Question

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

Assertion (A) : Gypsum is commonly used for the reclamation of sodic soil.
Reason (R) : Reclamation process involves reduction in exchangeable sodium with calcium and its removal from soil solution through leaching.

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:

Leaching is essential during sodic soil reclamation. Without adequate drainage to remove displaced sodium, the soil cannot be successfully reclaimed.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Sodic soils are characterized by high levels of exchangeable sodium ions (\(\text{Na}^+\)), which disperse clay particles and destroy soil structure. Reclamation requires replacing exchangeable \(\text{Na}^+\) with calcium (\(\text{Ca}^{2+}\)) and leaching the displaced sodium out of the root zone.

Step 2: Detailed Explanation:
Assertion (A) is correct because Gypsum (\(\text{CaSO}_4 \cdot 2\text{H}_2\text{O}\)) is the most common, cost-effective amendment used to reclaim sodic soils.
Reason (R) is correct because when gypsum is applied, it dissolves to release soluble \(\text{Ca}^{2+}\) ions, which replace the \(\text{Na}^+\) ions held on the soil clay surfaces according to the following reaction:
\[ \text{Clay-Na}_2 + \text{CaSO}_4 \rightarrow \text{Clay-Ca} + \text{Na}_2\text{SO}_4 \]
The displaced sodium forms highly soluble sodium sulfate (\(\text{Na}_2\text{SO}_4\)), which is subsequently flushed deep into the ground via leaching water.
Thus, Reason (R) directly explains Assertion (A).

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