Prelims 2015 · archive
MediumWhat 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.
Answer & explanation
Answer: (c) 2 and 3 only
Too much nitrogen fertiliser can acidify the soil and push nitrate down into groundwater, so statements 2 and 3 are correct. It does not encourage nitrogen-fixing microbes. Readily available fertiliser nitrogen actually inhibits biological fixation, so statement 1 is wrong.
- ✗ 1. Adding inorganic nitrogen fertiliser significantly inhibits symbiotic nitrogen fixation in legume–rhizobia systems. When the soil is already supplied with nitrogen, nitrogen fixers gain no advantage, so excess fertiliser does not make them proliferate.
- ✓ 2. Improper, excessive fertilisation speeds up soil acidification, especially with acidic fertilisers such as ammonium sulphate. Nitrification of ammonium releases acid, and nitrate leaching out of the soil carries base cations with it, so acidity rises.
- ✓ 3. Nitrate dissolves easily and moves with water through the soil. Nitrate the crop does not use can leach below the root zone into groundwater. Groundwater is polluted mainly by nitrates.
Remember · Excess nitrogen fertiliser means acidified soil, nitrate in groundwater and eutrophication. It suppresses biological nitrogen fixation instead of encouraging it.
Sources
- FAO – Chapter 3: Fertilizers as water pollutants ↗ “Groundwater is being polluted mainly by nitrates. In all countries groundwater is an important source of drinking water.”
- Umweltbundesamt (German Environment Agency) – Nitrogen ↗ · reference work “Improper, excessive fertilization, especially with acidic fertilizers (such as ammonium sulfate), can contribute to accelerated soil acidification.”
- Nature Communications (via NIH PMC) – Inorganic nitrogen inhibits symbiotic nitrogen fixation in soybean nodules ↗ “Symbiotic nitrogen fixation (SNF) in legume-rhizobia serves as a sustainable source of nitrogen (N) in agriculture. However, the addition of inorganic N fertilizers significantly inhibits SNF”
Question: UPSC Civil Services (Preliminary) 2015, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·