Soil Fertility and Nutrient management (1+1)

RECLAMATION or MANAGEMENT OF ALKALI SOILS

I. Use of Amendments
For successful crops in alkali soils ESP of the soil must be lowered which can be achieved by application of amendments. Gypsum (CaSO4.2H2O) is the most commonly used amendment for reclamation. Elemental S and pyrite are also used.

Gypsum requirement (GR): The amount of gypsum needed for removal of exchangeable sodium from alkali soil and also to decrease the soil pH to a desired level is called gypsum requirement. 1 milli equivalent of Ca2+ is required to replace 1 milli equivalent of Na+ ion from the exchange complex of sodic soil.

Method of application of amendments
Amendment should normally be broadcasted and incorporated in the surface 10 cm soil. Deeper depth of mixing of gypsum becomes inactivated and thereby reduces the effectiveness of the applied gypsum and yield of crops. To ensure proper dissolution of gypsum and leaching of replaced exchangeable Na+, the water is to be ponded/stagnated continuously on the soil for a period of 8-10 days (80% of gypsum gets dissolved).
It brings down soil exchangeable sodium percentage (ESP) to a desired level before sowing. When pyrites or elemental Sulphur are used as an amendment, then a cycle of wetting and drying is needed to maintain proper moisture and aerobic conditions to ensure maximum oxidation and higher production of H2SO4.
Reactions amendments in soil
If Gypsum used
Na2CO3 + CaSO4- --------->CaCO3 + Na2SO4
2NaHCO3 + CaSO4- ---------> Ca(HCO3)2 + Na2SO4.
Or
2Na+--Soil+ + CaSO4- ------------>Ca2+ - Soil + Na2SO4.

If Elemental Sulphur used
2S + 3O2 -------------> 2 SO3 (Microbial oxdation)
SO3 + H20 ------------>H2SO4.
H2SO4 + CaCO3--------------->CaSO4 + CO2 + H2O
2Na X +CaSO4----------------->Ca-X2 + Na2SO4.
B. Organic Amendments: Addition of crop residues and other organic materials have got a tremendous influence on maintaining soil physical, chemical and biological properties of these soils. Organic amendments like straw, rice husk. Ground nut and safflower hulls, FYM, compost, poultry droppings, green manures, tree leaves and saw dust. They Produce CO2 (carbonic acid) and organic acids, they increase the solubility of calcite and lower the ESP.
C. Industrial by products as Amendments: Phospho-gypsum, Press mud, Molasses, Acid wash and Effluent from milk plants. They are used to provide soluble Ca directly/indirectly by dissolving soil lime. D. Cultural practices:
¥ Land leveling and shaping:- To ensure proper water management and uniform leaching of salts the field should be leveled properly.
¥ Maintain Plant population: Crop stand in alkali soils can be improved by increasing the seed rate and reducing the planting distance.
¥ Age of seedlings - planting old seedlings has proved to be beneficial.
¥ Green manuring: Increases organic matter content, there will be releasing of CO2 and formation carbonic acid. This lowers the pH and it enhances solubility of native CaCO3 and adds a considerable amount of plant nutrients in the soil.
Ex: Sesbania, diancha, subabul
¥ Continuous cropping: the land should be continuously cropped to keep the downward movement of replaced Na & soluble salts. Growing of rice crop, along with other practices has been observed to enhance the reclamation of alkali soils.
E. Water management: 1. Drainage: Alkali soils have got low infiltration rate and all the rain water accumulates to create surface water logging. This results oxygen stress. So, to avoid this problem provide surface and subsurface drainage system in the field.
2. Good irrigation management: Normally surface method of irrigation such as furrow or basin type flood method is used for alkali soils. However the sprinkler method could be promising because of its ability to supply water uniformly and in small quantities
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