SOIL GROUPS

SOIL GROUPS
The Indian Council of Agricultural Research (ICAR) has divided Indian soils into eight major types. These are red soils, black soils, the Indo-Gangetic alluvium or alluvial soils, the lateritic and laterite soils, forest and hill soils, alkaline and saline soils, desert soils and peaty and organic soils.

Red Soils They are mainly formed due to 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. The red soils are generally poor in nitrogen, hosphorous, humus but rich in potash. They are siliceous or aluminous in character. The clay fraction of the red soils generally consists of kaolinitic minerals.

Morphologically, they are divided into the cloddy structured red loams which have little of concretionary substances and the loose, friable red earths which have much of secondary concretions of sesquioxide clays.

Red soils cover almost the whole of Tamil Nadu, Karnataka, Andhra Pradesh, south-eastern Maharashtra, eastern parts of Madhya .Pradesh, parts of Orissa, Jharkhand and Bundelkhand. They practically encircle the entire black soil region on all sides. They extend northwards in the west along the Konkan coast of Maharashtra.

Though red soils are suitable for cultivating almost all crop types, they are most suitable for growing vegetables, rice, ragi and tobacco. Heavy clays at low-levelled lands are suitable for sugarcane cultivation. Red soils of coarse texture at high levels are good for potato and groundnut crops. Irrigation is a must for these soils.

Black Cotton Soils Also called regur, the soils are derived from basalts of Deccan Traps. They derive their name from their black colour which may be owing to presence of titanium, iron or some other organic com­pounds. Black soils are fine-grained and highly argillaceous and consist of calcium and magnesium carbonates. One 0f their chief characteristics is their swelling or shrinkage with increase or decrease in the moisture content. Black soils contain high quantities of iron, aluminium, lime and mag­nesia and generally show poor percentages of phospho­rous, nitrogen and organic matter.

Black soils are spread over north-west Deccan Plateau and are made up of lava flows. They cover the plateaus of Maharashtra, Saurashtra, Malwa, Madhya Pradesh, and parts of Chhattisgarh. They extend eastwards in the soutli along Godavari and Krishna valleys. The climatic conditioru and the nature of parent-rock materials are equally impor. tant in the formation of black soils. In. Madhya Pradesh, two distinct kinds of black soils are found: (i) deep heav} black soils covering the Narmada Valley, and (ii) shallo¥. black soils in other areas. The cotton-growing areas arE mainly covered by the deep heavy black soil.

Apart from cotton cultivation, these fertile soils arE suitable for growing cereals, oilseeds, citrus fruits ane vegetables, tobacco and sugarcane. Their moisture-reten­tiveness makes them suitable for dry farming. As they havE large amounts of water-soluble salts, heavy irrigation 0f these soils must be avoided.