Question

The formula for sodium absorption ratio (SAR) is

• A. \(\frac{\mathrm{Na}^+}{\sqrt{\frac{\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+}}{2}}}\)
• B. \(\frac{\mathrm{Na}^+}{\sqrt{\frac{\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+}}{2}}}\)
• C. \(\frac{\mathrm{Na}^+}{\sqrt{\frac{\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+}}{\mathrm{Na}^+}}}\)
• D. \(\frac{\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+}}{2}\)

Hint:

Sodium Adsorption Ratio (SAR):
- Measures sodium hazard.
- High SAR: Sodic soils.
- Formula: \(\mathrm{SAR} = \frac{\mathrm{Na}^+}{\sqrt{(\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+})/2}}\).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question tests knowledge of the sodium adsorption ratio (SAR) formula.

Step 2: Key Formula or Approach:
SAR is calculated using the formula:
\[ \mathrm{SAR} = \frac{\mathrm{Na}^+}{\sqrt{\frac{\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+}}{2}}} \] where concentrations are expressed in meq/L.

Step 3: Detailed Explanation:
The SAR formula measures the relative concentration of sodium to calcium and magnesium in soil solution.
A high SAR indicates a sodium hazard (alkali/sodic soil).
Option (A) is the correct formula.
Other options:
- (B): Same as (A) but written differently.
- (C): Incorrect (Na in denominator).
- (D): Incorrect (missing Na and square root).
Thus, the correct formula is option (A).
Final Answer:
Thus, the formula for SAR is \(\frac{\mathrm{Na}^+}{\sqrt{(\mathrm{Ca}^{2+} + \mathrm{Mg}^{2+})/2}}\), which corresponds to option (A).
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