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.

Statement 1: Excretion of urea by animals. Urea contains nitrogen. When animals excrete urea, it is deposited in the soil. Soil microorganisms convert urea into ammonium and then nitrates, which are forms of nitrogen usable by plants. Thus, it adds nitrogen to the soil. This statement is correct.

Statement 2: Burning of coal by man. Burning coal releases nitrogen oxides (NOx) into the atmosphere, contributing to air pollution and acid rain. While these gases contain nitrogen, they are primarily released into the atmosphere and do not directly add usable nitrogen to the soil as a nutrient. Their deposition on soil is indirect and often harmful. This statement is incorrect in the context of adding nitrogen to the soil as a nutrient.

Statement 3: Death of vegetation. When plants die, their organic matter, rich in nitrogen, decomposes. Decomposers break down this matter, releasing nitrogen compounds (like ammonia and ammonium) into the soil. This process, known as ammonification, is a crucial part of the nitrogen cycle and directly adds nitrogen to the soil. This statement is correct.

Therefore, statements 1 and 3 correctly describe processes that add nitrogen to the soil.