Question 82 from UPSC CSE 2015 - Environment

Question

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 codes given below.

IASCODEX · Accepted Answer

Correct Option: C. 2 and 3 only

Strategy: Identify the correct effects of excess nitrogenous fertilizers. Confirm that soil acidity and nitrate leaching are plausible outcomes. Eliminate the statement about nitrogen-fixing microorganism proliferation as it is unlikely when plants have ample external nitrogen.

Key Info: Nitrogenous fertilizers, chiefly containing ammonia (NH4+) or nitrate (NO3−), are widely used to enhance crop yield. Their excessive or improper use impacts soil and water in various ways:
- **Soil Acidity**: Continuous application, especially of ammonium-based fertilizers (like urea, ammonium sulfate), increases soil acidity. The nitrification process releases hydrogen ions (H+), lowering pH and impairing nutrient availability for plants.
- **Nitrate Leaching**: In well-drained soils, excess nitrate is not readily absorbed by plants and leaches down to the groundwater. This can lead to groundwater contamination, causing health hazards like methemoglobinemia ('blue baby syndrome') in humans and eutrophication in water bodies.
- **Nitrogen Fixation in Soil**: Nitrogen-fixing microorganisms (such as Rhizobium, Azotobacter, and cyanobacteria) convert atmospheric nitrogen into forms usable by plants. However, high external nitrogen reduces plant dependence on these microbes, often causing a decline—not proliferation—in their populations due to competitive disadvantages or reduced root nodulation.
- **Other Effects**: Over-fertilization can also lead to soil structure decline and nutrient imbalances, affecting crop productivity and soil sustainability.

Relevant Examples: The Green Revolution in India increased reliance on nitrogenous fertilizers, resulting in soil health issues in the Indo-Gangetic Plain and nitrate pollution in Punjab and Haryana groundwater.

IASCODEX · Answer

Option A: 1 and 3 only

IASCODEX · Answer

Option B: 2 only

IASCODEX · Answer

Option D: 1, 2, and 3