This report presents extensive Tables of cation exchange constants (selectivity coefficients) for sand, loess, clay and peat soils at different depths derived from simultaneous field measure-ments of adsorbed in dissolved concentrations of H, Al, Ca, Mg, K and Na in several hundreds of non-agricultural soils 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.
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