Soil salinity and sodicity are among the serious threats to irrigated agriculture in arid and semi-arid regions of the world. The salt-affected area is mostly characterized by water scarcity and is often underlain by aquifers having elevated levels of salinity and sodicity. Low rainfall, use of un-managed water resources and high evaporation in these regions are among the causes of soil salination and sodication. Among these problem soils, sodic nature show structural problems causing decrease in water up-take by plants, seedling emergence and root penetration. Salinity cause reduction in crop yield on about 10 m ha of worlds irrigated land. In Pakistan 6.2-6.67 m ha land is affected with various levels of salinity, but having predominance of sodium salts with varying levels and mixtures of salts.
Pakistan is facing an acute shortage of good quality irrigation water to raise crops.Groundwater used as a supplement source of irrigation is mostly of poor quality owing to high EC, SAR and/or RSC. About 6.79 × 1010 m3 groundwater is pumped, of which 70- 75% is hazardous for irrigation on the basis of the criteria of the Department of Agriculture, Punjab. Continuous use of low quality water without the application of amendment(s) could make soils saline/sodic.
The reclamation of problem soils is a very important goal throughout the world, especially with saline or saline-sodic soils. Sodic and saline-sodic soils possess poor physical properties and fertility problems that adversely affect the growth and yield of most crops. The worldwide occurrence of such soils on 560 × 106 ha emphasizes the need for efficient, inexpensive, and environmentally acceptable management. These soils can be ameliorated by providing a source of calcium to replace excess sodium from the cation exchange sites. The reclamation of saline soils used many different methods such as physical amelioration (deep ploughing, subsoiling, sanding, profile inversion), chemical amelioration (amending of soil with various reagents i.e. (gypsum, calcium chloride, limestone, sulphuric acid, sulphur, iron sulphate), electro-reclamation (treatment with electric current). The most effective methods are based on the removal and exchange of soluble sodium and changing the ionic composition of soils by added chemicals with simultaneous leaching of sodium salts out of the soil profile. The biological amelioration methods using living or dead organic matter have two principal beneficial effects on the saline and alkaline soils reclamation: the improvement of the soil structure and permeability, thus enhancing salt leaching, reducing surface evaporation, and inhibiting salt accumulation in the surface layers; and the release of carbon dioxide during respiration and decomposition.
Moreover for the reclamation of saline-sodic soil, different soil conditioners, a material having ability to improve both soil physical and chemical characteristic like infiltration rate, water holding capacity, bulk density, soil pH, soil electrical conductivity, sodium adsorption ratio and availability of nutrient in soil are used. On the basis of their configuration, mechanism to reclaim ameliorate soil these are of different types, i.e. organic, inorganic, water soluble polymeric (Polyethylene glycol, polyvinyl alcohol) and hydro gel polymeric (polyacrylates, polyacrylamide, polyvinyl acetate maleic anhydride and other gel forming polymers). Organic sources comprise of farmyard manure, green manure, humic substances, peat and mulch, while in inorganic type the gypsum and crude sulfur are used. The use of gypsum as a source of Ca2+ is a well-establishedpractice for the amelioration and management of sodium saturated water/soils. Being easily available and cheap source of calcium gypsum is commonly used in Pakistan.Because of low solubility of gypsum and calcareous nature of soils its efficiency is reduced. However, itseffect in the amelioration process continues for few months until the whole of gypsum reacts with the exchangeable sodium of the soil.