Biogeography and Soils — Practice Questions
UPSC Prelims-pattern practice questions on soils and biomes — alluvial, black, laterite and saline soils, soil profile, Mediterranean vegetation.
Questions
These are original UPSC-pattern practice questions. Attempt each one before revealing the answer.
Consider the following statements about alluvial soils of India:
- They are the most widespread soil group in India.
- Bhangar is newer alluvium than khadar.
- They are generally rich in potash but poor in phosphorus.
Which of the statements given above are correct?
Solution
- Statement 1 — correct. Alluvial soils cover about 40% of India’s area (NCERT).
- Statement 2 — wrong. It is the reverse: khadar is the new alluvium of floodplains, renewed almost every year; bhangar is the older alluvium on higher terraces, often with kankar.
- Statement 3 — correct.
Answer: C
Which one of the following is commonly applied to reclaim saline and alkaline (usar) soils?
Solution
Gypsum (calcium sulphate) supplies calcium that displaces excess sodium; with good drainage the sodium is then leached out, improving soil structure.
Lime is the standard amendment for acidic soils — a frequent trap. Urea and muriate of potash are fertilisers, not soil amendments for salinity.
Answer: A
In a soil profile, the horizon in which clay, iron and other materials washed down from the upper layer accumulate (the zone of illuviation) is the:
Solution
Water moving down through the A horizon carries fine particles and dissolved minerals away (eluviation). They accumulate in the B horizon (subsoil) — the zone of illuviation. The C horizon is weathered parent rock; the R horizon is solid bedrock.
Answer: B
Consider the following pairs:
| Soil type | Region |
|---|---|
| 1. Black soil | Malwa Plateau |
| 2. Laterite soil | Western Rajasthan |
| 3. Saline soil | Rann of Kachchh |
| 4. Red soil | Eastern and southern Deccan Plateau |
How many of the pairs given above are correctly matched?
Solution
- Pair 1 — correct. The Malwa Plateau is part of the basaltic Deccan Trap region.
- Pair 2 — wrong. Laterite needs heavy rainfall and high temperature (Kerala, Karnataka, hilly Odisha and Assam). Western Rajasthan has arid soils.
- Pair 3 — correct.
- Pair 4 — correct. Red soils form on the crystalline rocks of the eastern and southern Deccan.
So three pairs are correct.
Answer: C
Which of the following are characteristic of the Mediterranean type of natural vegetation and land use?
- Evergreen, drought-resistant shrubs
- Thick-barked trees such as the cork oak
- Orchards of citrus fruits, olives and grapes
Select the correct answer using the code given below.
Solution
All three. Because summers are hot and dry, Mediterranean plants are evergreen and drought-resistant, with thick bark and small, waxy leaves — maquis in Europe, chaparral in California; the cork oak is a classic species. The climate also suits citrus, olives and grapes, earning these regions the name “orchard lands of the world”.
Answer: D
Mains
Compare the formation, properties and agricultural use of the black, red and laterite soils of India.
Solution
Introduction: Black, red and laterite soils together cover much of peninsular India. Each reflects a different combination of parent rock and climate, and that combination decides its fertility and use.
Body:
- Black soil (regur):
- Formation: weathering of Deccan Trap basalt in the semi-arid north-western Deccan — Maharashtra, Malwa, Gujarat, parts of Telangana, Karnataka and Andhra Pradesh.
- Properties: clayey, deep, highly moisture-retentive; swells and cracks (self-ploughing); rich in lime, iron, magnesia and potash; poor in nitrogen, phosphorus and organic matter.
- Use: rain-fed cotton, soybean, jowar, sugarcane and pulses; becomes sticky when wet, making tillage difficult.
- Red and yellow soil:
- Formation: crystalline igneous and metamorphic rocks (granite, gneiss) under low to moderate rainfall — eastern and southern Deccan, Odisha, Chhattisgarh.
- Properties: red from diffused iron oxides, yellow when hydrated; porous; generally poor in nitrogen, phosphorus and humus.
- Use: millets, pulses, groundnut and tobacco; responds well to fertilisers and irrigation.
- Laterite soil:
- Formation: laterisation under high temperature and heavy rainfall with wet and dry seasons — Kerala, Karnataka, Tamil Nadu, Madhya Pradesh, hilly Odisha and Assam.
- Properties: lime and silica leached; rich in iron and aluminium oxides; poor in organic matter, nitrogen, phosphate and calcium; hardens on exposure.
- Use: plantation and tree crops such as cashew, tea, coffee and rubber with manuring; also cut as building bricks.
Conclusion: Parent rock explains black and red soils; climate explains laterite. Matching crops and inputs to these properties — through soil testing and balanced fertilisation — is the key to raising productivity sustainably.