For the management of problematic soils, some general principles has to be considered for proper implementation of the reclamation measures. The total soluble salt concentrations in the root zone have to be decreased to control osmotic effects on plant growth. Maintenance of total soil moisture tension must be ensured at optimum level so that plant roots can absorb an adequate amount of water.
Water flows through the soil in the direction of maximum decrease of hydraulic head and the flow velocity is proportional to the hydraulic gradient. The design and layout of drainage system are controlled by this principle.
The availability of good quality water is of paramount for leaching and drainage of soluble salts.
The Salt concentration in soil solution upward movement of salts and their accumulation increase with an increase in the evaporation and transpiration from the surface of the soil and the vegetation, especially when the ground water table is shallow.
Increase or decrease of salts in the root zone depends upon whether the salt inputs are higher or lower than the salt outputs.
The cations in the soil solution and those adsorbed on exchange complex are in equilibrium with each other. The dispersion and effectiveness of amendments are controlled by this principle.
Management of Saline and Non- saline alkali soil
Some chemicals are added to the soil as an integral part of the reclamation program adopted to improve the saline and alkali soils. These are known as chemical amendments. The principal purpose of the amendments is to furnish soluble calcium to replace exchangeable Na or to neutralize alkaline salts with acid. The various chemicals suitable for different soil conditions are:-
Gypsum: Gypsum a natural sulphate of calcium is found in large deposit in various parts of Rajasthan. It reacts with exchangeable Na with getting converted into sodium sulphate. Sodium sulphate is from the soil to reduce pH. The addition of gypsum improves the physical conditions of soil. Soils become flocculated and drainage improves.
CaSO4 + 2 Na X = Ca X + Na2SO4
Sulphur: Sulphur is a very effective chemical amendment to replaces exchangeable Na. Theoretically, one atom of sulphur replaces four Na ions by calcium. But under field conditions approximately, three exchangeable Na ions per atom of sulphur are replaced from the soil colloids.
Iron sulphate: Iron sulphate is sometimes used as a chemical amendment for improving alkali soil. Iron sulphate forms sulphuric acid, which is converted into calcium sulphate. Calcium sulphate, thus formed replaces exchangeable sodium as indicated by following equations.
FeSO4 + H2O ----- H2SO4 + FeO
H2SO4 + CaCO3 ------- CaSO4 + H2O + CO2
Lime stone: Ground limestone is applied to the soil having pH at 7.0 to 7.5. Since Calcium carbonate become insoluble as the pH increases, it is not effective on soils having pH more than 7.5. Following the reaction takes place:
2NaX + CaCO3 --------CaX2 + Na2CO3
When lime stone is applied to the soil, it gets dissolved in the soil solution. The Calcium of the lime stone reacts as with the spoil complex and replaces Na and Na combines with carbonate and form sodium carbonate which is leached down by flooding.
Flooding and leaching down of the soluble salts. The leaching can be done by ponding the water on the land and allowing it stand there for a week. Most of the soluble salts would leach down and below the root zone. After a week standing water is allowed to escape, such 2 to 3 times treatments given to reclaim highly saline soils. Sometime gypsum is also added to flood water when the soluble salts are low in Ca to check the development of alkalinity.
Scraping of the surface soil when the soluble salts accumulate on the soil surface, scraping helps to remove salts. This is a temporary cure and salinity again develops on such soils.
Providing proper drainage if the soil is not free draining artificial drains are opened or tile drains laid underground to help wash out the salts.
Few of salt free irrigation water good quality of irrigation should be given.
Proper use of irrigation water, it is known that as the amount of water in the soil decrease the concentration of the salts in the soil solution of the salts in the soil solution is increasing thus moisture should be kept at optimum field capacity.
Use of acidic fertilizes: In saline soil acid fertilizers such as ammonium sulphate should be used
Use of organic manures: When sufficient amount of manures is added the water holding capacity of soil increased and as a result the conductivity of the soil solution decreases.
Ploughing and levelling of the land: Ploughing increasing the infiltration and percolation rate. Therefore salts leached down to the lower levels.
Returning of water evaporation: Mulching with crop residues or plastic sheet helps in decrease evaporation.
Growing of the salt tolerance crops:
High salt tolerance crop: Barley, Sugar beet, Para grass etc.
