Question

The specified range of soil moisture tension at field capacity is

• A. 1/15 - 1/5
• B. 1/10 - 1/6
• C. 1/10 - 1/3
• D. 1/6 - 1/10

Hint:

Field capacity tension: \(0.1\text{ bar}\) (sandy soils) to \(0.33\text{ bar}\) (clayey soils).
Permanent wilting point tension is much higher, typically set at \(15\text{ bars}\).
The water held between these two limits is the available water for plants.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Field capacity is the amount of water held in the soil after excess gravitational water has drained away and the rate of downward movement has materially decreased.
This state is typically reached \(1\) to \(3\) days after a heavy rain or irrigation event in free-draining soils.

Step 2: Detailed Explanation:
Soil moisture tension (or suction) represents the force with which water is held by the soil matrix, usually expressed in atmospheres (atm) or bars:
- Immediately after irrigation, the soil is saturated, and the moisture tension is virtually zero.
- As water drains downward under gravity, the tension increases.
- For sandy soils, gravitational drainage is rapid due to large pore spaces, and field capacity is reached at a low tension of about \(1/10\text{ atm}\) (or \(0.1\text{ bar}\)).
- For fine-textured clay soils, water is held more tightly within smaller pores, and gravitational drainage slows down at a tension of about \(1/3\text{ atm}\) (or \(0.33\text{ bar}\)).
- Therefore, the standard range of soil moisture tension at field capacity across different soil textures is defined between \(1/10\text{ atm}\) and \(1/3\text{ atm}\).

Step 3: Final Answer:
The specified range of soil moisture tension at field capacity is 1/10 - 1/3.