A process where positively charged ions of one chemical are preferentially replaced by positive ions of another chemical. For example, water softeners replace Ca+2, and Mg+2 ions with the sodium (Na+2) ion.
The ability of clay and humus to attract and exchange positive ions.
The exchange of cations held by the soil adsorbing complex with other cations. Thus, if a soil adsorbing complex is rich in sodium, treatment with calcium sulphate (gypsum) causes some calcium cations to exchange with some sodium cations.