UPSC Prelims 2015 · GS Paper I
Question 11: Environment and Ecology
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 groundwater can occur.
Select the correct answer using the code given below.
AnswerUPSC’s answer is (c).
Heavy or wrong use of nitrogenous fertilizers harms soil and water. Ammonium-based fertilizers are converted to nitric acid in the soil, which makes it more acidic. Nitrate is highly soluble, so it leaches into groundwater, causing contamination and eutrophication. Excess nitrogen does not multiply nitrogen-fixing microbes; it tends to suppress them, because the plants no longer need their help. Statements 2 and 3 are correct.
- 1. Excess fertilizer nitrogen suppresses, not multiplies, nitrogen-fixing microorganisms.
- 2. Nitrification of ammonium-based fertilizers releases acid, so soil acidity rises.
- 3. Soluble nitrate leaches into groundwater.
How you could have got this
- If you were sure statement 1 is not correct, (a) and (d) go: each of them includes 1.
What you needed to know: Excess fertilizer nitrogen suppresses, not multiplies, nitrogen-fixing microorganisms.
- Then, if you were sure statement 3 is correct, (b) goes: it leaves 3 out.
What you needed to know: Soluble nitrate leaches into groundwater.
Only (c) is left. You didn’t need statement 2.
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: statement 1 is false, since extra fertilizer nitrogen discourages nitrogen-fixing microbes.
- (b) Incomplete: nitrate leaching to groundwater (statement 3) also occurs.
- (c) Correct: soil acidification and nitrate leaching both follow excess nitrogen use.
- (d) Wrong: statement 1 is false.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper I, Series A. The paper on upsc.gov.in.