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Cation Exchange Capacity and Component Variations of Soils of Southeastern USA¹

ABSTRACT

Several methods for determining CEC were employed for soils selected from southeastern United States to provide a wide range in acidity, clay mineralogy, clay content, and organic matter content. Unbuffered saturation was made with 1N CaCl₂, NaCl, NH₄Cl, or KCl. Soluble salts were removed by rapid stirring and centrifuging of the soil samples after each of three water and ethanol replacements. Buffered systems were used to measure CEC at pH 4.8, 7.0, and 8.3. Sum of exchangeable bases was not equivalent to values for CEC by unbuffered salts. Increases in CEC from the latter values to those found at pH 7 or pH 8.3 were not identical with corresponding values for titratable soil acidity. Standard deviations of the methods were much lower than differences in CEC between methods. All soils showed less CEC with NH₄⁺ or K⁺ saturation compared to Ca²⁺ or Na⁺ saturation; the difference was attributed chiefly to reaction with expanding phyllosilicates. For CEC measured at pH 7, component CEC of organic matter ranged from 40 to 180 between soil series, with the higher values associated with soils having free carbonate present. Under the same conditions, calculated CEC of clay ranged from 8 to 63 assumingnegligible CEC of the silt component. Apparent pH-dependent CEC of these soils was mainly attributed to hydroxy-Al associated with the organic matter and interlayering of expanding phyllosilicates.

¹ Florida Agr. Exp. Sta. Journal Series no. 3493.

² Professor, Soils Dept., Univ. of Florida, Gainesville. Soil samples were provided by Dr. G. I. Holmgren of the S. C. S. Laboratory at Lincoln, Nebr. and by members of the S-60 Regional Soil Research Technical Committee in addition to certain Florida soils.

Received for publication December 22, 1969. Accepted for publication May 28, 1970.