Soils of India: Types, Degradation and Conservation

What soil is and how it forms

Soil is the thin layer of loose material on the Earth's surface made of weathered rock particles, organic matter (humus), water, air and living organisms. It takes hundreds to thousands of years to form a few centimetres, which is why soil is treated as a non-renewable resource on a human time-scale. Five factors control soil formation: parent rock, climate (the most important), relief, vegetation and organisms, and time. A vertical cut through soil shows horizons: the A horizon (topsoil, rich in humus), the B horizon (subsoil, where minerals washed down from above accumulate) and the C horizon (weathered parent rock), resting on bedrock.

Soils in India are often described by their origin: in-situ (residual) soils develop where the parent rock lies, like black and red soils of the peninsula, while transported soils are carried by rivers, wind or glaciers, like the alluvium of the plains.

Classification of Indian soils

The Indian Council of Agricultural Research (ICAR) recognises eight major soil groups, based on the older All India Soil Survey. Today ICAR's National Bureau of Soil Survey and Land Use Planning (NBSS&LUP) also uses the international USDA Soil Taxonomy, under which Indian soils fall mostly into Inceptisols and Entisols (young alluvial soils), Alfisols (red soils), Vertisols (black soils) and Aridisols (desert soils).

1. Alluvial soils

• Extent: the most widespread soils, covering about 40 per cent of India's land – the Northern Plains, river valleys and the deltas of the east coast.
• Origin: deposited by the Indus, Ganga and Brahmaputra and by peninsular rivers.
• Types: Bhangar (older, with kankar nodules, less fertile) and Khadar (newer, renewed by floods, very fertile).
• Properties: sandy-loam to clayey; rich in potash and lime but poor in nitrogen and phosphorus.
• Crops: rice, wheat, sugarcane, pulses, oilseeds, jute in the delta.

2. Black soils (regur)

• Extent: about 15 per cent; the Deccan Trap region – Maharashtra, western Madhya Pradesh, Gujarat (Saurashtra), and parts of Karnataka, Telangana and Andhra Pradesh.
• Origin: weathering of basalt lava rocks; also called regur or black cotton soil.
• Properties: clayey and moisture-retentive; develop deep cracks when dry and become sticky when wet, so they are said to "self-plough"; rich in iron, lime, calcium, magnesium and alumina, poor in nitrogen, phosphorus and organic matter. The black colour comes from titaniferous magnetite and humus.
• Crops: cotton above all, plus soybean, jowar, groundnut, tobacco, sugarcane and citrus.

3. Red and yellow soils

• Extent: about 18 per cent; eastern and southern Deccan – Tamil Nadu, Karnataka, Odisha, Chhattisgarh, Jharkhand, parts of the north-east.
• Origin: weathering of crystalline granite and gneiss in areas of low to moderate rainfall.
• Colour: red because of iron oxide; yellow when the iron is hydrated.
• Properties: porous, light; poor in nitrogen, phosphorus and humus.
• Crops: millets, groundnut, pulses, tobacco; rice and sugarcane with irrigation and fertilisers.

4. Laterite soils

• Extent: areas of high temperature and heavy rainfall with alternating wet and dry seasons – the Western Ghats, Kerala, Karnataka, parts of Odisha, the Meghalaya plateau and the Eastern Ghats.
• Origin: intense leaching washes away silica and lime, leaving iron and aluminium oxides. The term comes from the Latin *later*, meaning brick – laterite hardens on exposure to air and is cut into building blocks.
• Properties: acidic, poor in nitrogen, potash, lime and humus.
• Crops: with manure and fertiliser – tea, coffee, rubber, cashew, coconut and tapioca.

5. Arid (desert) soils

• Extent: western Rajasthan, Kachchh and parts of Haryana and Punjab.
• Properties: sandy, low humus, high salt content; a kankar layer lower down restricts water infiltration.
• Use: bajra, pulses, guar and fodder; irrigation (Indira Gandhi Canal) allows wheat and cotton.

