Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Nitrogen is usually lost from applied ammonium and amide containing fertilizers after their conversion to nitrate form.
Reason (R): Application of N-Serve (2-chloro-6-trichloromethyl pyridine) and AM (2-amino-4-chloro-6 methyl-pyrimidine) can reduce these losses and increase the efficiency of applied nitrogen fertilizers.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Nitrate ($NO_{3}^{-}$) is the "mobile" form of nitrogen. It's like a traveler—if it's not taken up by the plant immediately, it tends to leave the root zone through water or air. Inhibitors like N-Serve act as "anchors" to keep it in the soil.

Answer 1

The Correct Option is A

Concept: Nitrogen management is a critical aspect of soil fertility. Nitrogen fertilizers, specifically those containing ammonium ($NH_{4}^{+}$) or amides (like urea), undergo biochemical transformations in the soil. The most significant loss pathway occurs after these forms are converted into nitrate ($NO_{3}^{-}$), a process known as nitrification.

Step 1: Evaluate Assertion (A).
When ammonium or amide fertilizers are applied, soil bacteria convert them into nitrate. Unlike ammonium, which is positively charged and held by soil particles, nitrate is negatively charged and does not bind to the soil. Consequently, it is highly susceptible to leaching (moving down with water) and denitrification (conversion to nitrogen gas in anaerobic conditions). Therefore, Assertion (A) is correct.

Step 2: Evaluate Reason (R).
To prevent these losses, Nitrification Inhibitors are used. Compounds like N-Serve and AM specifically inhibit the *Nitrosomonas* bacteria, which perform the first step of nitrification. By keeping nitrogen in the ammonium form for longer, these chemicals reduce leaching and denitrification losses, thereby increasing nitrogen use efficiency (NUE). Thus, Reason (R) is correct.

Step 3: Determine the relationship.
Because the application of these inhibitors (R) directly addresses the mechanism of loss described in the assertion (A), the reason is the correct explanation for the assertion.