Question

The soil infiltrability is

• A. supply controlled
• B. atmosphere controlled
• C. soil profile controlled
• D. only top few cm layer controlled

Hint:

Infiltration is like a "traffic flow."
Even if the highway entrance is clear, a "bottleneck" (clay pan) $10$ km ahead will eventually slow down the whole flow.
Thus, the entire profile determines the capacity.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify what primarily determines or limits the "soil infiltrability."
Soil infiltrability is defined as the maximum rate at which water can enter a soil at a given time and condition.
Detailed Explanation:

• Infiltration vs. Infiltrability:
The actual infiltration rate can be limited by the supply (rain/irrigation). However, the capacity of the soil to absorb water—its infiltrability—is a property of the soil itself.

• Profile Characteristics:
Infiltration is not just about the surface. Even if the surface is loose, a hardpan or a clay layer at a depth of $20-30$ cm will cause water to "back up," reducing the infiltration rate at the surface.
Therefore, the infiltrability is governed by the hydraulic properties of the entire soil profile, including its texture, structure, pore size distribution, and the presence of any restrictive layers.

• Comparison with other options:
Supply controlled: This defines the "Actual Infiltration Rate" when rain is less than the capacity. It does not define the potential capacity.
Atmosphere controlled: This usually refers to evaporation, not infiltration.
Only top few cm: While surface crusting affects infiltration, the steady-state infiltration rate is ultimately limited by the least permeable layer in the entire profile.

Step 2: Final Answer:
Soil infiltrability is determined by the physical and hydraulic characteristics of the whole soil profile.