Question

The average moisture extraction by plants from first 25% of soil depth is approximately

• A. 50 %
• B. 45 %
• C. 40 %
• D. 35 %

Hint:

Remember the 40-30-20-10 Rule: Top 25% depth = 40%; Next 25% = 30%; Next 25% = 20%; Deepest 25% = 10%.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Under unconstrained soil moisture conditions, plant root systems extract water from successive quarters of their active root zone depth according to the empirical 40-30-20-10 extraction rule.
Key Formula or Approach:
\[ \text{Extraction Profile} = 40\% : 30\% : 20\% : 10\% \quad (\text{from Top to Bottom quarters}) \]

Step 2: Detailed Explanation:
The standard root zone water extraction pattern across four equal depth increments is:
1. Top Quarter (0--25% depth): 40% of total crop water extraction.
2. Second Quarter (25--50% depth): 30% of total extraction.
3. Third Quarter (50--75% depth): 20% of total extraction.
4. Bottom Quarter (75--100% depth): 10% of total extraction.
Thus, the first 25% of root zone depth supplies approximately 40% of the total moisture requirement.

Step 3: Final Answer:
Hence, average moisture extraction from the first 25% of soil depth is 40 %, matching option (C).