UPSC Prelims 2015 Q11: Environment & Ecology – Pollution & Waste Management
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.
- (a) 1 and 3 only
- (b) 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer: (c) 2 and 3 only
Explanation
Excessive use of nitrogenous fertilizers
| Statement | Verdict | Fact |
|---|---|---|
| 1. Proliferation of nitrogen-fixing microorganisms in soil can occur | Incorrect | When nitrogen is plentiful, nitrogen-fixing microbes become less active |
| 2. Increase in the acidity of soil can take place | Correct | Ammonium fertilizers release acid as they turn into nitrate |
| 3. Leaching of nitrate to the groundwater can occur | Correct | Nitrate is very soluble and moves down with water |
Harmful effects in brief:
| Effect | Result |
|---|---|
| Nitrate in drinking water | Blue baby syndrome (methaemoglobinaemia) |
| Run-off into lakes | Eutrophication and algal blooms |
| Gas emission | Nitrous oxide, a greenhouse gas |
| Soil | Acidity; loss of micro-nutrients |
Answer: (c) 2 and 3 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is false; nitrogen-fixing microorganisms do not proliferate.
- (b) Incorrect. Statement 3 is also true: nitrate leaches to the groundwater.
- (c) CORRECT. Excess nitrogen causes soil acidity and leaching of nitrate.
- (d) Incorrect. Statement 1 is false; excess fertilizer suppresses nitrogen fixation.
Key point
Excess nitrogenous fertilizers: soil acidity, nitrate leaching (blue baby syndrome), eutrophication, nitrous oxide; nitrogen fixers decline.
Remember
Excess nitrogen: acid soil, nitrate in groundwater.
Common mistakes
- Assuming more nitrogen means more nitrogen-fixing microbes.
- Forgetting that urea and ammonium fertilizers acidify the soil.
- Linking blue baby syndrome to fluoride or arsenic instead of nitrate.
Exam tip
Microbes fix nitrogen only when the soil lacks it. Add fertilizer and they stop.
Sources
- NCERT Class XII — Biology (Environmental Issues)
- Indian Council of Agricultural Research — Balanced fertilizer use and nitrogen use efficiency