Interventions For Rehabilitation/management Of Salt Affected Soils

INTERVENTIONS FOR REHABILITATION / MANAGEMENT OF SALT AFFECTED SOILS

Dr. Nazir Hussain Soil & Water Salinity Expert

Dr. Shahzada Munawar Mehdi Agricultural Chemist

Soil Salinity Research Institute, (SSRI) Pindi Bhattian (Punjab) Pakistan

April, 2007

Hussian. N and S. M. Mehdi 9/16/2007

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INTERVENTIONS FOR REHABILITATION/MANAGEMENT OF SALT AFFECTED SOILS Soil salinity, sodicity, waterlogging and safe use of brackish water are the significant and peculiar problems of present agriculture in Pakistan. The yield of crops and resultant income of the farmers is cut down in accordance with the degree of these problems. In severe cases, the lands become barren and the sole source of livelihood of the poor farmers is snatched, leaving him unemployed. Tackling and management of such lands need specific awareness, training and implementation of site-specific interventions. In order to tackle the problem, two approaches are generally selected, which are as under: -

Rehabilitation of salt affected lands:

1. U

U

In this approach, efforts are made to convert the affected lands to their original potential. For this purpose, amendments are added to the soil, water is applied over and above the normal irrigations and specific agronomic practices are adopted.

Utilization of salt affected soils at the prevailing status:

2. U

The soils can also be utilized and managed at their prevailing status through special farming operations.

The main uses of such lands are: 1. 2. 3. 4. 5.

Growing of salt tolerant crops Growing of salt tolerant fruit plants through special techniques Growing of salt tolerant bushes and trees as forests or agro forestry Growing of salt tolerant fodders and raising of farm animals Fish farming

A specific knowledge and awareness of the subject is required for adopting any of the above approaches and subsequent management of salt affected lands. It will be good if the beginner becomes aware of a few technical terms that will frequently be used in the coming pages.

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Salinity: U

In its broader sense, this word is used to cover the soluble salts and sodium problem of soil or water. But in purely technical terms, it does indicate the problem of only excess soluble salts from soil and water for the plant growth. It is measured as Electrical Conductivity (EC) and its general limit for soil is more than 4 dSm-1 while for water is more than 1.5 dSm-1. P

P

P

P

Sodicity: U

It denotes the problem of excessive sodium, (Na+) in soil or water with reference to plant growth. It is measured through exchangeable sodium percentage (ESP) but more frequently sodium adsorption ratio (SAR) is used. The general critical limit for soil is more than 13, while for water it is more than 10. In Pakistani soils mostly salinity and sodicity coexist. P

P

Water logging: U

This denotes the problem coming through nearness of water table to the surface of the soil because presence of excess water can also create problems for normal plant growth. The general limit adopted is 3 meters (10 feet) water table depth from the soil surface.

Soil affected soils U

Soils having problem of salinity or sodicity or both combined so as to affect plant growth negatively.

Types of salt affected soils U

On the basis of problem of salinity or sodicity, the soils are classified into three broad groups.

Saline soils: U

These are the soils that have ECe more than 4 dSm-1 but SAR is less than 13. These soils are very easy to manage if good quality water is available. The physical condition remains good. B

Hussian. N and S. M. Mehdi 9/16/2007

B

P

P

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Saline sodic soils: U

These are the soils having ECe more than 4 dSm-1 and SAR more than 13. Such soils need some amendment like gypsum, acids or organic material along with water for their management and ultimate rehabilitation B

B

P

P

Sodic soils: U

Soil having EC less than 4 dSm-1 but SAR more than 13. These are worst soils to manage and rehabilitate. Usually, combination of amendments and agronomic/engineering approaches are used. P

P

Classes of salinity: U

The classes of salinity with respect to severity are as under: -

Classes Slightly saline Moderately saline Strongly saline

Criteria EC 4-8 dSm-1 EC 8-15 dSm-1 More than 15 dSm-1

Expected yield losses 10 – 25% 25-50% More than 50%

Criteria

Expected yield losses

P

P

P

P

P

P

Classes of sodicity: U

Classes Slightly sodic Moderately sodic Strongly sodic

Note: -

1. 2.

