Question

Which of the following processes cause losses of nitrogen from the cultivated soils
A. Leaching
B. Volatilization
C. Biological nitrogen fixation
D. Denitrification
E. Green manuring
Choose the most appropriate answer from the options given below:

• A. A and B only
• B. A and D only
• C. A, B and D only
• D. C and E only

Hint:

Losses = Moving away from the root zone (to ground water or air).
Gains = Moving into the soil (Fixation or Manuring).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question requires identifying the specific pathways through which nitrogen is lost from the soil ecosystem, thereby reducing nutrient availability for crops.

Step 2: Detailed Explanation:

• Leaching (A): Nitrate ($NO_3^-$) is highly soluble and negatively charged. Since soil particles are also negatively charged, nitrate is not held well and is easily washed down below the root zone by irrigation or rain. This is a major loss.

• Volatilization (B): This is the loss of nitrogen to the atmosphere in the form of Ammonia gas ($NH_3$). It occurs primarily when urea or ammonium fertilizers are applied to the surface of alkaline or dry soils. This is a major loss.

• Denitrification (D): Under waterlogged, anaerobic conditions, specific bacteria convert nitrates back into Nitrogen gas ($N_2$) or nitrous oxide ($N_2O$), which escapes into the air. This is a major biological loss.

• Note on Gains:
- Biological Nitrogen Fixation (C): This is a process of adding nitrogen to the soil from the atmosphere.
- Green Manuring (E): This is the practice of incorporating fresh plant tissue into the soil to enrich its nitrogen content.
Final Answer:
A, B, and D are loss mechanisms, while C and E are gain/enrichment mechanisms. Thus, option (C) is correct.