Residual sodium carbonate index

The RSC index is used to find the suitability of the water for irrigation in clay soils which have a high cation exchange capacity.

[7] Soda ash [Na2CO3] can be present in natural water from the weathering of basalt which is an igneous rock.

The excess soda ash after precipitating the calcium and magnesium salts is in carbonates & bicarbonates of sodium which imparts high pH or alkalinity to soil water.

Sodium carbonate and sodium hydroxide are in equilibrium with availability of dissolved carbon dioxide as given below in the chemical reaction During day time when sun light is available, Algae undergoes photosynthesis process which absorbs CO2 to shift the reaction towards NaOH formation and vice versa takes place during night time with the release of CO2 from the respiration process of Algae towards Na2CO3 and NaHCO3 formation.

In soda lake waters, carbonates of sodium act as catalyst for the algae growth by providing favourable higher concentration of dissolved CO2 during the day time.