SAR more than 13-25 SAR 25-45 SAR more than 45

15 – 30 % 30-60 % More than 60 %

Only crops tolerant to salinity/sodicity should be grown. Yield losses will vary in different crops due to their specified tolerance potential as well as soil texture and structure, quality of irrigation water and climatic conditions (rainfall and temperature).

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Salt Tolerant Crops: U

The selection of appropriate crops is very important when the soils are slat affected. Matching of salt tolerant limits of the crops with the prevailing status of soil with respect to salinity/sodicity is of prime importance otherwise chances of failure increase. The following guidelines are presented in this regard.

Crops

Soil EC (dSm-1) for expected yield of 100% 75% 50% 0%

Barley Cotton Sugarbeet Sorghum Wheat Rice Sugarcane Maize Tomato Spinach Cabbage Potato Jantar Alfalfa Berseem

P

8.0 7.7 7.0 6.8 6.0 3.0 1.7 1.7 2.5 2.0 1.8 1.7 2.3 2.0 1.5

13.0 13.0 11.0 8.4 9.5 5.1 5.9 3.8 5.0 5.3 4.4 3.8 5.9 5.4 5.9

P

18.0 17.0 15.0 9.9 13.0 7.2 10.0 5.9 7.6 8.6 7.0 5.9 9.4 8.8 10.0

28.0 18.0 16.0 13.0 20.0 11.0 10.0 10.0 13.0 15.0 12.0 10.0 17.0 16.0 19.0

Different Interventions: U

Selection of appropriate intervention to be employed by the owner of salt affected land will depend upon the farmer’s interest, soil salinity/sodicity status, quality of ground water and quantity of canal water related available facilities of the farmer and crops or plants to be grown. For successfulness of the intervention, it is highly important to select one that matches with all the factors.

1.

GROWING TOLERANT CROPS IN SLIGHTLY TO MODERATELY SALT AFFECTED LANDS

Tolerant crops can be grown in slightly to moderately salt affected lands with special managements practices. These soils can easily be managed for not only growing of specific crops but it is also possible to revert these towards their original potential. However, appropriate operations and activities will direly be needed. The slightly Hussian. N and S. M. Mehdi 9/16/2007

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affected soils are those that have either ECe 4-8 dSm-1 or SAR 13-25 or both within these ranges. The expected yield losses will depend upon the severity of the problem, texture of soil and the crop being grown. However, these may be from 10-25 %, if a sensitive crop is not being grown. B

B

P

P

Moderately affected soils will have ECe 8-15 dSm-1 or SAR 25-45 or both these parameters within these ranges. The yield losses may be 25-50 %, depending upon various factors mentioned above. B

B

P

P

Land preparation and cultural practices: U

Land levelling is a basic requirement. The field boundaries should be strengthened. The soil and tubewell water should be got tested. Deep ploughing or chiseling once is often recommended before levelling. Use of disc plough or rotavator is useful, especially after harvesting of crops so that crop residues are incorporated and mixed well in the soil.

Leaching and application of amendments: U

If the soils are only saline (have EC > 4 dSm-1), these can be used for growing of crops after 2-4 deep irrigations (12 cm) of good quality water or water of lesser EC than the soil in order to bring it within the tolerance limit of the crops to be grown. P

P

If the SAR of the soil is more than the critical limit (less than 13), then some amendment has also to be applied. This may be 20-40 bags of gypsum, 4-6 tons of farm yard manure, green manure (especially Jantar), pressmud, crop residues (rice or wheat straw, grasses) or compost or 50-100 kg of sulphuric acid or any other liquid amendment like fluvic acid etc. Of course 2-4 deep irrigations will follow. Puddling is totally prohibited in case of growing rice is these soils.

Selection of crops and crop rotations: U

Selection of crops in the appropriate sequence is very important otherwise there are chances of failure and there is loss of income to the farmers if sensitive crops are grown. The tolerance of crops must match the salinity/sodicity status of the soil. The suitable crop rotations well fitting the situation are as under:Rice - Wheat/Barley Rice (Coarse) - Rice (Fine) - Wheat/Barley Rice - Berseem Cotton - Wheat Wheat - Sorghum/Pearl millet Hussian. N and S. M. Mehdi 9/16/2007

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Sowing of crops: U

One of major problems for growing of crops in salt affected soils is obtaining appropriate plant population and its sustainability during later stages of growth. Hence, such methods and measures are devised that help in germination, establishing seedlings and maintaining the desired plant population to the end of cropping season. Mortality is many times more than the normal soil. To obtain this objective, 10-20 % higher seed rate is recommended. Two or more seedlings of rice per hill (hole) should be transplanted. Sowing of wheat and cotton on ridges (shoulder) is useful. The soil moisture content should be more than the normal soil at the time of seed sowing. Seed is also spread is the standing water if the soils are saline or have good drainage and water does not stand on the surface for many days, as in case of sodic soil or often in saline sodic conditions.

