A New Equilibration Method for Cation‐Exchange Capacity Measurement

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Abstract
A method is proposed for the measurement of cation‐exchange capacity (CEC) of leached soils carrying both variable and constant negative charges at conditions pertinent to the field. The method consists of equilibrating a soil with 0.01 M SrCl2 (five centrifuge washings), replacing the retained Sr with 0.5 M HCl (one centrifuge washing) and determining the replaced Sr by atomic absorption spectrophotometry. The equilibrium pH is measured with the final 0.01 M SrCl2 washing. If desired, exchangeable bases and Al can be determined by collecting the 0.01 M SrCl2 washings. This method was developed because we found that the Gillman's BaCl2‐MgSO4 CEC method has problems due to specific adsorption of SO2−4. For evaluation, the CEC obtained by the proposed method was compared with the sum of exchangeable bases and Al and with the CEC obtained by other methods including saturation‐equilibration with 1 M SrCl2‐0.01 M SrCl2 and 1 M NH4OAc‐0.05 M NH4OAc (pH 7.0), respectively.

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