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.Saline and alkaline soils

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.Saline and alkaline soils
  .Saline and alkaline soils and their management in agriculture It has been estimated that about 7 m ha’s of land in India are affected with Saline and alkaline soils out of total cropped area in Karnataka about lakh ha’s of land are salt affected. Salt affected soils are designated as problem soils and are unproductive unless excess salts are reduced or removed. These soils occur most extensively in arid climates, but these soils are also found in coastal sea areas where soils are inundated by ocean or sea water. Soils are said to be saline if they contain excess of soluble salts and sodic or alkaline if they contain an excess of sodium. Again the soils are said to be saline alkali if they contain appreciable amounts of both soluble salts and sodium. Saline soils Saline soils are defined as soils having a conductivity of the saturation extract >4dsm -1  and an exchangeable Na percentage is <15 and pH is <8.5. Formerly these soils were called as white alkali soils because of surface crust of white salts. Alkali soils or Sodic  Alkali soils or Sodic soils are defined as the soil having a conductivity of the saturation extract >4dsm -1  and an exchangeable Na percentage is >15 and pH is 8.5- 10. Saline alkali soils Saline alkali soils are defined as the soil having a conductivity of the saturation extract >4dsm -1  and an exchangeable Na percentage is >15 and pH is 8.5 depending on the relative amounts of exchangeable sodium and soluble salts. When soils dominated by exchangeable sodium then the  pH will be >8.5. When soils dominated by soluble salts pH will be <8.5. Degraded alkali or Sodic soils If the extensive leaching of saline- sodic soils occur in the absence of any source of Ca or Mg,  part of the exchangeable sodium is gradually replaced by hydrogen the resulting soil may be slightly acidic with unstable structure. Such soils are called as degraded alkali or sodic soils. Sodium carbonate dissolves humus and is deposited at the lower layer and thus low layer acquires a black colour. Sources of soluble salt There are various sources from which soluble salts are accumulated in soils. 1.   Primary minerals:  it is the srcinal and important source of all the salt constituents. During the process of chemical weathering involving hydrolysis, hydration, solution,  oxidation and carbonation, various constituents like Ca 2+,  Mg 2+ and Na +  are gradually released and made soluble. 2.   Arid and semiarid climate: Salt affected soils are mostly formed in arid and semiarid regions where low rainfall and high evaporation prevails. The low rainfall is precipitation in these regions is not sufficient to leach out the soluble weathered products and hence the salts accumulate in the soils. During rain the salts dissolve in rain water and migrate downwards. However due to limited rainfall the downward movement is restricted to a short distance only, in dry weather the salts move up along with water and brought up to the surface where they are deposited as the water evaporates. 3.   Ground water:  It contains large amounts of water soluble salts which depend upon nature and properties of the geological material with which water remains in contact where water table and evapo-transpiration rate is high. The salts along with water move upwards through capillary activity and the salts accumulate on the soil surface in the form of crystallization. 4.   Ocean or sea water:  Sea water enters into the land by inundation and deposited as soil surface salts. 5.   Irrigation water:  application of irrigation water without the drainage and leaching facilities in the salt affected soils increases the water table and surface salt content in soils. 6.   Salta blown by wind:  In the arid regions near the sea, appreciable amounts of salts are  blown by wind year after the year and get deposited on the surface soils. Due to low rainfall the deposited salts are not washed back to the sea or leached to the lower soil horizon and thereby develop salinity in the soil. The salinity of Rajasthan is mostly developed through this source. 7.   Excess use of basic fertilizers:  Use of basic fertilizers like sodium nitrate, basic slag etc may develop soil alkalinity.
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