India has varied relief features, landforms, climatic realms and vegetation types. These have contributed to the development of various types of soils in India. As products of natural environmental processes, they can be broadly divided into two groups: in situ soils and transported soils.
The in situ soils get their distinguishing features from the parent rocks, which are sieved by flowing water, sliding glaciers, and drifting wind and are deposited on landforms such as river valleys and coastal plains.
Soils of India: Classification and Characteristics
On the basis of genesis, colour, composition and location, the soils of India have been classified into:
- They are depositional soils.
- Found in northern plains and river valleys and cover about 40% of total area of the country.
- They are generally rich in potash but poor in phosphorous.
- New alluvium found on much of Indo-Gangetic floodplain is called khadar and is extremely fertile and uniform in texture; conversely, the old alluvium on the slightly elevated terraces, termed bhangar, carries patches of alkaline efflorescence’s, called usar, rendering some areas infertile.
- In the Ganges basin, sandy aquifers holding an enormous reserve of groundwater ensure irrigation and help make the plain the most agriculturally productive region of the country.
- These are in situ soils.
- Covers most of the Deccan Plateau. Those soils are also found on many peripheral tracts where the underlying basalt has been shifted from its original location by fluvial processes.
- Deep black soils are also known as the ‘Regur Soil’ or the ‘Black Cotton Soil’.
- The black soils are generally clayey, deep and impermeable.
- They swell and become sticky when wet and shrink when dried (self-ploughing soils).
- They are poor in humus yet highly moisture-retentive, thus responding well to irrigation.
- Chemically, the black soils are rich in lime, iron, magnesia and alumina. They also contain potash. But they lack in phosphorous, nitrogen and organic matter.
RED AND YELLOW SOILS
- Develops on crystalline igneous rocks. These are also in situ soils.
- The soil develops a reddish colour due to a wide diffusion of iron in crystalline and metamorphic rocks. It looks yellow when it occurs in a hydrated form.
- The fine-grained red and yellow soils are normally fertile, whereas coarse-grained soils found in dry upland areas are poor in fertility.
- They are generally poor in nitrogen, phosphorous and humus.
- It develops in areas with high temperature and high rainfall experiencing intense leaching.
- Lime and silica are leached away, and soils rich in iron oxide and aluminium compound are left behind.
- These soils are poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess. Hence, laterites are not suitable for cultivation.
- Red laterite soils in Tamil Nadu, Andhra Pradesh and Kerala are more suitable for tree crops like cashew nut.
- Laterite soils are widely cut as bricks for use in house construction.
- Sandy in structure and saline in nature. They lack moisture and humus.
- Nitrogen is insufficient and the phosphate content is normal.
- Lower horizons of the soil are occupied by ‘kankar’ layers which restricts the infiltration of water, and as such when irrigation is made available, the soil moisture is readily available for a sustainable plant growth.
- These soils are poor and contain little humus and organic matter.
- They are also known as Usara soils. They are infertile.
- They occur in arid and semi-arid regions, and in waterlogged and swampy areas.
- They lack in nitrogen and calcium.
- Saline soils are more widespread in western Gujarat, deltas of the eastern coast and in Sundarbans areas of West Bengal.
- Excessive irrigation with dry climatic conditions promotes capillary action, which results in the deposition of salt on the top layer of the soil.
- Gypsum is added to solve the problem of salinity in the soil.
- They are found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation.
- Large quantity of dead organic matter accumulates in these areas, and this gives a rich humus and organic content to the soil.
- At many places, they are alkaline also. It occurs widely in the northern part of Bihar, southern part of Uttarakhand and the coastal areas of West Bengal, Odisha and Tamil Nadu.
- They are loamy and silty on valley sides and coarse-grained in the upper slopes.
- In the snow-bound areas of Himalayas, they experience denudation, and are acidic with low humus content. The soils found in the lower valleys are fertile.