES AND FUTURE CHALLENGES

Based on the results of this review, the following research priorities have been identified: 1) Determine a predictive relationship for properties and qualities of biochar and its manufacture such that it can be optimised for use in soil. 2) Examine how the possibility of adverse impacts on the soil and atmosphere can be eliminated with certainty. 3) Model the impact of alternate bioenergy systems on the carbon cycle at the global scale, and in the context of national targets, in order to support policy decisions and devise suitable market instruments. Since the underlying context for biochar-based strategies is that of global climate change, research needs to provide answers that are applicable under diverse combinations of climate, agriculture and energy production systems. This requires a fundamental, mechanistic understanding of how biochar provides its unique functional characteristics, probably embodied in models, and would include its interactions with other living and nonliving components of soil. Globally coordinated research activity across a range of countries and climates is necessary if the global applicability of knowledge gained is to be rigorously assessed.

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5.1. Fundamental mechanisms The fundamental mechanisms by which biochar could provide beneficial function to soil and the wider function of the agro-ecosystem are poorly described in terms of providing the predictive capacity that is required. In short-term experiments of months to a few years, biochar addition seems to generally enhance plant growth and soil nutrient status and decrease N2O emissions. Yet surprisingly little is yet published concerning how these benefits occur, or particularly why the effects are quantitatively so variable according to crop, soil and application rate. Soil-biochar dynamics need to be investigated. The required understanding will have to be obtained in the following areas: a) Functional interactions with soil microbial communities. Biochar may modify the symbiotic relationships that exist in the rhizosphere, that is between plants and microbes in close proximity to the root. At the moment the net effect of physical protection provided to microbial colonies, and adequate access of the same colonies to labile and soluble carbon substrates is not yet known. The component of biochar stability provided by association of individual biochar particles and fine mineral particles has not been established, and the role of microbial and rhizosphere secretions in promoting them will be important. Fundamentally, the apparent conflict between high stability, soil organic matter accumulation and apparent enhancement of soil microbial activity needs to be resolved. Useful methods will separate indirect effects of increased water holding capacity or altered water release characteristics, pH effects, and allow for their potentially transitory nature. b) Surface interactions. It seems that as the exchange capacity of biochar surfaces develops over time, the contribution of feedstock and production parameters to the trajectory of its development will need to be established. Once the relative importance of biotic and abiotic processes in promoting this development are known, and the net effect of any simultaneous change in the ratio of external- to internal-surface resulting from physical disintegration under soil movement quantified, the net effect of climate might be predicted. Interaction of biochar with anions, most importantly phosphate, needs to be established, and the extent to which nutrient effects are internal, i.e. derived from within the biochar (finite), and external, supplied by the wider soil, must be determined. c) Nutrient use efficiency. Understanding the link between biochar function and its interaction with nutrient elements and crop roots may enable fertiliser use efficiency to be enhanced and diffuse pollution of watercourses and wetlands. d) Soil physical effects. The intrinsic contribution that biochar can make to the wetability of soil, water infiltration, water retention, macro-aggregation and soil stability is poorly understood – yet should be of critical importance in tropical environments in combating erosion, mitigating drought and nutrient loss, and in general to enhance groundwater quality. The loss of biochar through vertical or lateral flow is not well understood; only recently have studies been initiated to examine movement down the soil profile. e) Fate of biochar. The stability of biochar carbon is intrinsic to fulfilling its role as a significant CO2 sink, but in order to perform an agronomic role, it must also remain within the soil to which it is applied. The environmental role or impact of biochar once it has moved through a soil profile, or into watercourses, is yet to be assessed. Information on the extent to which physical breakdown of biochar changes the balance in its properties, particularly with respect to soil water dynamics, exchange capacity and soil micro-and macro-aggregation is lacking. Methods are urgently required to assess the long-term biological stability of specific biochar samples, possibly extrapolating from the dynamics of atypically high initial rates of decomposition. f) Impacts on soil N2O and CH4 emission. Published data for the effect on trace gas emission is extremely limited, but has a potentially great impact on the net benefit of a biochar strategy. Good predictive models will be necessary for this to be reflected in future

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accounting for biochar projects, and at the moment there is not a clear mechanism for the effect. g) Plant physiological responses to biochar ultimately dictate impacts on growth and yield and need to be directly targeted in future work.

5.2. Properties, qualities and environmental risk assessment As the mechanisms underlying biochar function in soil become understood, biochar products can be optimised to deliver specific benefits using a defined screening procedure based on relevant properties. Research tools for comparing different biochar products already exist from at least two decades of work on charcoal and other black carbon in soils: 13C nuclear magnetic resonance spectroscopy has proved perhaps the most useful in revealing gross differences in composition at the functional group level. However, a screening approach should be defined by relevant properties rather than available measurement techniques. Also a cheap and rapid method procedure appropriate to routine analysis has not been identified. The following research is needed: a)

Scoping. A comprehensive and systematic analysis of commercially available biochar products, including charcoal produced by industrial- and farm-scale carbonisation processes, to scope the boundaries of variation in compositional and functional characteristics of biochar. This should utilise all available techniques and link to a database recording the type of biomass from which the biochar was produced, and the type and details of the production process for correlative analysis.

b)

Benefits and risks. Thorough environmental and agronomic evaluation of biochar in soil will enhance its acceptability as a large-scale offsetting and sequestration strategy for CO2. However, the incorporation of biochar into soil is irreversible and therefore must be safe, with biochar products free of potentially harmful contaminants.

a)

Inventory. A systematic screening of biochar products is required, in tandem with the above, to establish the presence and absence of phytotoxic materials that could conceivably be formed during pyrolysis. This will establish the range of potentially harmful chemical contaminants present and their peak concentrations, providing evidence essential to the preparation of risk assessments. Key compounds will be polycyclic aromatic hydrocarbons, established products of partial combustion, and residual oils and acids.

b)

Air pollution. The environmental impact of vapours and gases produced in open combustion associated with traditional charcoal production and in sub-surface combustion, needs to be carefully evaluated, along with the technological developments required to address it. These emissions can cancel out carbon sequestration if not contained or used in the process.

c)

Waste pyrolysis. The potential for urban waste to be used in biochar production needs to be assessed. A risk-based approach may dictate that such materials are more suitable for gasification than pyrolysis if harmful compounds are abundant. It is not known whether the low quality biochar produced from these waste streams is suitable to deliver sequestration and soil benefits.

d)

Indirect impacts. The implications of rapid expansion in biomass pyrolysis on agricultural and natural land areas is a concern through, for example, the expansion of fast-growing plantation forest for production of feedstocks for biochar or charcoal production. There is also the possibility of increased deforestation if the technology is allowed to expand in an uncontrolled way.

e)

Scrubbing air pollutants. Biochar has been reported to scrub CO2, nitrous oxides and sulphur dioxide from fuel gas, creating a nitrogen-rich biochar product that could substitute conventionally produced chemical fertiliser. Since this approach addresses the practicality of application and offers added benefits, it needs to be pursued and refined.

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5.3. Carbon cycle modelling Two types of carbon modelling are required: static spreadsheet models to compare alternative scenarios for their relative carbon-equivalent gain, and mechanistic soil simulation models that capture information from short term experiments to predict longer-term impacts on soil function. In addition, socio-economic models that incorporate a spatial dimension are required to assess the workability of particular scenarios. a)

Modelling net carbon gain. So far only generic, theoretical analyses have been published. Full assessment spreadsheet models based on improved experimental evidence are required to conduct ‘what-if’ comparisons of alternative strategies for specific feedstock streams and pyrolysis facilities, taking the spatial dimension of feedstock supply and biochar use into account.

b)

Mechanistic soil modelling. Modelling of the linked carbon and nitrogen cycles in soil with and without intervention using biochar is essential to understanding the fundamental mechanisms referred to above, and the impact on soil-based emissions of greenhouse gases. Modelling of soil carbon currently relies on conceptual pools, and essentially ignores black carbon from a mechanistic perspective. Progress in this area is dependent on improved quantification methods for biochar in soil.

c)

Economic models. Conceptual and actual geographic boundaries must be carefully set when assessing a particular scenario, accounting for the entire supply chain. Socioeconomic constraints relevant to the application of biochar must be recognised.

d)

Audit. A standard methodology for validation and audit of biochar application is required that ideally permits the source of a particular biochar application to be confirmed retrospectively.

e)

Databases. International support for a global system that enables optimal biochar products to be selected for application in a particular location and system. The only such database initiated to date is CharDB, at Terra Carbona ().

5.4. Beneficiaries Pyrolysis enterprises. In areas where biochar may be produced for agricultural or environmental gain rather than energy production, NGOs may be interested in exploring the pyrolysis biochar technology. Market development would facilitate the dialogue between producers and investors as well as researchers and users. Currently the amount of biochar available for use as a soil amendment (and hence carbon sequestration) is limited to an extent where even assessment of products for non-energy use is limited. Charcoal producers. Traditional producers may experience expansion in the market for charcoal if its use as a soil amendment is supported by land-users for carbon sequestration or enhancing soil fertility. There is a precedent for charcoal being produced on a commercial scale within Europe, with almond charcoal supplied to power companies in Spain. Water companies. Larger scale production of activated charcoal from pyrolysis-derived biochar could reduce costs. Large scale use of biochar on agricultural land in intensively farmed areas may also reduce diffuse pollution and the need, and hence costs, for treatment of water. Land users. Individual farms or farming consortia would benefit due to greater profitability as a result of savings on energy and fertilisers. Remediation of degraded or contaminated land using biochar could be supported through Government, engaging the agricultural community and supported by environmentally-oriented incentives and subsidy.

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5.5. Commentary on likely barriers to the adoption of a large scale enterprises utilising Biochar If the technical limitations described above are addressed and if biochar-related techniques are judged to be viable methods to address climate and agricultural problems, then it is likely that additional barriers to widespread adoption will remain. This section provides a commentary on these barriers. The economics of biochar production will be fundamentally altered once methodology has been proposed and adopted with regard to carbon offset values, in the voluntary market, and as a longer-term possibility, certification under the United Nations Framework Convention on Climate Change (UNFCCC) clean development mechanism (CDM). A streamlined regulatory framework may be essential to avoid stifling initial interest in the use of biochar products in mainstream agriculture. Government policies to help ensure continuity of feedstock supply to pyrolysis enterprises could assist in establishment of the industry; subsidy arrangements could be adopted that favour rather than discriminate against the use of biochar in soil. A routine standard method to quantify biochar in soil is essential to realise the research agenda. Supply of biochar material from commercial pyrolysis facilities is currently extremely limited and localised, inhibiting research activity. Biochar is highly heterogeneous, so standards and quality control need to be defined and certified. Association of pyrolysis with wider bioenergy technology and specifically the biofuel debate presents an image problem in the wake of diminished global grain stocks and rising commodity prices. However, this could also present forums where the principle and multiple benefits of biochar-based strategies can be discriminated and promoted. The multi-disciplinary nature of the biochar concept seems to inhibit large-scale funding of the extensive research agenda, particularly the large sums required for long term trials. It also appears that assigning responsibility for researching biochar within Government and between public and private sectors is challenging. Funding for testing commercial products may be borne by companies producing the products, but such activities will need to be integrated with public sector science to address the wider climate change agenda.

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World Journal of Agricultural Sciences 3 (5): 572-575, 2007 ISSN 1817-3047 © IDOSI Publications, 2007

Response of Broiler Chickens to Wood Charcoal and Vegetable Oil Based Diets A.A. Odunsi, T.O. Oladele, A.O. Olaiya and O.S. Onifade Department of Animal Production and Health, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso, Nigeria Abstract: An experiment was carried out to determine whether Wood Charcoal (WC) would affect growth performance, carcass characteristics and blood profiles of broilers and to determine whether Vegetable Oil (VO) supplementation would influence similar parameters in broiler chickens fed WC. Dietary WC was incorporated into broiler starter and finisher diets at 0, 2.5, 5.0 and 7.5% levels while diets containing 2.5 and 5.0%WC were each supplemented with 1.5%VO to make six dietary treatments. Results showed that feed intake (F1) was significantly increased in broilers fed 5% WC with or without VO while birds on other diets had similar (p>0.05) intake. Body Weight Gain (BWG) and feed conversion ratio (FCR) were significantly better (p<0.05) on birds fed without WC compared to those fed on WC based diets. Supplementation with VO only gave marginal improvement on performance indices when compared with the corresponding WC based diets without VO. However, the performance criteria used (F1, BWG and FCR) were still not commensurate to the control diet. Carcass yield, liver, spleen and kidney did not show any major variations (p>0.05) among dietary treatments while lung, heart and gizzard indicated significant differences (p<0.05). The packed cell volume, haemoglobin, red blood cell and white blood cell, MCV, MCH, MCHC values obtained for the six treatments were not statistically (p>0.05) different from each other. The present study appeared not to justify the dietary inclusion of WC in broiler chicken diets and its use in broiler diets is not recommended. Key words: Wood charcoal % vegetable oil % broilers % growth performance % carcass yield % hematology whether Vegetable Oil (VO) supplementation would affect similar parameters in broiler chicken fed wood charcoal.

INTRODUCTION In Nigeria and indeed many other countries, various feeds and additives are incorporated into poultry diets to ensure maximum productivity. Most of the additives are used depending on area and the ease of use. Moreover, most of these materials are not cited in the scientific literature but are used locally, for instance wood charcoal [4, 6]. It was reported by Kutlu et al. [4] that some local poultry producers in Turkey claimed that 20-50 g wood charcoal per kg diet prevents fatness and improve performance of broilers and layers. In view of these assertions, we have attempted to validate this claim in our laboratory because wood charcoal is widely available in Nigeria and so far, no reports can be cited as to its nutritional use apart from being a suitable and alternative cheaper source of generating heat. The present study was therefore conceived to determine whether dietary wood charcoal applied at graded levels would influence growth performance, hematology and carcass characteristics and to determine

MATERIALS AND METHOD Experimental diets and their composition: Wood Charcoal (WC) was obtained from a local market in Ogbomoso and ground through a mill to pass a 1mm sieve. As ground, it contained 946g DM/Kg, 154g ash/kg, 97.5g crude fibre/kg, 10.8g ether extract/kg, 19.6g crude protein/kg and 664.1 g nitrogen free extracts/kg. Six diets each were formulated during the starter (1-5 weeks) and finisher (5-9 weeks) phases. Diet I was designated as the control without WC while diets 2, 3 and 4 contained 2.5, 5.0 and 7.5% WC respectively. Diets 5 and 6 were formulated to contain 2.5 and 5.0% WC respectively each supplemented with 1.5% Vegetable Oil (VO). The diet composition for the two phases is shown in Table 1. Experimental birds and management: A total of 200 unsexed Anak 2000 broiler chicks were procured from

Corresponding Author: Dr. A.A. Odunsi, Department of Animal Production and Health, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso, Nigeria

572

World J. Agric. Sci., 3 (5): 572-575, 2007 Table 1: Composition and nutrient contents of broiler starter and finisher diets (%) Starter diets

Finisher diets

---------------------------------------------------------------------------------- ---------------------------------------------------------------------------------1

2

3

4

5

6

1

2

3

4

5

6

Ingredients

0

2.5

5.0

7.5

2.5+VO

5.0+VO

0

2.5

5.0

7.5

2.5+VO

5+VO

Maize

52.7

49.7

43.7

47.7

47.8

44.9

58.4

55.4

53.4

49.4

52.5

49.5

Groundnut cake

30.6

31.1

31.6

32.1

31.5

32.0

25.4

25.9

26.4

26.9

27.3

27.8

Wood charcoala

0.0

2.5

5.0

7.5

2.5

5.0

-

2.5

5.0

7.5

2.5

5.0

Vegetable oil

-

-

-

-

1.5

1.5

-

-

-

-

1.5

1.5

Fish meal

5

5

5

5

5

5

Wheat offal

8

8

8

8

8

8

10

10

10

10

10

10

Bone meal

2

2

2

2

2

2

2

2

2

2

2

2

Oyster shell

1

1

1

1

1

1

1

1

1

1

1

1

Salt

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

Methionine

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

Premix

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

0.25

2.5

2.5

2.5

2.5

2.5

2.5

Analyses Dry matter

91.8

91.8

91.8

91.8

91.7

91.8

91.3

91.5

91.6

91.3

91.5

91.2

Crude protein

22.9

22.8

22.9

22.9

22.9

23.0

19.3

19.4

19.6

19.5

19.4

19.5

Ether extract

8.79

8.73

8.66

8.59

8.68

8.57

5.64

5.35

5.47

5.31

6.38

6.74

Crude fibre

3.46

3.50

3.52

3.56

3.46

3.49

4.84

4.05

4.25

4.65

4.28

4.15

Crude ash

3.47

3.66

3.86

4.05

3.67

3.86

2.85

2.96

2.39

3.14

2.94

NFE

53.2

53.1

52.9

52.7

53.0

52.9

59.5

59.8

58.6

58.6

58.4

2.59 58.2

Wood charcoal contains ( %); DM, 94.6, CP, 1.96; EE, 1.08; CF, 9.75; Ash, 15.4, NFE, 64.41

a

Farm Support Services, Ibadan and fed a commercial broiler starters mash (24%CP/2900 ME kcal/kg) for 1 week. Subsequently, one hundred and eighty birds were weighed and randomly allotted to the six dietary treatments in triplicate lots of 10 chicks each using the completely randomized design. The six experimental starter and finisher diets were provided to the birds during the starter (1-5 weeks) and finisher (5-9 weeks) phases respectively. The groups were kept in a floor-littered poultry house situated at the University Teaching and Research farm, Ogbomoso. Feed and water were provided ad libitum. Other routine management practices such as vaccination, drug administration and maintenance of cleanliness in and out of the poultry house were applied. Initial body weights of the birds were taken on replicate basis at the start of the study and thereafter on weekly basis. Weekly feed intake was also recorded. The mean daily weight gain, daily feed intake and feed to gain ratio were thus calculated from the data obtained during the starter, finisher and overall experimental period. On day 63, 2 birds of mean weight close to the average group weight were randomly selected from each of the 18 replicates and starved of feed for 12 hours in order to empty their crops. The birds were exsanguinated, defeathered, eviscerated and dressed. Each bird’s carcass,

cut-up parts and organs were separately weighed and expressed as a percentage of dressed weight. Blood samples were collected on the 63rd day of the trial from 3 birds per treatment during slaughter. The samples were collected in bottles containing ethylene tetra-acetic acid (EDTA) as anticoagulant. They were then taken to the laboratory for hematological analyses that included Packed Cell Volume (PCV), erythrocyte (red blood cell), leucocytes (white blood cell) and haemoglobin. The Mean Cell Volume (MCV), Mean Cell Haemoglobin (MCH) and Mean Cell Haemoglobin Concentration (MCHC) were calculated. The hematological parameters were determined as described by Davice and Lewis [2]. The proximate compositions of wood charcoal and experimental diets were determined according to AOAC [1]. Data collected were analyzed by analysis of variance technique and the Duncan’s multiple range technique was used to detect differences among treatment means [8]. RESULTS AND DISCUSSION The growth performance data of broiler chickens fed wood charcoal based diets supplemented with or without vegetable oil during the starter, finisher and overall experimental periods is shown in Table 2. At the starter

573

World J. Agric. Sci., 3 (5): 572-575, 2007 Table 2: Effect of providing wood charcoal and supplemental VO on growth, performance of broilers at starter, finisher and the overall experimental period Variable

