Soil is the loose material which forms the upper layer of the mantel rock, i.e., the layer of loose fragments which covers most of the earth’s land area. It has definite and constant composition. It contains both decayed plants and animals substances. The four main constituents of soils are:
Silica: The chief constituent of sand
Clay: is a mixture of silicates and contains several minerals such as iron, potassium, calcium, sodium and aluminum. Particles of clay absorb water and swell.
Chalk: (calcium carbonate) provides calcium, the most important element for the growth of plants.
Humus: is not a mineral, it is an organic matter. It is formed by decomposed plant remains, animal manure and dead animals and is the most important element in the fertility of the soil. It helps retain moisture in the soil and helps the plant in absorbing materials from the soil for building its body. A soil looks dark on account of the presence of humus.
Layers of Soil
Soil has mainly two layers i.e. Top soil and Sub soil. Top soil (the upper layer) is of greater importance. Top soil is responsible for the productivity of the vegetation thus its of vital importance from agricultural point of view. It is only a few meters deep. Millions of bacteria, insects and worms live in it. Top soils develop very slowly. It may take years to form top soil suitable for plants, but it can be washed away in a few years if proper precautions are not taken.
Sub soils consist of the parent material from which soil is formed. It also contains plant food and moisture but it is not a s productive as top soil.
Types of Soils and their characteristics:
Alluvial Soil
This is the most important and widespread group of soils. It covers about 15 lakh sq.km of the land area in Great Plains from Punjab to Assam and also in the valleys of the Narmada and Tapi, Mahanadi, Godavari, Krishna and Cauvery. These soils have been brought down and deposited by three great Himalayan rivers Sutlej, Ganga and Brahmaputra. These soils consist of varying proportions of sand, silt and clay. Khadar is the newer alluvium which is sandy, light coloured and occurs near river bedswhere deposition takes place regularly and bhangar or older alluvium. Alluvial soils as a whole are very fertile and therefore the best agricultural soils of the country. The regions of these of these soils constitute the’ wheat and rice bowls’ of India.
Black Soil
As the name indicates these soils are black in Colour and since they are ideal for growing cotton, they are also called cotton soil. These soils, covering an area of 5.46 lakh sq.km, are most typical of the Deccan trap (Basalt). The black Colour of regur is variously attributed to the presence of titaniferrous magnetite, compounds of iron and aluminum-Unsuitable for heavy irrigation. Ideally suited to dry farming. Suitable for cotton, cereals, oilseeds like linseed, castor and safflower, many kinds of vegetables and citrus fruits.
Red Soil
These soil occupy about 5-18 lakh sq.km over the peninsula reaching up to Rajmahal Hills in the east, Jhansi in the north and Kutch in the West. In North western peninsula is covered by the black soils and the remaining south-eastern half is covered by red soils- Entire black soil in the eastern part of Peninsula comprising of Chhotanagpur plateau, Orissa, east Madhya Pradesh, Telengana, the Niligris, Tamilnadu plateau and Karnataka. The soil have reddish colour due to iron compounds. It is suitable for rice, ragi, tobacco and vegetables.
Laterite Soil
These soils occupy an area of 1.26 lakh sq.km. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock. They are found capping in the flat uplands, and are spread in western coastal region which recieve very heavy rainfall. These soils are Poor in nitrogen, phosphoric acid, potash and lime. These are suitable for rice, ragi, tapioca and cashewnuts.
Forest and Mountain Soils
These soils occupy about 2.85 lakh sq.km in the hilly regions of the country. They are also called as soils in the making. These type of soil are found in the Himalayas and the other ranges in the North and high hill summits of the Sahyadris, Eastern Ghats and Peninsula. These soils are poor in Potash and Phosphorous content. The soil is suitable for the growth of Temperate fruits, maize, wheat and barley.
Arid and Desert Soil
This type of soil is found in the Northwestern parts of the country and occupy area in Rajasthan, south Haryana, north Punjab and Rann of Kutch. Thar Desert alone occupies an area of 1.06 sq. km. It contains high percentage of soluble salts and a low to very low organic matter.
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