1. Black soils The principal region of black soils is the Deccan plateau and its periphery extending from 8°45’to 26o north latitude and 68o to 83o45′ east longitude. They are formed from Deccan basalt trap rocks and occur in areas under the monsoon climate, mostly of semi-arid and sub-humid types. The overall climate of black soil region may be described as hot and dry summer, 40-100 cm rainfall per annum, mild to moderate winters and annual temperature ranges from 24-30o centigrade, mean maximum temperature during April-May ranges from 36~42°C arid mean minimum temperature during winter ranges from 15-24° centigrade.
Semi-arid to sub-humid, tropical to sub-tropical monsoon type climate with alternate dry and wet periods and calcification (formation of calcium carbonate) are favourable to the formation of black soils.
The soils are characterised by dark grey to black colour with 35-60% clay, neutral to slightly alkaline reaction, high swelling and shrinkage, plasticity, deep cracks during summer and poor status of organic matter, nitrogen and phosphorus.
Impeded drainage and low permeability are the major problems. Black soils. are divided into shallow black soil of a depth of 30-50 cms, medium black soils of 50-120 cm and deep black soils of more than 120 centimeters. The natural vegetation comprises dry deciduous species, viz palas (Butes frondoss), sisam (Dalbergia sisu), neem (Azadirachta indica) and teak (Tectona grandis).
Cotton, sugarcane, groundnut, millets, maize, pulses, safflower are the common crops grown on these soils. Because of their inherent drainage problem, they are prone to salinity and sodicity under irrigated conditions unless proper drainage is ensured.
Because of its high water retaining capacity, rainfed crops like minor millets, pulses like horse gram are vegetables of different types and citrus fruits can also be grown. These soils are also known as regurs, nullah regadi (a telugu word meaning black clay) and black cotton soils as cotton was the major crop grown in these soils.
2. Red soils These soils are derived from granite, gneiss and other metamorphic rocks. These soils are formed under well drained condition. The climate is semi-arid tropical with mean annual temperature of 25°C and mean annual rainfall from 75-100 cm. The soils are higher textured, friable structure and contains low soluble salts. They are slightly acidic to slightly alkaline, well drained with moderate permeability. They are generally poor in nitrogen, phosphorus, lime, humus etc. In this soil, lime concretions and free carbonates are absent. The red colour is due to the higher degree of hydration of the fericoxide in the soils. On uplands, they are gravelly sandy or stony and porous and light coloured on which food crops like bajra can be grown.
On the lower plains and valleys, they are dark, coloured fertile loams, irrigated crops like maize, wheat, pulses, potatoes, fruits, millets etc can be grown. These soils have also been found under forest vegetation. Sometimes they found along with black soils (side by side) and also yellow soils (red and yellow soils). Excessive gravelliness, surface crust formation and susceptibility to erosion due to high slopes are some of the problems in these soils which can be overcome by adopting suitable measures. Morphologically the red soils can be divided into red loams which have a cloddy structure and argillaceous soil and red earths with loose friable top soil rich in sesquioxide type of minerals.
3. Laterites and lateritic soils Laterite is a geological term and means literally a rock. The laterites and lateritic soils have been loosely used in the same sense. The lateritic soils are enriched with oxides of iron and aluminium, under the conditions of high rainfall with alternate dry and wet periods. During rainfall silica is leached downwards and iron and aluminium oxides remains in the top layers. Laterites are usually shallow and gravelly at higher lands, but are very deep loam to clay soils in the valleys where good paddy crops are produced. Higher landy soils are poor in nutrient status where as lower level soils are dark and richer in nutrients and organic matter. All lateritic soils are poor in calcium, magnesium, nitrogen, phosphorus and potash.
They are generally well drained and porous. The soil reaction is more on the acidic side. On laterites, as already mentioned, rice is grown at lower elevations and at higher elevations, tea, coffee, cinchona, rubber and cashewnut can be grown under good soil management conditions. On the whole, laterites are poor in fertility and readily respond to manuring and good cultivation. Based on the climate lateritic soils are grouped into high rainfall areas with strongly and weakly expressed dry season and humid zones with pronounced dry & wet periods.