Control

2.5%WC

20.5a 48.6b 2.37c

19.5a 50.9b 2.61b

22.4a 54.0a 2.41c

17.3b 49.0b 2.84a

22.2a 50.5b 2.73b

21.4a 51.0b 2.38c

0.95 1.44 0.46

Days 35-63 BWG Feed intake FCR

50.3a 129.2b 2.57c

44.5b 127.9b 2.87b

42.6b 135.4b 3.18a

41.8b 122.4c 2.93a

44.7b 127.4b 2.84b

44.5b 132.3a 2.97a

1.30 2.55 0.12

Days 7-63 BWG Feed intake FCR

35.3a 88.8b 2.52b

32.5b 94.7a 2.91a

29.6b 85.7c 2.90a

33.5b 88.8b 2.65c

33.0b 93.2a 2.68c

0.60 2.06 0.07

Days 7-35 BWG (g/b) Feed intake (g/b) FCR(F1/BWG)

5%WC

32.0b 89.4b 2.791b

7.5%WC

2.5%WC+VO

5.0%WC*VO

SEM

a, b, c: Means within a row with similar superscripts are not significantly different (p>0.05) Table 3: Effect of dietary charcoal wood on carcass weight, carcass yield, cut-up parts and organ weights of broilers

Variable

Diets ---------------------------------------------------------------------------------------------------------------------------------------------------------0%WC 2.5%WC 5%WC 7.5%WC 2.5%WC+P0 5%WC+P0 1 2 3 4 5 6 SEM

Carcass Carcass weight (g/b) Carcass yield (% ) Abdominal fat (%)

1445.3a 73.1a 0.95a

Relative cut-up parts (% of CW) Wing Thigh Drum stick Breast Back Neck Relative organ weights (% of CW) Liver Kidney Lung Heart Spleen Gizzard

1260.4b 70.3a 0.65b

1303.1ab 71.6a 0.61b

1155.3c 69.7b 0.54c

1470.8a 78.4a 0.69b

1387.9a 75.1a 0.71b

28.02 0.34 0.09

12.7 19.2 14.6 25.3 18.9 6.96

12.6 16.7 13.7 25.3 21.4 6.96

11.4 22.9 14.8 27.6 19.4 6.90

11.5 19.2 15.1 25.1 19.2 7.03

11.8 19.0 14.7 24.4 19.9 7.89

11.5 17.1 15.7 24.5 20.8 7.07

0.79 0.30 0.47 0.35 0.24 0.07

2.17 0.51 0.54 0.54 0.12 2.72

2.3 0.97 0.74 0.57 0.11 3.30

2.23 1.0 0.66 0.47 0.11 2.39

2.46 0.98 0.74 0.53 0.23 2.80

1.95 0.83 0.73 0.42 0.07 2.60

2.41 0.96 0.73 0.50 0.11 2.51

0.07 0.04 0.02 0.01 0.12 0.72

phase, feed intake was highest (p<0.05) for broilers on 5% WC diet while other treatments had similar intake. Body weight gain was similar across the dietary groups with the exception of broilers fed 7.5% WC based diets. Feed/gain ratio was significantly (p<0.05) better for birds fed on the control diet, 5% WC and 5% WC+VO diets compared to the other dietary groups however, broilers fed on 7.5% WC had the worst feed conversion ratio. During the finisher phase, birds fed the control diet significantly (p<0.05) gave the highest BWG. Broilers on 5% WC with or without VO had the highest (p<0.05) feed consumption while the least intake was recorded for birds fed 7.5% WC diet. The control diet exhibited the best-feed conversion ratio. Considering the overall feeding period (combined starter/finisher phases), feed intake was significantly

increased in broilers fed 5% WC with or without VO while birds fed 7.5%WC diet had the least (p<0.05) consumption. Body Weight Gain (BWG) and Feed Conversion Ratio (FCR) were significantly better (P<0.05) on birds fed the control diet compared to those fed WC based diets without VO. The increase in feed consumption for birds fed 5%WC did not really translate to higher weight gain. However, the slight improvement in weight gain observed with the addition of VO is a reflection of the positive attributes of vegetable oil in poultry diets. Vegetable oil increases energy density, reduces dustiness and increase vitamin A concentration in diets [7, 9]. Charcoal supplementation was reported to induce a small reduction in feed intake, egg production and feed conversion ratio [4]. The reduction in feed intake was 574

World J. Agric. Sci., 3 (5): 572-575, 2007 Table 4: Effect of dietary wood charcoal and supplemental vegetable oil on hematology of broilers Diets ---------------------------------------------------------------------------------------------------------------------------------------Variables

1

Packed cell volume (%)

29.00

26.50

25.50

24.50

26.00

25.00

0.24

Haemoglobin (gm %)

9.67

8.83

8.50

8.17

8.60

8.33

0.124

Red blood cell x106

4.83

4.42

4.25

4.05

4.30

4.15

0.58

White blood cell x103

8.83

9.03

9.95

9.60

6.23

6.35

0.57

59.90

60.00

60.00

60.60

60.50

60.40

0.58

3.33

3.33

3.33

3.33

3.31

3.33

0.003

199.90

199.90

200.00

201.80

200.00

201.20

Mean cell volume Mean cell Haemoglobin

2

3

4

5

6

SEM

Mean cellHaemoglobin concentrations

attributed to a higher bulk density of charcoal which was why VO was included in diets 5 and 6 to reduce bulkiness and dustiness. The blackening of the feed by the charcoal might cause a degree of unpalatability [3]. This might account for the significant reduction in intake for broilers on 7.5% WC. Previous studies [5, 6] opined that the use of charcoal had a beneficial effect on the development of chickens and turkeys. For instance [5] observed that after 7 weeks of growth, birds which received supplemental charcoal were about 1-6.5% heavier, had a 5.9% better feed conversion efficiency and a 1.6% better survival rate than the control group without wood charcoal. Similarly, Majewska et al. [6] reported that turkeys given charcoal supplemental feeds were 5.9% heavier and had a 6.5% better feed conversion ratio than the control birds. Survival in the groups that received charcoal was 99% as compared to the 87.3% in the control group. The carcass yield, cut-up parts and organ weights of broilers fed WC and supplemental vegetable oil diets are shown in Table 3 while the hematological indices are indicated in Table 4. Broiler chickens fed 7.5%WC had the least percentage carcass yield and abdominal fat among the dietary groups. Broiler cut-up parts and hematological parameters did not exhibit any major discernible response with the use of WC or supplemental VO in their diets. However, the lung, heart and gizzard showed slight (p>0.05) changes among the dietary groups. These showed that wood charcoal used in this study had no major physiological effects on tissue or organ development and functions. However a positive development is the reduction in the abdominal fat deposition in broilers fed WC based diets relative to the control group. This pilot study reported here demonstrated that the wood charcoal incorporated into broiler chicken diet did adversely affect broiler performance during the entire feeding period as opposed to reports by Kutlu et al. [4]

1.89

Majewska and Zaborowski, [5] Majewska, et al. [6]. So, using WC in broiler diets is not recommended. REFERENCES 1.

2.

3.

4.

5.

6.

7.

8.

9.

575

AOAC. 1990. The official methods of analysis. Association of Official Analytical Chemists, 13th Edn. Washinghton DC. Davice, J.U. and S.M. Lewis, 1991. Practical haematology 8th edition. Longman Ltd London, pp: 22-48. Jindal, N., S.K. Mahipal and N.K. Mahajan, 1994. Toxicity of aflatoxin B3 in broiler chicks and its reduction by activated charcoal, Res. Vet. Sci., 56: 37-40. Kutlu, H.R., I. Unsal and M. Gorgulu, 2001. Effect of providing dietary wood (oak) charcoal to broiler chicks and laying hens. Anim. Feed Sci. Tech., 90: 213-226. Majewska, T. and M. Zaborowski, 2003. Charcoal in the nutrition of broiler chickens. Medycyna Weterynaryjina, 59: 81-83. Majewska, T., D. Pyrek and A. Faruga, 2002. A note on the effect of charcoal supplementation on the performance of Big 6 heavy tom turkeys. J. Anim. Feed Sci., 11: 135-141. Odunsi, A.A. and A.A. Onifade, 1998. Effect of zinc bacitracin supplementation of broiler chick diets containing a low or high vegetable oil concentration in the tropics. Trop. Vet., 16: 51-57. Steel, R.G.D. and J.H. Torrie, 1980. Principles and procedures of statistics. A biometrical approach. 2nd edition McGraw Hill Books Co., New York, USA Zollitscha, W., W. Knausa, A. Aichinegera and F. Lettnera, 1997. Effects of different dietary fat sources on performance and carcass characteristics of broilers. Anim. Feed. Sci. Technol., 66: 283-287.

Majewska T., Pyrek D., Faruga A. T. Majewska, Department of Poultry Science, University of Warmia and Mazury in Olsztyn, Oczapowskiego 5, 10-718 Olsztyn, Poland A note on the effect of charcoal supplementation on the performance of Big 6 heavy tom turkeys

The experiment was conducted on 204 Big 6 heavy tom turkeys. One-day-old chicks were allocated to two feeding groups, each with three replicates of 34 birds. All of the birds were fed identical granulated standard feeds in a three-stage system. The control birds were fed unsupplemented feed, the birds in the treatment group received a feed supplemented with pulverized hardwood charcoal at a dose of 3 kg/ton. Charcoal was given from day one of life for the entire period of rearing. The use of charcoal had a beneficial effect on performance. After 18 weeks of rearing, turkeys given charcoal-supplemented feed were 5.9% heavier (on average 870 g) and had a 6.5% better feed conversion ratio than the control birds. Survival in the group receiving charcoal was 99% as compared with 87.3% in the control group. The crude protein content of the breast muscles of the experimental group increased significantly. The European Production Index equaled 393 for the control group and 504 for the charcoal-supplemented group. Journal of Animal and Feed Sciences 2002, vol: 11, number: 1, pages: 135-141

Majewska T., Zaborowski M. Charcoal in the nutrition of broiler chickens The aim of the research was to define the influence of charcoal added to the standard feed mixtures during their production or directly before feeding broiler chickens on the latter’s development. The experiment was conducted on 180 Starbro chickens. One-day-old chicks were allocated into 3 feeding groups, with two replicates of 30 birds each. The birds of all groups were fed identical standard mixtures in a three-stage system: Starter, Grower and Finisher. The control birds were fed only with standard mixtures. The birds in group 2 received the same mixtures but supplemented with pulverized hard-wood charcoal at a dose of 3 kg/ton (together 100.3%), added at the moment of production of the mixtures, about 2 weeks before the feeding. The birds from group 3 received mixtures with charcoal supplemented during the feeding at a dose of 0.3% (together 100.3%). In both cases the use of charcoal had a beneficial effect on the development of the chickens. After 7 weeks of growth, birds which received supplemented charcoal were from 22 g to 157 g (about 1 to 6.5 %) heavier, had a 5 to 9 % better feed conversion ratio and a 1.6% better survival rate than the control group. The Fattening Efficiency Index equaled 209 for the control group, 246 for group 2 and 262 for group 3.

Medycyna Weterynaryjna, 2003, vol: 59, number 1, pages 81-83

156 Evaluation of char and active carbon for the reduction of ammonia volatilization from poultry manure. C. Ritz*, A. Tasistro, B. Fairchild, and B. Bibens, University of Georgia, Athens. Locally available biomass materials, such as peanut hulls or tree clippings, have the potential for use as raw materials for producing chars and active carbons. Chars have long been known to possess properties that make them valuable environmental tools. One such application is the adsorption of NH3. By properly activating the char, ammonia can be captured on its surface. Active carbon can be found in numerous products designed to absorb moisture and odors, such as carbon filters for use in drinking water filtration and air purification. Chemical adsorption of ammonia is mostly due to its interaction with oxygen functional groups via hydrogen bonding. It is expected that chars used with poultry litter application will perform mostly based on their chemisorption capacity. The purpose of this study was to evaluate the effectiveness of char and active carbon on reducing ammonia volatilization from poultry manure when used as a surfaced-applied litter treatment. Char from peanut hull waste was produced by pyrolysis, wherein the material was heated to 400°C in the absence of oxygen for 30 minutes. The unamended peanut hull char (pH 9.20) and an acidified poultry litter char (53% sulfuric acid) were applied to replicate pens at rates of 50, 75 and 150 lbs per 1000 square feet. Broilers were raised in the pens at 0.75 square feet per bird to generate the manure ammonia. The unamended chars actually increased the release of ammonia an average of 14% over the control. The acidified char applied at the 50, 75 and 150 lb rates reduced overall ammonia release by 11, 25, and 35%, respectively over the control. The reduction in ammonia from the acidified char treatment is most likely due to litter pH reduction from the acid application and not from chemisorption by the carbon. Further investigation into the use of activated carbon products for ammonia control in poultry houses is warranted. Key Words: broiler, ammonia, char, active carbon, pyrolysis Reference:
Poultry
Science
Vol
88
(Suppl
1)
,
p.
49.

2009

USDA ARS Research Project: Agricultural by-Products As Adsorbents for Environmental Remediation Location: Commodity Utilization Research

Title: Efficacy of Activated Carbon from Broiler Litter in the Removal of Litter Generated Ammonia

Submitted to: Meeting Proceedings Publication Type: Proceedings/Symposium Publication Acceptance Date: July 19, 2007 Publication Date: September 16, 2007 Citation: Fitzmorris, K.B., Miles, D.M., Lima, I.M. 2007. Efficacy of Activated Carbon from Broiler Litter in the Removal of Litter Generated Ammonia. In: Proceedings of the International Symposium on Air Quality and Waste Management for Agriculture. ASABE. 6 pages. Interpretive Summary: Over the past 10 years, the production of broilers has increased by 29 percent to approximately 9 billion in 2005. Ammonia (NH3) pollution from broiler excreta is a primary concern for industry viability which requires innovative treatment options. This research focused on the use of broiler litter as activated carbon (BAC) to reduce aerial NH3 generated by litter, an opportunity to not only reuse the manure, but also treat the emissions from or within broiler houses. The objective of this study was to evaluate the efficacy of BAC to remove NH3 volatilized from litter samples in a laboratory acid-trap system. The BAC is a much cheaper alternative than commercially produced activated carbons. Preliminary studies using NH3/air mixture indicated that the BAC NH3 uptake was approximately double that of Vapure 612, a commercial carbon. In the litter emission study, the BAC and Vapure performance was comparable. The NH3 emission reductions using the activated carbon columns were 25% for BAC and 36% for Vapure relative to the litter only control. The results of the study demonstrate the potential for a cyclical waste utilization strategy in using broiler litter activated carbon to capture NH3 volatilized from litter.

Technical Abstract: Over the past 10 years, the production of broilers has increased by 29 percent to approximately 9 billion in 2005. Ammonia (NH3) pollution from broiler excreta is a primary concern for industry viability which requires innovative treatment options. This research focused on the use of broiler litter as activated carbon (BAC) to reduce aerial NH3 generated by litter, an opportunity to not only reuse the manure, but also treat the emissions from or within broiler houses. The use of activated carbon in the removal of NH3, specifically in broiler houses, has long been discarded primarily due to the high cost and low efficiency of the carbons. However, the study of BAC is a relatively new field that has focused on the removal of organics and/or metals from water. The objective of this study was to evaluate the efficacy of BAC to remove NH3 volatilized from litter samples in a laboratory acid-trap system. The BAC is a much cheaper alternative than commercially produced activated carbons. Preliminary studies using NH3/air mixture indicated that the BAC capacity to adsorb NH3 was approximately double that of Vapure 612, a commercial carbon. In the litter emission study, the BAC and Vapure performance was comparable. The NH3 emission reductions using the activated carbon columns were 25% for BAC and 36% for Vapure relative to the litter only control. The results of the study demonstrate the potential for a cyclical waste utilization strategy in using broiler litter activated carbon to capture NH3 volatilized from litter. 


Release of Inorganic Nitrogen and Phosphorus from Poultry Litter Amended with Acidified Biochar S.A. Doydora1, M.L. Cabrera1, K.C. Das2, J.W. Gaskin2, L.S. Sonon3, W. Miller1, and C. Steiner2 1Department

of Crop and Soil Sciences, University of Georgia, Athens, GA 30602 of Biological and Agricultural Engineering, University of Georgia, Athens, GA 30602 3Soil, Plant and Water Laboratory, 2400 College Station Road, Athens, GA 30602 [email protected]

2Department

Introduction Georgia generates an estimated average of two million Mg poultry litter (PL) annually. While this material is used as a fertilizer, its nitrogen (N) value decreases as a result of ammonia (NH3) volatilization, which may lead to losses of up to 60% of the applied N (Cabrera et al., 1993; Cabrera and Chiang, 1994). One possible way of minimizing NH3 volatilization from PL is by mixing it with biochar (or char), a by-product from bio-fuel production. When acidified, biochar may reduce NH3 volatilization from PL. This study aimed to 1) evaluate the effect of acidified biochar on NH3 volatilization, 2) examine its effect on CO2 evolution and 3) determine its influence on the release of inorganic N and P from surface-applied or incorporated PL.

Materials and Methods Pine chip (PC) or peanut hull (PH) biochars (produced at 400 or 600°C) were acidified using 0.5 N HCl (1 g:10 mL). Poultry litter (2.1 g) with or without acidified PC or PH (400 or 600) chars (2.1 g) were surface-applied or incorporated into the soil (64.5 g) and was incubated for 21 d. Volatilized NH3 was trapped in 0.1 N H2SO4 and measured colorimetrically. Carbon dioxide evolved was measured using a CO2 analyzer. Release of inorganic N and P was determined by leaching the soil with 0.01 M of CaCl2 followed by a N- and P-free nutrient solution at 14 and 21 d of incubation. At the end of the incubation period, each of the treatments was extracted with 1 M KCl.

Fig. 1. Cumulative NH3-N lost during a 21-d incubation of poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) a) surfaceapplied, or b) incorporated. (Error bars are standard deviations.)

Fig. 2. Cumulative CO2-C lost during a 7-d incubation (20°C) of soil (s, 64.5 g) and poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) a) surface-applied, or b) incorporated. (Error bars are standard deviations.)

Results Surface-applied, unamended PL volatilized 17% of its total N while PL amended with acidified biochars lost only 6 to 11% (Fig.1a). PC400 performed better than PC600 (F=20.92; p=0.0132) for reducing NH3 loss but there was no difference between PH400 and PH600 (F=2.12; p=0.2293). When PL was incorporated into the soil, the same trends were observed (Fig.1b).

Inorganic N released from surface-applied PL with acidified chars was comparable to that of unamended litter (F=3.05; p=0.1146) (Fig. 5). PL+PC400 had more inorganic N leached than PL+PC600 (F=9.06; p=0.0142). PL amended with PH biochar had greater inorganic N leached compared to PL amended with PC biochar (F=6.74; p=0.0289). No differences among treatments were observed under incorporated incubation (F=2.56; p=0.1093) (Fig. 6).

Fig. 6. Inorganic N leached from soil (s, 64.5 g) and incorporated poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) during the a) first, or b) second leaching. (Error bars are standard deviations.)

Fig. 7 Inorganic N extracted from soil (s, 64.5 g) and poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) when a) surfaceapplied, or b) incorporated. (Error bars are standard deviations.)

In the incorporated incubation (Fig 7b), char-amended PL had greater amounts of inorganic N (mainly nitrate) extracted than unamended PL (F=8.47; p=0.0173). Combining PL with PC600 and PH600 had larger amounts of extracted nitrate compared to PL with PC400 (F=17.35; p=0.0024) and PH400 (F=28.31; p=0.0005), respectively. However, in the surface incubation, this was only observed between PH chars (F=13.29; p=0.0054). Surface-applied char-amended PL did not increase the amounts of inorganic N, or nitrate, extracted at the end of the incubation (F=2.00; p=0.1908).

