Characteristics
• When the soil contains excess of sodium salts while in clay complex still contains preponderance of exchangeable calcium.
• The salts usually present in saline soils are the chlorides, sulphates, bicarbonates and sometimes nitrates of sodium.
• Soluble carbonate are usually absent.
• Among the anions, sulphates and chlorides are present in greater proportion than nitrates and bicarbonates.
• Sodium forms less than 50% of the total cations present in soil solution. The presence of chlorides and sulphates of sodium gives a white colour on the surface and such soil is known as “White alkali”. When nitrates are in excess, they give a brown colour to the soil and this soil is known as “brown alkali”.
• The pH of soil is <8.5, ESP <15 and EC while be >4 dSm-1.
• Wilting coefficient of saline soil is very high.
• Amount of available soil moisture is low.
• Excessive salts in the soil solution increases the osmotic pressure of soil solution in comparison to cell sap. This effect makes it more difficult for plant roots to extract water and nutrients.
• High concentration of soluble salts produces toxic effect directly to plants such as root injury, inhibition of seed germination.
Reclamation
In saline soils, reclamation consists mainly in removing the excess salts. This can be done either.
• By scraping the salt from the surface (or)
• Washing them down into lower layer beyond the root zone preferably completely out of the solum (or)
• By growing salt tolerant crops (or) by a combination of two (or) more of these methods.
Scraping helps to remove salts that have formed an encrustation on the surface, but it is never very helpful in complete reclamation. Substantial quantities of soluble salts are still present in the soil body and hinder plant growth.
The growing of salt tolerant plants with a view to remove salts is also not a practical proposition. Although these plants remove fairly substantial quantities of salts from the soil, comparatively larger quantities are still left behind. Salt formation is a continuous process, hence the reclamation is never complete.
(a) Leaching requirement (LR) – It may be defined as the fraction of the irrigation water that must be leached through the root zone to control the soil salinity at any specified level.
If the soil is not free draining, artificial drains are opened (or) tile drains laid underground to help in washing out the salts.
(b) Growing of salt tolerant crops
High salt tolerant crops – rice, sugarcane, sesbania, oats
Medium salt tolerant crops – castor, cotton, sorghum, cumbu
Low salt tolerant crops – pulses, pea, sunnhemp, sesamum
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