Management of acidic, saline and alkaline soils
There is a great variety in their physical, chemical and biological properties, but they can be made to yield a good crop by
But there are some extreme soil conditions which do not provide a suitable medium for the growth of plants and desirable micro organisms. Such soils are either too acidic or alkaline and special measures have to be adopted to bring them in proper condition before any crop can be raised on them satisfactory and economically. In high rainfall areas, acidic soils are formed due to leaching of bases or salts. In arid regions where rainfall is low and temperature high, soils become saline or alkaline due to alkaline due to accumulation of salts in the surface soil.
The soil may become acidic due to the following factors:
The rainfall carries lime and other bases downwards beyond the reach of plant roots. In areas where rainfall is more than 1,000 mm., there is heavy leaching of calcium and other bases and saturation of the exchange complex by hydrogen ions takes place.
Some soils have developed from parent material which is acidic in nature, e.g. granite.
Some fertilisers like ammonium sulphate and ammonium chloride increase soil acidity. If there is no sufficient free lime in the soil, continuous use of ammonium sulphate or chloride may cause soil acidity.
Micro-organisms decompose organic matter in the soil and organic acids are continuously being formed. If these acids are not neutralized by free lime or bases to make the soil acidic.
Effect of soil acidity on plants
Management of soil acidity
It can be corrected by liming. The liming material may be ground lime stone (CaCO3), burnt lime (CaO) or hydrated lime Ca (OH)2- When lime is added, the soil solution becomes charged with calcium ions which replace hydrogen ions in the exchange complex. When burnt (CaO) or slaked or hydrated lime Ca (OH)2 is added to acidic soil, it changes into calcium bicarbonate, which in solution reacts with soil colloids.
Lime should be applied before ploughing or on ploughed land well before cropping and should be thoroughly mixed with the soil by discing. Efficient way to use lime is to apply it in small quantities every year or once in two years. If the quantity is not more than five tons per hectare it can be applied in one dose. If the dose is more one half is applied before ploughing and the remaining half applied and worked in after ploughing.
For medium acidic soil with pH upto 5.6- jowar, maize, wheat, sweet potato, tobacco, tur, velvet bean, turnip. In strongly acidic soils with pH upto 5.1.- potato,rice, oats, rye,cowpea, linseed, grasses, tea and coffee.
Saline and alkali soils
Saline and alkali soils are generally noticed in arid and semi arid regions where there is low rainfall and high temperature causing intense evaporation.
The percentage of exchangeable sodium is more than 15. The pH is 8.5 and 10.0.and electrical conductivity less than 4 mmhos/cm., at 250C.
The exchangeable sodium percentage is less than 15 and the pH below 8.5 and electrical conductivity value of 4 or more mmhos/. cm. at 250C. It indicates white incrustation and therefore called as white alkali soil.
It contains exchangeable sodium in excess of 15 p.c. The pH is 8.5 or more and an electrical conductivity more than 4 mmhos/cm., at 250C.
Management of saline alkali soils
In these soils the exchangeable sodium is so great as to make the soil almost impervious to water. Large quantities of gypsum are applied to replace sodium and leached downward and out of reach of plant roots. Gypsum is applied on the soil surface and mixed by harrowing tow to four weeks before sowing @ 2.5 to 5.0 tons per hectare.
Leaching and draining away of salts by rain and irrigation water.
Scraping off surface salts from highly saline patches.
In extreme cases sulphur is used to reduce alkalinity. Ground sulphur is incorporated into the soil several weeks before planting of the crop. The quantity of sulphur required is depending upon the soil and climatic conditions. The pH upto 8-1.25to 2.5 tons of sulphur and 5 to 7.5 tons of organic matter per hectare will be required to reduce the pH to about 6.5.
Example of superphosphate or ammonium sulphate which increases acidity in soil and maintains fertility of soil impoverished by leaching and cropping.
In alkali soil green manuring of dhaincha has been found to be beneficial along with gypsum in resorting physical condition and enriching the soil in nitrogen and organic matter.
Molasses are used to reclaim alkali soils @ 5 tons/ha.alongwith with 2.5 to 5 tons of press mud and 50 to 100kg. It provide source of energy for micro-organisms and on fermentation, produce organic acids which reduce alkalinity while press mud help in reducing exchangeable sodium.
For moderately alkaline (pH upto 8.4) Barley, sugarbeet, cotton, sugarcane. For salty soils- date palm, coconut, arecanut. Garden beet, spinach and asparagus are very salt tolerant while radish and beans are sensitive to salt.