Soils of India Notes for UPSC

Soil is the thin top layer of the Earth's surface that supports plant life. It is made of broken rock particles, organic matter (humus), water, air and living organisms. Soil is the base of agriculture, and in a country like India, where a large part of the population depends on farming, its type, fertility and protection are very important. For UPSC, "Soils of India" appears often in the Prelims (type, region, crop, features) and in Mains (soil erosion, degradation and conservation). This note covers the major soils, their features and the policies related to soil health, in simple language.

How Soil Is Formed

Soil forms very slowly, often over thousands of years, through the weathering of rocks. The five main factors are the parent rock (the rock from which it is formed), climate (temperature and rainfall), relief (slope and height), living organisms (plants, microbes and earthworms) and time. A soil profile is made of layers called horizons: the topsoil (A horizon) rich in humus, the subsoil (B horizon), the weathered rock (C horizon) and the bedrock below it.

Classification of Indian Soils

The Indian Council of Agricultural Research (ICAR) groups Indian soils into eight major types: alluvial, black, red, laterite, arid (desert), saline and alkaline, peaty and marshy, and forest (mountain) soils. Each of these is described below.

1. Alluvial Soil

This is the most widespread and the most fertile soil in India, covering about 40 percent of the land. It is formed by the silt deposited by the Indus, Ganga and Brahmaputra river systems and is also found in the coastal plains and river deltas. It has two types: Khadar (new alluvium, light-coloured, found in the flood plains and renewed every year) and Bhangar (old alluvium, darker, with lime nodules called kankar, found on higher land). Alluvial soil is rich in potash and lime but poor in nitrogen, phosphorus and humus. It is ideal for wheat, rice, sugarcane, jute, maize and pulses.

2. Black Soil (Regur Soil)

Black soil is formed by the weathering of volcanic basalt rock (the Deccan Trap), mainly in Maharashtra, Madhya Pradesh, Gujarat, Karnataka, Telangana and Andhra Pradesh. Its black colour comes from titaniferous magnetite and iron. It has a high clay content, so it holds moisture for a long time. It becomes sticky when wet and develops deep cracks when dry, which helps in natural "self-ploughing". It is rich in calcium, magnesium, iron and lime but poor in nitrogen, phosphorus and organic matter. It is best for cotton (hence the name "black cotton soil"), soybean, sugarcane, jowar, tobacco and oilseeds.

3. Red Soil

Red soil develops on old crystalline rocks like granite and gneiss in areas of low rainfall. The red colour comes from iron oxide; when hydrated, it looks yellow. It covers parts of Tamil Nadu, Karnataka, Andhra Pradesh, Odisha, Chhattisgarh and the North-East. It is generally less fertile and lacks nitrogen, phosphorus, humus and lime, but it responds well to fertilisers and irrigation. Typical crops are millets, groundnut, pulses, tobacco and potato.

4. Laterite Soil

The word comes from the Latin later, meaning brick. Laterite forms in areas with heavy rainfall and high temperature, where the rain washes away (leaches) the silica and nutrients and leaves behind iron and aluminium. It is found on the Western Ghats, the Eastern Ghats, the Meghalaya plateau and parts of Kerala, Karnataka and Odisha. It is acidic, low in fertility and hard when dry, so it is used for making bricks. With good fertilisers it supports tea, coffee, rubber, cashew and tapioca.

5. Arid or Desert Soil

Found in Rajasthan, Haryana and Gujarat, this soil is sandy, low in humus and moisture and often rich in salts. With irrigation (for example the Indira Gandhi Canal), it can grow millets, barley and cotton.

6. Saline and Alkaline Soil

Also called Usar, Reh or Kallar, it contains excess salts such as sodium, magnesium and calcium and is found in parts of Punjab, Haryana, Uttar Pradesh, Rajasthan and Gujarat, as well as the coastal areas. Poor drainage and over-irrigation in dry regions increase it. It can be improved by applying gypsum, improving drainage and growing salt-tolerant crops.

7. Peaty and Marshy Soil

This soil forms in humid regions with plenty of organic matter from dead plants, and it is found in Kerala (Kuttanad, called kari soil), the Sundarbans of West Bengal and parts of Odisha and Tamil Nadu. It is black, heavy and acidic and can be used for rice after land reclamation.

8. Forest and Mountain Soil

Found in the Himalayan and other hilly regions, this soil has a lot of humus but is acidic and thin on steep slopes. It is suitable for tea, coffee, spices, apples and other fruits.

Soil Types at a Glance

Soil Erosion and Degradation

Soil erosion is the removal of the top fertile layer by water or wind. Its common types are sheet erosion, rill erosion, gully erosion (which forms deep channels such as the Chambal ravines) and wind erosion (in deserts). The causes include deforestation, overgrazing, heavy rain on slopes, poor farming methods and construction. Soil is also degraded by excess use of chemical fertilisers, loss of organic matter, waterlogging and salinity. Erosion reduces fertility and clogs rivers and dams with silt.

Soil Conservation Methods

• Contour ploughing and terrace farming on slopes.
• Strip cropping and crop rotation.
• Shelter belts (rows of trees) to stop wind erosion.
• Afforestation and controlled grazing.
• Check dams and gully plugging.