Fertilizer application: U

Care has to be taken for fertilizer use in salt-affected soils. Ideally, ammonium sulphate, single super phosphate (SSP) and potassium sulphate are the better sources of nitrogen, phosphorous and potassium respectively. However, in case of non-availability of these fertilizers, urea and triple super phosphate (TSP) / mono ammonium phosphate (MAP) can also be used. The recommended doses of fertilizer for different crops are presented in Table-1.

Table-1:

Recommended fertilizer for different crops in salt affected soils:

Sr. No. Crops 1 2 3 4 5 6

Wheat Rice Cotton Barley Berseem Sorghum/Pearl millet

Hussian. N and S. M. Mehdi 9/16/2007

Recommended fertilizer (kg/acre) N P K 55 45 35 55 10 30

50 20 35 50 70 15

25 20 25 25 -

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Irrigation: U

If both types of water (canal and tubewell) are available, these should be used in a cyclic manner. If the water is saline (having EC 1.5 – 3.0 dSm-1) with less SAR or RSC, then it should be used for wheat or cotton in the rotation. If it has high SAR (10-20) or RSC (1.5 to 3.0 m eq L-1), then it should be used for rice in the crop sequence. The other crop should be irrigated with canal water. If there is no canal water supply, then 10 – 15% more water (L.F) should be used coupled with gypsum application (as recommended after water test) in case of high SAR/RSC water. P

P

2.

P

P

REHABILITATION OF STRONGLY SALT AFFECTED LANDS AND SUBSEQUENT PLANT GROWTH

Strongly affected soils are those that have either EC more than 15 dS m-1 or SAR more than 45 or both of them combined. The yield losses of even salt tolerant crops are more than 50% but most often these lands are not being cultivated because there is very less germination and subsequent crop growth. Therefore, such soils are most often barren and rehabilitation is a must before these are brought under plough again. P

P

Preliminary steps: U

The soils should be levelled and boundaries be strengthened. Deep ploughing normally helps a lot. The soils should be got tested alongwith the tubewell water. For this purpose, the nearest District Soil and Water Testing Laboratory should be approached or services of Soil Salinity Research Institute (SSRI), Pindi Bhattian can be obtained. The reports of district laboratories can be submitted to SSRI for getting specific recommendations to manage salinity/sodicity of soil and water. Of course, additional information on soil texture, adopted crop rotation, availability of canal water, drainage, water table depth and the facilities of the farmer will be required for making appropriate recommendations.

Reclamation process: U

Reclamation process will be different for saline and saline-sodic soils. The test report will indicate whether the soil in saline, sodic or saline-sodic and in case of latter two categories, what will be the quantities of gypsum required for that particular soil. Proper land rehabilitation method will be selected accordingly.

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i.

Saline soils: U

If the soils are saline, their reclamation is comparatively easier. Application of farm yard manure, pressmud, compost or green manure ((4-6 t/acre) is recommended. The good quality water (or water having lesser EC than the soil) should be applied. Normally 3-5 deep irrigations will be required, depending upon the level of soil salinity. Then, the crops can be utilized for growing of crops. The preferable first crop is rice and good time is April – June, so that benefits of subsequent monsoon rains can also be obtained.

ii.

Saline sodic or sodic soils: U

After levelling and deep ploughing, gypsum (of good quality) should be applied in the quantities recommended by the laboratory through soil test. Two-third or three-fourth of this quantity should be uniformly spread on the surface and mixed well through ploughing twice. Remaining one third or one fourth should again be spread on the surface. Then the irrigation water (may be tubewell water but of less EC and SAR than the soil) should be enough to bring the soil EC and SAR favourable for rice. Leaching of rest of the salts will be obtained during subsequent rice growth because rice is the only preferred crop after amendment application. It must be remembered that purity of gypsum (At least more than 70% and 60% should pass through 30 mesh), application of gypsum in exact quantity, thoroughly mixing and subsequent irrigations are the key factors of gypsum technology. Missing any one may lead to failure or slow the rehabilitation process and yield losses of initial crops.

