Cation Exchange Capacity (CEC)

Clay particles carry electrical charges, of which the majority are negative. These negative charges can attract and bind with cations in the soil solution. The cations, which are positively charged forms, bond with the clay and can be displaced by other cations. The magnitude of negative charges present, to absorb cations, is referred to as the cation exchange capacity (CEC) of the soil and is expressed in centi-molar charge per kg soil (cmol+/kg). Organic matter also has a CEC, as well as an anion exchange capacity, like the CEC, but that absorb negatively-charged anions.

The CEC of soil depends on the clay content, the type of clay, and the organic matter content. Under certain circumstances, CEC may be pH-dependant, i.e. it will change when the pH changes.

Click here to view a video that explains cation exchange.