Which of the following adds/add nitrogen to the soil? 1. Excretion of urea by animals 2. Burning of coal by man 3. Death of vegetation Select the correct answer using the codes given below.
Explanation
Excretion of urea by animals - Correct: Urea (CO(NH₂)₂) contains nitrogen. When animals excrete urea, microbes in the soil convert it into ammonia, and later into nitrates and nitrites — forms usable by plants. Thus, urea adds nitrogen to the soil indirectly.
Burning of coal by man - Incorrect: Burning coal releases nitrogen oxides (NOₓ) into the atmosphere, not into the soil. These contribute to air pollution and acid rain, not direct soil enrichment.
Death of vegetation - Correct: When plants die, their tissues decompose. Decomposers (bacteria and fungi) break down organic matter, releasing nitrogen compounds back into the soil. Hence, this process adds nitrogen to the soil naturally.