Conclusions

Adding acidified chars to PL depressed CO2 evolved under surface incubation (F=9.24; p=0.0083) (Fig.2a). Conversely, when charamended PL was incorporated into the soil, total CO2 was greater compared to unamended PL (F=6.88; p=0.0255) (Fig. 2b). Inorganic P in the leachate and final KCl extraction was not different among treatments under both surface (F=0.68; p=0.6270) and incorporated (F=1.08; p=0.4227) incubations (Fig. 3 and 4). However, greater amounts of inorganic P were extracted from PL amended with PC400 than from PL amended with PC600 for surface (F=43.66; p=<0.0001) and incorporated (F=6.23; p=0.0341) incubations.

Fig. 5. Inorganic N leached from soil (s, 64.5 g) and surface-applied poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) during the a) first, or b) second leaching. (Error bars are standard deviations.)

Fig. 3. Inorganic P leached from soil (s, 64.5 g) and poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) a) surfaceapplied, or b) incorporated. (Error bars are standard deviations.)

Fig. 4. Final inorganic P extracted from soil (s, 64.5 g) and poultry litter (PL, 2.1 g) with or without acidified chars (PC400, PC600, PH400, PH600, 2.1 g) a) surface-applied, or b) incorporated. (Error bars are standard deviations.)

Nitrate leaching was the same for all treatments under surface and incorporated incubations (Fig. 5 and 6). Nitrate concentration in the leachate was generally smaller than ammonium concentration particularly in the first leaching. However, at the end of the studies, KCl-extracted concentrations were larger for nitrate than for ammonium (Fig. 7).

Amending PL with acidified chars:   Reduced NH3 loss in PL by 63 to 36% with surface incubation and by 60 to 43% with incorporated incubation.   Decreased CO2 evolved from surface-applied PL by as much as 21% but increased that from incorporated PL by as much as 37%.   Did not affect the release of both leachable and extractable inorganic P from both surface-applied and incorporated PL.   Did not affect the release of leachable inorganic N from PL under both surface and incorporated incubations but led to greater amounts of inorganic N, primarily in the form of nitrate, extracted from incorporated PL.

References

Cabrera, M.L. and S.C. Chiang. 1994. Water content effect on denitrification and ammonia volatilization in poultry litter. Soil Sci. Soc. Am. J. 58:811-816. Cabrera, M.L., S.C. Chiang, W.C. Merka, S.A. Thompson, and O.C. Pancorbo. 1993. Nitrogen transformations in surface-applied poultry litter: Effect of litter physical characteristics. Soil Sci. Soc. Am. J. 57:1519-1525.

Effects of feeding fowls with rice hull charcoal on the egg-laying performance and the odor of chicken droppings. Abstract; An investigation was conducted on the effects of feeding laying hens with charcoal made from rice hull upon laying performance and the odor of chicken droppings. When laying hens were fed with feed containing rice hull charcoal at 1%, ammonia gas concentration in accumulated chicken droppings and ammonia gas concentration in chicken house were significantly lower than those of a control with no addition of rice hull charcoal by 52% and 39%, respectively; and the rate of hen-day egg production, daily egg production, and the fructure strength of egg shell tended to be improved by 5%, 4%, and 8%, respectively, compared with those of the control. On the other hand, the amount of feed intake, body weight, Haugh Unit, egg shell weight, and the amount of chicken droppings were not different from those of the control, remaining within .+-.3% from those of the control. The above result indicated that the addition of rice hull charcoal to feed at 1% was effective for the suppression of odor in accumulated chicken droppings and within chicken house and for the improvement of the rate of hen-day egg production and fructure strength of egg shell.

Accession number;03A0266617 Title;Effects of feeding fowls with rice hull charcoal on the egg-laying performance and the odor of chicken droppings. Author;SAITO KATSUMI(Aomori Prefect. Livest. Exp. Stn., JPN) KUZUMAKI TAKEFUMI(Kitasato Univ.) HOSOKAWA YOSHIHARU(Kitasato Univ.) Journal Title;Tohoku Agricultural Research Journal Code:F0596B ISSN:0388-6727 VOL.;NO.55;PAGE.141-142(2002) Figure&Table&Reference;TBL.2, REF.3 Pub. Country;Japan Language;Japanese

Reasons for Pyrolysis of Poultry Litter • Traditionally, poultry litter is disposed by land application and used as cattle feed • Disposal of poultry litter in the U.S. poultry industry is becoming a major problem because of : – – – – – –

Excess nutrient in the soil due to land application Contamination of drinking water Eutrophication of surface waters Ammonia emission from poultry houses Soil acidification through nitrification and leaching Biosecurity concerns

Pyrolysis conditions • • • •

Feedstock---air-dried poultry litter Temperature---450 to 500 oC Residence time--- 2 to 5 s Fluidizing medium--- nitrogen or producer gas • Feed rate --- 200 g/h

Bench-Scale pyrolysis reactor system

Bio-oil derived from Broiler litter

Poultry litter biooil

Pyrolysis Char of Broiler Litter

Bio-oil properties Sample

C (%)

H (%)

Chicken bedding

55.25 6.54

Flock-1 litter

O (%)

N (%)

S (%)

Moit pH (%)

Ash (%)

HHV (MJ/kg

37.58 <0.5

<0.05

5.3

2.7

<0.08

22.64

63.24 7.22

23.89 5.05

0.46

4.6

6.1

<0.09

28.25

Flock-2 litter

64.06 8.14

22.27 4.94

0.41

4.6

6.3

<0.09

28.0

Broiler litter

62.84 8.31

20.72 7.23

<0.9

4.0

6.3

0.17

29.57

Starter turkey litter

64.90 8.44

20.31 5.60

0.4

3.7

4.2

0.10

29.76

2500

2000

Viscosity (cP)

1500

Neat Biooil MeOH + Biooil EtOH + Biooil 1000

Ace + Biooil

500

0 0

10

20

30 Time (days)

40

50

60

Potential Applications of bio-oil

SYNTHESIS GAS OPTIONS

Cat: Ni, Fe, Cu-Zn

HYDROGEN ETHANOL, MIXED ALCOHOLS

Cat: Cu-Zn, Cu-Co

BioBio-oil

FEED PREP

Cat: Cu-ZnO

METHANOL, DME

Cat: H3PO4, Cr2O3

OLEFINS LPG

Cat: Fe GASIFICATION

Cat: Ni

FTL

SYNGAS

NAPHTHA UPGRADING

Cat: Co/K

KEROSINE/DIESEL LUBES WAXES

Cat: Cu-ZnO

CLEANUP

Cat: Mixed Bases Na, Ca

CaCN

Cat = Catalytic Conversion Process

MeOH

Cat: Zeolite

GASOLINE OXOCHEMICALS e.g., KETONES AMMONIA

Cat: Ni/Mg

SNG

Combined Cycle

CHP

Cofiring/Reburn

CHP

Biomass Pyrolysis (liquefaction) Bio-oil Uses Bio-Oil From

Pyrolysis

• • • •

Fuel oil substitute Chemicals Hydrogen Turbines (Power)

75 Green ton/day (40 Dry) Commercial RTP™ Facility at Rhinelander, WI operating since 1995

Ensyn Technologies

Oriented Strand Boards and Plywood made from Bio-Oil – Phenolic Resins are being tested at mill scale

Flow chart of transportable pyrolysis unit Exhaust to Atmosphere

Dolomite

Poultry Litter Feeding System

Hot Filtration Cyclone Filter System

Poultry Litter Fluidized Bed Pyrolysis Reactor

Pyrolysis Oil Condensation System Cooli ng Tower

Ash and Char

Compress ed Air

LBG Reheat Burner

Startup LPG

LBG Compression

Excess LBG to Feed Dryer

ESP and Coalescing System

Raw Oil Product

Thermochemical conversion of biomass to biofuels Foster A. Agblevor, Biological Systems Engineering Virginia Tech, Blacksburg, VA. Email: [email protected] ICS-UNIDO Biofuels Workshop, Accra, Ghana, Dec 11-13, 2007

Outline of presentation • • • • • •

Overview of pyrolysis phenomena Slow pyrolysis Fast pyrolysis of biomass Fast pyrolysis reactors Biomass pyrolysis products Applications of biomass pyrolysis products

Outline of presentation • Environmental application of pyrolysis • Fractional catalytic pyrolysis • Where do we go from here?

What is pyrolysis? • Pyrolysis is the thermal conversion of organic materials in the absence of oxidizing agents such as oxygen. • Pyrolysis always occurs before any combustion process • Pyrolysis leads to thermochemical decomposition of organic materials into a complex mixture of compounds

Schematic depiction of Biomass pyrolysis

What is pyrolysis? • Pyrolysis products are usually not well defined especially when applied to complex natural materials such as biomass. • The pyrolysis phenomena can be divided into several regimes depending on the heating rate • Slow pyrolysis, fast pyrolysis, ultrafast pyrolysis, vacuum pyrolysis and high pressure pyrolysis

Fast pyrolysis biomass reactor designs • • • • • •

Bubbling fluid bed Circulating fluid bed Entrained flow Vortex Rotating cone Vacuum

Biomass Feedstocks

Forest Wood Residues Thinning Residues Wood chips Urban Wood waste pallets crate discards wood yard trimmings

Agricultural Residues Corn stover Rice hulls Sugarcane bagasse Animal residues

Energy Crops Hybrid poplar Switchgrass Willow

Hybrid poplar nursery

Biomass Constituents

H3CO HO

H3CO O

OCH3 O

O

OH OCH3OCH3

O OH

O

OCH3

Lignin: 15-25% Complex aromatic structure Very high energy content

OH

O HO OH H3CO OCH3

OH O

HO O HO O OH

Hemicellulose: 23-32%

O

HO

HO

O OH

O OH HO

OH O

HO

O HO

OH

OH O

OH O

O OH

O HO O OH

O OH HO

O HO

OH

OH O

O OH

OH O

O OH

OH O

OH

OH O HO

HO

Polymer of 5 & 6 carbon sugar

OH

O HO

OH

OH O

OH O

OH O

HO O HO

OH O

HO

O OH

OH O

OH

OH O

O HO

OH

OH O

OH O

O HO O OH

OH

O HO

OH

OH O

O

O O

O HO OH O O OH HO O HO O OH O OH

OH O

HO HO

OH

OH O

OH O

O

HO

O OH

OH

OH O

O OH

OH

OH

OH O

HO

O

O

O HO

OH O

O

HO

O OCH3

HO O OH

OH

OH

OCH3OCH3 OH

O

OH

O HO OH H3CO OCH3

OH O

OCH3

OH

HO

O

HO

O

OCH3

O HO

OH

O OH HO

OH O

O OH

OH O O HO

OH

O HO

OH

OH O

O OH

OH O

OH

Solid

OH O HO O HO

OH

O OH

OH O

Cellulose: 38-50% Polymer of glucose, very good biochemical feedstock

OH

Gas or Liquid

Minor biomass constituents • Extractives----2-10 wt% • Ash----1-20 wt% – N, P, K, Si, Ca, Cd, Hg, As

• These minor constituents strongly influence the pyrolysis reactions • quality of the pyrolysis oil

Environmental and fuel applications

Poultry Powered!!!

Broiler chicken litter

Reasons for Pyrolysis of Poultry Litter • Traditionally, poultry litter is disposed by land application and used as cattle feed • Disposal of poultry litter in the U.S. poultry industry is becoming a major problem because of : – – – – – –

Excess nutrient in the soil due to land application Contamination of drinking water Eutrophication of surface waters Ammonia emission from poultry houses Soil acidification through nitrification and leaching Biosecurity concerns

Pyrolysis conditions • • • •

Feedstock---air-dried poultry litter Temperature---450 to 500 oC Residence time--- 2 to 5 s Fluidizing medium--- nitrogen or producer gas • Feed rate --- 200 g/h

Bench-Scale pyrolysis reactor system

Bio-oil derived from Broiler litter

Poultry litter biooil

Pyrolysis Char of Broiler Litter

Bio-oil properties Sample

C (%)

H (%)

Chicken bedding

55.25 6.54

Flock-1 litter

O (%)

N (%)

S (%)

Moit pH (%)

Ash (%)

HHV (MJ/kg

37.58 <0.5

<0.05

5.3

2.7

<0.08

22.64

63.24 7.22

23.89 5.05

0.46

4.6

6.1

<0.09

28.25

Flock-2 litter

64.06 8.14

22.27 4.94

0.41

4.6

6.3

<0.09

28.0

Broiler litter

62.84 8.31

20.72 7.23

<0.9

4.0

6.3

0.17

29.57

Starter turkey litter

64.90 8.44

20.31 5.60

0.4

3.7

4.2

0.10

29.76

2500

2000

Viscosity (cP)

1500

Neat Biooil MeOH + Biooil EtOH + Biooil 1000

Ace + Biooil

500

0 0

10

20

30 Time (days)

40

50

60

Potential Applications of bio-oil

SYNTHESIS GAS OPTIONS

Cat: Ni, Fe, Cu-Zn

HYDROGEN ETHANOL, MIXED ALCOHOLS

Cat: Cu-Zn, Cu-Co

BioBio-oil

FEED PREP

Cat: Cu-ZnO

METHANOL, DME

Cat: H3PO4, Cr2O3

OLEFINS LPG

Cat: Fe

NAPHTHA GASIFICATION

Cat: Ni

FTL

SYNGAS

UPGRADING

Cat: Co/K

KEROSINE/DIESEL LUBES WAXES

Cat: Cu-ZnO CLEANUP Cat: Mixed Bases Na, Ca

CaCN

Cat = Catalytic Conversion Process

MeOH

Cat: Zeolite

GASOLINE OXOCHEMICALS e.g., KETONES AMMONIA

Cat: Ni/Mg

SNG

Combined Cycle

CHP

Cofiring/Reburn

CHP

Biomass Pyrolysis (liquefaction) Bio-oil Uses Bio-Oil From

Pyrolysis

• • • •

Fuel oil substitute Chemicals Hydrogen Turbines (Power)

75 Green ton/day (40 Dry) Commercial RTP™ Facility at Rhinelander, WI operating since 1995

Ensyn Technologies

Oriented Strand Boards and Plywood made from Bio-Oil – Phenolic Resins are being tested at mill scale

Flow chart of transportable pyrolysis unit Exhaust to Atmosphere

Dolomite

Poultry Litter Feeding System

Hot Filtration Cyclone Filter System

Poultry Litter Fluidized Bed Pyrolysis Reactor

Pyrolysis Oil Condensation System Cooli ng Tower

Ash and Char

Compress ed Air

LBG Reheat Burner

Startup LPG

LBG Compression

Excess LBG to Feed Dryer

ESP and Coalescing System

Raw Oil Product

Transportable Pyrolysis Unit

Rockingham County Cooperator • A pilot pyrolysis unit will be demonstrated on the property of our cooperator, Mr. Oren Heatwole. • The unit will be transportable from farm to farm, but most of the initial research will be done on-site. • Poultry litter from a neighboring farm will be used as the feedstock for the pilot project.

Modified Furnace for Using BioOil

ADI Stirling Engine System Runs on Heat Replace diesel generators for distributed power market

Quiet Output shaft power to Generator

Fuel Flexible • Natural gas • Propane • Ethyl alcohol • Biomass • Hydrogen • Waste heat • Solar Heat

Highest Efficiency of all heat engines with patented “Dual Shell Pressure Balancing Technology”

Fractional catalytic pyrolysis • A catalyst is used for the fluidizing bed • Catalyst fractionates biomass insitu • Carbohydrates gasified to CO, H2, CH4, CO2 • Lignin depolymerized and demethoxylated to monomeric phenols

Schematic Diagram of Fluidized Bed Reactor 1. Fluidized Bed Reactor 2. Furnace 3. Thermocouple 4. Mass Flow Controller 5. Heat Exchanger 6. Hopper 7. Sample Feeder 8. Computer 9. Heating Tape 10. Cyclone 11. Reservoir 12. Condenser 13. Electrostatic Precipitator 14. AC Power Supply 15. Filter 16. Wet Gas Meter 17. Gas Chromatograph

Conventional wood pyrolysis oil C-13 NMR

Fractional catalytic pyrolysis oil

Lignin moieties in biomass

Molecular weight distribution of conventional and FCP oils FCP oil Fractionated sugar cane Bagasse pyrolysis oil

Acknowledgement • We greatly appreciate the contribution of Virginia Poultry Federation, Chesapeake Bay Foundation and Shenandoah RC & Council for their foresight in funding this project. • National Fish and Wildlife Federation for Scaleup funding support • Mr Robert Clark for initiating the project, collecting samples and getting the growers in the Valley involved in the project. • Waste Solutions Forum for promoting the project

Acknowledgement • • • • • •

Dr Sedat Beis Dr Seug-Soo Kim Dr Serpil Besler-Guran Ryan Tarrant Ofei Mante Frederick Teye

Thank you • Questions?

Fluidized Bed Reactor

Viscosity of bioiol: Flock 1 litter, 450 ℃, 500 ℃, 550 ℃ 450

500 550

16 35

50 oC 60 oC

14

50 oC 60 oC

16

10 8 6 4

25

14

20

12

Viscosity [ Pa.sec ]

Viscosity [ Pa.sec ]

Viscosity [ Pa.sec ]

30

12

15

10

2 5

50 oC 60 oC

10 8 6 4

0 0

100

200

300 -1

Shear rate [ min ]

400

500

0 0

20

40

60

80

Shear rate [ min-1 ]

100

120

2 0 0

100

200

300 -1

Shear rate [ min ]

400

500

Viscosity of biooil ; Turkey Litter, 450 ℃, 500 ℃, 550 ℃ 14 50 oC 60 oC

10 14 50 oC 60 oC

8 12

4

2

0 0

100

200

300

400

500

10 70

8

o

6

4

-1

Shear rate [ min ]

50 C o 60 C

60

2

0 0

100

200

300

400

500

Viscosity [ Pa.sec ]

6

Viscosity [ Pa.sec ]

Viscosity [ Pa.s]

12

50

40

30

20

-1

Shear rate [ min ] 10

0 0

20

40

60

80 -1

Shear rate [ min ]

100

120

Comparison of HHV of biooil and litter samples Sample Chicken Bedding

Raw sample HHV (Btu/lb) 7,792

Biooil HHV (Btu/lb) 8,408

Flock 1

6,514

11,829

Flock 2

7005

12,689

Broiler

6,781

12,040

Turkey

8,064

11,291

Demonstration Unit • We propose to use the funding from the National Fish and Wildlife Federation to build a transportable pyrolysis unit to convert poultry litter into bio-oil and slow-release fertilizer in the Shenandoah Valley. • Work has began on the project. • A demonstration unit will be built on the farm of Mr Oren Heatwole, Poultry Specialties Inc, Dayton, VA.

Pyrolysis Project Overview • The project seeks to demonstrate a nutrient reduction and renewable energy technology called pyrolysis to convert poultry litter to a bio-oil, slow-release fertilizer, and producer gas. • This approach was identified as a priority during the 2005 Waste Solutions Forum – to create usable energy from animal manure and poultry litter while also reducing nutrients.

Site and Preparations for Pyrolysis

Water and Heat Lines

Slow pyrolysis • The slow pyrolysis process is very old and has been used since ancient times to produce charcoal. • In modern era, the slow pyrolysis process has been modified and used to produce charcoal. • The modifications are focused on the improvement in the yield of charcoal.

