What can be the impact of excessive/inappropriate use of nitrogenous fertilizers in agriculture? 1. Proliferation of nitrogen-fixing microorganisms in soil can occur. 2. Increase in the acidity of soil can take place. 3. Leaching of nitrate to the ground-water can occur. Select the correct answer using the code given below.
- (a) 1 and 3 only
- (b) 2 only
- (c) 2 and 3 only ✓ UPSC's answer
- (d) 1, 2 and 3
Why the answer is (c)
• Excess ammonium-based fertiliser (urea, ammonium sulphate) releases hydrogen ions during nitrification, acidifying the soil over time (statement 2).
• Nitrate, being highly soluble and not held by soil, leaches into groundwater, causing nitrate pollution and 'blue baby syndrome' (statement 3).
• Statement 1 is wrong: abundant mineral nitrogen suppresses nitrogen-fixing microbes such as Rhizobium and Azotobacter, since fixation becomes unnecessary and energetically costly.
• Hence 2 and 3 only, option (c).
Why the other options are wrong
- (a) 1 and 3 only
- Statement 1 is wrong: N-fixers decline, not proliferate.
- (b) 2 only
- Statement 3 on nitrate leaching is also correct.
- (d) 1, 2 and 3
- Statement 1 is wrong.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2015, held on 23 August 2015. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.