Question Bank • QB_IDE_SWP_002 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Soil-Water-Plant Relationship

Subtopic: Water requirement of crops

Question Statement:

A sandy clay loam soil has a field capacity $FC = 28\%$ and permanent wilting point $PWP = 14\%$ on dry mass basis. The bulk density of dry soil is $\rho_b = 1.40\text{ g/cm}^3$ and water density is $\rho_w = 1.0\text{ g/cm}^3$. The effective root zone depth of the crop is $D = 75\text{ cm}$. If the Management Allowed Depletion (MAD) is $60\%$ of available soil water, the readily available moisture ($RAM$) in $\text{mm}$ is ________ (round off to 1 decimal place).

Answer Key:

88.2

Step-by-Step Solution & Explanation

1. Available Water Capacity ($AWC$): $AWC = \frac{\rho_b}{\rho_w} \cdot D \cdot (FC - PWP)$ $AWC = 1.40 \times 750\text{ mm} \times (0.28 - 0.14) = 1050 \times 0.14 = 147.0\text{ mm}$ 2. Readily Available Moisture ($RAM$): $RAM = \text{MAD} \times AWC = 0.60 \times 147.0 = 88.2\text{ mm}$
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