Soil Biology & Biochemistry 36 (2004) 2067–2073 www.elsevier.com/locate/soilbio

Activated carbon amendments to soil alters nitrification rates in Scots pine forests L.M. Berglunda,*, T.H. DeLucaa,b, O. Zackrissona a

Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences, 901 83 Umea˚, Sweden Department of Ecosystem and Conservation Sciences, The University of Montana, Missoula, MT 59812, USA

b

Received 20 February 2004; received in revised form 25 June 2004; accepted 28 June 2004

Abstract The influence of charcoal on biotic processes in soils remains poorly understood. Charcoal is a natural product of wildfires that burned on a historic return interval of w100 years in Scots pine (Pinus sylvestris L.) forests of northern Sweden. Fire suppression and changes in forest stand management have resulted in a lack of charcoal production in these ecosystems. It is thought that charcoal may alter N mineralization and nitrification rates, however, previous studies have not been conclusive. Replicated field studies were conducted at three late-succession field sites in northern Sweden and supporting laboratory incubations were conducted using soil humus collected from these sites. We used activated carbon (AC), as a surrogate for natural-occurring fire-produced charcoal. Two rates of AC (0 and 2000 kg haK1), and glycine (0 and 100 kg N as glycine haK1) were applied in factorial combination to field microplots in a randomized complete block pattern. Net nitrification, N mineralization, and free phenol concentrations were measured using ionic and non-ionic resin capsules, respectively. These same treatments and also two rates of birch leaf litter (0 and 1000 kg haK1) were applied in a laboratory incubation and soils from this incubation K were extracted with KCl and analyzed for NHC 4 and NO3 . Nitrification rates increased with AC amendments in laboratory incubations, but this was not supported by field studies. Ammonification rates, as measured by NHC 4 accumulation on ionic resins, were increased considerably by glycine applications, but some NHC 4 was apparently lost to surface sorption to the AC. Phenolic accumulation on non-ionic resin capsules was significantly reduced by AC amendments. We conclude that charcoal exhibits important characteristics that affect regulating steps in the transformation and cycling of N. q 2004 Elsevier Ltd. All rights reserved. Keywords: Activated carbon; Charcoal; Boreal forest; Birch litter; Fire; Nitrogen transformations; Nitrification; Phenolic compounds

1. Introduction There is limited understanding of the role of charcoal in N mineralization and nitrification rates in boreal forest ecosystems. Charcoal is a product of forest fires that historically burned on a w100 years fire return interval in northern Fennoscandia (Zackrisson, 1977) and amounts up to 2000 kg haK1 of charcoal can be present in the soil of such ecosystems (Zackrisson et al., 1996). Forest fires are a major form of disturbance that has an immediate and longterm effect on ecosystem processes. This effect vary depending on fire severity, but involve alterations to nutrient * Corresponding author. Tel.: C46-90-786-86-01; fax: C46-90-78681-66. E-mail address: [email protected] (L.M. Berglund). 0038-0717/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2004.06.005

cycling and changes in species composition, plant growth and soil biota (Hart et al., 2004). The presence of fire in these forests has been reduced considerably due to active fire suppression and passive fire exclusion as a result of road building and changes in forest stand management. A prolonged absence of fire results in a change in understory species composition shifting to a predominance of dwarf ericaceous shrubs including Empetrum hermaphroditum Hagerup, a ground cover of feathermosses such as Pleurozium schreberi (Bird.) Mitt. and an increase in the presence of Norway spruce (Picea abies Karst. (L.)) in the overstory (Steijlen and Zackrisson, 1987; Linder et al., 1997; DeLuca et al., 2002). It is clear that fire temporarily increases N mineralization and nitrification rates (Neary et al., 1999; DeLuca and Zouhar, 2000; Choromanska and Deluca, 2001). The high

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L.M. Berglund et al. / Soil Biology & Biochemistry 36 (2004) 2067–2073

concentrations of available ammonium (NHC 4 ) present after fire are produced chemically by soil heating during fire and also by increased microbial activity following fire (Choromanska and DeLuca, 2002). A pulse of available K nitrate (NOK 3 ) occurs within a year after fire and since NO3 is not produced directly by heating this is commonly attributed to increased nitrification in excess of ammonium (Wan et al., 2001). The long-term effect of fire on N mineralization rates is not clear. Although fire appears to reduce stocks of mineralizable N (Monleon et al., 1997; Kaye and Hart, 1998; DeLuca and Zouhar, 2000) through volatilization and fuel combustion, other changes in N transformation are normally attributed to changes in the composition of plant communities and soil biota (Hart et al., 2004). Many of the dwarf shrubs commonly found in late successional Swedish boreal forests are known to produce large quantities of phenolic compounds (Gallet and Lebreton, 1995; Nilsson et al., 1998) that may directly influence nutrient turnover and microbial activity (Wardle et al., 1997). Polyphenolic compounds can affect N cycling by stimulating microbial soil processes. Microorganisms use polyphenols as a C source and with increased need of N this promotes N immobilization. Formation of protein– tannin complexes by polyphenolic compounds may also impede mineralization and help to build up thick mor layers of recalcitrant organic material (Northup et al., 1995). The influence of charcoal on maintaining N availability has been addressed by Wardle et al. (1998) and DeLuca et al. (2002). Fire-produced charcoal has a porous structure and sorptive surfaces which are shown to have the capacity to adsorb significant amounts of polyphenolic compounds (Zackrisson et al., 1996) and this effect is similar to commercially-produced activated carbon (AC). Such adsorption may result in deactivating the phenols through chemical condensation of the phenols (Piccolo et al., 1999) preventing toxic allelopatic effects and an increase in microbial activity due to accumulation of dissolved C as a food source and thereby increase mineralization. Charcoal has been shown to harbour and support specific or unique microbial communities (Pietika¨inen et al., 2000), although little is known on the functional differences of these special communities. The porous structure of charcoal has also been suggested to shelter microbial organisms from soil faunal predators (Wardle et al., 1998). Studies in our laboratory suggested that nitrification rates are directly influenced by the addition of AC, used as a surrogate for soil charcoal (DeLuca et al., 2002). In these

short-term studies, we only observed a nitrification response to AC at a relatively high and potentially unrealistic application rate and the work was performed at only one field site. Thus it is not clear if nitrification rates would be significantly altered by AC additions to forest soils at lower, naturally-occurring quantities. Furthermore, it was not clear whether the presence of birch (Betula pubescence Ehrh) litter (as is common in early succession) would also influence nitrification rates as has been found in studies involving aspen litter (Ste-Marie and Pare´, 1999). We hypothesized that charcoal would enhance rates of nitrification in boreal forest soils. We used AC, as a surrogate for natural-occurring fire-produced charcoal with the intention of investigating the effect of AC on net N mineralization and nitrification rates in Scots pine forests. We also attempted to determine whether these effects were related to AC adsorption of free phenolic compounds from the soil.

2. Materials and methods 2.1. Site descriptions Studies were conducted on a total of three forest stands in northern Sweden. All sites are situated in forests reserves within the northern boreal zone and consist of latesuccessional Pinus sylvestris L. dominated forest of ericaceous-cladina type on sandy glacial soils (Ahti et al., 1968), classified as either Typic or Entic Haplocryods. Pleurozium schreberi (Bird.) Mitt. and Cladina spp are the dominant bottom-layer moss and lichen taxa and the fieldlayer mainly consists of the ericaceous shrubs Empetrum hermaphroditum Hagerup and Vaccinium vitis-idaea L. Composite samples of the forest duff layer (Oe/Oa horizons) were collected at each site and analyzed for pH, total C and total N. General soil and site characteristics are presented in Table 1. 2.2. Laboratory study A laboratory incubation experiment was conducted to assess the influence of charcoal and litter on net N mineralization rates and nitrification rates in boreal soils under controlled conditions. Samples from humus layer were collected from the three P. sylvestris dominated sites. The humus was sieved (!5 mm) to remove coarse roots, mixed thoroughly and then air dried (20 8C) for 3 days.

Table 1 General soil and site characteristics for each site Site

Location

pH (GSE)

Humus C (%)

Humus N (%)

Soil C (%)

Soil N (%)

Reivo Vaksliden Stro¨mforsheden

65846 0 N, 19806 0 E 65842 0 N, 18845 0 E 65808 0 N, 18853 0 E

4.06 (0.03) 4.14 (0.02) 4.06 (0.06)

45.85 44.98 48.31

1.05 1.00 1.20

3.3 1.2 2.3

0.09 0.04 0.10

L.M. Berglund et al. / Soil Biology & Biochemistry 36 (2004) 2067–2073

Then 10 g of humus (dry weight) was placed in 300 ml (9 cm diameter) polyethylene jars. The humus was then amended with one of the following treatments: 1) 0 or 100 kg N haK1 as glycine (Sigma Scientific) as an organic N source; 2) 0 or 2000 kg AC haK1; 3) 0, or 1200 kg birch litter haK1. This combination of treatments resulted in a 2!2!2 factorial experiment of 6 replicates for each of the three sites, in total 144 jars. Treatments were applied by mixing each component thoroughly with humus and then placing the combined material into the polyethylene jar. The AC was applied as 1.28 g of activated C (representing 2000 kg haK1) added to each pot and the glycine was applied to the humus as a solution of 340 mg glycine (535 kg glycine haK1 representing 100 kg N haK1) mixed with distilled water. Dried birch leaf litter (Betula pubescence Ehrh) was fragmented (4–5 mm) and 800 mg was mixed into the humus. All the samples were adjusted to a moisture content of 60% of maximum water holding capacity (MWHC) and this was checked, and amended once a week during the experiment. The jars were covered with plastic lids with air-holes and incubated for 8 weeks at 13 8C and 70% relative humidity. At the end of the experiment soil samples were dried in 70 8C for 3 days and stored until analysis. 2.3. Field study Field experiments were carried out at the three latesuccession pine-dominated forests at forest reserves in northern Sweden. Treatments consisted of two rates (0 or 100 kg N haK1) of glycine (Sigma Scientific) as an organic N source and two rates (0 or 2000 kg AC haK1) of AC resulting in a 2 by 2 factorial experiment. With ten replicates of four treatments at three sites, this represent in total 120 plots. Treatments were applied to 20 cm!20 cm microplots from 0 to 10 cm depth within the forest floor as a solution (glycine) or suspension (AC) by using a 50 ml syringe with a 80 mm long, 2.10 mm wide steel needle. This approach allowed for rapid incorporation of the AC throughout the microplot with minimal disturbance to the forest floor. The AC treatment was applied as 200 ml of the 40 g AC lK1 suspension. The glycine treatment was applied as 100 ml of glycine solution (21.4 g glycine lK1). Distilled water was added at the same rate as in the glycine and AC treatment. Net N mineralization and nitrification were monitored in situ at these sites by using ionic resin capsules and free polyphenols were monitored in situ by using non-ionic carbonaceous resin capsules (DeLuca et al., 2002). This C approach allows NOK and polyphenols to be 3 , NH4 assessed over a specific period rather than taking a single point-in-time sample or using disruptive net N mineralization techniques. One polyester capsules containing 10 ml (approximately 1 g dwt) of mixed bed ionic resins (PST-2, Unibest, Bozeman, MT) were placed at the bottom of the Oa horizon or near the interface with the mineral soil in each

2069

microplot. Free phenols were monitored by placing one polyester capsule (Unibest, Bozeman, MT) filled with approximately 1 g dwt (about 1100 m2 of surface area) of XAD-7 resin (Rohm and Hass Inc., Philadelphia, PA), near the ionic resin capsule at the interface of the O horizon and mineral soil in each microplot. In total, 120 ionic and 120 non-ionic resin capsules were used. In order to locate the buried capsules, a thin nylon-line had been attached to each resin capsule and the line was then attached to a marker above ground when the capsule was buried. The resin capsules were allowed to remain in the field for 2.5 months from 11–18 June to 23 September, 2002. All capsules were then removed from each plot, and stored at K20 8C until analysis. 2.4. Chemical analyses Forest O horizon samples were analyzed for total C and N by dry combustion using an elemental analyzer (PerkinElmer 2400 CHN, Norwalk, Connecticut, USA). Soil pH was determined in distilled water using a 2:1 solution to soil ratio. Soil mineral N in 2.5 g of the incubated soil samples was extracted with 25 ml 2 M KCl on a shaker for 1 h, followed by filtration through Whatman No 42 filters. The extractable K NHC 4 and NO3 were then analyzed by using a segmented flow injection analyzer (Autoanalyzer III, Bran Luebbe, Chicago, K1 K IL) and reported as mg NHC . 4 –N or NO3 –N g soil C Ionic resin capsules were extracted for NH4 and NOK 3 analysis by placing each capsule into 10 ml of 1 M HCl and shaking for 30 min. The extracting solution was then decanted into a clean storage bottle and this process was repeated for a second and third time to create a total extraction volume solution of 30 ml. The extractant was K then analyzed for NHC 4 and NO3 as described above and C K reported as mg NH4 –N or NO3 –N capsuleK1. Non-ionic resin capsules were analyzed for polyphenols following a sequential extraction with water followed by 50% aqueous methanol (Morse et al., 2000). Each capsule was placed in a polypropylene centrifuge tube with 30 ml of distilled water, shaken for 30 min, and the aqueous fraction was decanted into a glass vial and stored at K20 8C until analysis. The resin capsule was then immersed in 10 ml of 50% aqueous methanol and shaken for 30 min. Extracts were decanted into clean glass vials and this process was repeated for a second and third time to create a total extraction volume of 30 ml. The methanol extracts were stored at K20 8C until analysis for polyphenolic compounds. Polyphenol analysis was performed by using the Prussian blue technique (Stern et al., 1996) measured against catechin standards at 720 nm. 2.5. Statistical analysis The N and polyphenol data were analyzed using ANOVA. All data were analyzed for normality and homogeneity of variance. Data found to violate assumptions

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L.M. Berglund et al. / Soil Biology & Biochemistry 36 (2004) 2067–2073 Table 2 Average pH in laboratory incubation from all three boreal forest sites, incubated for 8 weeks Treatment

pH

0 CC CL CG CCCL CLCG CCCG CCCGCL

3.62 3.88 3.85 5.59* 4.06 5.62* 5.75* 5.73*

0Zcontrol; CCZAC addition; CGZglycine addition. Values followed by an asterisk are significantly different at P!0.05. K1 Fig. 1. Average soil NOK soil) for all three boreal 3 –N concentration (mg g forest sites in northern Sweden after 8 weeks of incubation. 0Zcontrol, CCZAC addition, CGZglycine addition, CLZbirch litter addition. Values followed by an asterisk are significantly different at P!0.05.

of ANOVA were analyzed using the non-parametric Kruskal–Wallis test. Correlations were analyzed using Pearson’s correlation test. All data analyses were performed using SPSS Version 10.0 for Windows (SPSS Inc. Chicago, IL).

amendment of glycine and AC was 20% lower compared to when only glycine were added (Fig. 2). Birch litter resulted in the immobilization of added N (Fig. 2) and did not have a significant effect on net nitrification (Fig. 1). Addition of AC or birch litter did not significantly increase soil pH, but the addition of glycine resulted in a slight, yet significant increase in pH (Table 2). 3.2. Field study

3. Results 3.1. Laboratory incubation Amendment of soils with AC in the presence of glycine increased net nitrification compared to the control and in the treatment, where glycine was added alone (Fig. 1). The amount of NOK 3 in the presence of AC and glycine was K1 almost double (5–6 mg NOK compared to 3 mg 3 –N g soil K K1 NO3 –N g soil ) that in the control treatment. Although glycine greatly increased net ammonification (Fig. 2), this did not translate to an increase in nitrification unless AC was added. The amount of extractable NHC 4 –N in soil after

K1 Fig. 2. Average soil NHC soil) for all three boreal 4 –N concentration (mg g forest sites in northern Sweden after 8 weeks of incubation. 0Zcontrol, CCZAC addition, CGZglycine addition, CLZbirch litter addition. Values followed by different letters are significantly different at P!0.001.

Accumulation of NHC 4 on ionic resin capsules during the 2.5 months in the field was approximately 20 times higher in plots, where glycine had been added as an organic N source (Fig. 3). The glycine treatment also exhibited higher K1 ) than did the treatment amounts of NHC 4 –N (mg capsule with both glycine and charcoal (Fig. 3). The NOK 3 –N accumulation on ionic resin capsules in the field was small (Fig. 4) and there were no significant differences in the between treatments or amount of accumulated NOK 3 between sites. Total resin-sorbed polyphenols were significantly lower on plots, where AC and glycine were added in combination compared to the amounts in control plots (Fig. 5). Amendment of glycine increased the amount of resin-sorbed phenols. Despite this increase, AC did adsorb significant amounts of phenols. When AC was added alone

K1 Fig. 3. Average resin-sorbed NHC ) for all three boreal 4 –N (mg capsule forest sites in northern Sweden after 2.5 month in the field. 0Zcontrol, CCZAC addition, CGZglycine addition. Values followed by an asterisk are significantly different at P!0.01.

L.M. Berglund et al. / Soil Biology & Biochemistry 36 (2004) 2067–2073

K1 Fig. 4. Average resin-sorbed NOK ) for each of three 3 –N (mg capsule boreal forest sites in northern Sweden after 2.5 month in the field. 0Zcontrol, CCZAC addition, CGZglycine addition.

the amount of polyphenols was lower as well, although this effect was not statistically significant (Fig. 5). There was no clear correlation (data not shown) between net nitrification rates and total phenols in the field.

4. Discussion 4.1. Laboratory incubation Amendment of soils with AC in the presence of glycine increased net nitrification compared to the control and in the treatment, where glycine was added alone. Although glycine greatly increased net ammonification this did not result in an increase in nitrification unless AC was added. This positive effect by AC confirms the findings by DeLuca et al. (2002) and suggests that AC improves specific mechanisms or environmental conditions that otherwise limit the nitrification process and underscores the notion that net nitrification in boreal forests is not limited by availability of substrate (NHC 4 ). Nitrification in boreal humus depends on a range of factors such as pH

Fig. 5. Average sorption of free polyphenols (mg capsuleK1) for all three boreal forest sites in northern Sweden, after 2.5 month in the field. 0Zcontrol, CCZAC addition, CGZglycine addition. Values followed by different letters are significantly different at P!0.05.

