1. Alluvial soil
- Formation: deposited by rivers (Indus, Ganga, Brahmaputra systems; east-coast deltas).
- Distribution: largest soil group (roughly two-fifths of India) — Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal, Assam valley; deltas of the Mahanadi, Godavari, Krishna, Kaveri; coastal plains.
- Composition: sand, silt, clay; generally rich in potash and lime, poor in nitrogen and humus; coarse near the foothills, finer downstream.
- Khadar: new alluvium on low floodplains, renewed by floods, light-coloured, very fertile.
- Bhangar: old alluvium on higher terraces above flood level, more clayey, less fertile, contains kankar.
- Crops: wheat, rice, sugarcane, jute (deltas), pulses, oilseeds.
| Head | Khadar | Bhangar |
|---|---|---|
| Age | New | Old |
| Position | Low floodplain | Higher terrace |
| Floods | Renewed often | Above flood level |
| Fertility | High | Lower |
| Kankar | Absent | Present |
Key terms
- Khadar
New alluvium on the low floodplains of rivers, renewed by floods almost every year.
- Bhangar
Old alluvium on higher river terraces, above normal flood level, often containing kankar.
- Kankar
Nodules (lumps) of lime found in bhangar soil.
2. Black soil (regur)
- Formation: weathering of basalt (Deccan trap lava).
- Distribution: Maharashtra, Malwa plateau (Madhya Pradesh), Saurashtra (Gujarat), parts of Karnataka, Telangana, Andhra Pradesh.
- Characteristics: fine, clayey; retains moisture; sticky when wet; deep cracks when dry (self-ploughing); rich in lime, iron, magnesia, potash; poor in nitrogen, phosphorus, humus.
- Crops: cotton (black cotton soil), sugarcane, jowar, wheat, groundnut, tobacco.
| Property | Effect for the farmer |
|---|---|
| Clayey | Holds water; sticky when wet |
| Cracks when dry | Aeration, self-ploughing |
| Rich in lime and potash | Good for cotton |
Key terms
- Regur
Another name for the black soil of the Deccan plateau.
- Self-ploughing
The turning over of black soil as loose soil falls into the deep cracks that open in the dry season.
3. Red soil
- Formation: weathering of old crystalline and metamorphic rocks (granite, gneiss) in low to moderate rainfall.
- Colour: red from iron oxide spread through the soil; yellow where the oxide is hydrated.
- Distribution: Tamil Nadu, Karnataka, Telangana, Andhra Pradesh, Odisha, Chhattisgarh, Chota Nagpur (Jharkhand).
- Characteristics: sandy to loamy, porous, light; low water retention; poor in nitrogen, phosphorus, humus.
- Crops (with fertilisers, irrigation): ragi, jowar, groundnut, pulses, tobacco; rice in lowlands.
| Feature | Red soil |
|---|---|
| Parent rock | Granite, gneiss |
| Texture | Sandy to loamy |
| Crops | Millets, groundnut |
Key terms
- Iron oxide
The compound that gives red soil its colour; it looks yellow when hydrated.
4. Laterite soil
- Formation: high temperature and heavy rain with alternate wet and dry seasons; leaching removes lime and silica, leaving oxides of iron and aluminium. (Latin later = brick.)
- Distribution: summits of the Western and Eastern Ghats, Kerala, Karnataka, Goa, Odisha hills, Meghalaya.
- Characteristics: coarse, acidic, infertile; poor in nitrogen, lime, humus; hardens in air (used as building bricks).
- Crops (with manure): cashew, tea, coffee, rubber, coconut.
| Head | Red | Laterite |
|---|---|---|
| Rainfall | Low to moderate | Heavy |
| Process | Weathering | Leaching |
| Fertility | Low | Very low, acidic |
| Crops | Millets, groundnut | Cashew, tea, coffee |
| Step | What happens |
|---|---|
| Heavy rain | Water percolates through soil |
| Leaching | Lime and silica removed |
| Residue | Iron and aluminium oxides remain |
Key terms
- Leaching
The washing down of soluble minerals such as lime and silica by water percolating through soil.
5. Soil erosion
- Soil erosion: removal of topsoil by natural agents faster than new soil forms.
- Agents: running water, wind, waves, glaciers.
- Sheet erosion: thin, even layer removed from a wide area by running water.
- Gully erosion: deep channels cut by running water; badly gullied land becomes ravines (Chambal valley).
- Wind erosion: dry, loose, bare soil blown away (western Rajasthan).
- Human causes: deforestation, overgrazing, ploughing up and down slopes, shifting cultivation, mining and construction.
| Type | Agent | Example area |
|---|---|---|
| Sheet | Running water | Gentle slopes |
| Gully | Running water | Chambal valley |
| Wind | Wind | Western Rajasthan |
Key terms
- Soil erosion
The removal of the top layer of soil by water, wind or other agents faster than it can form.
- Ravines
Land cut up by deep, joined gullies, unfit for farming.
6. Soil conservation
- Meaning: protecting soil from erosion and maintaining its fertility.
- Importance: soil forms slowly; agriculture depends on it; eroded silt fills reservoirs and worsens floods; loss of land hurts livelihoods.
- Terrace farming: flat steps on steep slopes (Himalayas, north-east).
- Contour ploughing: furrows across the slope on gentle slopes.
- Strip cropping: alternate strips of crops and grass.
- Shelter belts: rows of trees across the wind in dry, windy plains (western Rajasthan).
- Afforestation: trees on bare slopes and wasteland.
- Plugging gullies: check dams and planting in gullied land (Chambal).
- Controlled grazing: pasture rotation.
| Method | Suits |
|---|---|
| Terraces | Steep slopes |
| Contour ploughing | Gentle slopes |
| Shelter belts | Windy dry plains |
| Check dams | Gullies |
Key terms
- Shelter belt
Rows of trees planted across the path of the wind to slow it and protect fields from wind erosion.
- Contour ploughing
Ploughing across a slope along lines of equal height so that furrows hold back running water.
Exam tips
Common mistakes
- Calling bhangar new alluvium, or saying khadar contains kankar.
- Saying black soil forms from river silt (it forms from basalt lava).
- Describing laterite as fertile.
- Writing that contour ploughing runs up and down the slope.
How marks are usually awarded
- Soil questions: formation, distribution, characteristics and crops (1 mark each point with a named area).
- "Give a geographical reason": the property and how it causes the effect.
- Conservation: method plus the type of land and a named region.