Main Types of Salt Affected Soils Found in India

This article throws light upon the five main types of salt affected soils found in India. The types are: 1. Saline Soils 2. Coastal Saline Soils 3. Sodic Soils 4. Acid Sulphate Soils 5. Potential Acid Sulphate Soils.

Salt Affected Soil: Type # 1. Saline Soils:

Soluble salts containing chlorides and sulphates of sodium, calcium and magnesium accumulate in soils. The concentrations of potassium, carbonates, bicarbonates and nitrates are comparatively low. Soluble salt concentrations are measured by the electrical conductivity of the soil extract. The sources of salts in soils are soil itself, parent materials, ground and irrigation water lead to the salinity in soil.

Soluble salts move upwards along with rise in water table as well as high rate of evapotranspiration through capillary movement. Soil salinisation in coastal areas is due to accumulation of salts from inundated sea water.

In the Indo-Gangetic Plain of Punjab, Haryana, Uttar Pradesh and Bihar saline sodic soils are usually found in high pH (9.0-10.2) high soluble salt content (EC in between 10 and 100 dSm-1) and high ESP> 40/SAR>13.

The saline soils have high soluble salts (ECe> 4 dSm-1) of chlorides and sulphates of sodium, calcium and magnesium, low ESP (< 15) or low SAR (<13) and have pH values of less than 8.5. High osmotic pressure prevails in such soils which prevents absorption of water and nutrients by the plants.

Salt Affected Soil: Type # 2. Coastal Saline Soils:

Most coastal saline soils are found in the deltaic regions of major rivers in India falling either into Bay of Bengal or the Arabian Sea. The coastal soils of deltaic region are generally formed from the deposits of alluvial materials entering into the sea and transported back by the tides and re-deposited in the estuarian/deltaic regions.

Both groundwater and the soils are rich in chlorides and sulphates of sodium, calcium and magnesium. The soil salinity and the depth of groundwater table vary with seasons—maximum and minimum in dry and monsoon months respectively.

The pH of such soils normally vary from slightly acidic to slightly alkaline excepting soils with high amount of pyrite which becomes strongly acidic on drying or under aerobic conditions. Such soils are present in the coastal regions of Kerala, Sundarban area of West Bengal, and in Andaman & Nicobar Islands. 

Salt Affected Soil: Type # 3. Sodic Soils:

The process of formation of sodic soils is due to the exchange of cations in the soil solution with those present on exchange complex of the soil. In India, sodic soils are dominant in areas where mean annual rainfall is 55-90 cm. These soils usually occur in relatively low lying areas with lack of drainage where the weathering products accumulate during the monsoon period.

In arid regions as the soil solution becomes concentrated through evaporation of water absorption by plants, the solubility limits of calcium sulphate, calcium carbonate and magnesium carbonate are often exceeded, in which case they are precipitated with a corresponding increase in sodium concentration.

Under such conditions, a part of the original exchangeable calcium and magnesium is replaced by sodium resulting sodic soil. Besides, saline-sodic and degraded soils are also found in some areas of India.

Salt Affected Soil: Type # 4. Acid Sulphate Soils:

Acid sulphate soils develop due to leaching of soils containing high amount of pyrite minerals especially FeS2- It is also called as cat clays. In recent coastal plains and inter-tidal swamps, there are an estimated 12 Mha, mostly in the tropics where the top soil will become extremely acidic (pH< 4.0). There is probably a much greater area of potentially acid material covered by a shallow layer of non-acid peat or alluvium.

Acid sulphate soils occur more or less in parts of Kerala, (Kari soils), Tamil Nadu (South-east coast), Indian Sundarbans (parts of West Bengal and mangrove areas of Andaman & Nicobar Islands). The acid sulphate soils in addition to having pH less than 4 under aerobic condition is associated with yellow mottles or coatings of Jarosite and deposition of ochre in the soil or in drainage waters.

Sometimes, in poorly drained soils, Jarosite cannot be seen even under severely acid conditions. Old acid sulphate clays that have ripened or matured naturally typically have very dark coloured topsoil, prominently mottled subsoil with reddish-brown mottles and nodules of iron oxides, and yellow Jarosite mottles at greater depth.

Salt Affected Soil: Type # 5. Potential Acid Sulphate Soils:

Potential acid sulphate soils are not acid but will become acid if they are drained. Typically, they are immature, saline and give off a strong smell of hydrogen sulphide when disturbed. Mineral soils are very dark grey and rich in organic matter. They do not contain sufficient shell or other carbonates. Saline and brackish water tidal swamp and marsh constitute by far the most extensive potential acid sulphate environment.