Question

The steady-state soil infiltration rate is:

• A. Soil surface controlled
• B. Water supply controlled
• C. Soil Profile controlled
• D. Groundwater controlled

Hint:

The initial infiltration rate is controlled by the soil surface (matric suction).
The final, steady-state infiltration rate is controlled by the soil profile (specifically, the layer with the lowest saturated hydraulic conductivity).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Infiltration is the downward entry of water into the soil surface.
The infiltration rate is the volume of water entering the soil per unit area per unit time.
As water application continues, the infiltration rate declines from a high initial rate and eventually stabilizes at a nearly constant rate, known as the steady-state infiltration rate.

Step 2: Detailed Explanation:
During the initial stages of infiltration into a dry soil, water movement is driven by both gravitational forces and strong matric suction forces near the dry soil surface.
At this stage, the process is primarily soil surface controlled, influenced by surface crusts, pore size distribution, and initial soil moisture.
As the wetting front moves deeper, the matric suction gradient decreases, and water flow becomes driven primarily by gravity.
At this stage, the soil becomes saturated, and the infiltration rate reaches a steady state.
This steady-state rate is determined by the saturated hydraulic conductivity of the most restrictive layer within the soil profile (e.g., claypans, plow pans, or dense Bt horizons).
Even if the surface has high permeability, water cannot enter faster than it can pass through this restrictive subsurface layer.
Therefore, the steady-state soil infiltration rate is soil profile controlled.

Step 3: Final Answer:
The steady-state soil infiltration rate is controlled by the soil profile.