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and moisture, and is generally thought to be substratelimited. Many studies have shown a strong correlation K between the amount of NHC 4 in the soil and NO3 conversion (Currie, 1999; De Boer and Kowalchuk, 2001). It is important to note that there was no increase in nitrification with glycine alone in spite of the increase NHC 4 hydrolysis induced increase in soil pH following rapid ammonification of the added glycine. Conversely, there was no increase in pH with addition of AC alone, but there was a significant increase in net nitrification when AC was added with glycine. This suggests that pH by itself is not a major determining factor for nitrification in our study, but may reflect some synergy between the AC and increased pH associated with the glycine. The positive effect of AC on nitrification could also be a result of the adsorption of phenolics, since phenolics have a generally negative effect on nitrifying bacteria (Paavolainen et al., 1998). The main negative effect of phenolics on nitrification is suggested to be inhibition of enzymes crucial for transformation of NHC 4 to NOK 3 (White, 1994). It is also plausible that nitrifiers aggregate around particles of AC, as AC can act as food source supply for microorganisms due to the adsorption of various soluble C substances. This aggregation of nitrifiers could then produce a biofilm structure essential for nitrification. De Boer et al. (1991), De Boer and Kowalchuk (2001) have suggested that nitrifiers in acid environment have developed a mechanism by which it is possible to escape the negative effect of low soil pH on nitrification via biofilm formation. Charcoal also have strongly hydrophobic characteristics and could, when mixed into soil, alter moisture conditions in soils, which may affect nitrifying bacteria (Tate, 1995). Fierer and Schimel (2002) studied the influence of repeated dry-wetting disturbance on nitrifying bacteria and found an increase in population size with increased number of disturbance events, and suggested that nitrifiers are more drought-tolerant than other bacteria. Our results show that the amount of extractable NHC 4 –N in soil after amendment of glycine and AC was 20% lower compared to when only glycine were added. Since nitrification increased with addition of AC, a part of the K extractable NHC 4 is oxidized to NO3 . However, this does not explain the whole difference, it is plausible that some of the glycine could have been adsorbed by AC. Birch litter resulted in an immobilization of added N. This could be due to the high glucose content in newly shed birch litter (Pietika¨inen et al., 2000) which increased microbial activity and subsequently increased the demand for N. This did not occur in the treatment with no N amendment, probably because here N was a limiting resource. The addition of birch litter to the soil did not have any significant effect on net nitrification. This result is somewhat surprising because we had expected an increase of nitrification after litter addition because birch stands are often associated with higher nitrification potential. Ste-Marie and Pare´ (1999) found that net nitrification rates in deciduous forest floors were significantly higher than in

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L.M. Berglund et al. / Soil Biology & Biochemistry 36 (2004) 2067–2073

nitrifying coniferous samples. The reason for the lack of response in our study could simply be due to the short time period and the fact that we used coniferous humus samples which could have buffered the nitrification response. 4.2. Field study Ammonium accumulation on ionic resin capsules during the 2.5 months in the field was approximately 20 times higher in plots, where glycine had been added as an organic N source. This was not surprising considering that boreal humus is generally assumed to be N limited, and glycine is an easily mineralized organic N source. The glycine treatment also exhibited higher amount of mg NHC 4 –N capsuleK1 than did the treatment with combined glycine and AC amendment. Although this effect was not statistically significant, it corresponds well to the results found in the soil incubation study which showed a hampering effect of AC. The NOK 3 –N accumulation on ionic resin capsules in the field was small and there were no significant differences in the amount of accumulated NOK 3 between treatments or between sites. This result diverges from the results found in the laboratory incubation and from field investigations that used higher rates of AC (DeLuca et al., 2002). Microbial assimilation and plant uptake from areas outside these microsites might have consumed excess of NOK 3 , and masked any increase in NOK 3 production. Thus, there might have been an increase in gross nitrification but not net nitrification. Stark and Hart (1997) demonstrated that there is large gross nitrification in late coniferous soil although the net nitrification is hardly detectable. In our previous field studie, a similar injection approach was used to distribute the AC, however, the rate that effectively altered nitrification was 5 times greater (DeLuca et al., 2002) than the rate used in this study, thereby allowing for greater coverage of the humus in the microplots. AC addition did reduce the amount of total free polyphenols in the soil. Total resin-sorbed polyphenols were significantly lower on plots, where AC and glycine were added in combination compared to the amounts in control plots. Amendment of glycine increased the amount of resin-sorbed phenols, probably because glycine may have increased decomposition of polyphenolic compound and thus increased the amount of free phenolics. Despite this increase, AC did adsorb significant amounts of phenols. However, the amount of polyphenols accumulated on the resin capsules was highly variable and there was a site by treatment interaction. There was no clear correlation between net nitrification rates and total phenols in the field as was found by DeLuca et al. (2002). Total free phenols are a large and variable group of compounds, so it is likely that only some of the phenolic compounds influence nitrification. Further work would have to be performed to determine how soluble phenolic compounds in boreal forest soils actually influence nitrifier activity.

5. Conclusions We conclude that charcoal exhibits important characteristics that affect regulating steps in N cycling. In this study we found that nitrification was limited both by a lack of available NHC 4 and a physical or biochemical factor that was altered by the AC amendment. Further studies are being conducted to elucidate the mechanism responsible for charcoal induced nitrification. Understanding how N is regulated in fire-dominated ecosystems is important given the dramatically altered fire regimes in northern Sweden, as well as other portions of the globe, over the last century.

Acknowledgements The authors wish to thank Derek MacKenzie and Tracie Graafstra for their efforts in the laboratory.

References Ahti, T., Ha¨met-Ahti, L., Jalas, J., 1968. Vegetation zones and their sections in Northwestern Europe. Annales Botanici Fennici 5, 169–211. Choromanska, U., Deluca, T.H., 2001. Prescribed fire alters the effect of wildfire on soil biochemical properties in a ponderosa pine forest. Soil Science Society of America Journal 65, 232–238. Choromanska, U., DeLuca, T.H., 2002. Microbial activity and nitrogen mineralization in forest mineral soils following heating: evaluation of post-fire effects. Soil Biology & Biochemistry 34, 263–271. Currie, W.S., 1999. The responsive C and N biogeochemistry of the temperate forest floor. Trends in Ecology and Evolution 14, 316–320. De Boer, W., Kowalchuk, G.A., 2001. Nitrification in acid soils: microorganisms and mechanisms. Soil Biology & Biochemistry 33, 853–866. De Boer, W., Klein Gunnewiek, P.J.A., Veenhuis, M., Bock, E., Laanbroek, H.J., 1991. Nitrification at low pH by aggregated autotrophic bacteria. Applied and Environmental Microbiology 57, 3600–3604. DeLuca, T.H., Zouhar, K.L., 2000. Effects of selection harvest and prescribed fire on the soil nitrogen status of ponderosa pine forests. Forest Ecology and Management 138, 263–271. DeLuca, T.H., Nilsson, M.-C., Zackrisson, O., 2002. Nitrogen mineralization and phenol accumulation along a fire chronosequence in northern Sweden. Oecologia 133, 206–214. Fierer, N., Schimel, J.P., 2002. Effects of drying-rewetting frequency on soil carbon and nitrogen transformations. Soil Biology & Biochemistry 34, 777–787. Gallet, C., Lebreton, P., 1995. Evolution of phenolic patterns in plants and associated litters and humus of a mountain forest. Soil Biology & Biochemistry 27, 157–165. Hart, S.C., DeLuca, T.H., Newman, G.S., MacKenzie, M.D., Boyle, S.I., 2004. Post-fire vegetative dynamics as drivers of microbial community structure and function in forest soils. Forest Ecology and Management 2004 (in press). Kaye, J.P., Hart, S.C., 1998. Ecological restoration alters nitrogen transformations in a ponderosa pine-bunchgrass ecosystem. Ecological Applications 8, 1052–1060. Linder, P., Elfving, B., Zackrisson, O., 1997. Stand structure and successional trends in virgin boreal forest reserves in Sweden. Forest Ecology and Management 98, 17–33.

L.M. Berglund et al. / Soil Biology & Biochemistry 36 (2004) 2067–2073 Monleon, V.J., Cromack Jr.., K., Landsberg, J.D., 1997. Short- and longterm effects of prescribed underburning on nitrogen availability in ponderosa pine stands in central Oregon. Canadian Journal of Forest Research 27, 369–378. Morse, C.C., Yevdokimov, I.V., DeLuca, T.H., 2000. In situ extraction and analysis of rhizosphere carbon of native and invasive plant species. Community of Soil Science and Plant Analysis 31, 725–742. Neary, D.G., Klopatek, C.C., DeBano, L.F., Ffolliott, P.F., 1999. Fire effects on belowground sustainability: a review and synthesis. Forest Ecology and Management 122, 51–71. Nilsson, M.-C., Gallet, C., Wallstedt, A., 1998. Temporal variability of phenolics and batatasin III in Empetrum hemaphroditum leaves over an eight year period: interpretation of ecological function. Oikos 81, 6–16. Northup, R., Yu, Z., Dahlgren, R.A., Vogt, K., 1995. Polyphenol control of nitrogen release from pine litter. Nature 377, 227–229. Paavolainen, L., Kitunen, V., Smolander, A., 1998. Inhibition of nitrification in forest soil by monoterpens. Plant and Soil 205, 147–157. Piccolo, A., Spaccini, R., Haberhauer, G., Gerzabek, M.H., 1999. Increased sequestration of organic carbon in soil by hydrophobic protection. Naturwissenschaften 86, 496–499. Pietika¨inen, J., Kiikkila¨, O., Fritze, H., 2000. Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus. Oikos 89, 231–242. Stark, J.M., Hart, S.C., 1997. High rates of nitrification and nitrate turnover in undisturbed coniferous forests. Nature 385, 61–64.

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Steijlen, I., Zackrisson, O., 1987. Long-term dynamics and successional trends in a northern Swedish coniferous forest stand. Canadian Journal of Botany 65, 879–898. Ste-Marie, C., Pare´, D., 1999. Soil pH and N availability effects on net nitrification in the forest floors of a range of boreal forest stands. Soil Biology & Biochemistry 31, 1575–1589. Stern, J.L., Hagerman, A.E., Steinber, P.D., Winter, F.C., Estes, J.A., 1996. A new assay for quantifying brown algal phlorotannins and comparisons to previous methods. Journal of Chemical Ecology 22, 1273–1294. Tate, R.L., 1995. Soil Microbiology. Wiley, New York. Wan, S., Hui, D., Luo, Y., 2001. Fire effects on nitrogen pools and dynamics in terrestrial ecosystems: a meta-analysis. Ecological Applications 11, 1349–1365. Wardle, D.A., Zackrisson, O., Ho¨rnberg, G., Gallet, C., 1997. The influence of island area on ecosystem properties. Science 277, 1296–1299. Wardle, D.A., Zackrisson, O., Nilsson, M.-C., 1998. The charcoal effect on boreal forests: mechanisms and ecological consequences. Oecologia 115, 419–426. White, C.S., 1994. Monoterpens- their effect on ecosystem nutrient cycling. Journal of Chemical Ecology 20, 1381–1406. Zackrisson, O., 1977. Influence of forest fires on the north Sweden boreal forest. Oikos 29, 22–32. Zackrisson, O., Nilsson, M.-C., Wardle, D.A., 1996. Key ecological function of charcoal from wildfire in the boreal forest. Oikos 77, 10–19.

Biol Fertil Soils (2007) 43:303–311 DOI 10.1007/s00374-006-0106-5

ORIGINAL PAPER

Charcoal effects on soil solution chemistry and growth of Koeleria macrantha in the ponderosa pine/Douglasfir ecosystem Michael J. Gundale & Thomas H. DeLuca

Received: 26 July 2005 / Revised: 10 April 2006 / Accepted: 12 April 2006 / Published online: 3 June 2006 # Springer-Verlag 2006

Abstract We conducted laboratory and greenhouse experiments to determine whether charcoal derived from the ponderosa pine/Douglas-fir ecosystem may influence soil solution chemistry and growth of Koeleria macrantha, a perennial grass that thrives after fire. In our first experiment, we incubated forest soils with a factorial combination of Douglas-fir wood charcoal generated at 350°C and extracts of Arctostaphylos uva-ursi with and without the addition of glycine as a labile N source. These results showed that charcoal increased N mineralization and nitrification when glycine was added, but reduced N mineralization and nitrification without the addition of glycine. Charcoal significantly reduced the solution concentration of soluble phenols from litter extracts, but may have contributed bioavailable C to the soil that resulted in N immobilization in the no-glycine trial. In our second experiment, we grew K. macrantha in soil amended with charcoal made at 350°C from ponderosa pine and Douglasfir bark. Growth of K. macrantha was significantly diminished by both of these charcoal types relative to the control. In our third experiment, we grew K. macrantha in soil amended with six concentrations (0, 0.5, 1, 2, 5, and 10%) of charcoal collected from a wildfire. The data showed increasing growth of K. macrantha with charcoal addition, suggesting some fundamental differences between M. J. Gundale (*) : T. H. DeLuca Department of Ecosystem and Conservation Sciences University of Montana, 32 Campus Drive, Missoula, MT 59812, USA e-mail: [email protected] T. H. DeLuca e-mail: [email protected]

laboratory-generated charcoal and wildfire-produced charcoal. Furthermore, they suggest a need for a better understanding of how temperature and substrate influence the chemical properties of charcoal. Keywords Charcoal . Soil solution chemistry . Douglas-fir and ponderosa pine ecosystems

Introduction It is well-established that fire alters N cycling in the ponderosa pine/Douglas-fir (Pinus ponderosa/Psuedotsuga menziesii) ecosystem (Neary et al. 1999; Hart et al. 2005). Nitrogen availability has been shown to increase immediately after fire (Covington and Sackett 1990, 1992; DeLuca and Zouhar 2000) and may remain elevated on the scale of months to years as a result of enhanced mineralization (Covington and Sackett 1990, 1992; Monleon et al. 1997; Kaye and Hart 1998; Gundale et al. 2005). Numerous processes that increase N mineralization after fire have been identified, including improved substrate quality (White 1991, 1994; Fernandez et al. 1997; Pietikainen et al. 2000a), death of roots and soil organisms resulting in a large labile organic N pool (DeBano et al. 1979; Dunn et al. 1979; Diaz-Ravina et al. 1996; Neary et al. 1999), and a reduction in C to N ratios due to preferential loss of C during combustion (Gundale et al. 2005). A potentially overlooked factor that may also enhance N cycling after fire is the addition of charcoal to soils. Several recent studies have shown that charcoal has the potential to greatly enhance soil fertility. Amazonian forest soils amended centuries ago with charcoal and manure still maintain some of the highest biodiversity and productivity

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of any soils within the Amazon basin (Glaser et al. 2001, 2002; Mann 2002). In boreal forest soils, charcoal was shown to enhance N cycling by ameliorating the inhibitory effects of litter extracts from late-successional species, which in turn promotes growth of early-successional species (Zackrisson et al. 1996; Wardle et al. 1998; DeLuca et al. 2002; Berglund et al. 2004). Recently, DeLuca et al. (2006) found that the addition of wildfire-formed charcoal to ponderosa pine forest soils increased nitrification rates. Charcoal may enhance soil fertility through a variety of mechanisms. Increased N turnover may occur by charcoal sorption of high C:N organic molecules from the soil solution (Zackrisson et al. 1996; Wardle et al. 1998; Glaser et al. 2002), resulting in reduced microbial N immobilization and higher net mineralization and nitrification rates. In addition, charcoal may remove specific groups of organic molecules, including polyphenol or monoterpene compounds that are thought to inhibit nitrification (Rice and Pancholy 1972; Zackrisson et al. 1996; DeLuca et al. 2002; Berglund et al. 2004). Sorption of organic molecules, along with the gradual breakdown of charcoal, may initiate humus formation and, thus, enhance long-term soil fertility (Glaser et al. 2002). Charcoal may also enhance soil fertility by creating habitat for microbes within its porous structure (Pietikainen et al. 2000b). Despite these potential roles that charcoal may have in increasing soil fertility, its ecological role in forest ecosystems, such as ponderosa pine/Douglas-fir, has received little attention. We conducted three separate experiments using low-temperature charcoal to investigate whether charcoal influences soil solution chemistry and growth of an early successional species. In our first experiment, our objective was to determine whether charcoal had an influence on soil solution chemistry after addition of the extracts of a late successional species, Arctostapholos uvi-ursi, via surface adsorption of phenolic compounds. We hypothesized that charcoal added to a ponderosa pine forest soil will effectively sorb the phenol fraction in litter extracts, which would correspond with enhanced N cycling. In our second experiment, our objective was to compare the influence of charcoal made from the bark of two species, ponderosa pine and Douglas-fir, on growth of Koeleria macrantha, a perennial grass species that thrives after fire disturbance in western Montana ponderosa pine/ Douglas-fir forests. Bark charring during low-intensity wildfire is a potentially significant source of charcoal in this system. Charred bark may gradually slough from trees after fire and become incorporated in the soils surrounding trees. It is recognized that ponderosa pine is a more fireadapted species than Douglas-fir; thus, an intriguing hypothesis is that charred bark of the more fire-adapted species will have a stronger positive effect on N cycling processes and plant growth.

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In our third experiment, our objective was to determine whether charcoal generated during a wildfire would have any effect on K. macrantha growth and to determine whether this relationship is dependent on soil charcoal concentration. We hypothesized that wildfire charcoal will positively influence K. macrantha and that this effect will increase as a function of soil charcoal concentration. Collectively, these three experiments address our central hypothesis that charcoal will alter solution chemistry by sorbing phenols and enhancing N cycling, which in turn will improve the growth of early successional species.

Materials and methods All three experiments utilized field-collected soil, which was collected from the subsurface horizon (20–30 cm, Bw Horizon) of a forest soil associated with low elevation (1,100 m) ponderosa pine/Douglas-fir vegetation in western Montana, USA. The soil is a sandy-skeletal, mixed, frigid Typic Dystrustepts. This ecosystem is characterized by low annual rainfall (<350 mm annually) with approximately 50% falling as snow during the winter months. Soil was collected during the month of September, returned to the lab, upon which they were sieved (4 mm) and homogenized. We then added one part sand to three parts field moist soil (by mass) to decrease fertility and increase porosity and gas exchange, such that nitrification would not be limited by low O2 availability. The sand fraction was purchased as filter grade silica sand (for pool filters) and was washed with 1 M HCl, followed by distilled water, before being homogenized with field collected soil. This sand-amended soil had a pH of 6.8, electrical conductance of 91.2 μS m−1, and had a textural distribution of 71% sand, 21% silt, and 8% clay. All experiments also included the addition of either laboratory-generated charcoal from Douglas-fir and ponderosa pine or charcoal collected in the field after a wildfire. Laboratory charcoal was generated by burying wood or bark from these species in silica sand and heating at 350°C for 2 h. Charcoal was then ground and sieved as specified for each experiment. Various physical and chemical properties of these charcoals were measured (Table 1). Charcoal pH was measured from a 4:1 slurry of deionized water to charcoal. Electrical conductance (EC) was measured from charcoal paste (2:1 distilled water and charcoal). Cation exchange capacity (CEC) was estimated on charcoal samples via NHþ 4 replacement where 1 g of charcoal was rinsed twice with 25 ml of 1 M ammonium acetate (pH 7) to saturate exchange sites. Excess saturating solution was removed from charcoal samples with three consecutive washes with 25 ml of 95% ethyl alcohol. Sorbed NHþ 4 was then extracted with 25 ml of 2 M KCl and analyzed on a segmented flow analyzer (Auto

