UPSC Prelims 2018 Q82: Geography – Physical Geography & Geomorphology
- (a) 1 and 2 only
- (b) 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (b) 3 only
Explanation
Agricultural Soils - Basic Properties
| Statement | Claim | Verdict | Detail |
|---|---|---|---|
| 1 | High organic matter drastically REDUCES water holding capacity | FALSE | Reverse is true - organic matter INCREASES water holding capacity because humus can hold multiple times its weight in water. That is why compost, mulch and cover crops boost drought tolerance. |
| 2 | Soil plays NO role in sulphur cycle | FALSE | Soil plays a central role in the sulphur cycle - sulphur is stored in soil organic matter, mineralised by microbes, taken up by plants as sulphate (SO4^2-), and cycled through decomposition. Soil is a major sulphur reservoir. |
| 3 | Irrigation over time can contribute to salinization of agricultural lands | TRUE | Secondary salinization from irrigation is a well-known problem globally, especially in canal-irrigated areas with poor drainage. Water evaporates leaving salts at the surface - devastating soil productivity. Punjab, Haryana, coastal Andhra face this problem. |
Answer: (b) 3 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is factually reversed - organic matter INCREASES water holding capacity, not reduces it.
- (b) CORRECT. Only Statement 3 is right - irrigation over time can cause secondary salinization.
- (c) Incorrect. Statement 1 is factually wrong about organic matter.
- (d) Incorrect. Statement 2 is wrong - soil is central to the sulphur cycle.
Key point
Soil facts: Organic matter INCREASES water holding capacity. Soil is central to N, P, K, S, C cycles. Irrigation without drainage causes salinization (surface salt accumulation from evaporation) - a major degradation problem in Punjab/Haryana canal command areas.
Remember
High organic matter INCREASES a soil's water holding capacity (not reduces it), and soil plays a central role in the sulphur cycle as a storage and cycling medium. However, prolonged irrigation without proper drainage can cause secondary salinization - a serious form of land degradation in canal-irrigated areas of Punjab, Haryana and coastal Andhra Pradesh.
Common mistakes
- Confusing organic matter's effect - it dramatically INCREASES water retention (up to 90% of humus weight in water).
- Assuming soil is inert in nutrient cycles - soil is the primary reservoir for macro and micro nutrients including S.
- Missing secondary salinization - one of the biggest sustainability issues of canal irrigation without proper drainage.
Exam tip
Soil health boosters: Organic matter (compost, FYM), cover crops, crop rotation, minimum tillage. Soil health killers: Excess irrigation without drainage (salinization), monoculture, chemical overuse, tillage erosion.
Sources
- NCERT Class 11 Geography - Fundamentals of Physical Geography (Soils chapter)
- ICAR - Soil Health Card Scheme Technical Guidelines