Sodium Adsorption Ratio

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

Variables

SARsodium adsorption ratio (-)

Nasodium concentration (meq/L)

Cacalcium concentration (meq/L)

Mgmagnesium concentration (meq/L)

Description

What is this formula?

The Sodium Adsorption Ratio (SAR) evaluates the relative abundance of sodium compared with calcium and magnesium in water. It is widely used to assess irrigation water suitability and potential soil sodicity hazards.

When to use it

Use it when evaluating groundwater, surface water, reclaimed water, or agricultural irrigation water.

Example

Data:

Na = 8 meq/L

Ca = 4 meq/L

Mg = 2 meq/L

Formula:

SAR = Na / √((Ca + Mg)/2)

Substitution:

SAR = 8 / √((4 + 2)/2)

SAR = 8 / √3

Result:

SAR = 4.62

Applications

Irrigation water quality assessment, agricultural engineering, soil management, groundwater studies, environmental monitoring, and water reuse projects.

Note

SAR is an empirical water quality indicator used to estimate the potential for sodium accumulation in soils. High SAR values may reduce soil permeability and negatively affect crop growth. Various guidelines classify irrigation water based on SAR ranges and salinity levels.