Question Bank • QB_IDE_EXP_002 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Soil-Water-Plant Relationship

Subtopic: Measurement of infiltration, soil moisture and irrigation water infiltration

Question Statement:

A soil root zone has a depth of $0.80\text{ m}$, dry bulk density $\rho_b = 1.50\text{ g/cm}^3$, field capacity $FC = 26\%$, and permanent wilting point $PWP = 12\%$. Taking density of water $\rho_w = 1.0\text{ g/cm}^3$, the available water holding capacity ($AWC$) of the root zone in millimeters is ________ (answer in integer).

Answer Key:

168

Step-by-Step Solution & Explanation

Available water capacity ($d_{aw}$) formula: $d_{aw} = \frac{\rho_b}{\rho_w} \times D \times (FC - PWP)$ Given: • $\frac{\rho_b}{\rho_w} = 1.50$ • $D = 0.80\text{ m} = 800\text{ mm}$ • $FC - PWP = 0.26 - 0.12 = 0.14$ $d_{aw} = 1.50 \times 800\text{ mm} \times 0.14 = 1200 \times 0.14 = 168\text{ mm}$
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