Red soils denote the second largest soil group of the country covering an area of about 6.1 lakh sq. km (18.6% of the Country’s area) over the Peninsula from Tamil Nadu in the south to Bundelkhand in the north and Rajmahal hills in the east to Kachchh in the west. They surround the black soils on their south, east and north.
These soils are found in large tracts of western Tamil Nadu, Karnataka, southern Maharashtra, Chhattisgarh, Andhra Pradesh, Orissa and Chotanagpur plateau of Jharkhand. Scattered patches are also seen in Birbhum (West Bengal), Mirzapur, Jhansi, Banda, Hamirpur (Uttar Pradesh), Udaipur, Chittaurgarh, Dungarpur, Banswara and Bhilwara districts (Rajasthan).
These soils, also known as the omnibus group, have been developed over Archaean granite, gneiss and other crystalline rocks, the sedimentaries of the Cuddapah and Vindhayan basins and mixed Dharwarian group of rocks. Their colour is mainly due to ferric oxides occurring as thin coatings on the soil particles while the iron oxide occurs as haematite or as hydrous ferric oxide, the colour is red and when it occurs in the hydrate form as limonite the soil gets a yellow colour. Ordinarily the surface soils are red while the horizon below gets yellowish colour.
The texture of red soils varies from sand to clay, the majority being loams. Their other characteristics include porous and friable structure, absence of lime, kankar and free cabonates, and small quantity of soluble salts. Their chemical composition include non-soluble material 90.47%, iron 3.61 %, aluminium 2.92%, organic matter 1.01%, magnesium 0.70%, lime 0.56%, carbon-di-oxide 0.30%, potash 0.24%, soda 0.12%, phophorus 0.09% and nitrogen 0.08%. However significant regional differences are observed in the chemical composition.
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In general these soils are deficient in lime, magnesia, phosphates, nitrogen, humus and potash. Intense leaching is a menace to these soils. On the uplands, they are thin, poor and gravelly, sandy, or stony and porous, light-coloured soils on which food crops like bajra can be grown. But on the lower plains and valleys they are rich, deep, dark coloured fertile loam on which, under irrigation, can be produced excellent crops like cotton, wheat, pulses, tobacco, jowar, linseed, millets, potatoes and fruits. These are also characterised by stunted forest growth and are suited to dry farming.
Ray Chaudhary (1941) has morphologically grouped red soils into following two categories:
(a) Red Loam Soil-these soils have been formed by the decomposition of granite, gneiss charnocite and diorite rocks. It is cloddy porous and deficient in concretionary materials. It is poorer in nirogen, phosphorus and organic materials but rich in potash. Leaching is dominant.
These soils have thin layers and are less fertile. These soils are mainly found in Karnataka (Shimoga, Chikmaglur and Hassan districts), Andhra Pradesh (Telangana), estern Tamil Nadu, Orissa, Jharkhand (Chotanagpur), Uttar Pradesh (Bundelkhand), Madhya Pradesh (Balaghat and Chhindwara), Rajasthan (Banswara, Bhilwara, Bundi, Chittaurgarh, Kota and Ajmer districts), Meghalaya, Mizoram, Manipur and Nagaland.
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(b) Sandy Red Soil-these soils have formed by the disintegration of granite, grani gneiss, quartzite and sandstone. These are 1 friable soil with high content of secondary conc tions of sesquioxide clays.
Due to presence of haem tite and limonite its colour ranges from red to yello These soils have been rightly leached occupyi parts of former eastern Madhya Pradesh (exce Chhattisgarh region), neighbouring hills of Oriss Andhra Pradesh, and Tamil Nadu (Eastern Ghats and Sahyadris.
ICAR has divided red soils into four categ ries-(a) red soils, (b) red gravelly soils, (c) red and yellow soils, and (d) mixed red and black soils.