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 ?
- (a) 1 and 2 only
- (b) 3 only ✓ UPSC's answer
- (c) 1 and 3 only
- (d) 1, 2 and 3
Why the answer is (b)
• Statement 3 is correct: irrigation water carries dissolved salts which accumulate as water evaporates, especially with poor drainage, causing salinisation (as in Punjab, Haryana and the Indira Gandhi canal command).
• Statement 1 is wrong: organic matter (humus) greatly increases soil's water-holding capacity.
• Statement 2 is wrong: soil is central to the sulphur cycle — soil bacteria mineralise organic sulphur and oxidise/reduce sulphur compounds, and plants take up sulphate from soil.
• Hence 3 only, option (b).
Why the other options are wrong
- (a) 1 and 2 only
- Statements 1 and 2 are wrong: humus raises water holding and soil is part of the sulphur cycle.
- (c) 1 and 3 only
- Statement 1 is wrong: organic matter increases water holding.
- (d) 1, 2 and 3
- Statements 1 and 2 are wrong.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2018, held on 3 June 2018. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.