Question

Which of the following methods CANNOT be used to prevent N loss through denitrification?

• A. Use of non-nitrate fertiliser
• B. Use of nitrate fertiliser
• C. Split application of fertiliser
• D. Deep placement of fertiliser

Hint:

Denitrification needs Nitrate.
If you want to stop it, don't give it nitrate!
This is why ammoniacal fertilizers (like Ammonium Sulfate) are preferred for submerged paddy crops.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
Denitrification is the biological reduction of nitrate ($NO_3^-$) to nitrogen gas ($N_2$) or nitrous oxide ($N_2O$) in anaerobic conditions. The question asks which practice promotes rather than prevents this loss.
Detailed Explanation:

• Mechanism of Denitrification:
It requires three things: Nitrate (as the substrate), anaerobic conditions (waterlogging), and organic carbon (as energy for bacteria).

• Evaluating Options:
(A) Non-nitrate fertilizers: Using ammoniacal ($NH_4^+$) or amide (Urea) fertilizers keeps nitrogen in a form that cannot be denitrified until it is converted to nitrate. This helps prevent loss.
(B) Nitrate fertilizers: Applying fertilizers like Sodium Nitrate or Calcium Nitrate provides the immediate substrate for denitrification. In waterlogged soils (like paddy), this leads to massive N loss. Therefore, this cannot be used to prevent the loss.
(C) Split application: Providing N in small doses as the plant needs it prevents a large "pool" of nitrate from accumulating and being lost. This helps prevent loss.
(D) Deep placement: Placing urea/ammonium in the reduced zone of soil prevents its conversion into nitrate (nitrification), thus preventing the subsequent denitrification. This helps prevent loss.

Step 2: Final Answer:
Using nitrate fertilizers directly provides the material for denitrification; hence, it is the method that cannot be used to prevent such loss.