Soil Formation and the Soils of India
Soil formation factors and processes, the soil profile, India's eight major soil types with properties and crops, and soil degradation, for UPSC.
SyllabusGS I · Salient features of world physical geography; distribution of key natural resources
Prerequisites: Biogeography and Soils — overview · Landforms and Agents of Erosion
The Hook: A Health Card for the Soil
In February 2015, the Government of India launched the Soil Health Card scheme at Suratgarh in Rajasthan. Each farm’s soil is tested and the farmer gets a card listing its nutrient status — nitrogen, phosphorus, potassium, micronutrients, pH and organic carbon — with fertiliser advice. The same year was declared the International Year of Soils by the United Nations, and 5 December is observed every year as World Soil Day.
Why should two farms a few hundred kilometres apart need completely different fertilisers? Because soil is not “just dirt”: it is shaped by rock, climate, slope, living organisms and time — and India has almost every combination.
The Core Concept
Soil is the thin upper layer of the Earth’s crust made of weathered rock particles, organic matter (humus), water and air, in which plants grow. Forming even a few centimetres of soil can take centuries, which is why soil is treated as a practically non-renewable resource on a human time scale.
Factors of soil formation
| Factor | Role |
|---|---|
| Parent material | Supplies minerals; decides texture and colour in young soils (basalt gives black soil; granite gives red soil) |
| Climate | The most important active factor — temperature and rainfall control weathering, leaching and the breakdown of organic matter |
| Topography (relief) | Steep slopes have thin soils (erosion); flat lowlands have deep soils and may be waterlogged |
| Biological activity | Plants add organic matter; bacteria, fungi, earthworms and termites decompose it into humus and mix the soil |
| Time | Older soils show well-developed horizons and depend less on parent rock |
Soil-forming processes
| Process | Conditions | Result |
|---|---|---|
| Laterisation | Hot, wet tropics with alternate wet and dry seasons | Silica and bases leached away; iron and aluminium oxides remain — laterite |
| Podzolisation | Cool, humid climates under coniferous forests | Acidic leaching; grey, ash-like upper layer — podzols |
| Calcification | Dry and semi-arid climates (evaporation exceeds rainfall) | Calcium carbonate accumulates in lower layers (the kankar layer in Indian arid soils) |
| Salinisation | Arid areas and over-irrigated land with poor drainage | Salts rise by capillary action and crust the surface |
| Gleisation | Waterlogged soils | Poor aeration; bluish-grey colours |
The soil profile
A vertical section through the soil shows layers called horizons:
| Horizon | Name | Features |
|---|---|---|
| O | Organic layer | Leaf litter and decomposing matter |
| A | Topsoil | Mixture of humus and minerals; most biological activity; zone of eluviation (minerals washed down) |
| B | Subsoil | Zone of illuviation — accumulation of clay, iron and other materials washed down from above |
| C | Weathered parent material | Partly broken parent rock |
| R | Bedrock | Unweathered rock |
The soils of India
NCERT’s widely used classification, based on genesis, colour, composition and location, groups India’s soils into eight types.
| Soil | Formation and distribution | Properties | Main crops |
|---|---|---|---|
| Alluvial | Deposited by rivers; the northern plains (Indus–Ganga–Brahmaputra) and the deltas and valleys of peninsular rivers. The most widespread soil — about 40% of India’s area (NCERT) | Sandy loam to clay; rich in potash, poor in phosphorus; khadar (new, renewed by floods, fine) and bhangar (old, on higher ground, with lime nodules called kankar) | Rice, wheat, sugarcane, pulses, oilseeds |
| Black (regur) | Weathering of basalt (Deccan Traps); Maharashtra, Malwa (Madhya Pradesh), Gujarat, parts of Andhra Pradesh, Telangana, Karnataka and Tamil Nadu | Clayey, deep, high moisture retention; swells when wet and develops deep cracks when dry (“self-ploughing”); rich in lime, iron, magnesia and potash; poor in nitrogen, phosphorus and organic matter | Cotton (“black cotton soil”), soybean, jowar, groundnut, sugarcane |
| Red and yellow | Crystalline igneous and metamorphic rocks in areas of low to moderate rainfall — eastern and southern Deccan, Odisha, Chhattisgarh, parts of the Western Ghats piedmont | Red from diffused iron oxides; yellow when the iron is hydrated; generally poor in nitrogen, phosphorus and humus; fine-grained types fertile, coarse ones poor | Millets, pulses, groundnut, tobacco (with fertilisers) |
| Laterite | High temperature and heavy rainfall with alternate wet and dry seasons — laterisation (intense leaching); Kerala, Karnataka, Tamil Nadu, Madhya Pradesh, and hilly parts of Odisha and Assam | Lime and silica leached; rich in iron and aluminium oxides; poor in organic matter, nitrogen, phosphate and calcium; hardens on exposure — used as building bricks (Latin later = brick) | Plantation and tree crops such as cashew, tea, coffee, rubber (with fertilisers) |
