Soils of India: Classification and Characteristics Notes for UPSC

Dear students, soil is the base of agriculture, and agriculture is the base of the Indian economy. The question "which soil is suitable for which crop" is asked almost every year in the Prelims. This chapter gives you the full classification of the soils of India, with the distribution, features and the crops of each type. Learn the table below well, because it is the most important table in the Indian geography.

What Is Soil? Factors of Soil Formation

Soil is the loose, upper layer of the Earth's crust made of weathered rock particles (minerals), humus (organic matter), water, air and living organisms. It takes hundreds of years to form 1 cm of soil. The factors of soil formation are:

• Parent rock (decides the colour, texture, minerals), climate (temperature and rainfall decide the weathering and leaching), relief (topography), organisms (vegetation, microbes, earthworms) and time.

The soil profile has the horizons: O (organic), A (topsoil), B (subsoil), C (weathered parent material), R (bedrock). The soil texture (sand, silt, clay proportions) decides water-holding capacity; loam (a balanced mix) is the best for agriculture. The soil pH tells acidity or alkalinity: acid (below 7), neutral (7), alkaline (above 7).

Classification of the Soils of India (ICAR)

1. Alluvial Soils

• Formation: Deposited by the rivers (the Indus, Ganga, Brahmaputra and their tributaries) in the northern plains, and by the east-flowing rivers of the Peninsula in the coastal plains and deltas (Mahanadi, Godavari, Krishna, Cauvery). Also in the Narmada-Tapi valleys and in the Gujarat plains.
• Area: The largest group, covering about 40 percent of the land (the northern plains, the Brahmaputra valley, the eastern coastal plains).
• Types: Bhangar (old alluvium, higher, with the kankar nodules, less fertile) and Khadar (new alluvium, lower, renewed by the floods every year, very fertile).
• Features: Light to dark grey or greyish-brown; sandy loam to clay; rich in potash, phosphoric acid and lime; poor in nitrogen and humus; highly fertile.
• Crops: Wheat, rice, sugarcane, maize, pulses, oilseeds, jute and vegetables.

2. Black Soils (Regur, Black Cotton Soils)

• Formation: Weathering of the basalt (Deccan Traps lava) with the climate being hot and moderate rain. Black colour is due to titaniferous magnetite and iron, not the humus.
• Area: The Deccan Plateau: Maharashtra, Madhya Pradesh, Gujarat, Karnataka, Andhra Pradesh, Telangana and parts of Tamil Nadu; the Malwa plateau and the Krishna and Godavari valleys.
• Features: Clayey, deep, with high water retention (becomes sticky when wet and cracks deeply when dry; "self-ploughing"); rich in lime, iron, magnesium, calcium, potash and aluminium; poor in nitrogen, phosphorus and humus.
• Crops: Cotton (hence the black cotton soil), soybean, sugarcane, jowar, wheat, citrus fruits, oilseeds, tobacco, groundnut.

3. Red and Yellow Soils

• Formation: Crystalline rocks (granite, gneiss) in a low rainfall area; the red colour is due to the diffusion of iron in the crystalline and metamorphic rocks (ferric oxide); it turns yellow when hydrated.
• Area: The eastern and southern parts of the Deccan plateau: Tamil Nadu, Karnataka, Andhra Pradesh, Chhattisgarh, Odisha, Jharkhand, and the Piedmont zone of the Western Ghats; also parts of Meghalaya, Nagaland, Rajasthan.
• Features: Porous, friable structure; light texture; poor in nitrogen, phosphorus, humus and lime; low water-holding capacity and need irrigation and fertilisers; deficient in lime and humus.
• Crops: Millets, groundnut, ragi, pulses, tobacco, potato; with irrigation, wheat, cotton, rice.

4. Laterite Soils

• Formation: From leaching in the areas of high temperature and heavy seasonal rainfall (alternate wet and dry spells); silica is washed out and iron and aluminium oxides remain. "Later" means brick in Latin; it hardens like a brick on drying.
• Area: The summits of the Western Ghats and the Eastern Ghats, Karnataka, Kerala, Tamil Nadu, Maharashtra (Konkan), Odisha, Assam hills, Meghalaya, and Chhota Nagpur.
• Features: Acidic, low in nitrogen, potash, lime, humus; infertile, but improved with manure and fertilizers; used for making bricks (laterite stones in Kerala and Goa).
• Crops: Tea, coffee, rubber, cashew, coconut, areca nut, tapioca, spices (plantation crops).

5. Arid (Desert) Soils

• Formation: In the dry climate, with high temperatures, evaporation and little rain; the wind-blown sand.
• Area: Western Rajasthan (Thar), Kutch, parts of Haryana and Punjab.
• Features: Sandy, saline, low in humus and moisture, rich in soluble salts and phosphate; kankar layer in the lower horizon restricts water infiltration. With irrigation (the Indira Gandhi Canal), they can be cultivated.
• Crops: Bajra, jowar, guar, barley, cotton (with irrigation), millets.

