Response Of Acacia Angustissima To Potassium Fertilization

Newton de Lucena Costa1 and Valdinei Tadeu Paulino2. 1EMBRAPA/Centro de Pesquisa Agroflorestal de Rondônia, Caixa Postal 406, 78.900-970, Porto Velho, Rondônia, Brazil; 2 Instituto de Zootecnia, 13.160-000, Nova Odessa, São Paulo, Brazil.

Response of Acacia angustissima to potassium fertilization Introduction Potassium contents of Rondônia’s soils has traditionally been considered as adequate. In recent years, however, there has been a growing awareness of the importance of K in forage production. These deficiencies are consequences of K depletion under intensive pasture management (utilization of continuous grazing with high stocking rates, and no fertilizer application, mainly P and K). Under favorable conditions, maximum yield levels of more than 20 to 30 t/ha/year have been recorded for tropical forage legumes (Costa et al., 1991, 1992). Normally the K content of such herbage would be between 1.5 and 2.0 percent, resulting in the removal of 300–600 kg K/ha. Thus, K applications are needed to maintain the soil K status. In this study, we evaluated the effects of K fertilization on the growth, mineral composition, and nodulation of Acacia angustissima. Methods The trial was carried out under greenhouse conditions using samples from a yellow Latosol (Oxisol), having the following chemical characteristics: pH 4.8; Al 1.3 cmol/dm3; Ca + Mg 1.7 cmol/dm3; P 2 mg/kg, and K 33 mg/kg. A randomized complete block design was used, with five treatments (0, 15, 30, 45, and 60 mg K/kg) and four replicates. Potassium levels as muriate of potash were applied at sowing and mixed uniformly with the soil. Basal fertilization consisted of 22 mg P/kg as triple superphosphate. Each experimental unit was represented by a pot with 3 kg dry soil capacity. Pots were sown with seeds not inoculated with Rhizobium. Eight days after emergence, seedlings were thinned to three plants per pot. Soil water content was assessed daily by weighing the pots and keeping soil at 80% field moisture capacity. Three harvests of the tops were made with a cutting frequency of 45 days, and plants were cut at 15 cm height. At 180 days after thinning, the plants were cut at the soil level and oven dried at 65°C for 48 hours. Shoot dry matter (DM) was analyzed for N and K concentrations. The nodules, detached from the extracted root system, were cleaned and oven dried at 65°C for 48 hours, counted, and weighed. Results Legume growth was significantly improved by K fertilization (Table 1). DM yields were increased by K fertilization up to 45 mg K/kg. However, the application of 15 mg K/ kg produced increases over the control of 74.3, 89.9, and 49.5 percent in the DM yield and N and K uptake, respectively. This high response can be attributable to the initial low content of the soil. Positive effects of K fertilization in several forage legumes were also described by Brolmann and Sonoda (1975), Monteiro et al. (1980), and Costa and Paulino (1992). The effects of K fertilization on DM yield were estimating according to a quadratic model (y = a + bx – cx2) (Table 2). K requirement for maximum DM yield was 53.8 mg K/ kg. This value was lower than those reported by Gutteridge (1978) for Centrosema pubescens (150 mg K/kg) and Costa and Paulino (1992) for Cajanus cajan (60 mg K/kg). N content and uptake were significantly increased up to the level of 15 and 30 mg K/ kg, respectively. K requirements for maximum N content and uptake were estimated at 35.1 and 49.5 mg K/kg, respectively. These data agree with previous observations (Monteiro et

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5.33 9.29 11.85 12.88 13.29

g/pot d c b ab a

Dry matter yield

2.73 2.95 3.16 2.89 2.95

% b ab a ab ab

Nitrogen

145.5 273.4 374.5 372.2 392.4

mg/pot c b a a a

1.46 1.76 1.92 2.06 2.08

% c b ab a a

11.7 17.9 22.5 27.4 33.7

d c bc ab a

Number

1

0.722 0.995 1.238 1.655 1.812

d c b a a

mg/pot

Nodulation

5.395 2.745 147.537 1.466

Dry matter N content N uptake K content

** Significant at the 1% probability by F-test

a

Variables 0.26171 0.01769 10.0230 0.02148

b – 0.2943651 – 0.0002518 – 0.1012064 – 0.0001873

c

0.99** 0.98** 0.98** 0.99**

R2

53.8 35.1 49.5 57.3

K requirement (mg K/kg)