| Arid | Western Rajasthan and adjoining dry areas | Sandy, red to brown, saline in places; low humus and moisture; kankar layer in lower horizons (calcium increases downward) restricts water infiltration | Bajra, pulses, guar; productive with irrigation |
| Saline (usar, reh, kallar) | Arid and semi-arid areas, waterlogged and swampy coasts — western Gujarat, the Rann of Kachchh, deltas of the east coast, the Sundarbans; also over-irrigated parts of Punjab and Haryana | High sodium, potassium and magnesium; infertile; poor drainage | Little; reclaimed with gypsum, drainage and salt-tolerant crops |
| Peaty and marshy | Areas of heavy rainfall and high humidity with dense vegetation — northern Bihar, southern Uttarakhand, coastal Odisha, West Bengal and Tamil Nadu | Large accumulation of organic matter; heavy, black; often alkaline | Rice in some areas |
| Forest and mountain | Forested hill and mountain slopes with enough rainfall | Loamy on valley sides, coarse on upper slopes; acidic and low in humus in snowy upper Himalaya; fertile in lower valleys | Tea, coffee, spices, temperate fruits |
graph TD
A[Parent rock + climate] --> B[Basalt, semi-arid Deccan: Black soil]
A --> C[Granite and gneiss, lower rainfall: Red soil]
A --> D[Heavy rain + high temperature: Laterite]
A --> E[River deposits: Alluvial soil]
A --> F[Dry climate: Arid soil with kankar]
A --> G[Poor drainage + evaporation: Saline soil]Soil degradation and conservation
| Problem | Causes | Remedies |
|---|---|---|
| Water erosion — sheet, rill and gully erosion (gullies form ravines, as in the Chambal valley) | Deforestation, overgrazing, cultivation on slopes, heavy rain | Contour ploughing, terracing, check dams, afforestation, plugging gullies |
| Wind erosion | Loose sandy soil, no vegetation cover (western Rajasthan) | Shelter belts of trees, strip cropping, mulching, sand-dune stabilisation |
| Salinity and waterlogging | Excess canal irrigation with poor drainage | Drainage, gypsum, salt-tolerant crops, efficient irrigation |
| Loss of fertility | Imbalanced fertiliser use, crop-residue burning, monocropping | Soil testing, balanced nutrients, organic manure, crop rotation |
| Desertification | Land degradation in dry areas through climate variations and human activity (UNCCD definition) | Integrated watershed management, afforestation, sustainable grazing |
India has committed to restore 26 million hectares of degraded land by 2030, a target announced when it hosted the 14th Conference of the Parties (COP14) of the UN Convention to Combat Desertification in September 2019.
Memory Anchors
Soil-forming factors — “CLORPT”: Climate · Organisms · Relief · Parent material · Time.
Black soil — “Black Basalt Breathes Cracks”: from Basalt, self-ploughing cracks, best for cotton.
Laterite — “Leached by Lots of rain, Left with Iron”: rainfall leaches lime and silica; iron and aluminium are left; used as bricks.
Khadar vs bhangar: Khadar = Kid (young, new, renewed every flood); Bhangar = Bold (old, high, with kankar).
Profile from top: “Old Ants Build Colonies Rapidly” → O, A, B, C, R.
For Prelims
- Climate is the most important active factor of soil formation; parent material is the passive base.
- Alluvial soil covers the largest area (~40%); rich in potash, poor in phosphorus.
- Black soil forms from basalt; high moisture retention; self-ploughing; rich in lime, iron, magnesia, potash; poor in nitrogen, phosphorus and organic matter; ideal for cotton.
- Red colour comes from iron oxides; the soil turns yellow when hydrated.
- Laterite forms by intense leaching in hot, wet climates; poor in nitrogen, phosphate and calcium; used for bricks; suits cashew.
- Arid soils have a kankar layer; saline soils are reclaimed with gypsum.
- Soil Health Card scheme — launched February 2015 at Suratgarh, Rajasthan. World Soil Day — 5 December.
- India’s land-restoration target: 26 million hectares by 2030 (UNCCD COP14, 2019).
For Mains
- Dimensions: physical (formation, processes, distribution); agricultural (fertility, nutrient imbalance, crop suitability); environmental (erosion, salinisation, desertification, carbon storage); economic (productivity, input costs); policy (soil testing, balanced fertilisation, watershed management, land-degradation neutrality).
- Keywords: pedogenesis, leaching, laterisation, humus, soil organic carbon, soil health, nutrient imbalance, land-degradation neutrality, salinisation, sustainable land management.
- Value-addition: the Soil Health Card scheme (2015) tests soils for 12 parameters (macro-, secondary and micronutrients, pH, electrical conductivity and organic carbon) to guide fertiliser use; the excessive use of urea relative to phosphate and potash is widely cited as a cause of imbalanced fertilisation; India’s 2030 restoration target links soils to climate and biodiversity commitments.
