Question Bank • QB_IDE_ADV_077 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Agricultural Drainage

Subtopic: Irrigation and drainage water quality and reuse

Question Statement:

A laboratory chemical analysis of an agricultural tube-well water sample yields the following cation concentrations: Sodium $\text{Na}^+ = 12.0\text{ meq/L}$, Calcium $\text{Ca}^{2+} = 4.50\text{ meq/L}$, and Magnesium $\text{Mg}^{2+} = 3.50\text{ meq/L}$. The Sodium Adsorption Ratio ($SAR$) of the irrigation water is ________ (round off to two decimal places).

Answer Key:

6.00

Step-by-Step Solution & Explanation

1. Sodium Adsorption Ratio formula: $SAR = \frac{\text{Na}^+}{\sqrt{\frac{\text{Ca}^{2+} + \text{Mg}^{2+}}{2}}}$ 2. Evaluating terms with concentrations in $\text{meq/L}$: $\text{Ca}^{2+} + \text{Mg}^{2+} = 4.50 + 3.50 = 8.00\text{ meq/L}$ $\frac{\text{Ca}^{2+} + \text{Mg}^{2+}}{2} = \frac{8.00}{2} = 4.00$ $\sqrt{4.00} = 2.00$ 3. Computing $SAR$: $SAR = \frac{12.0}{2.00} = 6.00$
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