A comparison of the surface impedance factors of Ca, Na, Rb and Cs derived from their self-diffusion coefficients in various soils
1990
Staunton, S.
Self-diffusion coefficients of calcium, sodium, rubidium and caesium on the topsoils and subsoils of contrasting soil series are presented. The distribution ratios of each cation on each soil, at the moisture content of the diffusion experiments, have been calculated by extrapolation from series of suspensions. Diffusion coefficients were found in each case to be greater than expected by considering the liquid phase alone. Surface-phase impedance factors, fs, were calculated. Although impedance factors are considerably smaller on the surface than in solution, the surface flux may exceed the flux in the liquid phase. Differences of an order of magnitude separated average values of fs for each cation. For a given cation, variations between soils were considerably less. No correlation was found between fs and soil mineralogy or composition. Values of fs were found to decrease with increasing distribution ratio. Reasons for this observation are discussed, in particular the energy of adsorption of the cations. The possibility of extrapolating these findings to other soils, to potassium and to other cations is discussed.
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