Sources that add nitrogen to soil — UPSC Prelims PYQ 2013
Which of the following adds/add nitrogen to the soil?
- Excretion of urea by animals
- Burning of coal by man
- Death of vegetation
Select the correct answer using the codes given below.
- 1 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Explanation
Statement 1 is correct
- Animals excrete urea, which is converted by soil microorganisms into ammonia and then nitrates through processes like ammonification and nitrification. This adds nitrogen to the soil.
Statement 2 is incorrect
- Burning coal releases nitrogen oxides (NOₓ) into the atmosphere rather than directly into the soil. These gases mainly contribute to air pollution and acid rain, and do not directly enhance soil nitrogen levels.
Statement 3 is correct
- When plants die, their organic matter decomposes through the action of bacteria and fungi. This process releases nitrogen compounds back into the soil, naturally replenishing its nutrient content
Answer: (c) 1 and 3 only; Difficulty Level: Medium