6. Saline and Alkaline Soils (Usar, Reh, Kallar, Chopan)

• Formation: Accumulation of salts (sodium, calcium, magnesium) due to the poor drainage, the capillary action in the dry areas, the over-irrigation, and the sea water in the coastal areas.
• Area: Parts of Punjab, Haryana, Uttar Pradesh, Bihar, Rajasthan, Maharashtra, Gujarat, the Sundarbans and Kerala coasts. Approximately 6.7 million hectares affected. They are called by the local names: reh, kallar, usar, thur, rakar, karl, chopan.
• Features: Infertile, whitish crust; lack nitrogen and calcium. The Green Revolution's excessive canal irrigation in Punjab and Haryana caused salinity.
• Reclamation: Gypsum application, flushing with water, salt-tolerant crops (barley, cotton, rice, sugarbeet), green manure and better drainage.

7. Peaty and Marshy Soils

• Formation: In the humid regions where the dead vegetation accumulates (peat), under waterlogged conditions.
• Area: Kottayam and Alappuzha (Kuttanad) in Kerala (where it is called kari), the Sundarbans in West Bengal, coastal Odisha and Tamil Nadu, parts of Bihar and Uttarakhand (Almora).
• Features: Heavy, black, highly acidic with a large amount of humus (up to 40 to 50 percent organic matter), but less in phosphate and potash.
• Crops: Rice, jute (paddy-fish farming in Kuttanad).

8. Forest and Mountain Soils

• Formation: In the hilly and mountainous areas with the forest cover; varies with the altitude and relief.
• Area: The Himalayas, the Western and Eastern Ghats, the Nilgiris, the north-eastern hills.
• Features: Loamy and silty in the valleys; coarse and thin on the upper slopes; acidic with low humus in the snow-covered areas; fertile in the valleys.
• Crops: Tea, coffee, spices, fruits (apples, peaches), potato, maize, barley, and rice in the valleys.

Summary Table

Soil Fertility, Nutrients and Common Problems

• The macronutrients: nitrogen (N), phosphorus (P) and potassium (K) (NPK); the secondary nutrients: calcium, magnesium and sulphur; the micronutrients: zinc, iron, boron, copper, manganese, molybdenum. Most Indian soils lack nitrogen and organic carbon, many lack zinc.
• Alluvial soils are the "food bowl" of India, but intensive farming causes nutrient depletion; black soil is retentive but difficult to plough; red and laterite soils need manure; saline soils need reclamation.
• The Government's Soil Health Card Scheme (2015) gives farmers a card with the soil nutrient status and the recommendations on fertiliser use.

Soil Distribution Map: Teacher's Memory Map

Students, memorize the map in this simple way: (1) North = alluvial; (2) Deccan middle-west = black; (3) Southeast and east of Peninsula = red; (4) Western Ghats top, Kerala coast, Assam hills = laterite; (5) Rajasthan = arid; (6) Kerala backwaters and Sundarbans = peaty and marshy; (7) Himalayas = mountain soils; (8) Punjab-Haryana patches = saline. And always remember the crop pair, such as cotton–black soil, tea–laterite or hill soil.

Common Mistakes Students Make

• Saying that black soil's black colour is due to humus. It is due to the titaniferous magnetite.
• Writing that alluvial soil is rich in nitrogen. It is poor in nitrogen and humus.
• Confusing laterite and red soils. Laterite is formed by leaching in a heavy rainfall area; red soil is from crystalline rocks.
• Mixing up the bhangar and the khadar.

Important Points for the Exam

• Eight soil groups by ICAR; alluvial soil: about 40 percent; black soil: cotton; laterite: plantations; red soil: iron oxide.
• Black soil is formed from basalt in the Deccan; arid soils have kankar; saline soils are called reh/usar/kallar.
• The Soil Health Card (2015) and the Green Revolution salinity issue.

Related Reading

Students, read this chapter together with our notes on Soils of India (overview), Indian Agriculture and our UPSC blog.

Frequently Asked Questions (FAQ)

How many major soil groups does ICAR identify in India?

Eight.

Which is the most widespread soil in India?

Alluvial soil.

What are bhangar and khadar?

Old and new alluvium.

Which nutrients are poor in alluvial soil?

Nitrogen and humus.

Which soil is best for cotton?

Black soil (regur).

What is black soil formed from?

The weathering of basalt lava.

Why is black soil black?

Because of titaniferous magnetite and iron.

Where is red soil found?

The eastern and southern Deccan, Tamil Nadu, Karnataka, Odisha and Jharkhand.

Why is red soil red?

Because of iron oxide in crystalline rocks.

How is laterite soil formed?

By intense leaching in hot, heavy-rainfall regions.

Which crops grow on laterite soil?

Tea, coffee, rubber, cashew and spices.

Which soil is found in Rajasthan?

Arid (desert) soil.

What are reh and usar?

Local names of saline and alkaline soils.

How are saline soils reclaimed?

By applying gypsum, flushing with water and improving drainage.

Where is peaty soil found?

Kerala's Kuttanad, the Sundarbans and coastal Odisha.

What is the Soil Health Card Scheme?

A scheme (2015) that gives farmers a card on their soil nutrient status.