Question Bank • QB_EXP_IDE_SAL_013 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Leaching Requirement, Salinity & Drainage Water Quality

Subtopic: Leaching requirement calculation

Question Statement:

An agricultural crop has an electrical conductivity tolerance threshold of the saturated soil extract $EC_e = 4.0\text{ dS/m}$. The irrigation water has an electrical conductivity of $EC_w = 1.8\text{ dS/m}$. According to the USDA-FAO formula $LR = \frac{EC_w}{5 EC_e - EC_w}$, the leaching requirement is ________ $\%$ (round off to two decimal places).

Answer Key:

9.89

Step-by-Step Solution & Explanation

Applying the leaching requirement equation: $LR = \frac{EC_w}{5 EC_e - EC_w} = \frac{1.8}{5(4.0) - 1.8} = \frac{1.8}{20.0 - 1.8} = \frac{1.8}{18.2} = 0.0989$ In percentage: $LR = 9.89\%$.
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