Gapon's equation is widely-used equation to describe

Gapon’s equation is a widely used equation to describe the CEC of soils. CEC is the cation exchange capacity of the soil and it is a measure of how many cations can be retained on the soil particle surface.
The Gapon exchange equation is commonly used to study binary heterovalent exchange reactions. The Gapon equation help to maintain the ratio of sodium to calcium on the soil colloid surface content.