Subtopic: Available water capacity and readily available moisture
Question Statement:
A crop root zone of depth $80\text{ cm}$ has a soil bulk density of $1.45\text{ g/cm}^3$. The field capacity and permanent wilting point of the soil are $32.0\%$ and $14.0\%$ (on dry weight basis), respectively. The total available water holding capacity of the root zone is ________ $\text{cm}$ (round off to two decimal places). (Variation QB_PARAMETRIC_IDE_SWP_010)
Answer Key:
20.88
Step-by-Step Solution & Explanation
The available water depth $AW$ is calculated as:
$AW = \frac{\rho_b \cdot D}{\rho_w \cdot 100} (FC - PWP)$
Given $\rho_b = 1.45\text{ g/cm}^3$, $\rho_w = 1.0\text{ g/cm}^3$, $D = 80\text{ cm}$, $FC = 32.0\%$, and $PWP = 14.0\%$:
$AW = \frac{1.45 \times 80}{100} \times (32.0 - 14.0) = 1.160 \times 18.0 = 20.88\text{ cm}$