Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: The imbalance of air and water in the root zone causes adverse effects on crop growth due to waterlogging and salt accumulation.
Reason R: The physical condition of the soil deteriorates due to excess soluble salts and salinity in the crop root zone.
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:

Waterlogging causes anoxia (lack of oxygen), while salinity causes osmotic stress. While they often occur together in poorly drained soils, their direct physiological mechanisms are distinct.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Waterlogging occurs when the soil pores in the crop root zone are filled with water, restricting aeration.
Salinity develops when dissolved salts accumulate in the soil profile, often accelerated by waterlogging and subsequent capillary rise under high evaporation rates.
Detailed Explanation:
Let us analyze the statements:
- Assertion A: An imbalance of air and water in the root zone causes oxygen depletion (anoxia), which inhibits root respiration, nutrient uptake, and crop growth. Additionally, poor drainage in waterlogged soils promotes salt accumulation as water evaporates and leaves salts behind in the root zone. This statement is correct.
- Reason R: Salinity and excess soluble salts can deteriorate the physical condition of the soil, particularly when sodium ions dominate (which disperses clay particles and blocks soil pores). Even in non-sodic saline soils, salt accumulation creates osmotic stress that restricts water uptake. This statement is correct.
However, the physiological damage caused by waterlogging (such as anoxia and a lack of root respiration) is a physical consequence of water displacing air in soil pores.
This is distinct from the physical deterioration of soil structure caused by high sodium levels.
Therefore, while both statements are true, Reason R is not the correct explanation for Assertion A.

Step 2: Final Answer:
Both A and R are true, but R is not the correct explanation of A, corresponding to Option (B).