Question Bank • QB_EXP_IDE_SCH_013 NAT • 1 Mark

Section 5: Irrigation and Drainage Engineering

Irrigation Scheduling & Soil Moisture Depletion

Subtopic: Irrigation interval calculation

Question Statement:

A crop root zone has a total available soil water capacity of $AW = 150\text{ mm}$. The management allowed depletion ($MAD$) is set to $50\%$. If the average daily crop evapotranspiration rate is $ET_c = 6.0\text{ mm/day}$, the allowable irrigation interval is ________ $\text{days}$ (round off to one decimal place).

Answer Key:

12.5

Step-by-Step Solution & Explanation

Readily available water ($RAW$) is: $RAW = MAD \times AW = 0.5 \times 150 = 75.0\text{ mm}$ Irrigation interval is: $\text{Interval} = \frac{RAW}{ET_c} = \frac{75.0}{6.0} = 12.5\text{ days}$
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