Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A) : Ammonium-based fertilisers are the major contributors to soil acidification.
Reason (R) : Especially the non-leachable nitrogen ions which have been taken up by plants contribute to the soil acidity.

In light of the above statements, choose the correct answer from the options given below.

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

Hint:

Nitrification of 1 mole of \(\text{NH}_4^+\) releases 2 moles of \(\text{H}^+\) ions, making ammonium fertilizers more acidifying than nitrate-based fertilizers.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil acidification can be accelerated by agricultural practices, especially through the biochemical conversion and uptake of nitrogen fertilizers.

Step 2: Detailed Explanation:
Assertion (A) is correct because the use of ammonium (\(\text{NH}_4^+\))-based fertilizers (e.g., ammonium sulfate, urea) releases hydrogen ions (\(\text{H}^+\)) during the nitrification process, leading to soil acidification.
Reason (R) is correct because ammonium is a relatively non-leachable cation that binds to soil exchange sites.
When plants take up this positively charged \(\text{NH}_4^+\) ion, the roots must exude an equivalent positive charge (an \(\text{H}^+\) ion) into the soil solution to maintain electrochemical neutrality inside the plant cells.
This continuous release of \(\text{H}^+\) ions directly increases rhizosphere acidity.
Thus, both statements are true and (R) provides the underlying chemical explanation.

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).