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Table 1 Chemical properties of four charcoal types (df Douglas-fir, pp ponderosa pine, wildfire wildfire collected) used in the laboratory and greenhouse experiments

pH EC (μS g−1) CEC (cmolc kg−1) Density (g cm−3) Total C (%) Soluble phenols (μg g−1) Total phenols (μg g−1) −1 PO3 4 (μg g ) −1 þ NH4 (μg g ) −1 NO 3 (μg g )

df Wood

df Bark

pp Bark

Wildfire

4.15 20.5 20.66 0.30 72.9 34.9 441.7 0.94 7.12 0.12

4.18 24.2 19.42 0.08 72.4 30.7 148.1 0.84 9.0 0.3

4.81 111.6 34.48 0.21 71.5 43.4 810.4 2.46 5.6 0.0

5.74 141.5 29.35 0.29 82.3 48.2 393.8 0.95 38.3 4.4

Analyzer III, Bran Luebbe, Chicago, IL) using the Berthelot reaction (Willis et al. 1993). Charcoal density was measured by measuring dry mass of intact charcoal pieces and measuring volume displacement in deionized water. Total C was measured via dry combustion on a Fissions Elemental Analyzer (Milano, Italy). Soluble and total phenols were measured by extracting 1 g of ground charcoal in 25 ml of deionized water and 50% methanol, respectively, and were analyzed using the Prussian Blue Method (Stern et al. 1996).  Extractable NHþ 4 and NO3 (Mulvaney 1996) were extracted by shaking 1 g of charcoal for 30 min in 25 ml of 2 M KCl, and then filtering through Whatman #2 filters. The extracts were analyzed for NHþ 4 –N using the Berthelot reaction (Willis et al. 1993) and NO 3 –N by the cadmium reduction method (Willis and Gentry 1987) on a segmented flow analyzer (Auto Analyzer III). Soluble PO3 4 was extracted by placing 1 g of charcoal in 25 ml of 0.01 M CaCl2 for 30 min. Extracts were filtered through Whatman #42 filter paper and then analyzed on a segmented flow analyzer using the molybdate method as described by Kuo (1996). Experiment 1: charcoal sorption potential We conducted a laboratory incubation study using the soil described above, where Douglas-fir charcoal and extract of Arctostaphylos uva-ursi were added in a factorial combination yielding four treatments (Charcoal/Extract, Charcoal/ No extract, No Charcoal/Extract, and No Charcoal/No extract). Each treatment was replicated five times and consisted of 300 g of soil and placed into mason jars. The treatments receiving charcoal addition received a 2% charcoal amendment (20 g/kg). Charcoal was generated in a muffle furnace by submerging Douglas-fir wood in sand and heating it at 350°C for 2 h. Charcoal was ground and sieved through a 4.75-mm sieve. A. uva-ursi extract was made by extracting 100 g of A. uva-ursi leaves in 1 l of deionized water for 24 h and filtering this extract through Whatman #42 filters. The total phenol concentration of this

extract was 267.5 mg/l. Extract treatments received 25 ml of this extract. No-extract treatments received an equivalent volume of deionized water. Soils were homogenized following this addition. This addition brought the soil in each mason jar to a water content of approximately 60% WHC. Mason jars were incubated in the dark for 14 days after which a portion of the soil was extracted and analyzed. This entire experiment was repeated exactly as described above but with glycine added to all mason jars as a source of highly labile organic N to stimulate a more marked N response. Glycine, a simple amino acid that is readily mineralized to NHþ 4 , was added to each mason jar at a rate of 75 mg/jar (250 mg/kg of soil). These two experiments will hereafter be referred to as the glycine and no-glycine trials. Experiment 2: effects of bark charcoal on plant growth This greenhouse experiment consisted of three treatments (Douglas-fir charcoal, ponderosa pine charcoal, and a control) using the sand-amended soil described above to evaluate the influence of charcoal source on K. macrantha. Each treatment consisted of 20 replicate pots where each pot received 1.5 kg of soil, and charcoal treatments received a 2% (by mass) charcoal amendment. One percent of this charcoal was homogenized into the soil, while the other 1% was evenly distributed on the soil surface. We made charcoal from Douglas-fir and ponderosa pine in the laboratory by burying bark of each species in silica sand and heating to 350°C in a muffle furnace for 2 h. Charcoal was ground and sieved (<1 mm) using a Wiley mill. Organic horizons (Oi, Oe, and Oa) were added to the surface of each pot to add an additional and substantial mineralizable pool of plant essential nutrients, as well as to provide a source of bioavailable organic C that may influence soil nutrient transformations. This organic material was randomly collected (as described in Gundale et al. 2005) from a ponderosa pine/Douglas-fir forest that had not been exposed to fire for approximately 80 years and originated from numerous species, including understory and overstory species, but appeared to be primarily composed of undecomposed ponderosa pine and Douglas-fir litter. The organic material was homogenized and 100 g was added to the surface of each pot. A mixed bed ionic resin capsule (Unibest, Bozeman, MT) was placed in the center of each pot to sorb nutrients throughout the duration of the experiment. K. macrantha was grown in these pots between October 2004 and March 2005 under ambient light conditions. An average greenhouse temperature of 21°C was maintained. K. macrantha seeds (Western Native Seeds, Coaldale, CO) were germinated in a separate soil medium, and a single seedling was transplanted into each pot. Pots were watered 3 days a week throughout the duration of the experiment. At

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the end of the experiment, resin capsules were recovered, and soil was rinsed from roots. Plants were oven-dried at 65°C, and above- and belowground masses were measured. Experiment 3: effect of wildfire charcoal on plant growth Charcoal collected from a wildfire site was added to the soil described above at a rate of 0, 0.5, 1, 2, 5, and 10%, and placed in greenhouse pots seeded with K. macrantha to determine whether an increase in soil charcoal content has any influence on the growth of K. macrantha. Each treatment (n=10) was established by adding 1.0 kg of charcoal-amended soil per pot. The charcoal used in this experiment differed from both previous experiments because it was collected after a wildfire rather than generated in the laboratory. Large particles (>5-cm diameter) of charcoal were collected in the spring of 2004 from the Black Mountain Fire (August 2003), Missoula, MT, (DeLuca et al. 2006). It was impossible to decipher the species origin of this charcoal, but it was likely primarily Douglas-fir and ponderosa pine wood and bark char. The charcoal particles were crushed, using a mallet, producing fragments ranging from a diameter of 2 cm to microscopic. No attempt was made to discriminate against any size class in an attempt to simulate the range of charcoal particle sizes likely incorporated into the soil under natural conditions. Organic horizon materials (50 g) were collected from a forest stand not exposed to fire for over 80 years and added to the surface of each pot as described earlier. All other experimental conditions were run identically to experiment 2. Laboratory analyses At the end of experiment 1, 30 g of soil were extracted with  2 M KCl and analyzed for NHþ 4 and NO3 as described above. Amino N was measured on these same extracts using the ninhydrin method (Moore 1968). Soluble phenols were extracted by shaking 30 g of soil for 1 h with 50 ml of deionized water followed by filtration. Sorbed phenols were extracted by shaking 30 g of soil with 50% methanol for 24 h followed by filtration. Phenols in these extracts were measured using the Prussian blue method (Stern et al. 1996). Respiration was measured at the end of the incubation by incubating 50 g dry weight equivalent soil in a sealed container with 20 ml 1 M NaOH traps for 3 days (Zibilske 1994). Mixed bed ionic resin capsules (Unibest) were used in  experiments 2 and 3 to determine solution NHþ 4 ; NO3 , and  PO4 throughout the duration of the experiments. Capsules were placed in the center of each pot, directly beneath each plant, and were removed and extracted in 10 ml of 2-M KCl  three consecutive times. We analyzed NHþ 4 ; NO3 , and 3 PO4 from these extracts as described previously.

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Statistical analyses Data in experiment 1 meeting assumptions of normality and homoscedasticity were analyzed using two-factor analysis of variance (ANOVA), where extract and charcoal were entered as fixed factors under the general linear model. Variables not meeting these assumptions were analyzed using a Kruskal–Wallis test (K–W test). This analysis tests for differences among treatments but does not evaluate the significance of individual factors or interactions between factors. Data in experiments 2 and 3 were analyzed using onefactor ANOVA followed by the Student–Newman–Keuls post hoc procedure. Different letters are used to display post hoc differences. Data not meeting assumption of normality and homoscedasticity were compared using K–W tests, which were not followed by post hoc procedures. All analyses were conducted using SPSS 12.0 software.

Results and discussion Experiment 1: low temperature charcoal sorption potential Both charcoal and litter extract significantly influenced numerous soil chemical variables (Fig. 1). In both glycine and no-glycine trials, litter extract negatively influenced extractable NO 3 concentrations. The negative influence of A. uva-ursi on extractable NO 3 reported here is consistent with our previous studies in ponderosa pine forest soils (DeLuca et al. 2006) and with studies that showed that litter from late-successional boreal species, such as the ericaceous shrub Empetrum hermaphroditum, diminishes net nitrification (DeLuca et al. 2002; Berglund et al. 2004). Charcoal had an unexpected negative effect on NO 3 in the no-glycine trial. In contrast, the addition of charcoal increased NO 3 concentrations in the glycine trial. These results may be a function of the charcoal we used in this study, which was generated at a low temperature (350°C). Charcoal contains a significant concentration of bioavailable C, specifically soluble phenols (Table 1) that may have caused net NO 3 immobilization (Schimel et al. 1996) in the no-glycine trial where low NHþ 4 concentrations existed (Rice and Tiedje  1989). The NO3 immobilization effect did not occur in the glycine trial because NHþ 4 limitations were drastically reduced with glycine addition. In addition, higher rates of nitrification in the glycine trial likely occurred because this process was not limited by a lack of substrate availability (glycine additions resulted in high NHþ 4 concentrations). The higher rate of nitrification associated with charcoal in the glycine trial is consistent with the finding reported by DeLuca et al. (2006), which suggests that charcoal may sorb compounds from litter extract and the soil solution that

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307

20

200

Extractable N (µg g-1)

a

Amino N NH4+

15

NO3-

10

Amino N Charcoal * Extract *** Charcoal x Extract ** 150 Ammonium KW test *** Nitrate Charcoal *** 100 Extract *** Charcoal x Extract *

5

50

0

0 20

20

Phenols (µg g-1)

c

Soluble Phenols Sorbed Phenols

15

Soluble Phenols KW test ** Sorbed Phenols Charcoal *** Extract *** Charcoal x Extract NS

15

10

5

5

0

0 0.5

e

-1

Soluble Phenols KW test * Sorbed Phenols Charcoal *** Extract ** Charcoal x Extract NS

d

10

0.5

Respiration (µg CO day )

Amino N Charcoal *** Extract * Charcoal X Extract NS Ammonium Charcoal *** Extract ** Charcoal x Extract NS Nitrate KW test ***

b

Respiration Charcoal NS Extract * Charcoal x Extract NS

0.4

2

0.4

Respiration Charcoal NS Extract NS Charcoal x Extract **

f

0.3

0.3

0.2

0.2

0.1

0.1

0.0

0.0

S

S+E

S+C

S+C+E

No-Glycine Trial

S

S+E

S+C

S+C+E

Glycine Trial

Fig. 1 Extractable amino N, NH4þ , and NO 3 [mean (SE)] without (a) and with (b) glycine addition; soluble (water extracted) and sorbed phenols (methanol extracted) [mean (SE)] without (c) and with (d) glycine addition; and basal soil respiration [mean (SE)] without (e) and with (f) glycine addition, from a 14-d soil incubation experiment where soils were amended with a factorial combination of charcoal and extracts from Arctostaphylos uva-ursi leaves (S soil only, S+E soil plus extract, S+C soil

plus charcoal, S+C+E soil plus charcoal plus extract). Data were analyzed with a two-factor ANOVA where significance was tested for Charcoal, Extract, and Charcoal × Extract interaction. Data that did not meet parametric assumptions of normality or homoscedasticity were analyzed using a Kruskal–Wallis (KW) test. Asterisks represent statistical significance (p value, ns >0.1, *<0.05, **<0.01, ***<0.001)

are inhibitory to nitrifying bacteria, or sorb carbon-rich molecules that would otherwise stimulate microbial immobilization of N. A. uva-ursi extract had a strong positive effect on NHþ 4 in both no-glycine and glycine trials because it likely contained some NHþ 4 and substrates that are rapidly mineralized to NHþ . Charcoal had a strong negative effect 4 þ on NH4 in both no-glycine and glycine trials. The

mechanisms for this pattern may differ between the two trials. In the no-glycine trial, the most likely explanation for reduced NHþ 4 is that immobilization occurred as a function of N limitations in these soils. In the glycine trial, higher rates of nitrification associated with charcoal likely contributed to lower NHþ 4 concentrations. Both charcoal and extract significantly influenced concentrations of amino N that represent a highly labile

308

Biol Fertil Soils (2007) 43:303–311

Table 2 Plant mass and resin sorbed nutrients (mean±SE, n=20) from a greenhouse experiment where soil was amended with 2% charcoal made from Douglas-fir (df) and ponderosa pine (pp) bark at 350°C

Total mass (g) Root mass (g) Aboveground mass (g) Root to shoot ratio NHþ 4 (μg resin capsule−1) NO 3 (μg resin capsule−1)

PO3 4 (μg resin capsule−1)

df Charcoal

pp Charcoal

no Charcoal

p value

a1.6 (0.2) a0.8 (0.1) a0.7 (0.1)

a1.9 (0.1) a0.9 (0.1) b1.0 (0.1)

b2.5 (1.0) b1.2 (0.1) c1.3 (0.1)

<0.001 <0.05 <0.001

a1.1 (0.1)

b0.9 (0.1)

b0.9 (0.1)

<0.01

a4.6 (0.9)

b1.4 (0.6)

b2.2 (0.8)

<0.05

a1,770.8 (286.2) a5.1 (1.4)

b935.8 (241.9) a5.6 (0.9)

b581.5 (211.8) b0.5 (1.2)

<0.01 <0.05

Letters in bold indicate differences using the Student–Newman–Keuls post hoc procedure

fraction of organic N that can be rapidly mineralized. Glycine, which is a simple amino N molecule, stimulated rapid rates of N mineralization and resulted in increased amino N concentrations, which suggests that the added glycine was not completely utilized and that substrate limitations were eliminated during this trial. In glycine and no-glycine trials, the litter extract resulted in higher concentrations of amino N to soils. The effect of charcoal on amino N, however, differed in glycine and no-glycine trials. In the no-glycine trial, charcoal significantly increased amino N concentrations. This response may have occurred because charcoal sorbed phenolic molecules that otherwise would form insoluble complexes with amino N groups. In contrast, charcoal had a negative effect on amino N in the glycine trial, which is likely the result of charcoal enhancing microbial utilization of glycine. As expected, A. uva-ursi extract significantly increased phenols (soluble and sorbed) in both trials. The addition of charcoal to soil significantly diminished the soluble phenol concentration while increasing the pool of sorbed phenol. This result is consistent with several studies in the boreal forest that have demonstrated a high capacity of charcoal to adsorb phenolic compounds (Zackrisson et al. 1996; Wardle et al. 1998; DeLuca et al. 2002; Berglund et al. 2004). Solubility of these fractions likely influences the degree to which they are bioavailable and, therefore, their ability to interfere with N transformations (Harborne 1997). It is interesting to note that total phenols (sorbed and soluble) was higher in the charcoal-only treatment of both trials than the control, demonstrating that charcoal itself adds a substantial amount of total phenol to the soil (Table 1). These phenols are likely derived from the components of

wood, such as lignin that are degraded during charcoal formation. It is unclear what effect these phenols have on soil processes, but it is likely that they could be utilized as a food source by microbes, stimulating N immobilization. Soil respiration showed little response to charcoal in glycine or no-glycine trials. In the no-glycine trial, the extract significantly increased soil respiration. Extract and charcoal had no individual effect on soil respiration in the glycine trial; however, the interaction between charcoal and extract showed a significant effect. We speculate that this response may reflect that amines and degradable carbon substrates were better utilized by microbes when phenolic molecules in the same extract were sorbed by charcoal. These data demonstrate that low-temperature charcoal effectively sorbs soluble phenols from A. uva-ursi extracts, which in turn stimulates nitrification, provided nitrification is not substrate-limited. Our results are consistent with Berglund et al. 2004 and DeLuca et al. (2002), who showed that the effect of charcoal on nitrification only occurred when a labile N source was also present. These studies are also consistent with the Terra Preta phenomenon reported in the Amazonian basin where charcoal and manure (high labile N concentration) were historically incorporated into the soil (Glaser et al. 2001, 2002). Today, these soils maintain the highest fertility in the region, which may in part be a function of the interactive effect of charcoal and manure. Experiment 2: effects of bark charcoal on plant growth In this experiment, we unexpectedly found that charcoal from both species diminished growth of K. macrantha relative to the control with reduced mass in both aboveground and belowground growth (Table 2). K. macrantha growing in pots with Douglas-fir charcoal had a significantly higher root to shoot ratio than the other treatments that appeared to be primarily driven by low aboveground biomass. This data suggests that there is likely no difference in the effect of ponderosa pine and Douglas-fir charcoal on plant species in this ecosystem.  We found that resin-sorbed NHþ 4 and NO3 were significantly higher in the Douglas-fir charcoal treatment relative to the ponderosa pine charcoal treatment and the control. Resin-sorbed PO3 4 was significantly higher in both Douglas-fir and ponderosa pine charcoal treatments than the control. These results may be interpreted in several ways. First, they may indicate higher mineralization and nitrification rates in the presence of charcoal as suggested by experiment 1. If higher mineralization occurred in the presence of charcoal, it is unclear why a corresponding increase in plant growth did not occur. It is possible that some toxic substance was generated during charcoal formation that inhibited root growth of K. macrantha, despite a positive effect on nutrient availability (Fritze et al.

Biol Fertil Soils (2007) 43:303–311

309

Table 3 Plant mass and resin sorbed nutrients (mean±SE, n=10) from a greenhouse experiment where soil was amended with 0, 0.5, 1, 2, 5, and 10% charcoal collected from a wildfire Percent charcoal

Total mass (g) Root mass (g) Aboveground mass (g) Root to shoot ratio −1 NHþ 4 (μg resin capsule )  NO3 (μg resin capsule−1) −1 PO3 4 (μg resin capsule )

0%

0.5%

1%

2%

5%

10%

p

a0.5 (0.2) 0.3 (0.2) a0.2 (0.1) 1.5 (0.2) 55.6 (4.0) a1,539.8 (463.4) a10.1 (1.4)

ab1.0 (0.3) 0.6 (0.2) ab0.4 (0.1) 1.5 (0.3) 49.8 (4.6) b947.9 (128.4) a8.8 (2.1)

ab1.1 (0.2) 0.7 (0.1) ab0.4 (0.1) 1.8 (0.2) 36.9 (6.0) bc552.3 (116.3) ab5.8 (1.2)

ab1.1 (0.2) 0.7 (0.1) ab0.4 (0.1) 1.7 (0.3) 42.7 (2.2) bc556.1 (93.4) ab6.5 (1.7)

b1.3 (0.1) 0.8 (0.1) b0.5 (0.1) 1.6 (0.2) 43.0 (1.3) bc561.8 (278.7) bc1.7 (1.0)

b1.4 (0.1) 0.8 (0.1) b0.6 (0.1) 1.3 (0.1) 44.4 (2.9) c248.6 (29.8) c0.0 (1.2)

<0.05 >0.05 <0.01 >0.05 <0.05a <0.001 <0.001

Letters in bold indicate differences using the Student–Newman–Keuls post hoc procedure All p values are for one-way ANOVA, unless otherwise noted a Kruskal–Wallis test p value

1998; Villar et al. 1998). These toxic substances are likely to be more abundant in low temperature charcoals, such as used in this experiment, and may be prone to volatilization at higher temperatures. An additional explanation is that charcoal may have enhanced soil macroporosity, allowing more soil solution to pass through capsules, resulting in misleading resin-sorbed nutrient concentrations. Experiment 3: effect of wildfire charcoal on plant growth In support of our hypothesis, natural charcoal collected from a wildfire showed a positive effect on growth of K. macrantha (Table 3). Both total and aboveground masses were significantly higher in pots amended with 5 and 10% charcoal addition than the control. Pots with lower charcoal content (0.5–2%) showed an intermediate growth response. No significant shift in allocation to above- or belowground structures was detected across the charcoal gradient. As in 3 experiment 2, resin-sorbed NO 3 and PO4 decreased as plant growth increased. These results suggest that these measurements do not reflect any direct effect charcoal may have on nutrient cycling, but are rather indicative of the solution nutrient concentration as influenced by plant uptake. No difference in resin sorbed NHþ 4 occurred across the charcoal gradient. The different responses of K. macrantha to charcoal in experiments 2 and 3 suggest that charcoal produced in a laboratory may be greatly different from charcoal generated during wildfire. Differences in charring conditions may influence the chemical and structural nature of charcoal and may therefore change its influence on soil solution chemistry. One potentially important difference between laboratory- and wildfire-collected charcoal was the ratio of soluble phenols to NHþ 4 concentration extracted from the charcoals (Table 1). While all charcoal had relatively similar soluble phenol contents, which may stimulate microbial N immobilization, high NHþ 4 concentrations

may have offset this immobilization effect when wildfire charcoal was used. Another potentially important difference is the different pH of laboratory charcoal and wildfire charcoal (Table 1). The low pH associated with the lab charcoals may have indirectly diminished P availability in these treatments. Another difference between the charcoal used in experiments 2 and 3 was the range of charcoal particle size used. Experiment 3 incorporated charcoal ranging from large (1–2 cm) to microscopic fractions. We noted substantial root penetration into large charcoal particles at the end of this greenhouse experiment, which suggests that some resource, such as water, is more available inside large charcoal particles. It is also possible that grinding charcoal to a smaller size class, in some way, eliminates its beneficial effects on soil fertility. For instance, grinding may enhance the availability of organic carbon because it is very immobile, whereas N ions are significantly more mobile; thus, nutrient immobilization may be more substantial when charcoal is ground.

