An evaluation of cation exchange capacity measurements for soils in the tropics

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Abstract
Comparisons of CEC [cation exchange capacity] and exchange acidity measurements were made on a group of selected West African soils using 3 commonly used analytical procedures, neutral-acetate displacement, BaCl2-TEA [triethanolamine] leaching at pH 8 and unbuffered KCl extraction. The 3 methods gave large differences in CEC values which followed the order of BaCl2-CEC .mchgt. NH4OAc-CEC > KCl-CEC. Results of exchange acidity also followed the same order. The high exchange acidity values obtained by the BaCl2-TEA (pH 8) method were mainly due to changes in surface charge characteristics of Fe and Al oxides and hydrous oxides. The effective CEC method is recommended for routine soil analysis for highly weathered soils in the tropics. Regression analysis of the base saturation values obtained from the 3 methods indicated the data followed a curvilinear relationship. The acetate method was more highly correlated with the effective CEC method than with the BaCl2 method.