Rehabilitation of dense soils and salt affected clayey soils: U

Some times salt affected soils have hard layer in its profile or the texture of the soil is clayey. Reclamation of these soils is most difficult and needs some special operations. At the first step, breaking of hard layer is essential for which chisel/subsoiler or ripper is to be used, depending upon the depth of the hard layer. The passage of water through soil (hydraulic conductivity) has to be increased in clayey soil by combining 50-100 Kg of sulphuric acid with recommended quantity of gypsum. Similarly, application of farm yard manure, green manure, and press mud or compost at the rate of 4 – 6 tons/acre will be helpful greatly. Horizontal flushing is also recommended. In this technique, water is applied, kept in the field for 18 – 24 hours and flushed out of the field into a side channel or a pit in order to remove the salts that otherwise cannot move into deeper depths. Hussian. N and S. M. Mehdi 9/16/2007

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Cultural practices and fertilizer: U

All the cultural practices, sowing methods, seed rate, fertilizer and irrigation will be those that have already been presented for slightly to moderately affected soils. However, it should be kept in mind that the reclamation procedure detailed above should be completed at least 15 days before sowing of crops.

3.

ADDRESSING PATCHY SALINITY:

Salinity/sodicity found in smaller or bigger salt affected patches of various number within almost normal field is called patchy salinity. Yields are reduced significantly in these soils, in spite of application of all the inputs with full doses. Hence, many times the income is cut short to the level (sometimes 50%) at which growing of crops becomes uneconomical. Therefore, addressing these patches is very important to obtain full potential of such lands. Reclamation activities should be restricted only to remove these patches.

Appropriate technique for removal of salt affected patches: U

The patches should be identified and marked. These patches are, generally, at the higher level than the other whole field and are very high in degree of salinity/sodicity. One option is to scrap and remove 5-6 cm surface layer and pile the salty soil in some depression or pits.

Use of Acids: U

Best addressing is possible when rice or any other crop is growing. Sulphuric acid is normally recommended but any other acid based liquid amendment can also be used. Acid is diluted 20-25 times. Acid is poured in water, taken in a plastic bucket or tub. After half an hour, the reaction completes and dilute acid is ready for use. The diluted acid is sprayed with plastic shower on the patches (which are normally devoid of any crop) in standing water. Acid when diluted according to method recommended does not remain harmful to the body. The quantity of acid to be applied will depend upon the severity of the problem. Generally, 1-2 kg for patch of one Marla (0.006 acre) is recommended.

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Use of gypsum: U

Gypsum can also be used for addressing patchy salinity. Gypsum can be applied before sowing of crops or while crops other than rice are growing. The generally recommended rate of gypsum is one bag per Marla of the patchy area. The required quantity is applied and mixed through hoeing or ploughing (in case of bigger patches) and water is applied or the irrigations given to the other field will suffice the purpose.

Fertilizer and cultural practices: U

All the cultural practices, fertilizer, seed rate and sowing methods of normal soils can be adopted but it will be preferable if the production technology given for slightly affected soils is employed. Seed rate should be increased by 10-15% on the patches, if identified already and being addressed. Levelling of land, of course, will be of great help to avoid the emergence of patches as well as dealing with the patches.

4.

GROWING OF FOREST/FRUIT PLANTS IN SALT AFFECTED SOILS

The salt tolerant bushes forest trees and fruit plants can also be grown in salt affected soils, if the farmer has the interest. However, for successful plantations improved transplantation techniques have to be adopted for this purpose. It may be pointed out that fruit plants become permanent source of income for the farmers from marginal lands. Similarly, forest plants and bushes may also be permanent source of fodder, fuel, timber and shade. These can also bring lump sum income for the farmers.

