Soils of India UPSC

Soils of India

The mixture of rock debris and organic materials which develop on the earth‘s surface. 

• The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time. 

• Components of the soil are mineral particles, humus, water and air.

Soil Profile of India

The soil profile is made up of layers, running parallel to the surface, called Soil Horizons. These layers are distinguished by their physical and chemical properties.

1. O-Horizon: 

The O-horizon is very common to surfaces with lots of vegetative cover. It is the layer made up of organic materials such as dead leaves and surface organisms, twigs and fallen trees. In fact, the ‘O’ designation refers to this horizon’s high content of organic debris and humus. It is often black or dark brown in colour, because of its organic content. It is the layer in which the roots of small grass are found.

2. The A-Horizon: 

The A horizon, immediately below the O horizon, is usually known as the topsoil. It is the top layer soil for many grasslands and agricultural lands. In general, A horizons  are dark because they contain decomposed organic matter.

3. The E-Horizon: 

The E horizon is usually lighter in colour, often below the O and A horizons. It is often rich in nutrients that are leached from the top A and O horizons. It has lower clay content and is common in forested lands or areas with high-quality O and A

horizons.

4. The B-Horizon: 

Below the E-horizon is the B-horizon, a zone of accumulation, where much of the nutrients removed from the A and E horizons are deposited. It is the layer in which the roots of big trees end. There is a close relationship between the A and B horizons. Translocations, as well as, many biological and chemical reactions take place between them. The B horizon, however, tends to be more stable than the A for short term differences.

5. The C-Horizon: 

The C horizon is the weathered parent material from which the soil has developed. This layer is the first stage in the soil formation process and eventually forms the above two layers. The C horizon is also known as saprolite.

6. The R-Horizon: 

It is the unweathered parent material.

Classification of Indian Soils: 

• In ancient times, soils used to be classified into two main groups – Urvara and Usara, which were fertile and sterile, respectively.

• Indian Council of Agricultural Research (ICAR) has

classified the Indian soils into 8 categories.

• On the basis of genesis, colour, composition and location, the soils of India have been classified into:

1. Alluvial Soils of India :

• Alluvial soils are widespread in the northern plains and the river valleys. These soils cover about 40 per cent of the total area of the country. 

• They are depositional soils, transported and deposited by rivers and streams. 

• Through a narrow corridor in Rajasthan, they extend into the plains of Gujarat. In the Peninsular region, they are found in deltas of the east coast and in the river valleys. 

• They vary in nature from sandy loam to clay and are rich in potash but poor in phosphorous. 

Bangar –old alluvium Khaddar- new alluvium Kankar –calcerous deposits 

• Alluvial soils are intensively cultivated. 

2. Black Soil of India :

• Black soil covers most of the Deccan Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu. 

• These soils are also known as the ‘RegurSoil‘ or the ‘Black Cotton Soil‘. Generally clayey, deep and impermeable. 

• They swell and become sticky when wet and shrink when dried. So, during the dry season, these soil develop wide cracks like‘self ploughing‘. 

• Because of this character of slow absorption and loss of moisture, the black soil retains the moisture for a very long time, which helps the crops, especially, the rain fed ones, to sustain even during the dry season. 

• 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. The colour of the soil ranges from deep black

to grey.

3. Red and Yellow Soil of India :

• Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and southern part of the Deccan Plateau. Yellow and red soils are also found in parts of Odisha and Chattisgarh and in the southern parts of the middle Ganga plain. 

• 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.

4. Laterite Soil of India : 

• Laterite has been derived from the Latin word ‘Later‘ which means brick. 

• The laterite soils develop in areas with high temperature and high rainfall. These are the result of intense leaching due to tropical rains. With rain, lime and silica are leached away, and soils rich in iron oxide and aluminium compound are left behind. 

• Humus content of the soil is removed fast by bacteria that thrives well in high temperature. 

• 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 cashewnut. 

• The laterite soils are commonly found in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh and the hilly areas of Odisha and Assam. 

5. Arid Soils of India :

• Arid soils range from red to brown in colour. 

• They are generally 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 because of the increasing calcium content downwards.

• The ‘Kankar‘ (calcium)layer formation in the bottom horizons restricts the infiltration of water, and as such when irrigation is made available, the soil moisture is readily available for a sustainable plant growth. 

• Arid soils are characteristically developed in western Rajasthan, which exhibit characteristic arid

topography. These soils are poor and contain little humus and organic matter. 

6. Saline Soils of India :

• Also known as Usara soils. Saline soils contain a larger proportion of sodium, potassium and magnesium, and thus, they are infertile, and do not support any vegetative growth. 

• They occur in arid and semi-arid regions, and in waterlogged and swampy areas. 

• Their structure ranges from sandy to loamy. 

• They lack in nitrogen and calcium. 

• Saline soils are more widespread in western Gujarat, deltas of the eastern coast and in Sunderban areas of West Bengal. 

7. Peaty Soils of India : 

• Found in the areas of heavy rainfall and high humidity, where there is a good growth of vegetation. 

• Thus, large quantity of dead organic matter accumulates in these areas, and this gives a rich humus and organic content to the soil. Organic matter in these soils may go even up to 40-50 per cent. 

• Soils are normally heavy and black in colour. 

• Occurs widely in the northern part of Bihar, southern part of Uttaranchal and the coastal areas of West Bengal, Orissa and Tamil Nadu. 

8. Forest Soils of India : 

• Forest soils are formed in the forest areas where sufficient rainfall is available. 

• They are Loamy and silty on valley sides and coarse-grained in the upper slopes.

• In the snow-bound areas of the Himalayas, they experience denudation, and are acidic with low humus content. The soils found in the lower valleys are fertile.