Agricultural Drainage and Salinity

The Sodium Adsorption Ratio ($SAR$) of irrigation water with cation concentrations in $\text{meq/L}$ is defined as:

Options:

• (A) $SAR = \frac{\text{Na}^+}{\sqrt{(\text{Ca}^{2+} + \text{Mg}^{2+}) / 2}}$
• (B) $SAR = \frac{\text{Na}^+}{\text{Ca}^{2+} + \text{Mg}^{2+}}$
• (C) $SAR = \frac{\text{Ca}^{2+} + \text{Mg}^{2+}}{\text{Na}^+}$
• (D) $SAR = \frac{\text{Na}^+ + \text{K}^+}{\sqrt{\text{Ca}^{2+}}}$