Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: The infiltration rate decreases during heavy rainfall and tends to approach a constant value. Reason R: The matric potential of soil water decreases with accumulated infiltration. In the 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:

Infiltration trend with time: \[ \boxed{ \text{High initially} \rightarrow \text{Decreases gradually} \rightarrow \text{Constant basic infiltration} } \] Reason: \[ \boxed{ \text{Reduction in soil suction (matric potential)} } \]

Answer 1

The Correct Option is A

Concept: Infiltration is the process by which water enters the soil surface. Initially:
• Soil is relatively dry
• Suction forces are high
• Infiltration rate is high As infiltration continues:
• Soil becomes wetter
• Suction decreases
• Infiltration rate reduces Eventually infiltration approaches a nearly constant value called: \[ \boxed{ \text{Basic infiltration rate} } \]

Step 1: Analyzing Assertion A. Assertion A states: \[ \text{“The infiltration rate decreases during heavy rainfall and tends to approach a constant value.”} \] This statement is correct. Reason:
• Initially dry soil absorbs water rapidly
• With time soil pores become wetter
• Capillary suction reduces
• Rate gradually stabilizes Hence: \[ \boxed{ \text{Assertion A is correct} } \]

Step 2: Analyzing Reason R. Reason R states: \[ \text{“The matric potential of soil water decreases with accumulated infiltration.”} \] This statement is also correct. Matric potential represents soil suction. As soil gets wetter:
• Negative pressure reduces
• Capillary attraction weakens
• Infiltration driving force decreases Thus: \[ \boxed{ \text{Reason R is correct} } \]

Step 3: Checking whether Reason explains Assertion. The reduction in matric suction directly causes:
• Reduction in infiltration rate
• Approach toward constant infiltration Therefore: \[ \boxed{ \text{Reason R correctly explains Assertion A} } \]

Step 4: Selecting the correct option. We conclude:
• Assertion A is correct
• Reason R is correct
• Reason explains Assertion Hence: \[ \boxed{ (A) } \] is the correct answer. Final Conclusion: The infiltration rate decreases because soil suction decreases with increasing wetness. Hence the correct answer is: \[ \boxed{ (A) } \]