Soils of India and Natural Vegetation: Soil Types, Forest Types and Conservation

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How soils are classified

Soil is the thin top layer of the land, formed from weathered rock mixed with humus, and it takes a very long time, centuries or more, to build even a few centimetres. Its type depends on the parent rock, climate, relief, vegetation and time. The Indian Council of Agricultural Research (ICAR), set up in 1929, groups Indian soils into eight major types: alluvial, black, red and yellow, laterite, arid, saline, peaty (marshy) and forest soils. Exams ask where each is found, what gives it its colour or character, and which crops suit it.

Alluvial and black soils

Alluvial soil, laid down by rivers, is the most widespread, covering about 40 percent of the country across the Northern Plains, the river valleys and the deltas of the east coast. It is rich in potash but poor in phosphorus; the old alluvium (bhangar) has kankar nodules, while the new alluvium (khadar) is finer and more fertile. It suits rice, wheat, sugarcane, pulses and oilseeds. Black soil, or regur, formed from the weathering of the basalt of the Deccan Trap, covers most of Maharashtra and parts of Gujarat, Madhya Pradesh, Karnataka, Telangana, Andhra Pradesh and Tamil Nadu. It is clayey and holds moisture for long, and in summer it develops deep cracks that let air in, so it is called self-ploughing. It is rich in lime, iron, magnesia and potash but poor in phosphorus, nitrogen and organic matter. It is ideal for cotton, hence the name black cotton soil.

Red, laterite and other soils

Red and yellow soil forms on old crystalline rocks in the low-rainfall eastern and southern Deccan, in Tamil Nadu, Karnataka, Odisha, Chhattisgarh and Jharkhand; it is red because iron is spread through the rock and yellow where that iron is hydrated, and it grows millets, pulses and groundnut. Laterite soil (from the Latin later, meaning brick) forms under high temperature and heavy rainfall, which wash away lime and silica and leave iron and aluminium oxides; found in Kerala, Karnataka, Tamil Nadu and the hills of Odisha and Assam, it is used for bricks and, with manure, grows tea, coffee and cashew. Arid soil of Rajasthan is sandy and saline, with a kankar layer below, and yields well when irrigated. Saline soil (usar, reh or kallar) holds too much sodium and magnesium; it occurs in western Gujarat, the eastern deltas, the Sundarbans and over-irrigated parts of Punjab and Haryana, and is treated with gypsum. Peaty soil, rich in organic matter, forms in waterlogged areas of north Bihar and the coasts of West Bengal, Odisha and Tamil Nadu. Forest soils on Himalayan slopes are thin and acidic higher up.

Soil erosion and conservation

Soil erosion is the removal of top soil by running water and wind, speeded up by deforestation, over-grazing, mining and careless farming. Running water causes sheet, rill and gully erosion, and deep gullies turn land into badlands, like the Chambal ravines, while wind blows away the loose soil of the desert. Conservation methods include contour ploughing across the slope, terrace or step farming on hill slopes, strip cropping with grass between crops, shelter belts of trees to break the wind in western India, afforestation, check dams across gullies, and controlled grazing.

Forests by rainfall

The type of natural forest in India depends mainly on rainfall. Tropical evergreen forests grow where rain is over 200 cm, on the Western Ghats, in the north-east hills and in the Andaman and Nicobar Islands; they are dense, tall, many-layered and green all year, with ebony, mahogany, rosewood, rubber and cinchona. Tropical deciduous or monsoon forests are the most widespread and shed their leaves in the dry season. The moist deciduous type (200 to 100 cm of rain) has teak, sal, shisham, sandalwood and bamboo and grows in the north-east, along the Himalayan foothills and in Jharkhand, Odisha and Chhattisgarh; the dry deciduous type (100 to 70 cm) has teak, peepal and neem. Tropical thorn forests and scrub grow where rain is below 70 cm, in Rajasthan, Gujarat and the dry Deccan, with acacia, babool, khejri, cactus and euphorbia.

Mountain forests and mangroves

In the mountains vegetation changes with height: wet temperate forests of oak and chestnut between 1,000 and 2,000 m; coniferous forests of pine, deodar, silver fir and spruce between 1,500 and 3,000 m; alpine forests of silver fir, juniper and birch above about 3,600 m; then alpine meadows, called bugyals in Uttarakhand and margs in Kashmir, and mosses and lichens near the snow line. Mangrove or tidal forests grow in salt water on the deltas of the Ganga, Mahanadi, Godavari, Krishna and Kaveri. The Sundarbans of West Bengal, named after the sundari tree and home of the Royal Bengal tiger, form part of the largest mangrove forest in the world; Bhitarkanika (Odisha) and Pichavaram (Tamil Nadu) are other mangroves. The National Forest Policy of 1988 aims to keep one-third (33 percent) of the land under forest or tree cover, and two-thirds in the hills.

Key facts

ICAR (1929) groups Indian soils into eight types: alluvial, black, red and yellow, laterite, arid, saline, peaty and forest.
Alluvial soil: most widespread (about 40 percent of the area), rich in potash, poor in phosphorus; bhangar is old alluvium, khadar new; rice, wheat, sugarcane.
Black soil (regur): from Deccan Trap basalt; holds moisture, self-ploughing cracks; rich in lime, iron, magnesia, potash; poor in phosphorus and nitrogen; best for cotton.
Red soil gets its colour from iron in crystalline rock (yellow when hydrated); laterite (Latin later = brick) forms by leaching in hot, wet areas and suits tea, coffee and cashew.
Saline soil (usar, reh, kallar) is treated with gypsum; peaty soil forms in waterlogged north Bihar and the coasts of West Bengal, Odisha and Tamil Nadu.
Conservation: contour ploughing, terrace farming, strip cropping, shelter belts, check dams, afforestation; Chambal ravines are badlands formed by gully erosion.
Forest by rainfall: evergreen over 200 cm (ebony, mahogany, rosewood), moist deciduous 200-100 cm (teak, sal), dry deciduous 100-70 cm, thorn below 70 cm (babool, khejri).
Montane zones: oak and chestnut 1,000-2,000 m; pine, deodar, silver fir 1,500-3,000 m; alpine above 3,600 m; meadows are bugyals in Uttarakhand.
Mangroves: Sundarbans (sundari tree, Royal Bengal tiger), Bhitarkanika (Odisha), Pichavaram (Tamil Nadu); Forest Policy 1988 aims at 33 percent forest cover.

Quick revision

ICAR (1929): 8 soil groups; alluvial most widespread (about 40%), rich in potash; black regur from Deccan basalt, self-ploughing, cotton; red from iron; laterite from leaching, tea, coffee, cashew; saline (usar, reh) treated with gypsum; contour ploughing, terracing, shelter belts check erosion; evergreen forests over 200 cm, deciduous most widespread (teak, sal), thorn below 70 cm; conifers 1,500-3,000 m; Sundarbans mangroves; Forest Policy 1988 aims at 33%.

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