Residual Sodium Carbonate

\[RSC=(HCO_3^-+CO_3^{2-})-(Ca^{2+}+Mg^{2+})\]

Variables

RSCresidual sodium carbonate (meq/L)

HCO3bicarbonate concentration (meq/L)

CO3carbonate concentration (meq/L)

Cacalcium concentration (meq/L)

Mgmagnesium concentration (meq/L)

Description

What is this formula?

Residual Sodium Carbonate (RSC) evaluates the potential hazard caused by excess carbonate and bicarbonate relative to calcium and magnesium in irrigation water.

When to use it

Use it when assessing irrigation water quality and the risk of soil sodicity caused by precipitation of calcium and magnesium.

Example

Data:

HCO3 = 5 meq/L

CO3 = 1 meq/L

Ca = 3 meq/L

Mg = 2 meq/L

Formula:

RSC = (HCO3 + CO3) − (Ca + Mg)

Substitution:

RSC = (5 + 1) − (3 + 2)

Result:

RSC = 1 meq/L

Applications

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

Note

RSC is an empirical irrigation-water indicator. High values suggest that calcium and magnesium may precipitate from solution, increasing the relative sodium hazard and potentially degrading soil structure. Various classification systems use different threshold values.