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.

The correct answer is C. Statements 1 and 3 add nitrogen to the soil, while statement 2 does not.

The core concept is the return of organic nitrogen to soil within the nitrogen cycle. Statement 1 is right: animal urine is rich in urea, which soil microbes convert through ammonification into ammonium, and nitrifying bacteria then convert that into nitrates. Statement 3 is right: when vegetation dies, decomposers break down its proteins and nucleic acids, releasing nitrogen back into the soil through mineralisation.

Statement 2 is wrong. Burning coal releases oxides of nitrogen (NOx) into the atmosphere, not into the soil. Those oxides form acid rain, which can actually reduce soil fertility rather than add nitrogen to it.

• Option A leaves out decomposition of dead vegetation.
• Options B and D include statement 2, which is wrong.

For Mains, this links to nutrient management, organic farming and the imbalance in nitrogenous fertiliser use in Indian agriculture.

Trap: Aspirants pick D by assuming every human activity adds nitrogen to the soil, forgetting that combustion emissions go to the atmosphere.