Question

Which of the following term represents an empirical measurement supposed to represent the soil profile's ability to retain water after the process of internal drainage has ceased?

• A. Water holding capacity
• B. Field Capacity
• C. Available water capacity
• D. Moisture retention capacity

Hint:

Think of Field Capacity as the "holding limit" of a soil against gravity.
Water content above field capacity drains away rapidly and is unavailable to plants, while water held at field capacity is easily absorbed by plant roots.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
When a soil is thoroughly wetted (e.g., by heavy rain or irrigation), gravity pulls water downward through the large pores (internal drainage).
After a few days, this rapid drainage slows down significantly, and the soil retains a certain amount of water against gravity.
Detailed Explanation:
- Field Capacity is defined as the amount of water remaining in the soil after excess water has drained away and the rate of downward movement has materially decreased.
- This state is typically reached within 2 to 3 days after a thorough wetting of a well-drained soil.
- At field capacity, the soil macro-pores are filled with air, while the micro-pores are still filled with water.
- It represents the upper limit of water storage in agricultural fields and is physically associated with a soil moisture tension of approximately $-0.1 \text{ to } -0.33 \text{ bar}$ (or $-10 \text{ to } -33 \text{ kPa}$).
- Water holding capacity refers to the maximum water the soil can hold when saturated.
- Available water capacity is the range of water available to plants (between field capacity and permanent wilting point).

Step 2: Final Answer:
The term representing this state is Field Capacity, corresponding to option (B).