Conclusion It is clear that charcoal has the potential to significantly alter soil solution chemistry and growth of K. macrantha. Charcoal did not appear to stimulate N cycling in a low-nutrient setting, but when glycine was added to soil, charcoal greatly enhanced N mineralization and nitrification. This result may indicate that low temperature charcoal contributes bioavailable carbon that causes N immobilization under low nutrient conditions. As hypothesized, charcoal effectively sorbed soluble phenols from litter extracts. This sorption may effectively reduce the inhibitory effect of litter extracts on soil microorganisms, plants, and biogeochemical processes. Low-temperature, laboratory-generated charcoal had a negative effect on growth of K. macrantha, possibly as a result of

310

a toxicity effect caused by some compound formed during low temperature charring or by N immobilization, as suggested by the no-glycine soil incubation. In contrast, charcoal created during a wildfire had a positive effect on the growth of K. macrantha, suggesting low-temperature, laboratory charcoal may not adequately represent field-collected charcoal. Field-collected charcoal may have been generated in a higher oxygen, higher temperature environment and may have been exposed to leaching by rainwater and occlusion by soil organic compounds before collection. Further investigation is required to evaluate how charcoal formation conditions alter its effect on soil processes and plant growth and how these processes manifest themselves in natural ecosystems. Acknowledgements We thank V. Kurth, D. Mackenzie, and T. Burgoyne for their assistance in the laboratory and greenhouse. We also acknowledge funding from the NSF (NSF-DEB-03171108) and the USDA Joint Fire Sciences Program (FFS #107) for this research.

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Springer 2005

Plant and Soil (2005) 272: 291–300 DOI 10.1007/s11104-004-5485-5

Adsorption of allelopathic compounds by wood-derived charcoal: the role of wood porosity Olivier Keech1,2,4, Christopher Carcaillet3 & Marie-Charlotte Nilsson1 1

Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences, SE-901 83, Umea˚, Sweden. 2Present address: Department of Plant Physiology, Umea˚ Plant Science Centre, University of Umea˚, SE-901 87, Umea˚, Sweden. 3Centre of Bio-Archaeology and Ecology (UMR 5059), CNRS/ Universite´ Montpellier 2, EPHE, Institut de Botanique, 163 rue Broussonet, F-34090 Montpellier, France. 4 Corresponding author* Received 21 July 2004. Accepted in revised form 26 October 2004

Key words: adsorption, allelopathy, boreal forests, Empetrum hermaphroditum, germination, woodderived charcoal anatomy

Abstract In Swedish boreal forests, areas dominated by the dwarf shrub Empetrum hermaphroditum Hagerup are known for their poor regeneration of trees and one of the causes of this poor regeneration has been attributed to allelopathy (i.e. chemical interferences) by E. hermaphroditum. Fire-produced charcoal is suggested to play an important role in rejuvenating those ecosystems by adsorbing allelopathic compounds, such as phenols, released by E. hermaphroditum. In this study, we firstly investigated whether the adsorption capacity of charcoal of different plant species varies according to the wood anatomical structures of these, and secondly we tried to relate the adsorption capacity to wood anatomical structure. Charcoal was produced from eight boreal and one temperate woody plant species and the adsorption capacity of charcoal was tested by bioassays technique. Seed germination was used as a measurement of the ability of charcoal to adsorb allelochemicals. The charcoal porosity was estimated and the pore size distribution was then calculated in order to relate the wood anatomical features to the adsorption capacity. The results showed that the adsorption capacity of charcoal was significantly different between plant species and that deciduous trees had a significantly higher adsorption capacity than conifers and ericaceous species. The presence of macro-pores rather than a high porosity appears to be the most important for the adsorption capacity. These results suggest that fire-produced charcoal has different ability to adsorb phenols in boreal forest soil, and therefore may have differing effects on the germination of seeds of establishing tree seedlings. Introduction Wildfire is the most important disturbance factor in boreal forests (Johnson, 1992; Payette, 1992) occurring with 50–100 years of intervals in Fennoscandia (e.g., Engelmark, 1984, 1999; Hellberg et al., 2004; Lehtonen and Huttunen, 1997; Niklasson and Granstro¨m, 2000; Zackrisson, * FAX No: +46-90-786-6676 E-mail: [email protected]

1977). In Northern Sweden, early post-fire successions are usually dominated by Pinus sylvestris L., Populus tremula L. and Betula pubescens Ehrh. in the overstorey and, Vaccinium myrtillus L. in the understorey. Long periods without fire favour the growth of Picea abies (L.) H. Karst and of the small fire sensitive dwarf shrub Empetrum hermaphroditum Hagerup (Haapasaari, 1988; Steijlen and Zackrisson, 1987). The fire suppression over the last 100 years in Swedish boreal forests has led to an intensive use of

292 mechanical soil scarification on clear-cuts and has triggered the expansion and the dominance of E. hermaphroditum (Zackrisson, 1977). E. hermaphroditum is today one of the most common species on northern inland clear-cuts (Data from the Swedish National Forest Survey) where it through chemical interference causes tree regeneration failures (Nilsson and Zackrisson, 1992). Allelopathy, which involves the release of secondary plant metabolites, is a key process regulating plant regeneration in many world ecosystems (e.g., Fisher, 1987; Keeley et al., 1985; Li and Romane, 1997; Pellissier, 1993; Rice, 1979; Richardson and Williamson, 1988; Waller, 1987; Wardle et al., 1998a). In the boreal forests of northern Sweden, E. hermaphroditum releases phenolic compounds, and in particularly the dihydrostilbene Batatasin-III, from green leaves and litter (Nilsson et al., 1998; Ode´n et al., 1992; Wardle et al., 1998b; Zackrisson and Nilsson, 1992) which inhibits seed germination and seedling emergence, disturbs the plasmalemma integrity of target roots’ cells (Wallstedt et al., 2001) and negatively affects mycorrhizal symbiosis of coniferous trees (Nilsson et al., 1993). Further, Batatasin-III impairs soil microbial activity and slows down decomposition which both contribute to an increased accumulation of soil organic material with time since last fire disturbance (DeLuca et al., 2002; Zackrisson et al., 1996). Many phenolic compounds also form recalcitrant complexes with soil organic nitrogen reducing the nitrogen accessibility to vascular plants (Bending and Read, 1996; Gallet and Lebreton, 1995; Wardle et al., 1998b). Therefore, the phenol-regulated accumulation of humus and the reduction of nitrogen available for plants inhibit tree seedling establishment and growth of P. sylvestris (Nilsson and Zackrisson 1992; Zackrisson et al., 1996), one of the most commonly occurring tree species in the European and the Asian boreal forests and one of the most important species for the forest industry. In field experiments, activated carbon has been shown to adsorb phenols released by E. hermaphroditum vegetation and to eliminate the inhibitory effects of E. hermaphroditum on tree seedlings establishment and growth (DeLuca et al., 2002; Nilsson, 1994; Thoss et al., 2004; Zackrisson and Nilsson 1992). When added to field plots, activated carbon also increases humus

nitrogen mineralization and stimulates soil microbial activity (Zackrisson et al., 1996). After a forest fire, up to 2000 kg ha)1 of wood charcoal is produced (Zackrisson et al., 1996) and wood charcoal produced by wild fire has similar properties as commercially manufactured activated carbon (Bansal et al., 1988; Chereminisoff and Ellerbusch, 1978). Fire-produced charcoal is thus able to adsorb phenolic compounds released by ericoid plants (Zackrisson et al., 1996). However, the possible differential phenolic adsorption capacities of charcoal produced by different woody species have not been investigated before whereas the wood anatomy varies between species (e.g., Hellberg and Carcaillet, 2003; Schweingruber, 1990). The aim of the present study is (1) to determine whether the charcoal from different plant species differs in its ability to adsorb allelopathic compounds produced by E. hermaphroditum and (2) to investigate whether this adsorption can be related to the wood charcoal anatomy of individual plant species. The ultimate aim of this study is to contribute to a better understanding of the functional role of fire-produced charcoal in the boreal forest ecosystem.

Materials and methods Plant species and production of charcoal Twigs of eight plant species abundant in the north European boreal forest were collected close to Umea˚, northern Sweden (6349¢N; 2018¢E). The species consisted of five angiosperms (Betula pubescens Ehrh., Empetrum hermaphroditum Hagerup, Ledum palustre L., Populus tremula L. and Vaccinium myrtillus L.) and three gymnosperms (Juniperus communis L., Picea abies (L.) H. Karst and Pinus sylvestris L.). In addition, twigs of Ulmus minor Mill. were collected in southern France (4226¢N; 310¢E). Ulmus minor has been selected for its very large vessels (Jacquiot et al., 1973) and therefore provides a better possibility to test the effects of vessels size on the adsorption capacity of charcoal. Twigs of 3–4 mm in diameter from each species were cut into segments of approximately 30 mm of length and were then left to dry at room temperature for 1 month. Charcoal was

293 produced in a ‘‘muffle furnace’’ (Nabertherm, L9/S27) according to the following protocol: wood fragments of each species were put in an iron pan. Wood fragments from one species were separated from the others by vertically inserting a glass slide into the pan. The position of wood samples was randomized in the pan and samples were covered with sand to reduce the exposure to oxygen during the burning process. This procedure facilitates production of charcoal and avoids total combustion of organic material and production of ashes. The pan was put in the muffle furnace for 35 min to reach 450 C and then for an additional 15 min at 450 C after which the charcoal samples were removed from the muffle furnace. The selected temperature mimics the temperature at the ground surface during wildfire (Chandler et al., 1983; Wiedemann et al., 1988). Then, charcoal samples were sieved to retain material of 0.8–1.6 mm in size that corresponds to the main size of soil charcoal (Carcaillet and Talon, 2001). The burning procedure was replicated three times for each species. Adsorption of allelopathic compounds The ability of charcoal to adsorb phenolic compounds from an aqueous solution produced from green leaves of E. hermaphroditum was determined by the use of a bioassay method following Zackrisson and Nilsson (1992). In short, this method involved collecting green leaves of E. hermaphroditum (At Rova˚gern, N. Sweden, 6350¢N; 2015¢E), which were allowed to air-dry for 2 weeks. Deionized water was added to 50 g of dry leaves per litre and the solution was agitated during 48 h on a rotary shaker, and producing in this way a 5% weight/volume water extract. This solution was then filtered through a Munktell No. 3 filter paper and diluted with deionized water to produce a 2% solution E. hermaphroditum extract. This extract had a total inhibitory effect on seed germination of Populus tremula seeds (see below). For each species of charcoal, 0.4 g of charcoal fragments were added to 20 mL of the 2% solution E. hermaphroditum and placed on a rotary shaker for 12 h. Charcoal fragments were then removed from the solution by filtration through a filter paper (Munktell No. 3) and 2 mL of the remaining solution was added to each of five Petri dishes (50 mm in

diameter). This latter procedure is reiterated for the three replicates of burning. To each dish, 25 P. tremula seeds (99.6% viability, stored at )18 C) are added on a Munktell No. 3 filter paper. The inhibitory effect of the solution on P. tremula seeds was monitored and the number of germinated seeds was used as a measure of charcoal adsorption capacity (Zackrisson et al., 1996). To verify whether the charcoal itself might influence on P. tremula germination, five dishes were set up with 2 mL of deionized water that was soaked with 0.4 g of charcoal for 12 h; this experiment is performed for all species. The Petri dishes is placed in a climate chamber at 20 C during 20 h per day of artificial illumination. The total seed germination in each dish was recorded after 7 days. Charcoal porosity: estimation and size of pores In this study, pores were defined as all longitudinal cells that represent more than 95% of the total wood composition in the selected species, i.e. the vessels, the fibres and the parenchyma in angiosperms and most of the tracheids in gymnosperms (Figure 1). The porosity of charcoal is defined as a ratio between the total volume of all pores and the total volume of wood. A transversal section of each fragment of charcoal was used to estimate the charcoal porosity. The total area covered by pores was measured within an observation surface of 5250–5500 lm2. The ratio between the total area of all pores and the observation surface is performed for each species of charcoal to obtain a two-dimensional measurement of porosity called ‘transversal porosity’. This ratio serves to investigate whether the adsorption capacity of charcoal is related to the porosity of charcoal. A high value of this ratio corresponds to a high charcoal porosity and conversely, a low value to a low charcoal porosity. The charcoal porosity was measured on 10 transversal sections for each species of charcoal. The final ratio is thus based on the average of the 10 measurements by species of charcoal. All measurements were performed under an episcopic-analysing microscope (magnification: ·500). Values of surface were obtained with the image analysing software ‘OPTIMAS 5.2’. The pore area from each observation surface was used to test whether the pores size might be related to

294

Figure 1. Scanning electronic microscope (SEM) pictures of transversal sections of wood charcoal. All pictures are at the same scale and magnification (·200). The top three pictures (ericoids) show small diameter vessels and fibres. Betula pubescens and Populus tremula have larger but less abundant vessels. Elm (Ulmus minor) has little but very large vessels. The porosity of the three gymnosperms (Juniperus communis, Picea abies and Pinus sylvestris) is mostly composed of tracheids with thin wall in the early wood and thick wall in the late wood.

the adsorption capacity. The pores are classified according to the size of their area into micropores (<50 lm2), meso-pores (from 50 to 250 lm2) and macro-pores (>250 lm2). This classification is based on the frequency of pores area per species (Figure 2). A ratio between the total area occupied by each class of pores and the transversal porosity was calculated. The transversal porosity is thus defined as the sum of three areas i.e. micro-, meso- and macropores. Only charcoal produced from wood of ericoı¨ d plants (E. hermaphroditum, L. palustre and V. myrtillus) and broad-leaved deciduous trees (B. pubescens, P. tremula and U. minor) were selected because conifers (gymnosperms) are mostly composed of tracheids that do not show such a distinction between micro-, meso- and macro-pores.

ANOVA. Firstly, data relative to adsorption capacity of charcoal (Figure 3) was arsine square root transformed prior to analysis. ANOVA were performed to determine whether the adsorption capacity of different species of charcoal was significantly different from each other. Significant differences between species (P
0.05) were log10 transformed and further analyzed by LSD test (least significant difference). Secondly, ANOVA used to determine whether the transversal porosity of each species of charcoal was significantly different between species of charcoal (Figure 4). Significant differences (P
0.05) between species are analyzed by Tukey test (honestly significant difference). All statistics are computed with the statistical package ‘SPSS 10.0’.

Results Statistical analysis of data Homogeneity of variances (Levene test) of data was tested in accordance with the assumptions of

The ability of charcoal to adsorb allelopathic compounds in E. hermaphroditum leaf water extract differs significantly (ANOVA: F8.18 ¼ 9.633;

295

Frequency of pores

100 Populus Betula Ledum Vaccinium Empetrum Ulmus

80

60

Mesopores

Macropores

40

20

Micropores 0 0

50

100 150 200 250 300 350 400 500

1500

3500

2500

Transversal pore area (µm2) Figure 2. Frequency of pores per area of wood charcoal of different plant species.

Adsorption capacity of charcoal (%)

100.0 A

90.0 80.0 70.0 60.0 50.0 40.0

BC B

30.0

BC

20.0

D

CD

CD

D

10.0

D ris

P.

sy

lv e

ab

st

ie

s

is un m m

P.

s lu co J.

m

yr

lu

E.

he

V.

pa

rm

L.

hr ap

til

st

itu od

es c ub

.p B

re

m

s en

a ul em tr

P.

U

.m

in

or

0.0

Figure 3. Adsorption capacity of charcoal from different plant species measured as the mean (±SE) number of germinated Populus tremula seeds. The shaded bars correspond to angiosperm and open bars to gymnosperms. Data are expressed as the percentage of seeds germinated in deionised water (control). Bars topped with different letters are significantly different from each other at P
0.05 (LSD test following ANOVA).

P
0.001) between species (Figure 3). With the exception of Juniperus communis, the adsorption of allelopathic compounds by charcoal produced from broad-leaved deciduous trees (B. pubescens, P. tremula and U. minor) are higher than the adsorption by charcoal from ericoid species (E. hermaphroditum, L. palustre and V. myrtillus) and conifers (P. abies and P. sylvestris) (Figure 3). Charcoal produced from U. minor wood shows the

highest adsorbing capacity amongst the tested plant species, i.e. about three times higher than P. tremula and about 15 times higher than P. sylvestris. Juniperus communis adsorbs allelopathic compounds in the same range as B. pubescens and P. tremula. The overall lowest adsorption capacities are found for charcoal produced from V. myrtillus and P. sylvestris (<5% of germinated P. tremula seeds). Adsorption capacity of charcoal

296 80.0

Transversal porosity (%)

70.0

BCD

60.0

BCD

ACD

AC

B

B

BD

BCD

A

50.0 40.0 30.0 20.0 10.0

is

bi es P. a

m m un

J.

co

st

ris

ns yl ve

ce es ub

.p

P. s

m ul a re B

e tr lu s pa L.

P. t

til lu s

itu

V. m yr

od hr

E. h

er

m ap

U

.m in o

r

m

0.0

Figure 4. Mean (±SE) of transversal porosity of charcoal from different plant species expressed as percent of the relative total area of pores in the wood. Shaded bars correspond to angiosperms and open bars to gymnosperms. Bars topped with different letters are significantly different from each other at P
0.05 (Tukey’s HSD test following ANOVA).

produced from J. communis, B. pubescens, P. abies and E. hermaphroditum are not significantly different from each other at P
0.05 (Figure 3). The overall transversal porosity varies between 47 and 67% among the species (Figure 4). The highest transversal porosity is found for P. abies and the lowest for P. sylvestris. The values are significantly different from each other at P
0.05 (ANOVA: F8.81 ¼ 7.986; P
0.001). The transversal porosity for P. sylvestris is significantly lower than the transversal porosity (<55%) of the other species (Figure 4). The transversal porosity of U. minor is also relatively low, but is only significantly different from V. myrtillus, E. hermaphroditum and P. sylvestris. When transversal porosity is tested against the adsorption capacity of charcoal, no correlation between the two is evidenced (Figure 5). The frequency of pores per transversal pore areas displays three classes of pores that differ between species (Figure 2). For the broad-leaved deciduous trees, the surface corresponding to the sum of macro-pores represents more than 50% of the transversal porosity (i.e. U. minor and P. tremula) and almost 40% for B. pubescens (Figure 6). The species with the largest relative amount of macro-pores are also the species with highest adsorption capacity (Figure 3). Macropores are almost non-existent in L. palustre, which is mainly constituted of meso-pores

representing more than 75% of the transversal porosity (Figure 6). For E. hermaphroditum and V. myrtillus, species with relatively low adsorption capacity, the surface of the sum of meso-pores ranges between 40 and 50% of the transversal porosity. The percentage of micropores does not differ between species and ranges between 20 and 40% (Figure 6). Examples of transversal wood pattern of selected species are displayed in Figure 1.