Government Initiatives for Soil Health

The Soil Health Card Scheme (2015) gives farmers a report on the nutrient status of their soil and advice on fertiliser use. The Paramparagat Krishi Vikas Yojana promotes organic farming, and the National Mission for Sustainable Agriculture supports soil and water conservation. The Central Soil Salinity Research Institute is in Karnal, and World Soil Day is observed on 5 December.

Soil Properties You Should Understand

Three simple properties explain most of what UPSC asks. Texture is the size of the soil particles: sand is coarse, silt is medium and clay is fine, and loam, a mixture of all three, is the best for farming. Water holding capacity is high in clay (like black soil) and low in sand (like desert soil). pH shows whether soil is acidic (below 7), neutral (7) or alkaline (above 7). Most crops grow best near a neutral pH, so lime is added to acidic soil and gypsum to alkaline soil. Humus, the dark, decayed organic matter, increases fertility and water-holding power and is highest in forest and peaty soils.

Soil and Climate Change

Soil also helps the climate: it stores a large amount of carbon, more than the atmosphere and all plants together. When forests are cut or soil is ploughed excessively, this carbon is released as carbon dioxide. Healthy soil with organic matter acts as a carbon sink, and practices like no-till farming, cover crops, agroforestry and organic manures increase this storage. This is why the idea of "carbon farming" and the "4 per 1000" initiative are discussed in global climate talks, and why soil health is linked with the sustainable development goals.

How to Study Soils for UPSC

1. Make a one-page table with soil, parent material, colour, nutrient strength and weakness, regions and crops.
2. Locate each soil on a blank map of India, using the physical regions as a guide.
3. Link soil with crops and rainfall so that you can solve application-type questions.
4. Read current news on the Soil Health Card, natural farming and desertification to add examples to Mains answers.

Mains Angle: Soil Health and Food Security

You can write that India's soils are under stress due to the Green Revolution's heavy use of chemicals, falling organic carbon, salinity in canal-irrigated areas, erosion in hills and waterlogging. The solutions include balanced fertiliser use based on soil testing, organic and natural farming, crop diversification, micro-irrigation, conservation agriculture and community-led watershed development. Healthy soil is essential for food security, climate resilience and farmers' income.

Practice Statements and Common Mistakes

• "Black soil is formed from granite." Wrong. It forms from basalt.
• "Alluvial soil is poor in potash." Wrong. It is rich in potash and lime.
• "Laterite soil is formed in heavy rainfall regions by leaching." Correct.
• Do not confuse Khadar (new alluvium) and Bhangar (old alluvium).

Quick Revision

• Alluvial: most fertile; black: cotton; red: iron oxide; laterite: leaching and bricks.
• Saline soil: Usar or Reh; remedy: gypsum and drainage.
• Soil Health Card: 2015; World Soil Day: 5 December.

Soil is the silent partner of every farmer. Learn each soil with its region, colour, nutrient status and crops, practise using a small table, and revise the causes and control of soil erosion, and you will find this topic simple and rewarding.

Related Notes to Read Next

Continue your preparation with these related notes from the same subject:

• Physiographic Divisions of India and the Himalayas Notes for UPSC
• Indian Agriculture and Green Revolution Notes for UPSC
• Natural Vegetation and Forests of India Notes for UPSC
• All Indian Geography notes

Frequently Asked Questions (FAQ)

Which is the most widespread soil in India?

Alluvial soil is the most widespread and fertile soil in India, covering about 40 percent of the land, mainly in the northern plains and coastal areas.

What is the difference between Khadar and Bhangar?

Khadar is new alluvium found in flood plains and renewed every year, while Bhangar is older alluvium found on higher land and has kankar (lime nodules).

Why is black soil called Regur soil?

Black soil is called Regur, from a Telugu word, and is also known as black cotton soil because it is formed from basalt and is ideal for growing cotton.

Which soil is best for cotton?

Black soil (Regur) is best for cotton, because it retains moisture and is rich in lime, iron and magnesium.

What gives red soil its colour?

Red soil gets its colour from the presence of iron oxide in the old crystalline rocks from which it is formed.

What is laterite soil and where is it found?

Laterite soil forms in areas of heavy rain and high temperature through leaching. It is found in the Western Ghats, Eastern Ghats, Meghalaya, Kerala, Karnataka and Odisha and is used for bricks.

What is saline soil and how can it be improved?

Saline soil, also called Usar or Reh, has excess salts. It can be improved by applying gypsum, improving drainage and growing salt-tolerant crops.

What are the main types of soil erosion?

The main types are sheet erosion, rill erosion, gully erosion and wind erosion, caused by water or wind removing the topsoil.

What are the methods of soil conservation?

Important methods are contour ploughing, terrace farming, strip cropping, crop rotation, shelter belts, afforestation and building check dams.

What is the Soil Health Card Scheme?

Launched in 2015, the Soil Health Card Scheme provides farmers with a report on the nutrient status of their soil and recommends the right amount of fertilisers and soil improvements.

Which soils are suitable for tea and coffee?

Laterite and forest or mountain soils, which are acidic and rich in humus in regions of good rainfall, are suitable for tea, coffee and rubber.

When is World Soil Day celebrated?

World Soil Day is celebrated on 5 December every year to spread awareness about the importance of healthy soil.