Moderately salt tolerant crops: Wheat, rice, maize, sorghum
Low salt tolerance crops: Beans, radish, white clover etc.
Sensitive crops: Tomato, potato, onion, carrot etc.
Management of Organic Soils:
All sorts of vegetable crops may be grown on organic soils. In some cases peat is used for field crops, but the higher valued vegetables and nursery crops are more common. In fact, almost any crop will grow on organic soil if properly managed.
Structural Management: Ploughing is not necessary every year since peat is porous and open unless it contains considerable silt and clay. The longer a peat has been cropped the more important compaction is likely to be a cultivation tends to destroy the organic granular structure, leaving the soil in a powdery condition when dry. It is then susceptible to wind erosion a very serious problem.
Use of lime: Lime, which so often must be used on mineral soils. Ordinary is less necessary on organic soils unless they have developed in regions low in calcium in the surrounding uplands. On acid mucks containing appreciate quantities of inorganic matter, however, the situation is quite different. The highly acid conditions result in the dissolution of Fe, Al, and Mn in toxic quantities. Under these conditions large amounts of lime may be necessary to obtain normal plant growth.
Commercial fertilizers: Of greater important than lime or commercial fertilizers. In fact, these materials are needed for crop production especially vegetables. As organic soils are very low in phosphorus and potash these elements must be added. Since vegetables usually are rapid growing plants succulence often being an essential quality, large amounts of ready available nitrogen are necessary. Newly cleared peat soil requires at the beginning only a small amount of nitrogen with the phosphorus and potash.
Micronutrients: Peat soils are in need of not only N, P and K but also often some of the trace elements as well. Copper sulphate and salts of manganese and Zinc are used to meet plant needs on peat and muck soils. Boron deficiency is also becoming evident.
Management of waterlogged soils:
Water logged soils are managed in the following ways:
Drainage: drainage removes excess water from the root zone that is harmful for the plant growth. Land can be drained by surface drainage, sub-surface drainage and drainage good method.
Controlled irrigation: Excess use of water in the irrigation results in water logged area.
To check the seepage of canal: Due to seepage land becomes water logged.
Flood control measures: Construction of bund may check water flows river of the cultivated land.
Plantation of trees having a higher evaporation rate: Transpiration rate of certain trees like Eucalyptus, Acacia is very high. In transpiration process the underground water is consumed by trees, thus lowering the ground water table.
Selection of crops and their varieties: Certain crops like paddy, water nut, jute and Sesbenia can tolerate waterlogged conditions. In trice crop sub-merged varies from variety to variety. Generally lowland and deep water varieties can tolerate water logging, but upland varieties do not have this capacity.
Methods of sowing: In water logged areas, sowing should be done on bunds or ridges. In this method there is a scope of good aeration near the root zone.
Nutrient management: Low nitrogen fertility is an important constraint in the waterlogged soil. The predominant form of nitrogen in water logged soils is NH4.
Management of calcareous soils:
Management and reclamation of calcareous soils are not difficult because the pH in such soil is not very high. Generally, this is no need of chemical amendments for reclamation of calcareous soil. The calcareous soils can be managed in the following ways:
- Tillage operation: Light (Sandy) calcareous soil develops a large number of pore spaces due to flocculation. This type of soil has poor water holding capacity. Therefore, such types of soils are needed compaction by plank and roller to increase the water holding capacity.
- Application of organic manure: When sufficient amount of farmyard manure composts and green manure is added, the amount of carbon dioxide and acid increase and as a result pH of soil decreases.
- Use of chemical fertilizers: Availability of phosphorus is less in calcareous soil. To increase the availability of P, the phosphorus fertilizers should be used in the following manner
- Phosphatic fertilizers should be used near the root of the plant.
- Use of Phosphatic fertilizer in ball form also increases the availability of P.
- P may be used in split form.
- Use of micronutrients: Addition of micronutrients like Zn, Fe and Cu would be helpful in increasing the yield.
Jugal K. Malav1, K. D. Gulkari2 and N. D. Dholariya3
1Ph. D. Scholar, Department of Agricultural Chemistry & Soil Science, B. A. College of Agriculture, Anand Agricultural University, Anand-388110 Gujarat.
2Research Scholar,Sardar Patel Museum, Anand Agricultural University, Anand Gujarat.
3Agricullture Officer Main Vegetable Research Station, Anand Agricultural University, Anand Gujarat.