Discussion The results of the present study show that charcoal of different plant species has differing capacity to adsorb phenolic compounds released by E. hermaphroditum. The adsorption capacity of charcoal from U. minor, deliberately selected for its large pores (vessels), is about double than all other species (Figure 3). Amongst the angiosperms, the adsorption capacity is higher for charcoal produced from broad-leaved deciduous trees than charcoal from ericoid species. Most Ericaceous species are characterized by small pores diameter, whereas broad-leaved trees have larger pores diameter (Figure 1). The adsorption capacity of gymnosperm charcoal differs significantly among the selected species. We expected, however wrongly, the total surface of adsorption

297 90.0

Adsorption capacity of charcoal (%)

80.0

U. m

70.0 60.0 50.0 40.0

y = -0.7577x + 63.9 2

R = 0.0443 30.0 P. t

J. c

20.0

B. p

10.0

E. h P. s

P. a

L. p V .m

0.0 40

45

50

55

60

65

70

Transversal porosity (%) Figure 5. Adsorption capacity and transversal porosity of charcoal from different plant species. U. m: Ulmus minor; P. t: Populus tremula; B. p: Betula pubescens; E. h: Empetrum hermaphroditum; L. p: Ledum palustre; V. m: Vaccinium myrtillus; J. c: Juniperus communis; P. a: Picea abies; P. s: Pinus sylvestris.

to be higher for those charcoal containing small diameter pores than those charcoal having large diameter pores. This is because the relative porosity could have been lower when there was a higher abundance of cell wall material. However, although different species differ in adsorption capacity (presumably due to wood anatom ical differences), transversal porosity of the wood does not emerge as a driver of differences in adsorptive capacities among species because the process seems more complex and involves other factors such as pore size distribution. If the total porosity was a significant factor explaining the adsorption, we should expect charcoal of P. abies which had the largest transversal (Figure 4) to also have the largest adsorption capacity (Figure 3), whereas this is not the case (Figure 5). Furthermore, the transversal porosity of P. abies and of P. tremula are not significantly different from each other (Figure 4), while the adsorption capacity is significantly different (Figure 3). The pore size distribution for each charcoal species shows that the surface represented by

macro-pores is generally higher for broad-leaved deciduous trees than for ericoid species where macro-pores can be almost non-existent like in L. palustre (Figure 6). Charcoal species with a high density of macro-pores are also those with the highest adsorption capacity, e.g., U. minor, B. pub- escens and P. tremula (Figure 3 and 6). This observation suggests that a high adsorption capacity is linked with the total volume of macropores. This result is strengthened by the observations of Chereminisoff and Ellerbusch (1978) showing that adsorption capacities of charcoal were the results of both chemical and physical properties. Macro-pores may have a lower surface tension than meso- and micro-pores, which should in turn facilitate the penetration of water and dissolved compounds within charcoal. Among the gymnosperms, J. communis and P. abies have a higher total porosity than P. sylvestris (Figure 4). SEM pictures (Figure 1) and literature on wood anatomy (Schweingruber, 1990) show that Pinus is generally characterized by thick late wood relatively to the thickness of

298 100.0

Micro-pores

Pore size distribution (%)

90.0

Meso-pores

80.0

Macro-pores

70.0 60.0 50.0 40.0 30.0 20.0 10.0

tr e lu s pa

m

E.

he

L.

yr til lu s

m

rm ap

.p B

V.

hr od

es ub

itu

ns ce

tr em ul a P.

U

.m in o

r

0.0

Figure 6. Pore size distribution in charcoal of six angiosperm species. Micro- ( lm2), meso- (50–250 lm2) and macro-porosity (>250 lm2) are expressed as percentage of the total number of transversal pores of each species.

early wood, whereas Juniperus and Picea generally have a narrow late wood. Although the diameter of conifer tracheids is relatively independent of the position within the tree ring, the wall thickness varies significantly which influences the volume of the porosity. Our data indicate that species with a high proportion of late wood material in their tree-rings appear to be linked to a lower adsorption capacity. The differences in adsorption capacity between all species tested might also be influenced by the presence of wood tar. Tar is produced during the burning process and could block the pores reducing the adsorption capacity of charcoal (www.fao.org/docrep/X5328f/ x5328f00.htm#Contents) but also modify the chemical properties of the charred surface. However, it is also likely that the different tree species do not produce the same amount of tar during the burning process, which also could explain why the adsorption capacity is not linked to porosity. The presence of resins within conifers trees might also influence the adsorption capacity of the charcoal produced, by modifying the internal chemical structure of the pores. One of the limitations of the present study relates to the two dimensional estimation of the porosity that we used. The adsorption by charcoal could be influ-

enced by other physical properties such as the length of the pores (i.e. mostly length of vessels for angiosperms and length of tracheids for gymnosperms), the density and the diameter of pit orifices and the shape of the perforations that control the penetration of phenolic compounds into charred cells. To conclude, the present study supports previous work showing that fire-produced charcoal is able to regulate soil phenolic compounds released by E. hermaphroditum in the European boreal forests (Pietikainen et al., 2000; Wardle et al., 1998b; Zackrisson et al., 1996). Obviously, the simple volumetric process of adsorption occurs during the first days, but we stress the need to understand the mechanism and kinetics of the physico-chemical process of adsorption. The identity of the plant producing the charcoal can be important for determining the adsorption capacity. Therefore, it is expected that variations in seed germination and success of establishing new trees seedlings are dependent on differences in charcoal properties. It is likely that the regeneration of trees is less important after a fire in areas dominated by ericoid species associated with conifers than in areas dominated by broadleaved deciduous tree species notably those with large and abundant vessels, e.g., Ulmus, Quercus,

299 Fraxinus, Castanea in temperate forests and, Salix, Populus, Betula and Sorbus in boreal forests. The present study highlights the need for conservation of broad-leaved deciduous trees in boreal forests.

Acknowledgements This research was funded through a European Union scholarship to Olivier Keech and the French Centre National de la Recherche Scientifique (CNRS) to Christopher Carcaillet.

References Bansal R C, Donnet J B and Stoeckli F 1988 Active carbon. Marcel Dekker Inc., New York, NY. 482 pp. Bending G D and Read D J 1996 Nitrogen mobilization from protein-polyphenol complex by ericoid and ectomycorrhizal fungi. Soil Biol. Biochem. 28, 1603–1612. Carcaillet C and Talon B 2001 Soil carbon sequestration by Holocene fires inferred from soil charcoal in the dry French Alps. Arct. Antarct. Alp. Res. 33, 282–288. Chandler C, Cheney P, Thomas P, Trabaud L and Williams D 1983 Fire in Forestry. Vol 1. John Wiley and Sons, New York, NY. 450 pp. Cheremisinoff P N and Ellerbusch F 1978 Carbon adsorption handbook. Ann Arbor Science, Ann Arbor, MI. 1054 pp. DeLuca T H, Nilsson M C and Zackrisson O 2002 Nitrogen mineralization and phenol accumulation along a fire chronosequence in northern Sweden. Oecologia 133, 206–214. Engelmark O 1984 Forest fires in the Muddus National Park (northern Sweden) during the past 600 years. Can. J. Bot. 62, 893–898. Engelmark O 1999 Boreal forest disturbances in Ecosystem of the World. In Ecosystems of disturbed world. Vol 16. Ed. Walker R. pp. 161–186. Elsevier Science BV, Amsterdam. Fisher R F 1987 Allelopathy: a potential cause of forest regeneration failure. In Role in Agriculture and Forestry. Ed. Waller GR. Allelochemicals: pp. 176–184. ACS Symposium Series 330, Washington, DC. Gallet C and Lebreton P 1995 Evolution of phenolic patterns in plants and associated litters and humus of a forest ecosystem. Soil Biol. Biochem. 27, 157–165. Haapasaari M 1988 The oligotrophic heath vegetation of northern Fennoscandia and its zonation. Acta. Bot. Fenn. 135, 1–219. Hellberg E and Carcaillet C 2003 Wood anatomy of West European Betula: quantitative descriptions and applications for routine identification in paleoecological studies. Ecoscience 10, 370–379. Hellberg E, Niklasson M and Granstro¨m A 2004 Influence of landscape structure on patterns of forest fires in boreal forest landscapes in Sweden. Can. J. Forest Res. 34, 332–338. Jacquiot C, Trenard Y and Dirol D 1973 Atlas d’anatomie des bois des Angiospermes (Essences feuillues). Centre technique du bois, Paris. 175 pp.

Johnson E A 1992 Fire and vegetation dynamics: studies from the North American boreal forest. University Press, Cambridge. 129 pp. Keeley J E, Morton B A, Pedrosa A and Trotter P 1985 Role of allelopathy, heat and charred wood in the germination of chapparal herbs and suffrutescents. J. Ecol. 73, 445–458. Lehtonen H and Huttunen P 1997 History of forest fires in eastern Finland from the fifteenth century AD – the possible effects of slash-and-burn cultivation. Holocene 7, 223– 228. Li J and Romane F 1997 Effects of germination inhibition on the dynamics of Quercus ilex stands. J. Veg. Sci. 8, 287– 294. Niklasson M and Granstro¨m A 2000 Numbers and sizes of fires: long-term spatially explicit fire history in a Swedish boreal landscape. Ecology 81, 1484–1499. Nilsson M C 1994 Separation of Allelopathy and Resource Competition by the Boreal Dwarf Shrub Empetrum hermaphroditum Hagerup. Oecologia 98, 1–7. Nilsson M C, Gallet C and Wallstedt A 1998 Temporal variability of phenolics and batatasin-III in Empetrum hermaphroditum leaves over an eight-year period: interpretations of ecological function. Oikos 81, 6–16. Nilsson M C, Ho¨gberg P, Zackrisson O and Fengyou W 1993 Allelopathic effects of Empetrum hermaphroditum on development and nitrogen uptake by roots and mycorrhizae of Pinus sylvestris. Can. J. Bot. 71, 620–628. Nilsson M C and Zackrisson O 1992 Inhibition of Scots pine seedling establishment by Empetrum hermaphroditum. J. Chem. Ecol. 18, 1857–1869. Ode´n P C, Brandtberg P O, Andersson R, Gref R, Zackrisson O and Nilsson M C 1992 Isolation and characterization of a germination inhibitor from leaves of Empetrum hermaphroditum Hagerup. Scan. J. Forest Res. 7, 497–502. Payette S 1992 Fire as a controlling process in the North American boreal forest. In A systems analysis of the global boreal forest. Eds. Shugart HH, Leemans R, Bonan GB. pp. 144–169. Cambridge University Press, Cambridge. Pellissier F 1993 Allelopathic inhibition of spruce germination. Acta. Oecol. 14, 211–218. Pietikainen J, Kiikkila O and Fritze H 2000 Charcoal as a habitat for microbes and its effect on the microbial community of the underlying humus. Oikos 89, 231–242. Rice E L 1979 Allelopathy, an update. Bot. Rev. 45, 15–109. Richardson D R and Williamsom G B 1988 Allelopathic effects of shrubs of the sand pine scrub on pine and grasses of the sandhills. Forest Sci. 34, 592–605. Schweingruber F H 1990 Anatomie europa¨ischer Ho¨lzer.–Anatomy of European woods. Eidgeno¨ssische Forschungsanstalt fu¨r Wald, Schnee und Landschaft, Birmensdorf (Hrsg.). Verlag Paul Haupt, Bern. 800 pp. Steijlen I and Zackrisson O 1987 Long-term regeneration dynamics and successional trends in a northern Swedish coniferous forest stand. Can. J. Bot. 65, 839–898. Thoss V, Shevtsova A and Nilsson M C 2004 Environmental manipulation treatment effects on the reactivity of watersoluble phenolics in a subalpine tundra ecosystem. Plant Soil 259, 355–365. Waller G R 1987 Allelochemicals. Role in agriculture and forestry. ACS. Symp. Ser. 330. 606 pp. Wallstedt A, Sommarin M, Nilsson M C, Munson A D and Margolis H A 2001 The inhibition of ammonium uptake in excised birch (Betula pubescens) roots by batatasin-III. Physiol. Plant. 113, 368–376.

300 Wardle D A, Nilsson M C, Gallet C and Zackrisson O 1998a An ecosystem-level perspective of allelopathy. Biol. Rev. 73, 305–319. Wardle D A, Zackrisson O and Nilsson M C 1998b The charcoal effect in Boreal forests: mechanisms and ecological consequences. Oecologia 115, 419–426. Wiedemann H G, Riesen R, Boller A and Bayer G 1988 From wood to coal: a compositional thermogravimetric analysis. In Compositional Analysis by Thermogravimetry. Ed. Ernest C M. pp. 227–244. American Society for Testing and Materials, New York, NY.

Zackrisson O 1977 Influence of forest fires on the north Swedish boreal forest. Oikos 29, 22–32. Zackrisson O and Nilsson M C 1992 Allelopathic effects by Empetrum hermaphroditum on seed germination of two boreal tree species. Can. J. Forest Res. 22, 1310–1319. Zackrisson O Nilsson M C and Wardle D A 1996 Key ecological function of charcoal from wildfire in the Boreal forest. Oikos 77, 10–19. Section editor: H. Lambers

BREVIA

David A. Wardle,* Marie-Charlotte Nilsson, Olle Zackrisson oreal forests serve as important global sources or sinks of carbon (C), and wildfire is a major driver of C storage in these forests. Although fire releases CO2 to the atmosphere, it also converts plant biomass into forms of black carbon, such as charcoal, that are resistant to microbial attack and persist in the soil for thousands of years (1). It has frequently been suggested that, because of its resistance, black C can serve as an important long-term C sink that may help offset the release of human-induced CO2 to the atmosphere (2, 3). However, charcoal is not biologically inert and can have important effects on soil biological processes (4, 5). The influence of charcoal on the decomposition of native soil organic matter remains poorly understood. We conducted a simple experiment in each of three contrasting boreal forest sites in northern Sweden (6). Mesh bags were filled with pure humus collected from the forest, pure charcoal created in the laboratory, or a 50:50 mixture of humus plus charcoal (6). These bags were left in the field and harvested over 10 years. This approach is conceptually identical to that used for the litter-mix studies that have greatly advanced our understanding of the consequences of mixing different litter types (7). This approach allowscomparisons of observed valuesinthe mixture with what would be expected on the basis of each of the components of the mixture considered separately. We found that, over the 10-year period, loss of mass and C from the bags containing mixtures of charcoal and humus was substantially greater than what was expected on the basis of the components considered separately [Fig. 1, Mix (obs)

B

versus Mix (exp)]. Further, nitrogen immobilization was less than expected in the mixture bags (Fig. 1). For these measurements, substrate mixing effects [i.e., values for (observed – expected)/ expected] never differed significantly across the three sites [P value always greater than 0.20 according to analysis of variance (ANOVA)]. This result is despite the sites differing in both stand history and soil fertility (6) and points to similar effects of charcoal across contrasting sites. Given that charcoal decomposition rates in soil are extremely slow (2, 8) and that in our study system charcoal persists for thousands of years in the humus layer without evidence of mass loss (4), most of the enhanced loss of mass and C caused by mixing charcoal and humus must have resulted from charcoal promoting humus loss rather than humus promoting charcoal loss. Substrate (i.e., glucose)-induced respiration (SIR), a relative measure of active microbial biomass (6), was always significantly greater in the mixture bags than the value predicted on the basis of the charcoal and humus components considered separately [Fig. 1, Mix (obs) versus Mix (exp)]. These results are consistent with charcoal particles serving as foci for adsorption of organic compounds and microbial growth and activity (4, 5), leading to enhanced decomposition rates and mass loss of associated humus. The enhanced microbial activity in the mixture bags may have led to greater mass and C loss through either greater respiration or greater leaching of soluble compounds (9). Previous short-term laboratory studies have shown that charred plant material causes accelerated breakdown of simple carbohydrates (10).

Fig. 1. Changes in litterbag properties over a 10-year period. Humus, Charcoal, and Mix (obs) correspond to litterbags containing pure humus, pure charcoal, and a 50:50 mixture of charcoal and humus, respectively. Mix (exp) corresponds to expected values for litterbags containing 50:50 mixtures of charcoal and humus if no interactive effects between the components occur (6). Each data point is the www.sciencemag.org

Downloaded from www.sciencemag.org on May 2, 2008

Fire-Derived Charcoal Causes Loss of Forest Humus

Our results extend these findings by indicating that charcoal can promote rapid loss of forest humus and belowground C during the first decade after its formation. Fire often causes substantial losses of ecosystem C, and our results provide evidence for a previously unreported mechanism that could contribute to these losses. Our results are specific to boreal forests and to the type of charcoal that we used, and further work is needed to determine the importance of this mechanism in other biomes and for other types of charcoal (11). Although several studies have recognized the potential of black C for enhancing ecosystem C sequestration (2, 3), our results show that these effects can be partially offset by its capacity to stimulate loss of native soil C, at least for boreal forests. The effect of charcoal on native soil C needs to be explicitly considered to better understand the potential of black C as an ecosystem C sink and agent of C sequestration. References and Notes 1. J. W. Harden et al., Global Change Biol. 6 (suppl.), 174 (2000). 2. M. W. Schmidt, A. C. Nowak, Global Biogeochem. Cycles 14, 777 (2000). 3. J. Lehmann, Nature 447, 143 (2007). 4. O. Zackrisson, M.-C. Nilsson, D. A. Wardle, Oikos 77, 10 (1996). 5. J. Pietikäinen, O. Kikkila, H. Fritze, Oikos 89, 231 (2000). 6. Materials and methods are available on Science Online. 7. B. Gartner, Z. G. Cardon, Oikos 104, 230 (2004). 8. C. M. Preston, M. W. Schmidt, Biogeoscience 3, 397 (2006). 9. J. C. Neff, D. U. Hooper, Global Change Biol. 8, 872 (2002). 10. U. Hamer, B. Marschner, S. Brodowski, Org. Geochem. 35, 823 (2004). 11. K. Hammes et al., Global Biogeochem. Cycles 21, GB3016 (2007). 12. We thank A. Sundberg, K. Boot, G. Rattray, and A. Mahomoud for technical assistance and T. Fukami, M. Gundale, and anonymous reviewers for helpful comments.

Supporting Online Material www.sciencemag.org/cgi/content/full/320/5876/629/DC1 Materials and Methods 8 January 2008; accepted 3 March 2008 10.1126/science.1154960

Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE901-83 Umeå, Sweden. *To whom correspondence should be addressed. E-mail: [email protected]

average of all three sites with 11 replicates per site, and vertical bars are mean within-site standard error. For all measurements at all dates and sites, values for Mix (exp) and Mix (obs) differ significantly at P = 0.01 (paired t tests). (A) Total mass loss. (B) SIR. (C and D) Loss of C and N from litter bags (per unit initial mass) over 10 years; negative values in (D) reflect net N gain through immobilization.

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