This article throws light upon the three main process of reclamation of saline soils. The processes are: 1. Physical and Hydrological Techniques 2. Biotechnology 3. Chemical Amelioration.
Process # 1. Physical and Hydrological Techniques:
The two main components of this process are:
1. Drainage
2. Leaching
1. Drainage:
Drainage means removal of excess of water and along with it the salts from lands. In general drainage can be of two types viz.
(i) Surface Drainage:
Surface drainage is the collection and removal of water from the surface of the soil. Two conditions favouring the use of surface drainage are low areas that receive water from surrounding higher land and impermeable soils that have insufficient capacity of dispose of the excess water by movement downward through the soil profile.
(ii) Subsurface Drainage:
In subsurface drainage ditches can be quickly and inexpensively made to remove gravitational water. Drainage ditches, however, require periodic cleaning andare inconvenient for die use of machinery.
Both these drainage systems have their values and limitations according to particular local situations.
For this the following factors will be of interest:
(a) The natural hydrological conditions of the area;
(b) The magnitude of seepage through canal irrigation and other sources that may augment the ground water recharge, and
(c) The additional leaching requirement for hydro technical soil improvement.
2. Leaching:
Leaching is the removal of soluble material by the passage of water through soil. Leaching is an essential part of the reclamation process, whether the soil is saline or alkali. Leaching is a very old process of removing salts from the soil and ameliorating saline-alkaline conditions. In leaching the field was embanked to hold rain water and subsequently ploughed in.
Leaching and Flushing:
Leaching is the method of transporting the soluble salts by downward movement of water through the soil. Flushing is the surface washing out of salts with the run-off water to be collected at the sloppy end of the field. Leaching is a more effective way of removing salts from the surface soil; the flushing is also occasionally resorted to supplement leaching in the reclamation process. Effects of Leaching on soil nutrients
The effects of leaching on soil nutrients are:
1. Leaching brought about losses of many important plant nutrients like nitrogen, phosphorus and manganese.
2. With heavy leaching trace element deficiency may occur.
Process # 2. Biotechnology:
It is well known that the decomposition of cattle manures and plant residues, in the soil, liberates carbon dioxide and organic acids which help to dissolve any insoluble calcium salts in the soil solution and also neutralize the alkali present. Decomposing organic matter improves soil permeability and increases water-stable aggregates.
The organic amendments for improvement of saline soil are:
Farmyard manure, molasses, sugar factory pressmud, green manures, crop residues and different weeds. The sugar factory molasses are no longer feasible on economic considerations. In the coastal alluvial soils of Masuliputain, Andhra Pradesh, molasses applied to sandy saline soils, with higher water-table, gave consistently better yield of paddy for four years, with a small dose of 2-5 tonne per hectare per year.
1. Green manuring and crop residues:
The common crops used for green manuring are dhaicha or Jantar (Sesbania aculeata), Sunnhemps (Crotalaria juncea) barseem (Trifolium alexandrieutn) sengi (.Melioletus parviflora) and cowpea (Vigna sinensis) etc.
They serve on decomposition as sources of readily available nutrients besides acting as solubilizing agent for calcium and neutralizing high pH of alkali soils. Consequent improvement in soil permeability and also increased biological activity, help in slowly regenerating the soil. Of all the plants used as green manure, Sesbania aculeata has been found most successful on saline soils.
The important characteristics of green manuring crops are:
1. Legume crops can neutralize alkalinity.
2. Highest calcium content on ash basis.
3. Thrive well under moderately saline conditions.
The application of 5- 0 tonnes per hectare of Sesbania green manure has been quite effective in gelling higher yields of paddy on saline soils of the mm coast in Andhra Pradesh.
2. Afforestation:
The plant species like Acacia arabica, Melia azadirachta, prosopis juliflora, Butea monosperrna, Tamarix articulata and Albizzia lebbeck can grow within certain limits on the salt-affected soils. Some species like Capparis aphylla, Capparis horrida, Salvadora oleoides and Zizyphus can be grown or even occur naturally on certain types of salty lands.
The forest growth exerts ameliorative effect on the soil by loosening the subsoil and improving permeability through the action of the root system. Organic matter is added by the leaf litter and root residues. Carbonic acid produced through root activity and decay of organic material, mobilizes calcium for replacement of exchangeable sodium. Besides, there is a general soil and ecological improvement through microbial activity and moderation of the micro-climate.
3. Bulky organic manures:
Farm manures has been successfully tried in the treatment of saline-alkaline soils in Haryana and Punjab. The application of 10 tonnes of farmyard manure with 15 tonnes of Sesbania green leaves proved almost as beneficial as 30 tonnes per hectare of Sesbania green manuring, in increasing the yield of paddy.
Process # 3. Chemical Amelioration:
Chemical amendments for the purpose of reclamation are either soluble calcium salts like calcium chloride and gypsum or relatively less soluble ground limestone and pressmud from sugar factories and slag from iron factories or acid and acid formers which work as calcium mobilizers like sulphuric acid, sulphur, iron sulphate, aluminium sulphate, lime sulphur etc.
Gypsum:
Sharma et al (1981) suggested that 0.59 mm fineness of gypsum was more effective in reclamation of saline and alkaline soils. It is safe, less costly and the supply of calcium for decreasing exchangeable sodium percentage of soils results in increased permeability of water to soil. It also helps in reducing the salts from root zone depth by the smooth flow of water in the soil profile. Conclusion
For successful desalinization of saline soils it is necessary that the zone of salt accumulation goes down to a depth from where resalinization is not possible. Along with this the ground-water, if not very deep, should also not rise beyond the critical depth, nor their mineralization increased to pose salinization problem subsequently.
It is not always possible to predict from the chemical and physical properties of soils whether they will reclaim rapidly or not. It is therefore desirable that leaching trials should be performed in advance, of development in doubtful cases. This may be expensive, but is justified if it resolves doubts as to be the behaviour of the soil under irrigation, or though most soils can be brought into use, the need for a prolonged period of reclamation may have a huge effect on the economics of development.