Soil is one of the major natural resources, like air and water. It is the topmost layer of the earth’s crust and is a mixture of fine powdered rocks, organic matter, liquids, myriad organisms and other minerals. It acts as an interface between hydrosphere, lithosphere, earth’s atmosphere and biosphere. The proportion of the key ingredients determines the type of soil. But, factors such as vegetation, climatic conditions, human activities for e.g. grazing, farming, gardening etc also influence soil formation.

Soil is a valuable resource of India. Much of the Indian agriculture depends upon the extent and qualities of soil. Weathering prepares loose materials on the surface of the Earth and mixed with decayed organic matters it forms soil. Soil can be simply defined as a mixture of small rock particles/debris and organic materials/ humus which develop on the earth surface and support growth of plants.

India is a large country and witnesses diverse range of climatic and other natural conditions. The nature of soil in a place is largely influenced by such factors as climate, natural vegetation and rocks.

Soil Classification – Urvara vs Usara

In India, soil had been classified from the ancient period itself even though it was not as detail as the modern classifications.
In the ancient period, the classification was based on only two things; whether the soil is fertile or sterile. Thus the classification were:

• Urvara (fertile)
• Usara (sterile)

Soil Classification – Agencies involved

• In the modern period, when men started to know about the various characteristics of soil they began to classify soil on the basis of texture, colour, moisture etc.
• When the Soil survey of India was established in 1956, they studied soils of India and their characteristics.
• The National Bureau of Soil Survey and the Land Use Planning, an institute under the control of Indian Council of Agriculture
• Research did a lot of studies on Indian soil.

Indian Soils with Percentage of Coverage

Alluvial soil:-

• Materials deposited by rivers, winds, glaciers and sea waves are called alluvium and soils made up of alluvium are alluvial soils.
• In peninsular-India, they are mostly found in deltas and estuaries.
• Humus, lime and organic matters are present.
• Highly fertile.
• Indus-Ganga-Brahmaputhra plain, Narmada-Tapi plain etc are examples.
• They are depositional soil – transported and deposited by rivers, streams etc.
• Sand content decreases from west to east of the country.
• New alluvium is termed as Khadar and old alluvium is termed as Bhangar.
• Colour: Light Grey to Ash Grey.
• Texture: Sandy to silty loam or clay.
• Rich in: potash
• Poor in: phosphorous.
• Wheat, rice, maize, sugarcane, pulses, oilseed etc are cultivated mainly.

Black Soil:-

• Also called Regur and is ideal for cotton crop. These soils have been formed due to the solidification of lava spread over large areas during volcanic activity in the Deccan Plateau, thousands of years ago.
• They are black due to compounds of iron and aluminium (also because of titaniferous magnetite). Mainly found in Deccan
• Plateau – Maharashtra, Gujarat, M.P, Karnataka, Andhra Pradesh, and Tamil Nadu.
• Apart from cotton cultivation, these fertile soils are suitable for growing cereals, oilseeds, citrus fruits and vegetables, tobacco and sugarcane.
• They have high moisture retention level.
• Self-ploughing is a characteristic of the black soil as it develops wide cracks when dried.
• Rich in: Iron, lime, calcium, potassium, aluminum and magnesium.
• Deficient in: Nitrogen, Phosphorous and organic matter.
• Colour: Deep black to light black.
• Texture: Clayey.

Red Soil:-

• They are mainly formed due to the decomposition of ancient crystalline rocks like granites and gneisses and from rock types rich in minerals such as iron and magnesium.
• The term ‘red soil’ is due to the wide diffusion of iron oxides through the materials of the soil.
• Covers almost the whole of Tamil Nadu, Karnataka, Andhra Pradesh, S.E. Maharashtra, and Chhattisgarh, parts of Orissa, Jharkhand and Bundelkhand.
• Suitable for rice, millets, tobacco and vegetables (also groundnuts and potatoes at higher elevations).
• Deficient in: lime, phosphate, manganese, nitrogen, humus and potash.
• Colour: Red because of Ferric oxide. The lower layer is reddish yellow or yellow.
• Texture: Sandy to clay and loamy.

Laterite Soil:-

• Found in typical monsoon conditions – under conditions of high temperature and heavy rainfall with alternate wet and dry periods.
• The alterations of wet and dry season leads to the leaching away of siliceous matter and lime of the rocks and a soil rich in oxides of iron and aluminium compounds is left behind.
• Found in parts of Western Ghats, Eastern Ghats, Rajmahal hills, Maharashtra, Karnataka, Kerala, Orissa, West Bengal, Assam, Tamil Nadu, etc.
• Best for tea, coffee, rubber, cinchona, coconut and suitable for rice and millet cultivation if manured.
• Rich in: Iron and Aluminum
• Deficient in: Nitrogen, Potash, Potassium, Lime, Humus
• Colour: Red colour due to iron oxide.

Forest and Mountain Soil:-

• Such soils are mainly found on the hill slopes covered by forests.
• The formation of these soils is mainly governed by the characteristic deposition of organic matter derived from forest growth.
• In the Himalayan region, such soils are mainly found in valley basins, depressions and less steeply inclined slopes. Apart from the Himalayan region, the forest soils occur in higher hills in south and the peninsular region.
• Very rich in humus but are deficient in Potash, phosphorous and lime and needs fertilizers.
• Plantation of tea, coffee, spices and tropical fruits.

Arid and Desert Soil:-

• A large part of the arid and semi-arid region in Rajasthan and adjoining areas of Punjab and Haryana lying between the Indus and the Aravallis receiving less than 50 cm of annual rainfall is affected by desert conditions.
• This area is covered by a mantle of sand which inhibits soil growth.
• The phosphate content of these soils is as high as in normal alluvial soils. Nitrogen is originally low but its deficiency is made up to some extent by the availability of nitrogen in the form of nitrates. Thus the presence of phosphates and nitrates make them fertile soils wherever moisture is available.
• The changes in the cropping pattern in the Indira Gandhi Canal Command Area are a living example of the utility of the desert soils.
• Texture: Sandy
• Colour: Red to Brown.

Saline and Alkaline Soil:-

• In the drier parts of Bihar, Up Haryana, Punjab, Rajasthan and Maharashtra, are the salt-impregnated or alkaline soils. Known by different names: Reh, kallar, USAR, etc.
• Some of the salts are transported in solution by the rivers and canals, which percolates in the sub-soils of the plains.
• The accumulation of salts makes the soil infertile and renders it unfit for agriculture.

Peaty and Marshy Soil:-

• Originate in the humid regions as a result of accumulation of large amounts of organic matter in the soil. They contain considerable amounts of soluble salts and 10 – 40% of organic matter.
• Peaty soils are found in Kottayam and Alappuzha districts of Kerala, where it is called Kari.
• Marshy soils, high in vegetable matter, are found in northern Bihar, coastal parts of Orissa, Tamil Nadu and West Bengal and parts of UP.
• Heavy soil with black colour.

Soil Erosion in India

• Acute in hilly and dry regions
• Causes – depletion of forests, wrong use of lands such as cultivation on very steep slopes, cattle rearing. It ultimately leads to Badland Topography.
• Remedy – Afforestation, contour cultivation etc.