Table 2. Coefficients for K response data fitted to the model y = a + bx – cx2, and K requirement for maximum dry matter yield, N content and uptake, and K content of Acacia angustissima.

b b a a a

mg/pot 77.8 116.3 227.5 265.3 276.6

Potassium

Means followed by the same letters in each column are not significantly different at the 5% probability by Tukey´s test. 1 Values analyzed after sq.rt. (X + 1) transformation

0 15 30 45 60

mg K/kg

Rate

Table 1. Dry matter yield, N and P contents and uptake, and nodulation of Acacia angustissima as affected by rates of potassium fertilizers.

al. 1980, Costa and Paulino 1992). Koch and Mengel (1984) showed that plants well supplied with K were able to take more N and to convert the N more rapidly into protein. K fertilization up to the levels of 30 mg K/kg significantly increased K contents and uptake. Such increases are due to increased K availability in the soil, a function of the K added to the soil. Similar results were related by Sanzonowick and Vargas (1980) for Stylosanthes guianensis and Hussain et al. (1986) for leucaena. K requirement for maximum K content was estimated at 57.3 mg K/kg (Table 2). The effects of K fertilization on K uptake was adjusted according to a linear model (y = 83.41 + 3.644x, r2 = 0.92). K internal requirement for 80 percent maximum DM yield was 1.37 percent. The critical value was inferior to those related by Salinas (1987) for C. pubescens (1.50%) and Costa and Paulino (1992) for C. cajan (2.13%). Nodulation (number and dry weight of nodules) was significantly improved by K fertilization up to 45 mg K/kg (Table 1). Costa and Paulino (1992) also reported increases of 132 and 145 percent on number and dry weight nodules of pigeon pea with the application of 60 mg K/kg. The involvement of K in nitrogen fixation is manifested indirectly through effects on legume growth and total DM production. Several studies have shown accompanying increases in nodule mass, nodule numbers, and N fixation rates with increased DM yields when K is applied (Better Crops International 1988). References Better Crops International. 1988. Effects of potassium on biological nitrogen fixation. Vol. 4, no. 2. p. 30–33. Brolmann, J.B., and R.M. Sonoda. 1975. Differential response of three Stylosanthes guyanensis varieties to three levels of potassium. Trop. Agric. (Trinidad) 52(2):139– 142. Costa, N. de L., and V.T. Paulino. 1992. Potassium fertilization affects Cajanus cajan growth, mineral composition, and nodulation. Nitrogen Fixing Tree Res. Reports 10:121–122. Costa, N. de L., V.T. Paulino, and E.A. Veasey. 1991. Effect of cutting frequency on the productivity of leucaena. Leucaena Res. Reports 12:14–15. Costa, N. de L., C.A. Gonçalves, and J.R. da C. Oliveira. 1992. Biomass production of forage legumes in Southwest Brazilian Amazonia. Nitrogen Fixing Tree Res. Reports 10:43–44. Gutteridge, R.C. 1978. Potassium fertilizer studies on Brachiaria mutica/Centrosema pubescens pastures grown on acid soils derived from coral limestone, Malaita, Solomon Islands. Trop. Agric. (Trinidad) 58(1):359–367. Hussain, A., A.M. Ranjha, and M.T. Nawaz. 1986. Effect of potassium on growth, nodulation and nitrogen fixation of Leucaena leucocephala. Leucaena Res. Reports 9:86–87. Koch, K. and K. Mengel. 1974. The influence of the level of potassium supply to young tobacco plants. Trop. Agric. (Trinidad) 25(5):465–471. Monteiro, F.A., S.A.A. Lima, J.C. Werner, and H.B. Mattos. 1980. Adubação potássica em leguminosas e em capim colonião adubado com níveis de nitrogênio ou consorciado com leguminosas. Bol. Ind. Anim. 37(1):127–148. Salinas, J.G. 1987. Fertilización de pastos en suelos ácidos de los trópicos. Cali, Colombia. Centro Internacional de Agricultura Tropical. 215 p. Sanzonowick, C., and M.A.T. Vargas. 1980. Efeito do calcário e do potássio na produção e na composição química do Stylosanthes guyanensis em um Latossolo Vermelho-Escuro de cerrado. Rev. Bras. Ci. Solo 4(3):165–169.

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