Question Bank • QB_IDE_EXP_062 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Agricultural Drainage

Subtopic: Leaching requirement and salinity control

Question Statement:

Using the US Salinity Laboratory formula $LR = \frac{EC_w}{5 EC_e - EC_w}$, calculate the leaching requirement ($LR$) for irrigation water with electrical conductivity $EC_w = 1.5\text{ dS/m}$ applied to a crop with permissible root zone salinity $EC_e = 4.5\text{ dS/m}$.

Answer Key:

0.0714

Step-by-Step Solution & Explanation

$LR = \frac{1.5}{(5 \times 4.5) - 1.5} = \frac{1.5}{22.5 - 1.5} = \frac{1.5}{21.0} = \frac{1}{14} \approx 0.0714 = 7.14\%$
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