Methods for the cation exchange capacity of saline-sodic soils

cation exchange capacíties of four soil profiles representíng large ranges in salínity and Na saturation were measure by: 1) the sum of cations (CEC₃) extracted by NH₄OAc at ph 7 minus the cations in saturation extracts, 2) the method of bower et al (1952) (CEC₃) in which the soil is saturated using NaOAc, the excess salt is removed by washing with hethanol and the Na ís removed with NH₄OAc, and 3) the method of Polemio and Rhoades (1977) (CECpr) in whích the soíl ís saturated wíth Na using a solution of NaCL-NaOAc in 60% ethanol, the Na is replaced with Mg(NO₃) ₂ and the CL concentratíon in the Mg(NO₃) ₂ solution is used to correct occluded salt. Values for CEC were essentíalty the same for alL methods ín the non-saline and non-sodic yolo soil and in the surtace horizons of the other three soils which were relatively free of salts. Howeve. ín the moderately to líghly saline subsoíls of the Pescadero, Solano and Pescadero Variant soils, the CEC s greatly exceeded the CEC 8 and CECpr. Even though the CEC 8 and CECpr generally gave the same values, the CEC8 values were more híghly correlated wíth hygroscopic and saturation water contents. Using these correlations as criteria for a satisfactory method, the CEC8 appears to be the most reliable of the three methods that were compared.