CEC is determined by the summation of exchangeable Ca, Mg, Na, K, and Al. Base cations are extracted by leaching 3 g air dried soil (1 g for peat) with successive aliquots of 1 M NH4OAc, pH 7, to total 60 mL. The concentrations of the base cations in the leachate are determined by ICP-OES. The CEC is calculated from the sum of the base cations.
(See Method References No. 28 & 21)