In soil science, cation-exchange capacity (CEC) is the maximum quantity of total cations, of any class, that a soil is capable of holding, at a given pH value, available for exchange with the soil solution. CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination. It is expressed as milliequivalent of hydrogen per 100 g of dry soil(meq+/100g), or the SI unit centi-mol per kg (cmol+/kg). The numeric expression is coincident in both units.
Clay and humus have electrostatic surface charges that attract the solution ions, and hold them. This holding capacity varies for the different clay types and clay-blends present in soil, and is very dependent of the proportion of clay+humus that is present in a particular soil. One way to increase CEC is to favor the formation of humus.
In general, the higher the CEC, the higher the soil fertility.
Read more about Cation-exchange Capacity: Calculation of CEC, Base Saturation, PH and CEC, Aluminum and CEC, Organic Matter, Anion Exchange Capacity, Laboratory Determination, Standard Values
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