Under the classic empirical 40-30-20-10 soil water extraction model for deep, uniform agricultural soils with well-developed root systems, which of the following statements are correct?
Options:
(A) The uppermost quarter ($0 - 25\%$) of the root zone depth extracts $40\%$ of the total crop water requirement
(B) The second quarter ($25 - 50\%$) of the root zone depth extracts $30\%$ of the total crop water requirement
(C) The third quarter ($50 - 75\%$) of the root zone depth extracts $20\%$ of the total crop water requirement
(D) The bottom quarter ($75 - 100\%$) of the root zone depth extracts $10\%$ of the total crop water requirement
Answer Key:
A, B, C, D
Step-by-Step Solution & Explanation
All four statements describe the standard 40-30-20-10 root water uptake pattern documented by USDA and Michael:
- Top $25\%$ depth: $40\%$ extraction (highest root density and aeration).
- Second $25\%$ depth: $30\%$ extraction.
- Third $25\%$ depth: $20\%$ extraction.
- Bottom $25\%$ depth: $10\%$ extraction.
Together, the upper half of the root zone supplies $70\%$ of the crop's water needs.