Geography
Biogeography and Soils
GS Paper I
Biogeography and Soils — Quick Revision
One-page UPSC revision of soils and biomes: soil-forming factors and processes, soil profile, India's eight soil types, degradation, grasslands and biomes.
SyllabusGS I · Salient features of world physical geography; distribution of key natural resources
A last-week revision sheet for soils and biomes. Prelims tests the properties of Indian soils and the matching of grasslands to continents; Mains tests degradation and conservation.
Soil Formation
| Factor | Key point |
|---|---|
| Parent material | Passive factor; sets minerals and early colour/texture |
| Climate | Most important active factor |
| Relief | Thin soils on slopes, deep soils on plains |
| Organisms | Humus, mixing, nitrogen fixation |
| Time | Maturity of horizons |
| Process | Climate | Result |
|---|---|---|
| Laterisation | Hot, wet | Iron and aluminium oxides remain; laterite |
| Podzolisation | Cool, humid, coniferous | Acidic, ash-grey leached soils |
| Calcification | Dry | Calcium carbonate layer (kankar) |
| Salinisation | Arid, over-irrigated | Salt crust |
Profile: O (organic) → A (topsoil, eluviation) → B (subsoil, illuviation) → C (weathered parent rock) → R (bedrock).
Soils of India
| Soil | Parent / climate | Rich in | Poor in | Crops / use |
|---|---|---|---|---|
| Alluvial (~40% area) | River deposits | Potash | Phosphorus | Rice, wheat, sugarcane |
| Black (regur) | Basalt, semi-arid Deccan | Lime, iron, magnesia, potash | N, P, organic matter | Cotton, soybean |
| Red and yellow | Crystalline rocks, low–moderate rain | Iron oxides (colour) | N, P, humus | Millets, pulses, groundnut |
| Laterite | Heavy rain + high temperature | Iron and aluminium oxides | N, P, calcium, organic matter | Cashew, plantations; bricks |
| Arid | Dry western Rajasthan | Soluble salts in places | Humus, moisture, nitrogen | Bajra, guar; with irrigation more |
| Saline | Coasts, deltas, over-irrigated plains | Sodium, potassium, magnesium | — | Reclaim with gypsum |
| Peaty / marshy | Heavy rain, waterlogging | Organic matter | — | Rice in parts |
| Forest / mountain | Forested slopes | Humus in valleys | Humus at high altitudes (acidic) | Tea, coffee, spices, fruit |
High-yield facts
- Khadar = new alluvium (floodplains); bhangar = old alluvium with kankar.
- Black soil is self-ploughing (cracks when dry) and retains moisture — ideal for rain-fed cotton.
- Red soil turns yellow when its iron is hydrated.
- Laterite’s name comes from Latin later (brick); it hardens on exposure.
- Soil Health Card scheme — launched February 2015 (Suratgarh, Rajasthan); tests 12 parameters.
- World Soil Day — 5 December; 2015 — International Year of Soils.
- UNCCD COP14 (India, 2019): restore 26 million hectares of degraded land by 2030.
Soil Erosion and Conservation
| Erosion | Conservation |
|---|---|
| Sheet, rill, gully (ravines — Chambal) | Contour ploughing, terracing, check dams, gully plugging |
| Wind (western Rajasthan) | Shelter belts, strip cropping, mulching, dune fixing |
| Salinity, waterlogging | Drainage, gypsum, efficient irrigation |
Biomes and Grasslands
| Biome | Signature |
|---|---|
| Tropical rainforest | Highest biodiversity; leached, poor soils |
| Tropical deciduous | Teak, sal; leaves shed in dry season |
| Savanna | Grass + scattered trees; Africa, Llanos, Campos |
| Hot desert | Xerophytes |
| Mediterranean | Dry summers, wet winters; maquis, chaparral; citrus, olives, grapes |
| Temperate grassland | Wheat belts; chernozem |
| Taiga | Conifers; softwood; podzols |
| Tundra | Permafrost; mosses, lichens; no trees |
| Grassland | Region |
|---|---|
| Prairies | North America |
| Pampas | Argentina |
| Steppes | Eurasia |
| Veld | South Africa |
| Downs | Australia |
| Canterbury | New Zealand |
| Llanos | Venezuela, Colombia (tropical) |
| Campos | Brazil (tropical) |
Realms (Wallace): Palaearctic, Nearctic, Neotropical, Ethiopian, Oriental, Australian. Wallace’s Line: Bali–Lombok. India: Oriental realm; ten biogeographic zones.
Common Traps
Traps to avoid
- Black soil is poor in nitrogen and organic matter.
- Laterite forms under heavy rain, not in dry climates.
- Alluvial soil is rich in potash but poor in phosphorus.
- Llanos and Campos are tropical; Pampas are temperate.
- The tundra has no trees.
Related Topics
- Soil Formation and the Soils of India
- Major Biomes of the World
- Biogeography and Soils — practice questions
- Agricultural Geography
- Natural Vegetation and Wildlife
Advertisement