The committee appointed by the Indian Council of Agricultural Research (ICAR), classified the Indian soil in the following main groups:
1. Alluvial Soils
2. Black Soils
3. Red Soils
4. Laterite Soils
5. Mountain Soils
6. Desert Soils
1. Alluvial Soil:
It is the most important type of soil found in India covering about 40 per cent of the total land area. It is very fertile and contributes the largest share of agricultural wealth. This soil supports nearly half of the Indian population.
The alluvial soil is found mostly in the Northern Plains, starting from Punjab in the west to West Bengal and Assam in the east. It is also found in the deltas of the Mahanadi, Godavari, Krishna and Kaveri rivers in the Peninsular India. The northern parts and the coastal areas of Gujarat also have some deposits of alluvial soil.
Many rivers originate from the Himalayan Mountains and bring a large amount of sediment with them. It is deposited in the river valleys and the flood plains. Thus, the parent material of the alluvial soils is always of transported origin.
The fine particles of sand, silt and clay are called alluvium. The alluvial soil can be divided into old alluvium, also called bangar, and new alluvium, called khadar. Remember, the new alluvium can be about ten thousand years old.
i. The new alluvium is deposited in the flood plains and deltas. These areas are flooded almost every year.
ii. The old alluvium is found on the higher side of the river valleys, i.e. about 25 metres above the flood level.
iii. The khadar soil is sandy and light in colour, while the bhangar soil is clayey and dark.
iv. The khadar soil is more fertile than the bangar soil.
v. The alluvial soils contain adequate potash, phosphoric acid and lime.
vi. They are generally deficient in organic and nitrogenous contents.
vii. The old alluvium often contains lime nodules, known as kankar.
The fertility of the alluvial soil varies from place to place. Due to its softness and fertility, alluvial soil is most suited to irrigation and can produce bumper crops of rice, wheat, maize, sugar cane, tobacco, cotton, jute, oilseeds, etc.
2. Black Soil:
The black soil is locally called regur, a word derived from Telugu word ‘reguda’. It is also called the Black Cotton Soil, as cotton is the most important crop grown in this soil.
The black soil is mostly found in the Deccan Trap, covering large areas of Maharashtra, Gujarat and western Madhya Pradesh. It is also found in some parts of Godavari and Krishna river valleys, covering parts of Karnataka, Andhra Pradesh and Tamil Nadu.
i. The black soil has been formed thousands of years ago, due to the solidification of volcanic lava.
ii. This soil is made up of extremely fine clayey material.
iii. The black soil is well-known for its capacity to hold moisture.
iv. This soil is rich in calcium carbonate, magnesium carbonate, potash and lime, but poor in phosphoric content.
v. During the rainy season, black soil becomes sticky and is difficult to till as the plough gets stuck in the mud.
vi. During the hot dry season, the surface of this soil develops cracks.
vii. These cracks help in the aeration of the soil.
viii. Actually the black soil should be tilled immediately after the first or the pre-monsoon showers.
Generally, in the upland regions, the black soil has low fertility, while in the valleys or lowlands; this soil is darker, deeper and very fertile. Due to high fertility and capacity to hold moisture, black soil is widely used for producing cotton, wheat, linseed, millets, tobacco and oilseeds. With proper irrigation facilities, this soil can also produce rice and sugar cane.
3. Red Soil:
The red soil occupies about 10 per cent area of India, mostly in the south-eastern part of the Peninsular India. This area encircles the entire black soil region. The red soil is found in Tamil Nadu, parts of Karnataka, southeast Maharashtra, eastern parts of Andhra Pradesh, Madhya Pradesh, Orissa and Jharkhand.
i. Most of the red soil has been formed due to weathering of igneous and metamorphic rocks.
ii. The red colour is due to the high percentage of iron contents.
iii. The texture of the red soil varies from sandy to clayey, and the majority being loamy.
iv. On the uplands, the red soil is thin, poor, and porous and has loose gravel.
v. In the lower areas, the soil is deep, rich, fine grained and fertile.
vi. This soil is rich in potash, but poor in lime, phosphate, nitrogen and humus.
With proper doses of fertilizers and irrigation the red soils can give excellent yields of cotton, wheat, rice, pulses, millets, tobacco, oilseeds, etc.
4. Laterite Soil:
The word ‘laterite’ has been derived from a Latin word meaning ‘brick’. The laterite soil is widely spread in India and is mainly found on the summits of the Western Ghats, Eastern Ghats, Rajmahal Hills, Vindhyas, Satpuras and Malwa plateau. It is well- developed in southern Maharashtra, and parts of Orissa, West Bengal, Karnataka, Andhra Pradesh, Kerala, Bihar, Assam and Meghalaya.
i. The laterite soil is formed under conditions of high temperature and heavy rainfall with alternate wet and dry periods.
ii. Such climatic conditions promote leaching of soil. Leaching is a process in which heavy rains wash away the fertile part of the soil.
iii. The laterite soil is red in colour and composed of little clay and much gravel of red sandstones.
iv. Laterite soil generally is poor in lime and deficient in nitrogen. The phosphate contents are generally high.
Due to intensive leaching, the laterite soil generally lacks fertility and is of low value for crop production. But when manured and timely irrigated, the soil is suitable for producing plantation crops like tea, coffee, rubber, coconut, arecanut, etc. It also provides valuable building materials.
5. Mountain Soil:
The mountain soil is generally found on the hill slopes covered with forests. In the Himalayan region such soil is mainly found in the valley basins, the depressions and the lesser steep slopes. The north-facing slopes generally support soil cover. Apart from the Himalayan region, this soil is also found in the Western and Eastern Ghats and in some parts of the Peninsular India.
i. The mountain soil is formed mainly due to the deposition of organic matter provided by the forests.
ii. This soil is rich in humus, but poor in potash, phosphorus and lime.
iii. It is heterogeneous in nature and varies from place to place.
iv. The mountain soil is sandy with gravels and is porous.
For getting high yields of crops, heavy doses of fertilizers have to be applied. In the Himalayan region wheat, maize, barley and temperate fruits are grown on this soil. This soil is especially suitable for producing plantation crops, such as tea, coffee, spices and tropical fruits in Karnataka, Tamil Nadu and Kerala.
6. Desert Soil:
The desert soil is found mostly in the arid and semi-arid regions, receiving less than 50 cm of annual rainfall. Such regions are mostly found in Rajasthan and the adjoining areas of Haryana and Punjab. The Rann of Kachchh in Gujarat is an extension of this region.
i. The sand in the desert areas is partly of local origin and partly being blown in from the Indus Valley.
ii. It includes even the wind-blown loess.
iii. The desert soil has sand (90 to 95 per cent) and clay (5 to 10 per cent).
iv. In some regions this soil has high percentage of soluble salts, but lacks in organic matter.
v. The nitrogen content is low, but the phosphate content is as high as in normal alluvial soil.
When water is made available through irrigation, the desert soil can produce a variety of crops, such as wheat, millets, barley, maize, pulses, cotton, etc. Shortage of water in the arid regions is the main limiting factor for agriculture.