A crop with a root zone depth of $80\text{ cm}$ is grown on a sandy loam soil having field capacity $FC = 18\%$ and permanent wilting point $PWP = 8\%$ (both on dry weight basis). The dry bulk density of the soil is $1.5\text{ g/cm}^3$. If irrigation is applied when $50\%$ of available soil moisture is depleted, the net depth of water to be applied per irrigation is ________ $\text{mm}$ (answer in integer).
Answer Key:
60
Step-by-Step Solution & Explanation
1. Total Available Water ($TAW$):
$TAW = \frac{\rho_b}{\rho_w} \times d \times (FC - PWP) = 1.5 \times 800\text{ mm} \times (0.18 - 0.08) = 1200 \times 0.10 = 120\text{ mm}$
2. Readily Available Water ($RAW$) at $50\%$ depletion:
$RAW = 0.50 \times TAW = 0.50 \times 120\text{ mm} = 60.0\text{ mm}$
Thus, net depth of irrigation $= 60\text{ mm}$.