Type of Soils, Study Notes, Material - DSSSB & KVS (PRT & TGT)

Type of Soils

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

Alluvial Soils

• 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.
• The alluvial soils vary in nature from sandy loam to clay. They are generally rich in potash but poor in phosphorous. In the Upper and Middle Ganga plain, two different types of alluvial soils have developed, viz. Khadar and Bhangar.
• Khadar is the new alluvium and is deposited by floods annually, which enriches the soil by depositing fine silts. Bhangar represents a system of older alluvium, deposited away from the flood plains. Both the Khadar and Bhangar soils contain calcareous concretions (Kankars). These soils are more loamy and clayey in the lower and middle Ganga plain and the Brahmaputra valley. The sand content decreases from the west to the east.
• The colour of the alluvial soils varies from light grey to ash grey. Its shades depend on the depth of the deposition, the texture of the materials, and the time taken for attaining maturity. Alluvial soils are intensively cultivated.

Black Soils

1. Black soil covers most of the Deccan Plateau which include parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh and some parts of Tamil Nadu. In the upper reaches of the Godavari and the Krishna, and the northwestern part of the Deccan Plateau, the black soil is very deep.
2. These 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. So, during the dry season, this soil develops wide cracks. Thus, there occurs a kind of ‘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 phosphorous, nitrogen and organic matter. The colour of the soil ranges from deep black to grey.

Red and Yellow Soils

•  Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and southern part of the Deccan Plateau. Along the piedmont zone of the                     Western Ghat, a long stretch of area is occupied by red loamy soil.
• 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 of poor infertility.
• They are generally poor in nitrogen, phosphorous and humus.

Laterite Soils

• Laterite has been derived from the Latin word ‘Later’ which means brick.
• The laterite soils develop in areas with high temperatures 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 compounds are left behind. Humus content of the soil is removed fast by bacteria that thrive well in high temperatures.
• Laterite  Soils are poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess.
• Laterites are not suitable for cultivation; however, the application of manures and fertilisers are required for making the soils fertile for cultivation.
• Red laterite soils in Tamil Nadu, Andhra Pradesh and Kerala are more suitable for tree crops like cashew nuts.
• Laterite soils are widely cut as bricks for use in house construction. These soils have mainly developed in the higher areas of the Peninsular plateau.
• The laterite soils are commonly found in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh and the hilly areas of Odisha and Assam

Arid Soils

• Arid soils range from red to brown in colour.
• They are generally sandy in structure and saline in nature. In some areas, the salt content is so high that common salt is obtained by evaporating the saline water.
• Due to the dry climate, high temperature and accelerated evaporation, 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’ 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 sustainable plant growth.
• Arid soils are characteristically developed in western Rajasthan, which exhibits characteristic arid topography. These soils are poor and contain little humus and organic matter

 Types of Soil - Agroclimatic Zones

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