Derivation of cation exchange constants for sand, loess, clay and peat soils on the basis of field measurements in the Netherlands

Data are provided for the two most widely used cation exchange models (Gaines-Thomas and Gapon) and for all possible combinations of cations, including protons. Results show a wide range in exchange constants, especially when using the Gaines-Thomas exchange description. It appears that Gapon exchange constants are stronger correlated than the corresponding Gaines-Thomas exchange constants, especially for sandy soils. A strong positive correlation means that the ratio between two exchange constants is more characteristic, and less variable, of a certain soil (type) than their absolute numbers, which often vary by several orders of magnitude. In deriving exchange constants, the Al constants were related to free Al3+, the CEC was normalised to a buffered soil pH of 6.5 and the dissolved ion concentrations have all been derived while using a centrifugation method to extract the soil solution. Because of these methodological aspects, they cannot always be used directly in a particular model application. Nevertheless, they provide insight into the numerical ranges of and correlations between exchange constan, and are thus useful for constraining model parameters, e.g. in model calibrations.