Sodium Adsorption Ratio (SAR) Calculation in Excel

The Sodium Adsorption Ratio (SAR) is a key indicator used to evaluate the suitability of water for irrigation. It is calculated using the concentrations of sodium, calcium, and magnesium in the water.

Formula

The SAR can be calculated using the following formula:

[ SAR = \frac{Na^+}{\sqrt{\frac{Ca^{2+} + Mg^{2+}}{2}}} ]

Where:

• Na⁺ = Concentration of sodium (in meq/L)
• Ca²⁺ = Concentration of calcium (in meq/L)
• Mg²⁺ = Concentration of magnesium (in meq/L)

Excel Formula

Assuming:

• Cell A1 contains the sodium concentration (Na⁺)
• Cell B1 contains the calcium concentration (Ca²⁺)
• Cell C1 contains the magnesium concentration (Mg²⁺)

The formula in Excel to calculate the SAR would be:

= A1 / SQRT((B1 + C1) / 2)

Explanation of the Formula

1. A1: Represents the sodium concentration. This value is directly used as the numerator.
2. (B1 + C1) / 2: Takes the average of the calcium and magnesium concentrations.
3. SQRT(...): Calculates the square root of the average concentration of calcium and magnesium. This value serves as the denominator in the SAR equation.

Practical Example

Let us consider the following example data:

• Sodium ((Na^+)): 5 meq/L (Cell A1)
• Calcium ((Ca^{2+})): 10 meq/L (Cell B1)
• Magnesium ((Mg^{2+})): 5 meq/L (Cell C1)

Using the earlier Excel formula:

= 5 / SQRT((10 + 5) / 2)

Calculation Steps:

1. Calculate the average of calcium and magnesium:
   • (10 + 5) / 2 = 7.5
2. Calculate the square root:
   • SQRT(7.5) ≈ 2.74
3. Final Calculation:
   • SAR ≈ 5 / 2.74 ≈ 1.83 (rounded to two decimal places)

Thus, using the provided data, the Sodium Adsorption Ratio (SAR) is approximately 1.83.

Conclusion

The calculated SAR provides valuable insight into the sodium content of irrigation water compared to calcium and magnesium, which is essential for understanding soil health and crop suitability. For further insights and to enhance your analytical skills in Excel, you may explore courses offered by Enterprise DNA Platform.