(CEC) the sum of exchangeable bases plus total soil acidity at a specific pH, usually 7.0 or 8.0 —note 1. when acidity is expressed as salt extractable acidity, the cation exchange capacity is called the effective cation exchange capacity (ECEC) because this is considered to be the CEC of the exchanger at the native pH value —note 2. cation exchange capacity is usually expressed in centimoles of charge per kilogram of exchanger (cmol_c kg^-1) or millimoles of charge per kilogram of exchanger —see soil reaction This definition last updated 10/25/2008