Question Bank • QB_IDE_ADV_056 NAT • 1 Mark

Section 5: Irrigation and Drainage Engineering

Soil-Water-Plant Relationship

Subtopic: Consumptive use and evapotranspiration

Question Statement:

During the mid-season growth stage, a maize crop has a crop coefficient of $K_c = 1.15$. The average daily pan evaporation measured with a standard USWB Class-A pan is $E_p = 7.00\text{ mm/day}$ and the pan coefficient is $K_p = 0.70$. The crop evapotranspiration ($ET_c$) in millimeters per day ($\text{mm/day}$) is ________ (round off to two decimal places).

Answer Key:

5.64

Step-by-Step Solution & Explanation

1. Reference evapotranspiration ($ET_0$) from pan evaporation: $ET_0 = K_p \times E_p = 0.70 \times 7.00\text{ mm/day} = 4.90\text{ mm/day}$ 2. Crop evapotranspiration ($ET_c$): $ET_c = K_c \times ET_0 = 1.15 \times 4.90\text{ mm/day} = 5.635\text{ mm/day} \approx 5.64\text{ mm/day}$
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