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In this article we will discuss about:- 1. Stages of Reclamation of Saline and Alkali Soils 2. Process in Reclamation of Saline and Alkali Soils 3. Uses.
Stages of Reclamation of Saline and Alkali Soils:
1. Leaching and Amending Stage:
Saline soils are leached by ponding an appreciable depth of water with adequate drainage.
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The objectives and measures to be considered in the course of leaching are:
1. Removal of excess salts to the depth of deepest root system of the crops in rotation.
2. Reduction of groundwater salinity to below the critical level.
3. Lowering the groundwater table sufficiently to remove the danger of it resalinising the soil.
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4. Avoiding alkalisation of saline-alkali soils by application of gypsum late in leaching and when the rate of infiltration slows down. Gypsum should not be applied before leaching to avoid its removal with other soluble salts.
2. Cultivation and Improvement Stage:
Protection of leached and amended soil against desalinization or realkalisation can be achieved by:
1. Securing drainage to keep groundwater table below the critical depth.
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2. Continuing periodic leaching to maintain the desired salt balance in the soil.
3. Starting to grow salt tolerant crops or those needing high irrigation water, such as rice.
4. Land levelling, furrow irrigations, pre-planting/seeding flooding, etc.
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Physical, chemical and biological soil properties can be improved by:
a. Deep ploughing to loosen compacted layers for improving soil structure.
b. Application of organic manures and balanced fertiliser use to improve soil fertility.
Reclamation of alkali soils depends mainly on the addition of suitable fertilisers after loosening the compacted layers and breaking hard pans, in addition to periodic flooding and drying with effective drainage. The cost and time of reclamation increase as texture becomes heavier and clay fraction becomes dominated by montmorillonite type.
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It is not necessary to use chemicals as a source of soluble calcium in calcareous soils. Calcium carbonate may be converted into more soluble from through application of acids or high rates of organic manures including green manures.
Process in Reclamation of Saline and Alkali Soils:
Reclamation of saline and alkali soils include some basic processes, such as leaching, drainage, application of chemicals, fertilisers and deep ploughing.
1. Leaching of Salts:
Leaching efficiency depends mainly on soil characteristics, sufficiency and suitability of leaching water constituents and depth of groundwater and prevailing climatic conditions.
Important points to be considered are:
1. Internal leaching should be preferred where calcium salts are high in the crust. Surface leaching may be done where there is a dense accumulation of sodium salts in the crust.
2. Internal flooding and drying are especially useful in leaching slowly permeable soils.
3. Basins should be levelled after ploughing and before leaching.
4. Leaching may be completed while growing some salt tolerant crops.
5. Leaching is not complete until salts have been removed to the desired soil depth to below the critical level.
2. Drainage:
Provision of adequate drainage is a basic principle in reclamation of saline and alkali soils.
1. Appropriate drainage depth should be determined. Drainage depth increases as groundwater salinity increases. Where deep drainage network cannot be installed, drain spacing should be closer.
2. Open drainage are preferable in early stages of reclamation, especially in soils of low permeability.
3. Effective maintenance of drainage system is essential at all the stages of leaching, amelioration, improvement and cultivation.
3. Chemicals:
Several chemicals such as gypsum, calcium chloride, sulphur, sulphuric acid and ferrous sulphate are used for soil amelioration.
While applying chemicals, the following points need consideration:
1. To ensure the highest efficiency of exchange between soluble calcium and exchangeable sodium, soluble salts have to be leached out of the soil profile before chemicals are used.
2. Chemicals like gypsum migrate slowly from surface to subsoil. Hence, they should be evenly distributed and carefully mixed with soil by deep ploughing.
3. Use of chemicals, preferably accompanied by periodic flooding and drying improves physical and biological characteristics of the soil.
4. Deep Ploughing and Subsoiling:
It is important to plough before leaching the soil. It helps to mix surface substances with the soil. Deep ploughing helps chemicals to reach lower depths and to improve soil permeability. Thus, it aids to leaching and stimulating chemical reactions in the soil.
Uses of Saline and Alkali Soils:
Where reclamation of saline and alkali soils is not possible, some crops may still be grown up to certain degree of salinity or alkalinity.
Adequate Water and Inadequate Drainage:
1. Avoid over irrigation to prevent rise of groundwater table.
2. Apply water at short intervals and in small quantities.
3. Grow salt tolerant crops, shallow rooted and those that tolerate high soil moisture regime.
Adequate Drainage and Unsuitable Water:
1. Use higher water rates to cover leaching requirements, keeping in mind that its salinity should not exceed that of soil saturation extract.
2. Chemicals should be used if the SAR and residual sodium carbonate in irrigation water are high.
Inadequate Drainage and Unsuitable Water:
Whenever available, rain water should be used. Land may be used as pasture or growing salt resistant plants such as palm trees.
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