Effects of Temperature on the Measured Cation‐exchange Capacities of Ando Soils

Summary The CEC was measured by a method which eliminates washing for removal of excess saturating salt. The effect of temperature on the CEC of soils and clays varied and depended on their major cation‐exchange materials; the ratio of the CEC measured at 10–20 °C to that measured at 50–60 °C was 0.36 to 0.59 for allophane, imogolite, and/or humus, 0.62 to 0.75 for kaolin minerals, and 0.90 to 0.99 for montmorillonites. The CEC, increased at higher temperature in a neutral n acetate solution, was only partly reduced by lowering the temperature again. There was no evidence for an acceleration of cation diffusion with increasing temperature. A structural alteration in which some ‘bound’ functional groups are set free for ionization is proposed as a major cause of the large CEC increase observed for Ando soils at higher temperature.