Analyzing Nitrogen Fertilizer Loss and Inhibitors

This question examines the fate of nitrogen fertilizers in the soil and the role of specific additives in improving their efficiency.

Statement (A) Analysis: Nitrogen Loss Mechanism

Assertion (A) states that nitrogen is often lost from ammonium ($\text{NH}_4^+$) and amide fertilizers after they are converted to nitrate ($\text{NO}_3^-$). This is a well-established process in soil science:

• Ammonium and amide fertilizers (like urea) first convert to ammonium ($\text{NH}_4^+$) in the soil.
• Soil microbes then transform ammonium ($\text{NH}_4^+$) into nitrite ($\text{NO}_2^-$) and subsequently into nitrate ($\text{NO}_3^-$), a process called nitrification.
• Nitrate ($\text{NO}_3^-$) is negatively charged and highly soluble, making it prone to leaching out of the root zone with water movement.
• Nitrate can also be converted to nitrogen gases (like N$_2$) and lost to the atmosphere through denitrification, especially in waterlogged soils.

Therefore, Assertion (A) accurately describes a major pathway for nitrogen loss from these fertilizers. Assertion (A) is correct.

Statement (R) Analysis: Role of Nitrification Inhibitors

Reason (R) suggests that N-Serve (Nitrapyrin) and AM (a type of pyrazole derivative) can reduce these losses and enhance nitrogen fertilizer efficiency. These compounds are known as nitrification inhibitors:

• Nitrification inhibitors work by slowing down the activity of the soil bacteria responsible for converting ammonium ($\text{NH}_4^+$) to nitrate ($\text{NO}_3^-$).
• By keeping nitrogen in the ammonium ($\text{NH}_4^+$) form for a longer period, they minimize the accumulation of nitrate ($\text{NO}_3^-$) in the soil.
• This reduction in nitrate formation directly decreases losses due to leaching and denitrification.
• Consequently, more nitrogen remains available for plant uptake, increasing fertilizer efficiency.

Therefore, Reason (R) correctly describes the function and benefit of these additives. Reason (R) is correct.

Connecting Assertion (A) and Reason (R)

Assertion (A) identifies the problem: nitrogen loss occurring after conversion to nitrate. Reason (R) provides a solution by introducing nitrification inhibitors that specifically target and reduce this nitrate-related loss mechanism. Thus, Reason (R) serves as a direct and correct explanation for how to mitigate the issue described in Assertion (A).

Conclusion

Both statements (A) and (R) are factually correct, and statement (R) provides the specific mechanism by which the losses described in statement (A) can be reduced, making it the correct explanation.