Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Crop residue on soil surface in conservation tillage systems can decrease the rate of soil temperature change.
Reason (R) : Surface residue increases the reflection of incident solar radiation.
In light of the above statements, choose the most appropriate answer from the options given below.

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

Hint:

By insulating the soil surface and reducing evaporation, crop residues help conserve valuable soil moisture and protect soil microbes and plant roots from extreme heat during summer.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil temperature dynamics are governed by the surface energy balance.
Adding surface covers, such as mulches or crop residues in conservation tillage systems, significantly alters heat transfer between the atmosphere and the soil.

Step 3: Detailed Explanation:
Let us evaluate both statements:
- Assertion (A): This statement is correct.
In conservation tillage systems, crop residues are left on the soil surface.
These residues act as an insulating blanket that dampens diurnal and seasonal soil temperature fluctuations.
Consequently, residue-covered soils warm up more slowly in the morning and cool down more slowly at night compared to bare soils, decreasing the overall rate of soil temperature change.
- Reason (R): This statement is also correct.
Dry plant residues typically have a lighter color and a higher albedo (reflectivity) than wet, dark bare soils.
This lighter color reflects a larger fraction of incoming solar radiation back into space.
Because less solar energy is absorbed by the surface, less heat is conducted into the deeper soil layers. This directly explains why crop residues reduce soil heating and decrease the rate of soil temperature changes during the day.
Thus, both statements are true, and (R) is the correct explanation of (A).

Step 4: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A), corresponding to option (A).