Land preparation and transplantation of plants: The levelling of land is a pre-requisite. If the soil is clayey or has hard layer, deep ploughing, chiseling or ripping, only in the planting lines will be needed. Cultivation of the whole field will also be required to remove the weeds and keep the field clean, so that plants may not suffer from diseases and pest attack. The channels of 90 cm deep and 60 cm width are made. The pits of 60 cm long, 60 cm wide and 60 cm deep are dug on the shoulders of channel at the distance that will depend upon the plant itself. The pits are filled with mixture of silt + gypsum or silt + compost or silt + farmyard manure in 20:1 ratio. The plants are transplanted in these pits. The plastic bags around the saplings are removed or cut from the base. Subsequent irrigation is provided through the channels.

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Suitable plants: U

U

The salt tolerant fruit plants of economic importance are date palm, guava and Jamin while bushes and forest plants are Desi Kikar, Australian Kikar (Acacia ampliceps), Neem and Ipil Ipil.

Cultural practices, irrigation and fertilizer: U

The fields should be kept clean by frequent ploughing. Plants should be irrigated depending upon the season, nature of plants and stage of growth. Normally, weekly irrigation in early stage and fortnightly on later stages during summer season and after 2-3 weeks during the winter season is recommended. Fertilizer should be applied twice a year during February-March and September-October. The recommended dose is one Kg of Urea /plant in two splits during early stages. Phosphorus and potassium additions should be started when the plants reach the age of two years.

Sowing of crops within the plant lines: U

Crops can also be grown within plant lines for initial two years so that the farmers can get some income until the plants are grown up. The production technology already described in detail in previous pages for slightly to moderately salt affected lands can be used for the purpose.

5.

GROWING EUCALYPTUS PLANTS IN WATER LOGGED LANDS

Water logged lands are having high water table that can be a big constraint for growing of normal crops. Eucalyptus plants can successfully be grown on such lands which can not only lower the water-table but can also bring some income to the owners of these lands.

Land preparation, cultural practices and transplantation: U

Land leveling, cultural practices and fertilizer application will be the same as have already been described under the previous topic, “Growing of forest and fruit plants”.

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6.

GROWING OF GRASSES AND FODDERS IN SLIGHTLY TO MODERATELY SALT AFFECTED LANDS.

Salt affected soils with slight to moderate salinity can also be brought under production of annual and perennial fodders (bushes and grasses). Fodders like Kallar Grass, Ipil Ipil, Barley, Oats, Berseem, Lucern, Sorghum and Pearl Millets can be successful on such lands. The land should be levelled and the field boundaries should be strengthened. Two to three tons/acre (40-60 bags) of gypsum should be applied and mixed or 4 -6 tones of FYM/press-mud should be added and well mixed in the soil. Seed bed preparation, cultural practices, irrigations and fertilizer application will remain the same as described under intervention No.1.

7.

FISH FARMING:

The water logged and salt affected lands can also be used for establishing fish farms that may become a permanent source of income for the owners. Talapia breed of fish is well suited for saline conditions.

Preparation of fish pond and related operation U

The soil should be got tested and the report consulted with the Fisheries Department. In case of suitability, the soil should be excavated and piled up on all the four sides. The soil should not be sandy. The depth of the tank should be 5-6 feet (Two meters). The boundaries should be made strong and pressed well. The available water should also be got tested. If it is too sodic (high SAR or RSC) it will not be fit for fish pond because most often turbidity problem in water of the tank arises. The two feet water depth has to be kept clear from suspended soil for light penetration and normal fish growth. This problem can be managed by application of 20-30 bags for tank of one acre. It must be remembered that instead of Urea, ammonium sulphate must be applied. Similarly, DAP must not be added but instead single super phosphate (SSP) or triple super phosphate (TSP) or mono-ammonium phosphate (MAP) be added. Similarly, lime should not be added at any cost but gypsum should be used as alternate source of Ca that will also control sodicity/turbidity problem. Urea, DAP and lime increases the pH of the water tank, which is the most detrimental for living and growth of fish. The ideal pH should remain between 6.5 – 7.5. Well-decomposed farmyard manure may be added for source of energy and organic carbon until plants grow within the tank.

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Ways to Contact: U

Dr. Nazir Hussain T

Soil & Water Salinity Expert T

Soil Salinity Research Institute, T

Pindi Bhattian Hafizabad - 52180 - (Punjab) Pakistan T

Ph: 03018655485, +92-547-531573, +92-547-531376 T

Fax: +92-547-531576 T

Email: [email protected] /[email protected] T

HT

Hussian. N and S. M. Mehdi 9/16/2007

TH

HT

TH

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