In
soil science,
cation-exchange capacity or CEC is the number of exchangeable cations per dry weight that a
soil is capable of holding, at a given
pH value, and available for
exchange with the soil water solution. CEC is used as a measure of soil
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 values are the same in any system of units.