Saline-Sodic soils

Saline – Sodic soils

There are four major tracts where salt affected soils are commonly met within India. These are

(i) The Semi-arid Indo-Gangetic alluvial tracts (mainly in Punjab, Haryana, Uttar Pradesh and a part of Bihar)

(ii) The arid tracts of Rajasthan and Gujarat.

(iii)The arid and semi arid tracts of southern states, particularly of the irrigated rigor (Vertisol) soils.

(iv) The coastal alluvium

It is estimated that about 7 million hectares of land have been affected by salinity/ Sodicity conditions in India.

Classification of saline sodic soils

Based pH, electrical conductivity (EC) and Exchangeable sodium percentage (ESP = Exchangeable Na x 100) saline –sodic soils are classified as follows.

 Soil EC ESP pH

Saline > 4.0 < 15 < 8.5

Sodic < 4.0 > 15 > 8.5

Saline – sodic > 4.0 >15 < 8.5 or > 8.5

Saline soils / white/ alkali/ solonchak

Soils with high amount of soluble salts having EC > 4.0 dsm-1 and white encrustations are seen on the surface. Hence it is called as white alkali.

Brown alkali

Saline soils with high proportion of nitrate salts.

Sodic soils: Two types

1. Black alkali/ solonetz

These soils have PH> 8.5 and ESP > 15 and with precipitated CaCO3. Dispersed clay with decomposed organic mater (humus) give black Colour to these soils and hence these soils are called as black alkali / solonetz (Russian term)

2. Degraded sodic / degraded alkali / solodi soils

These soils have exchangeable sodium percentage > 15. But the PH of surface horizon acidic in nature and there is no precipitate CaCO3. However, the sub surface horizon may have PH>8.5. In the assume of CaCO3 and soluble salts the sodic clay with water degrades and Hydrogen clay is formed in the surface. This process is known as solodization,and the soil is called as solodi in Russian terminology.

Na-Micelle + H2O   ---->>  H-Micelle + NaOH

Genesis of saline – sodic soils

1. Parent material

Soils formed from rocks having high proportion of bases are become salinc / sodic in nature.

E.g.: Basalt, Sand stone.

2. Low rainfall

One of the important reason for the development of saline-sodic soils. Insufficient water to remove bases from soil horizon leach to accumulation of salts in soil. This is more common in semi arid and arid regions where the rainfall is usually low.

3. High Evaporation

High evaporation is a common feature in semi arid and arid regions. Because of high evaporation more capillary movement of water from sub surface to surface. on teaching the surface water along evaporates to atmosphere leaving the salt to accumulate in the surface of soils.

4. Poor drainage

Water logged salinity / sodicity is a common seen in low lying area of islands particularly in high clay soils. Improper drainage leads to accumulation of salts at surface horizon and becomes reason for entry of sodium in clay complex.

5. Poor quality irrigation waters

Continuous use of poor quality saline / sodic water for cultivation accumulates salts / sodium in the soils.

6. High water table

High water table at alluvial plains and other areas leads to improper drainage which leads to accumulation of salts in soils.

7. Sea water intrusion

In coastal regions sea water intrudes into land and pollutes the soil as well as ground water of that locality.

8. Base forming fertilizers

Continuous application of base forming fertilizers for cultivation is also causes soil salinity / sodicity. Eg. NaNO3