UPSC Prelims 2018 · GS Paper I
Question 82: Environment and Ecology
With reference to agricultural soils, consider the following statements :
- 1.A high content of organic matter in soil drastically reduces its water holding capacity.
- 2.Soil does not play any role in the sulphur cycle.
- 3.Irrigation over a period of time can contribute to the salinization of some agricultural lands.
Which of the statements given above is/are correct ?
AnswerUPSC’s answer is (b).
Organic matter holds water like a sponge, so soils rich in it hold more water, not less. Soil is central to the sulphur cycle: it stores sulphur and soil microbes convert it between organic and inorganic forms. Irrigation over many years, especially with poor drainage in dry regions, leaves salts behind as water evaporates and can salinise land. Only statement 3 is correct.
- 1. Organic matter increases water-holding capacity.
- 2. Soil stores sulphur and soil microbes cycle it.
- 3. Irrigation can leave salts behind and cause salinisation.
How you could have got this
- If you were sure statement 1 is not correct, (a), (c) and (d) go: each of them includes 1.
What you needed to know: Organic matter increases water-holding capacity.
Only (b) is left. You didn’t need statements 2 or 3.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: both statements 1 and 2 are false.
- (b) Right: only salinisation by irrigation is correct.
- (c) Wrong: statement 1 is false.
- (d) Wrong: statements 1 and 2 are false.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2018, General Studies Paper I, Series A. The paper on upsc.gov.in.