In this guide
Ask why cotton grows in the Deccan, why tea grows on laterite hillsides, or why Punjab's fields are showing signs of salinity, and the answer begins with soil. Soils are a steady Prelims topic, and they feed into Mains questions on agriculture, land degradation and food security.
How soil forms
Soil forms over long periods through the weathering of rock and the addition of organic matter. Five factors shape it:
| Factor | Role |
|---|---|
| Parent material | The rock from which soil forms decides its minerals — basalt gives black soil, crystalline rocks give red soil |
| Climate | Temperature and rainfall control weathering and leaching; heavy rain washes away soluble nutrients |
| Relief | Slopes lose soil to erosion; valleys and plains accumulate it |
| Organisms | Plants, microbes and animals add organic matter and mix the soil |
| Time | Mature soils develop distinct layers (horizons) over long periods |
In India, soils fall broadly into two groups: in situ soils formed from the rock beneath them (black, red, laterite), and transported soils carried and deposited by rivers or wind (alluvial, some arid soils).
The major soil types
The Indian Council of Agricultural Research (ICAR) recognises eight major groups.
| Soil | Where | Key features | Crops |
|---|---|---|---|
| Alluvial | Northern plains, river valleys, coastal deltas | Deposited by rivers; rich in potash; often poor in nitrogen and phosphorus | Rice, wheat, sugarcane, pulses |
| Black (regur) | Deccan plateau — Maharashtra, Gujarat, MP, parts of Karnataka and Telangana | Formed from basalt; high clay content; retains moisture; cracks when dry | Cotton, soybean, sugarcane, jowar |
| Red and yellow | Eastern and southern peninsula | Formed from crystalline rocks; red due to iron oxide; yellow when hydrated | Millets, pulses, groundnut; needs fertilisers |
| Laterite | Western Ghats, Eastern Ghats, north-east hills, parts of Kerala and Odisha | High temperature and heavy rain cause intense leaching; rich in iron and aluminium, poor in nutrients | Tea, coffee, cashew, rubber (with fertilisers) |
| Arid (desert) | Rajasthan and adjoining areas | Sandy, low in organic matter; often saline; kankar layers | Millets, with irrigation |
| Saline and alkaline | Parts of Punjab, Haryana, UP, Gujarat coast | Excess salts; locally called reh, kallar, usar | Poor until reclaimed (e.g. with gypsum) |
| Peaty and marshy | Kerala backwaters, Sundarbans, coastal Odisha | High organic matter; waterlogged; acidic | Rice in some areas |
| Forest and mountain | Himalaya and hill forests | Varies with altitude; often acidic, thin on slopes | Tea, fruits, forestry |
Alluvial soil in more detail
The alluvium of the northern plains is divided into:
- Khadar — newer alluvium in flood plains, renewed by floods every year; fertile.
- Bhangar — older alluvium on higher ground above flood levels; contains calcareous nodules called kankar.
Black soil in more detail
Black soil is rich in lime, iron, magnesia and potash, but poor in nitrogen, phosphorus and organic matter. Its high clay content (largely montmorillonite) makes it swell when wet and shrink and crack when dry — a process sometimes called "self-ploughing", because the cracks help aerate the soil. Its moisture retention makes it valuable for rain-fed cotton.
Soil degradation
India faces serious soil degradation. Its main forms:
- Water erosion — sheet, rill and gully erosion; the ravines of the Chambal valley are an extreme example.
- Wind erosion — in arid and semi-arid areas, especially western Rajasthan.
- Salinisation and alkalinisation — often caused by over-irrigation and poor drainage, which raise the water table and bring salts to the surface; a problem in canal-irrigated areas of Punjab, Haryana and elsewhere.
- Waterlogging — from excessive canal irrigation and poor drainage.
- Nutrient imbalance — heavy and unbalanced use of chemical fertilisers, especially nitrogen (urea), relative to phosphorus and potassium; declining organic carbon; micronutrient deficiencies such as zinc.
- Loss of topsoil from deforestation, overgrazing and shifting cultivation.
Conservation and restoration
| Measure | How it helps |
|---|---|
| Contour ploughing and bunding | Slows run-off on slopes |
| Terracing | Allows cultivation on hills with less erosion |
| Shelter belts and strip cropping | Reduce wind erosion |
| Afforestation and controlled grazing | Protect topsoil |
| Gully plugging and check dams | Control ravine formation |
| Gypsum application and drainage | Reclaim alkaline and saline soils |
| Balanced fertiliser use, organic manure, crop rotation | Restore soil health |
| Watershed management | Treats land and water together at the landscape level |
The Soil Health Card scheme (launched in 2015) provides farmers with information on the nutrient status of their soil and recommended doses of fertilisers, with the aim of more balanced nutrient use.
Practice questions
- Prelims-type: Which soil is known as regur? Why is laterite soil poor in nutrients despite heavy rainfall?
- Mains-type (150 words): Explain the characteristics of black soil and why it suits cotton cultivation.
- Mains-type (250 words): "Soil degradation is a silent threat to India's food security." Discuss its causes and suggest remedies.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Union Public Service Commission website .
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