Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : High concentration of sodium in irrigation water is not desirable.
Reason (R) : It causes deflocculation of soil aggregates and seals the pores.
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 and (R) is the not correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

High sodium causes soil dispersion (deflocculation), while calcium and magnesium promote soil flocculation (aggregation). This is a core concept in soil physics and irrigation water quality.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The quality of irrigation water is evaluated based on its salt concentration (salinity hazard) and sodium concentration relative to calcium and magnesium (sodicity hazard, measured by the Sodium Adsorption Ratio - SAR).
Detailed Explanation:
Let us evaluate both statements:
- Assertion (A) analysis: High sodium concentration in irrigation water is highly undesirable because it leads to sodium accumulation on the soil exchange complex (sodicity). Thus, Assertion (A) is true.
- Reason (R) analysis: When sodium dominates the soil exchange complex, it replaces calcium and magnesium. This causes clay particles to disperse (deflocculate) and swell when wet. The dispersed clay particles clog and seal the soil pores, reducing soil permeability, water infiltration, and aeration. Thus, Reason (R) is true.
- Evaluating the connection: Since the deflocculation of soil particles and subsequent pore sealing is the exact physical mechanism why high sodium water is undesirable, (R) is the correct explanation of (A).

Step 2: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A). This corresponds to Option (A).