Production of salts is caused by the process of weathering of original matter in the soil.
Soil becomes saline by transfer of salts from underground water or from the solution of soil which comes from the lower layer to the upper layer.
Thus, salinity develops from redistribution or transfer of salts in soil itself. In India, saline soils are found in an area of 71 lakh hectares, out of which 7.28 lakh hectares lie in Rajasthan.
Moreover, such types of soil are mostly found in dry areas, because suitable arrangement for exit of water does not exist in this type of soil and evaporation is also more, due to which soluble salts collect in the form of a layer on the surface of the soil. The main salts are Sodium, Calcium, Magnesium, Chloride of Potassium, Sulphate, Carbonate, Bicarbonate etc.
According to a salinity laboratory of United States of America, saline soils are of the following types:
1. Saline Soil:
Soluble salts of Sodium, Calcium, Magnesium, Potassium of Chloride and Sulphate collect in saline soils, which cover the land in the form of a white layer. Gedroij has called ii Solon-Chalk, which is also called as reh, kallar or barren land Saline soil means such soil in which electro conductivity of saturation extract of soil is more than 4 desisimens per metic (ds/m), exchangeable sodium is less than 15 per cent and pi I value of soil is less than 8.5.
2. Non-saline Sodic Soils:
Soils in which electro conductivity of saturation extract of soil is less than 4 desisimens per metre (ds/m), exchangeable sodium is more than 15 per cent and pH value of soil is more than 8.5 are called non-saline sodic soils. Due to sufficient sodium salt in these soils, quantity of exchangeable sodium is also more, as a result of which the physical condition of these soils is not good. There is lesser communication of water as well as air in non-saline soils. In the sub-surface soil, a layer of hard pebbles collects due to which water cannot percolate below it and the land becomes sticky. Some soil scientists have named it as black barren land and solonetz.
3. Saline Sodic Soils:
Due to more sodium salts in these lands, quantity of exchangeable sodium is also more, as a result of which physical condition of these soils becomes deformed and communication of water and air becomes lesser. It is also called barren land. In its main features, electro conductivity of saturated extract of soil is less than 4 ds/m, exchangeable sodium is more than 15 per cent and pH value of soil is more than 8.5.
Such classification can be clarified as under:
Effects:
When soil is affected by salts, its productive capacity decreases and plants sown therein cannot develop in a good condition. In saline soils, sprouting of seeds does not take place in a proper way while raising crops. When land becomes saline, water and organisms from I capillaries come back in the soluble soil, hence plants start withering and dying. The roots of plants are also not able to absorb water and nutritive elements in the required quantity. Even though humidity exists but plants feel absence of humidity.
Management of Saline and Alkaline Soils:
Saline and alkaline soils are the main hindrance in water management. Without their management, proper water management cannot take a scientific form, whereas agriculture is strongly dependent on them.
The following methods are adopted for their management:
1. Physical Measures
2. Chemical Measures
3. Soil Management Measures
1. Physical Measures:
1. Leaching:
When soil elements after dissolving with water go down from upper parts to the lower level, it is called leaching. In this method, saline elements of the soil are transferred to lower levels after dissolving with water. This water, along with the supply of water to crops, takes away salts after dissolving them. That is why more water is required in this method. This process is mostly adopted in dry season. The fields are divided into small fragments through bunding on the boundary so that water is conserved there, reducing the effect of salts.
2. Bringing Salts out of Soil after dissolving them:
Sometimes a layer of salts collects on the surface of the soil. Such salts are dissolved by spreading water and taken out. Though in this method there is a danger of loss of productive soil on the surface of soil also going out, but quantity of salts is reduced to a great extent and soil becomes fit for cultivation.
3. Scratching:
Many times the salts are collected in a large quantity and it looks like a heap. Then it has to be scratched out from the field to reduce salinity of the soil. This method not practicable on a large scale.
4. Water Discharge:
Discharge of additional water in excess of the required quantity in any field is called water discharge or exit. With discharge of additional water, concentration of salts does not take place. Drains may be constructed in the field so that excess water keeps on discharging.
2. Chemical Measures:
In alkaline soils, exchangeable sodium exists in different quantities hence leaching of sodium should be done.
Elements assisting in removal of exchangeable sodium from surface of soil can be divided in three categories:
1. Solvent Calcium Salt: Gypsum and Phospho Gypsum
2. Little Soluble Calcium Salt: Lime Stone
3. Acid and Acid Producing: Sulphur, Acid of Sulphur, Pyrites etc.
The above reformers are helpful in improving such soils but some are not available at all places. Gypsum and Iron Pyrite are comparatively costly but they are easily available. Gypsum should be mixed up to 10 or 15 cm. depth. Calcium ion found in gypsum displaces exchangeable sodium ion and converts sodium chloride into calcium. Iron Pyrite contains 22 per cent sulphur. Due to sufficient humidity in soil, its oxidization takes place.
3. Soil Management Measures:
Besides physical and chemical measures, soil improvement can also be done by soil management for which traditional knowledge of farmers is more important. If regular management of these soils is not done, they may again convert into saline soils.
The following methods are important among them:
1. Preparation of the Field:
Maintenance of fields is important for soil management. Fields should be kept leveled so that any soil improvement means can be easily adopted. Water distribution during irrigation is balanced in leveled field which prevents concentration of salts.
2. Method of Preparation of Basin and Sowing:
In saline and alkaline soils, due to effect of salts and alkaline on seeds, sprouting is not easily possible. Hence, it is advised that sowing of crop should be done on the slope by following furrow and basin method. In basin irrigation, the salt collects near the basin, the adverse effect of which is visible on plants. Special attention should be given to irrigation.
3. Make Crop Rotation Effective:
These soils should not be kept fallow but cultivation should be continuously done according to crop rotation. Crops should be sown which can bear salts, for example mainly beet, potato, barley, wheat, cotton etc.
4. Irrigation:
Salinity affects sprouting of seeds. Hence, during first irrigation, more quantity of water should be supplied to neutralize the effect of salts. Thereafter, even during subsequent irrigation, along with reducing the quantity of water, even duration between two irrigations should be reduced so that soil does not get dry and dissolution of salts continues in the humid soil.
5. Bring Reduction in Evaporation:
Saline and alkaline soils must be kept moist so that salts may not collect over the soil surface. Hence, prevention of evaporation is very essential. The cover of vegetation and grass etc. should be kept over the soil. Duration between crops should also be kept comparatively shorter.
6. Use of Carbonic Material:
Biotic and carbonic materials, along with bringing improvement in physical qualities of soil, also generate carbon dioxide during their breaking up, which forms carbonic acid on contact with water. This reduces the quantity of salinity. Use of green manure, cow dung manure, compost etc. also reduce salinity.
7. Use of Fertilizers:
Use of fertilizers in somewhat greater quantity than normal in saline and alkaline soils is beneficial. Normally deficit of zinc, iron, manganese, and nitrogen etc. elements is found in such soils, hence productivity can be increased by use of these elements.
8. Growing of Crops Bearing Salts and Alkaline:
In these soils, such crops may be sown which can bear salts. Such crops are mainly beet, rice, dhencha, mustard. Other normal crops are linseed, jowar, barley, jai, spinach, wheat, sugarcane, bajra, cotton, barseem, chari and rijka etc.