Subtopic: Measurement of infiltration, soil moisture and irrigation water infiltration
Question Statement:
Referring to the soil moisture characteristic retention curve (pF curve) shown in the accompanying diagram, which of the following soil moisture constants are CORRECTLY identified?
Options:
(A) Field capacity corresponds to a suction tension of approximately $0.33\text{ bar}$ ($\text{pF} \approx 2.53$)
(B) Permanent wilting point corresponds to a suction tension of approximately $15\text{ bar}$ ($\text{pF} \approx 4.18$)
(C) Available water capacity (AWC) is the depth of water held between field capacity and permanent wilting point
(D) Hygroscopic water is readily available for crop transpiration
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Field capacity is held at $1/3\text{ bar} = 330\text{ cm water} \implies \text{pF} = \log_{10}(330) \approx 2.52$. (Statement A True)
2. Permanent wilting point is at $15\text{ bar} = 15000\text{ cm water} \implies \text{pF} = \log_{10}(15000) \approx 4.18$. (Statement B True)
3. Available water is defined strictly between FC and PWP. (Statement C True)
4. Hygroscopic water is held at tension gt; 31\text{ bar}$ as an immovable molecular film; it cannot be absorbed by plant roots. (Statement D False)