4. Alluvial soils Alluvial soils, cover the largest area in India (approximately 7 lakh km2) and these are the most important soils from agricultural point of view. The main features of alluvial soils have been derived as silt deposition laid down by the Indian river systems like the Indus, the Ganges, the Brahmaputra and the rivers like Narmada, Tapti: Mahanadi, Godavari, Krishna and Cauvery. These rivers carry the products of weathering of rocks constituting the mountains and deposit them along their path as they flow down the plain land towards the sea. Geologically, the alluvium is divided into recent alluvium which is known as Khadar and old alluvium, as bhangar. The newer alluvium is sandy and light coloured whereas older alluvium is more clayey, dark coloured and contains lime concretions. The soils have a wide range in soil characteristics viz. acid to alkaline sandy to clay, normal to saline, sodic and calcareous, shallow to very deep. The climate ranges from arid to humid sub-tropical. The following groupings of alluvial soils may be recognised: alluvial soils (Khadar, bhangar and highly calcareous), deltaic alluvium, coastal alluvium, coastal sands, calcareous sierocomic and grey-brown soils.
a. Alluvial soils The alluvial soils occuring in the Indo-Gangetic plains and the Brahmaputra valley cover a large area. The soils are transported and deposited by the rivers from the parent material. The rivers are the Ganga, Jamuna, Brahmaputra and their tributaries. The soils are deep and hard pans in the subsoil are calcareous (made of calcium carbonate) and acidic. These are deficient in nitrogen, phosphorous and humus, but not in potash and lime. These soils are fertile amongst all the soils of India. They produce a wide variety of crops like rice, wheat, sugarcane, jute and potato. They are distributed mainly in the northern, north-western and north-eastern parts of our country.
b. Deltaic alluvial soils They are formed from sediments carried by rivers and deposited in the mouths of rivers joining the sea. The deltas of the Ganga, Brahmaputra, Mahanadi, Godavari, Krishna and Cauvery are the most important ones. In Gujarat, the deltaic alluvial soils which are sandy loam to clay loam are locally called Goradu soils. The Godavari and Krishna rivers pass through basaltic region having black soils and these soils are dark and fine textured. The Cauvery delta soils are significantly clayey and Ganga delta soils show high accumulation of organic matter, as in the Sunderbans of West Bengal, due to swampy vegetation. These soils are fertile and grow a wide variety of crops suited to climatic conditions.
c. Coastal alluvium Soils developed on coastal alluvium are found along, the sea coasts. Soils are dark coloured, coarse textured and poor in fertility. Some soils are saline due to the inundation of sea water. Such soils in the Konkan coast of Maharashtra are called Khar soils.
d. Coastal sands Sandy soils occur prominently in the coastal area of Tanjavur district of Tamil Nadu, along the Kerala coast, Bapatla in Guntur distrjct of Andhra Pradesh and Puri district in Orissa. If sandy soils are not saline, plantation crops like coconut, cashew and casuarina can be taken up for cultivation.
Other soils under alluvium are calcareous sierozomes and grey brown soils. Calcareous sierozomes can be seen in the desertic region of Haryana and Punjab. The word ‘sierozem” denotes a group of soils having a brownish-grey surface horizon with a sub-layer of carbonates which is developed under mixed shrub vegetation in a-temperate to cool, arid climate. Grey-brown soils as the name itself indicates its nature, can be found in, desert soils of Rajasthan.
5. Desert soils In the north-western part of India, desert soils occur over an area of 0.29 million hecta,res, which includes a major part of Rajasthan, south of Haryana and Punjab and northern part of Gujarat. Rainfall ranges from less than 10 cms to 50 cms, mostly contributed during monsoon season. The region consists of sand dunes and undulating sandy plains. The temperature regime is very high throughout the year and a maximum of 50-60°C is recorded during summer. Due to high temperature organic-matter built up is very low. The soils in the plains are mostly derived from alluvium and are pale brown to brown to yellow brown and fine sandy to loamy fine sand and are structureless. The clay contents low and presence of alkaline earth carbonates is an important feature. The nitrate nitrogen and phosphorus makes the desert soils fertile and productive under proper moisture supply. By increasing the water holding capacity, the productivity of the soils can be increased which involves addition of organic matter and clay.
6. Tarai soils The word “tarai” is a hindi word, which means moist. Thus, i is a wet regime having high water table. Tarai soils are foot hii soils and extend in strips of varying widths at the foot of Himalayas in Jammu and Kashmir, Uttar-Pradesh, Bihar and West-Bengal. Soils under the natural conditions are thickly vegetated and swampy. Several types of grasses and trees from the native vegetation on removal of which the soils become highly productive. The soils are formed from the materials that are washed down by the erosion of mountains. They are alluvial origin. High soil moisture content all through the year results in luxuriant vegetation dominated by tall grasses. They are neutral to slightly alkaline with significant amounts of organic matter. The texture varies from sandy loam to silty loam. Generally, these soils are fertile and by providing proper drainage, the productivity can be increased.