Correct Option
The correct option is 1 and 3 only
Explanation
Nitrogen enters the soil through the decomposition of organic matter and the deposition of nitrogenous waste products by living organisms. This process is a critical component of the terrestrial nitrogen cycle, where complex organic nitrogen is converted into inorganic forms like ammonium and nitrates that plants can assimilate.
- Statement 1 is Correct: Animals excrete nitrogenous waste products, such as urea, uric acid, and ammonia. When urea is deposited into the soil, it undergoes hydrolysis by the enzyme urease, produced by soil microorganisms, to form ammonia and carbon dioxide. This ammonia is subsequently converted into nitrates through the process of nitrification, thereby increasing the nitrogen content of the soil.
- Statement 2 is Incorrect: The combustion of coal releases nitrogen oxides (NOx) and other gases into the atmosphere. While these gases may eventually return to the earth through wet or dry deposition (acid rain), the act of burning coal itself does not directly add nitrogen to the soil; rather, it contributes to atmospheric nitrogen loading and air pollution.
- Statement 3 is Correct: The death and subsequent decay of vegetation return organic nitrogen stored in plant tissues back to the soil. Decomposers, such as bacteria and fungi, break down the proteins and nucleic acids in dead organic matter through a process called ammonification, which releases nitrogen in the form of ammonia into the soil environment.
Key Takeaway: Nitrogen is added to the soil primarily through biological processes involving the decomposition of organic matter (death of vegetation) and the excretion of metabolic wastes (urea) by animals.