A crop root zone depth is $D = 0.80\text{ m}$. The soil has field capacity $FC = 28\%$, permanent wilting point $PWP = 14\%$, and dry bulk density $\rho_b = 1400\text{ kg/m}^3$. If the allowable depletion of available moisture is $50\%$, calculate the net depth of irrigation water to be applied in $\text{mm}$. (Density of water $\rho_w = 1000\text{ kg/m}^3$)
Answer Key:
78.4
Step-by-Step Solution & Explanation
Available water capacity:
$AWC = \frac{\rho_b}{\rho_w} \times D \times (FC - PWP) = \frac{1400}{1000} \times 800\text{ mm} \times (0.28 - 0.14)$
$AWC = 1.4 \times 800 \times 0.14 = 156.8\text{ mm}$
Net irrigation requirement at $50\%$ depletion:
$d = 0.50 \times AWC = 0.50 \times 156.8 = 78.4\text{ mm}$