Common Traps
In the News
- February 2015 — Soil Health Card scheme launched at Suratgarh, Rajasthan.
- September 2019 — India hosted UNCCD COP14 and raised its land-restoration target to 26 million hectares by 2030.
Practice
Prelims
Consider the following statements about black soils of India:
- They are formed mainly from the weathering of basaltic rocks.
- They are rich in nitrogen and organic matter.
- They develop deep cracks during the dry season.
Which of the statements given above is/are correct?
Solution
- Statement 1 — correct. Black soils develop on the Deccan Trap basalts.
- Statement 2 — wrong. They are poor in nitrogen, phosphorus and organic matter, though rich in lime, iron, magnesia and potash.
- Statement 3 — correct. Being clayey, they swell when wet and shrink and crack when dry — the “self-ploughing” property.
Answer: B
Which one of the following soils is formed by intense leaching under conditions of high temperature and heavy rainfall, is rich in iron and aluminium oxides, and is used as a building material?
Solution
Laterite forms by laterisation: heavy rain leaches away lime and silica, leaving iron and aluminium oxides. It hardens on exposure to air and is cut into bricks — the name comes from the Latin later, brick. Arid and saline soils are products of dry climates; alluvial soils are river deposits.
Answer: C
Consider the following pairs:
| Term | Associated with |
|---|---|
| 1. Khadar | New alluvium renewed by floods |
| 2. Kankar | Calcareous nodules in older or arid soils |
| 3. Podzolisation | Hot, dry deserts |
Which of the pairs given above is/are correctly matched?
Solution
- Pair 1 — correct. Khadar is new alluvium on floodplains, renewed almost every year.
- Pair 2 — correct. Kankar nodules of calcium carbonate occur in bhangar (old alluvium) and in lower horizons of arid soils.
- Pair 3 — wrong. Podzolisation is acidic leaching in cool, humid climates under coniferous forest. In deserts, calcification and salinisation dominate.
Answer: A
Mains
Land degradation is a silent threat to India’s agriculture. Discuss its main forms and causes, and suggest measures for sustainable soil management.
Solution
Introduction: Soil forms over centuries but can be lost in a few seasons. Land degradation — the decline in the productive capacity of land — threatens food security, rural incomes and ecosystems. India has committed to restoring 26 million hectares of degraded land by 2030.
Body — forms and causes:
- Water erosion: sheet, rill and gully erosion on slopes and in ravine lands such as the Chambal; driven by deforestation, overgrazing and cultivation on slopes.
- Wind erosion and desertification: in western Rajasthan and other drylands; loss of vegetation cover and overgrazing.
- Salinity and waterlogging: excess canal irrigation and poor drainage in parts of Punjab, Haryana and command areas.
- Nutrient depletion and imbalance: overuse of nitrogenous fertilisers relative to phosphate and potash, monocropping, and burning of crop residue that removes organic matter.
- Other pressures: mining, urban expansion and pollution.
Body — measures:
- Soil testing and balanced nutrition: Soil Health Cards; integrated nutrient management combining fertilisers with organic manure.
- Watershed and slope management: contour bunding, terracing, check dams, afforestation.
- Drylands: shelter belts, dune stabilisation, sustainable grazing.
- Saline land: sub-surface drainage, gypsum, salt-tolerant varieties, efficient irrigation (micro-irrigation).
- Practices: crop rotation with legumes, residue retention, conservation agriculture.
Conclusion: Treating soil as a living, finite resource — measured, managed and restored — is essential for agricultural sustainability and for India’s land-degradation-neutrality goals.
Quick Revision
| Point | One-liner |
|---|---|
| Factors | Climate, organisms, relief, parent material, time |
| Most important active factor | Climate |
| Profile | O, A (eluviation), B (illuviation), C, R |
| Alluvial | ~40% area; potash-rich, phosphorus-poor; khadar and bhangar |
| Black | Basalt; moisture-retentive; self-ploughing; cotton |
| Red/yellow | Crystalline rocks; iron oxides; yellow when hydrated |
| Laterite | Leaching; iron and aluminium oxides; bricks; cashew |
| Arid | Kankar layer; western Rajasthan |
| Saline | Usar/reh/kallar; gypsum to reclaim |
| Soil Health Card | February 2015, Suratgarh |
Key Takeaways
- Parent rock sets the starting point; climate decides how a soil develops.
- Each Indian soil type is a story of rock plus climate: basalt makes black soil; heavy rain and heat make laterite; rivers make alluvium.
- Soil degradation — erosion, salinity, nutrient imbalance — is a slow-moving threat to food security that needs testing, balanced inputs and watershed-level conservation.
Related Topics
- Major Biomes of the World
- Biogeography and Soils — quick revision
- Biogeography and Soils — practice questions
- Agricultural Geography
- Agriculture and Food Security