Question Bank • QB_IDE_EXP_007 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Soil-Water-Plant Relationship

Subtopic: Consumptive use and evapotranspiration

Question Statement:

A Class-A pan evaporation reading is $8.0\text{ mm/day}$ and the pan coefficient $K_p = 0.75$. For an orchard crop with crop coefficient $K_c = 0.80$, the daily crop evapotranspiration $ET_c$ in $\text{mm/day}$ is ________ (round off to 2 decimal places).

Answer Key:

4.8

Step-by-Step Solution & Explanation

1. Reference evapotranspiration $ET_0$: $ET_0 = K_p \times E_{pan} = 0.75 \times 8.0 = 6.0\text{ mm/day}$ 2. Crop evapotranspiration $ET_c$: $ET_c = K_c \times ET_0 = 0.80 \times 6.0 = 4.80\text{ mm/day}$
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