In arid and semi-arid regions, rainfall is too low to leach or remove saline material from the topsoil. In addition, water moves upward by capillary action along with the dissolved alkali salts which evaporate on reaching the soil surface. The salts get deposited in the sub-soil as a hard layer or pan. Excessive removal of acidic ions results in the accumulation of basic ions which make the soil alkaline.
Factors that make the soil alkaline:
1. Due to the excessive accumulation of salts, the concentration of the soil solution becomes high. It reduces the absorption of nutrients by plants and causes plasmolysis of cell cytoplasm in plants which can sometimes be fatal. All these effects are responsible for the stunted growth of plants.
2. If sodium is absorbed by plants in excess, it shows toxic effects. Chloride salts of alkaline elements cause the death of trees. BaCO3 and BaCl2 are toxic to all plants.
3. The presence of excess salts in the soil retards seed germination and plant growth. Plants die before bearing fruit.
4. Alkali salts present in the soil also affect plant growth by reducing the size of leaves in alkaline soil, plant roots remain shallow, stem bark becomes brown or black, and green tissues are less developed. Sodicity has serious effects on agricultural production.
Caused of poor productivity of sodic soil:
1. High content of Na+ ions (exchangeable) coupled with high pH has a toxic effect on roots and damage roots. Under extreme cases, the roots and the soil organic matter present in the soil get dissolved.
2. Poor aeration is another important cause of the poor productivity of the soil. Roots cannot get sufficient oxygen from the soil atmosphere. CO2 of soil atm is very high and O2 is low. So, roots cannot respire which resulted in poor productivity.
3. Deflocculation and swelling of clay due to high exchangeable Na. This causes the tillage operation very difficult and causes poor productivity.
Alkali/Sodic Soil Reclamation
1. Chemical Methods:
2. Cultural method
3. Hydrological:
4. Physical Methods:
5. Biological method:
Management strategies:
1. Bulky organic manure, green manure, crop residues and other biological materials which produce weak organic acids help in creating temporary acid conditions and help in reclamation. The high content of Na+ ions (exchangeable) coupled with high pH has a toxic effect on roots and damage roots. Under extreme cases, the roots and the soil organic matter present in the soil get dissolved.
2. Leaching with good quality water (low SAR) must follow the application of the reclaiming materials.
3. A good crop rotation is an excellent insurance agt. Sodicity problem; rice- dhaincha-rice-berseem is good
4. Frequent irrigation with small quantities of water is the successful irrigation management practice
5. Sometimes, the permeability of soil can be increased by deep plowing.

свернуть