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.

Nitrogen is added to the soil through biological and chemical processes within the nitrogen cycle. Excretion of urea and urine by animals is a significant source, as the breakdown of nitrogen in livestock manure and urine returns nitrogen to the environment [1]. Upon the death of vegetation and other organisms, nitrogen is returned to the soil in the form of ammonia through decomposition [2]. While the burning of coal and fossil fuels releases nitrogen oxides (NOx) into the atmosphere, this process primarily contributes to atmospheric pollution and acid deposition rather than directly adding nitrogen to the soil in a beneficial or primary cycling manner like organic decomposition or excretion. Although atmospheric deposition of these pollutants can eventually reach the soil, standard ecological models of the nitrogen cycle focus on organic matter return (death and excretion) as the primary direct pathways for soil nitrogen enrichment.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 17: Climate Change > Human induced: > p. 257
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20