Question

The pF values at Saturation, Field capacity, Permanent wilting point and Hygroscopic coefficient respectively are

• A. 0, 2.53, 4.18 and 4.5
• B. 4.5, 4.18, 2.53 and 0
• C. 2.53, 4.5, 4.18 and 0
• D. 0, 4.18, 2.53 and 4.5

Hint:

pF summary: Saturation = 0. Field Capacity = 2.53 (1/3 bar). PWP = 4.18 (15 bar). Hygroscopic = 4.50 (31 bar). Oven Dry = 7.0.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Schofield (1935) introduced the pF scale as the common logarithm of the soil water matric suction head expressed in centimeters of water column.
Key Formula or Approach:
\[ \text{pF} = \log_{10}(h \text{ in cm of } \text{H}_2\text{O}) \]

Step 2: Detailed Explanation:
Standard diagnostic pF values of soil moisture constants:
1. Saturation (0 bar 0 cm head): \(\text{pF} = \log_{10}(1) = 0\).
2. Field Capacity (1/3 bar $\approx 346$ cm head): \(\text{pF} = \log_{10}(346) = 2.53\) (or $2.54$).
3. Permanent Wilting Point (15 bar $\approx 15,300$ cm head): \(\text{pF} = \log_{10}(15300) = 4.18\).
4. Hygroscopic Coefficient (31 bar $\approx 31,600$ cm head): \(\text{pF} = \log_{10}(31600) = 4.50\).
5. Oven Dry Soil (10,000 bar): \(\text{pF} = 7.0\).

Step 3: Final Answer:
Hence, the pF values are 0, 2.53, 4.18 and 4.5, matching option (A).