6. Saline and alkaline soils

Called reh, kallar or usar, they form where poor drainage and high evaporation draw salts to the surface, often due to over-irrigation in canal areas of Punjab, Haryana and western UP, and in coastal Gujarat and the Sundarbans. They are reclaimed by adding gypsum, improving drainage and growing salt-tolerant crops such as barley, berseem and dhaincha.

7. Peaty and marshy soils

Found in areas of heavy rain and poor drainage – Kerala's Kuttanad, coastal Odisha, the Sundarbans and parts of Bihar and Uttarakhand. They are rich in organic matter, black and highly acidic.

8. Forest and mountain soils

Found on the slopes of the Himalaya and the Western and Eastern Ghats. Soils are thin and coarse on upper slopes, loamy and silty in valleys, and acidic with low humus in high areas. They support tea, coffee, spices and tropical fruits at suitable heights.

Soil degradation

According to ISRO's Desertification and Land Degradation Atlas (2021), about 97.85 million hectares – nearly 29.7 per cent of India's land – was undergoing degradation in 2018–19. The main processes are:

• Water erosion – the biggest single cause; sheet, rill and gully erosion; the ravines of the Chambal (badlands) are an extreme example.
• Wind erosion in Rajasthan and Gujarat.
• Vegetation degradation through deforestation and overgrazing.
• Salinisation and waterlogging from over-irrigation.
• Loss of fertility from imbalanced fertiliser use (too much urea relative to phosphorus and potash), monocropping and stubble burning.

Conservation measures

• Mechanical: contour ploughing and contour bunding on slopes, terracing in hills, check dams and gully plugging.
• Biological: strip cropping with grasses between crops, shelter belts of trees to break wind in deserts, mulching, crop rotation with legumes, and afforestation.
• Policy: the Soil Health Card scheme (2015) tests soil and recommends balanced nutrients; the National Mission for Sustainable Agriculture; the watershed component of PMKSY; promotion of natural farming and nano-fertilisers; and India's pledge under the UNCCD to restore 26 million hectares of degraded land by 2030.

Soil, crops and regional development

Soils explain much of India's agricultural map. The deep, fertile alluvium of the Indo-Gangetic plain, combined with canal and tube-well irrigation, made Punjab, Haryana and western Uttar Pradesh the core of the Green Revolution. The moisture-holding black soils of the Deccan made Maharashtra and Gujarat the heart of India's cotton economy and of the textile mills that grew in Mumbai and Ahmedabad. The thin red and laterite soils of the plateau and the hills carry poorer farming, but they host plantations – tea in Assam and the Nilgiris, coffee in Kodagu and Chikkamagaluru, rubber and cashew in Kerala and coastal Karnataka. Poor soils in many tribal districts of the plateau, together with rain-fed farming, help explain persistent poverty in those areas.

Soil health is now a policy concern. Indian soils are low in organic carbon, often below 0.5 per cent, and many districts show deficiencies of zinc, sulphur and boron. The heavy subsidy on urea encourages farmers to use far more nitrogen than phosphorus and potash, which distorts the ideal N:P:K ratio of about 4:2:1. Remedies include neem-coated urea, customised and fortified fertilisers, crop diversification away from water-intensive paddy in the north-west, and organic manures such as compost and green manure.

Soil and climate change

Healthy soil stores carbon. Practices such as zero tillage, cover crops and agroforestry raise soil organic carbon, cut emissions and make farms more resilient to drought and heavy rain. Degraded and eroded land, by contrast, loses carbon, water and fertility. This is why land restoration, the "4 per 1000" idea of raising soil carbon, and the UN goal of Land Degradation Neutrality are linked to both food security and climate goals.

Mains practice question

Classify the major soil types of India and explain how climate and parent rock determine their characteristics. Suggest measures to check soil degradation. (250 words)

Answer framework

• Intro: soil-forming factors; ICAR 8 groups.
• Parent rock: black (basalt), red (granite), alluvial (river deposits).
• Climate: laterite (leaching), arid, saline.
• Degradation data and causes.
• Measures: mechanical, biological, policy (Soil Health Card, 26 Mha target).