Black soils, locally called regard or black cotton soils, and internationally known as 'tropical black earths' or 'tropical chernozems' have been developed by the weathering of the Deccan lava in majorparts of Maharashtra, western MadhyaPrades (Hoshangabad, Narsinghpur, Damoh, Jabalpur, Raisen and Shahdol districts), Gujarat (Surat, Bharuch, Vadodara, Kheda, Sabarkantha and Dang districts), Andhra Pradesh (Adilabad, Warangal, Khammam, Mahbubnagar, Kurnool, Guntur and Karimnagar districts), Karnataka (Bijapur, Dharwar, Gulbarga, Bidar, Belgaum, Raichur, Bellari and Chitradurga districts), Rajasthan (Kota, Bundi, Sawai Madhopur, Bharatpur and Banswara districts), Tamil Nadu (Ramnathpuram, Tirunelvelli, Coimbatore, Madurai and South Arcot districts) and Uttar Pradesh (Jalaun, Hamirpur, Banda and Jhansi districts). According to Krebs the regur soil is essentially a mature soil which has been produced by relief and climate rather than by a particular type of rock. It occurs where the annual rainfall is between 50 cm to 75 cm and the number of rainy days is from 30 to 50. The colour of these soils varies from deep black to light black and chestnut and is dependent on the colour of the mechanical fractions. The black color is attributed to the presence of titaniferous magnetite, compounds of iron and aluminum, accumulated humus and colloidal hydrated double iron and aluminum silicate. In general these soils have clay texture, average clay content being 50% and the range being 40-50%. Except in cases where there is stratification, the clay content down the profile is uniform.
Red soil is a group of soil that develops in a warm, temperate, moist climate under deciduous or mixed forests and that have thin organic and organic-mineral layers overlying a yellowish-brown leached layer resting on an illuvial (see illuviation) red layer. Red soils generally derived from crystalline rock. They are usually poor growing soils, low in nutrients and humus and difficult to cultivate because of its low water holding capacity. Red soils denote the second largest soil group of India covering an area of about 6.1 lakhs sq. km (18.6% of India'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 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 nitrogen, phosphorus and organic materials but rich in potash. Leaching is dominant.
These soils are formed due to intense leaching and are well developed on the summits of hills and uplands. They are commonly found in Kerala, Tamil Nadu, Maharashtra, Chhattisgarh and hilly areas of Orissa and Assam.
These soils are formed as a result of the accumulation of organic matter derived from forest growth. They are found in Himalayan region and vary in different regions according to altitude. Tea is grown in those areas which receive sufficient rainfall.