Sodium Adsorption Ratio (SAR)

Last Updated: August 27, 2018

Definition - What does Sodium Adsorption Ratio (SAR) mean?

Sodium Adsorption Ratio or SAR is an indicator used to identify salinity of soil. This measures the ratio of sodium (Na) to calcium (Ca) and magnesium (Mg) to determine the soil flocculation. Soil flocculation enables improved water absorption and plant root growth. Calcium and magnesium are good soil flocculators while sodium is not. So, SAR is key in determining the water absorption and plant root growth environment.

MaximumYield explains Sodium Adsorption Ratio (SAR)

SAR is a ratio of sodium and combination of calcium and magnesium that expresses the balance of both components. This balance is managed by soil ions and water extracts and the levels of salinity in this soil will help determine SAR. As a result, the soil structure is affected by SAR. In other words for an arable land with effective irrigation the SAR needs to be high in calcium and magnesium.

If the soil contains high levels of sodium or salinity then the soil can be categorized as dispersed soil or soil that is unfit for irrigation. SAR is dependent on the soil ions so there is no prescribed ideal ratio.

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