
%0 Journal Article
%A Alves, M. E. 
%A Lavorenti, A. 
%T Potassium&#8211;calcium exchange in electropositive oxisols: description of exchange sites
%J Soil Research
%D 2003/12/18
%V 41
%N 8
%P 1423-1438
%K caesium-adsorption method, Dufey&#8211;Delvaux multisite model, Gaines&#8211;Thomas, permanent negative charges, Rothmund&#8211;Kornfeld formulation.
%R https://doi.org/10.1071/SR03010
%U https://www.publish.csiro.au/paper/SR03010 
%X Potassium&#8211;calcium exchange was studied in batch experiments carried out with 2 oxisols exhibiting positive charge balance. The experimental data were quantitatively described with the Rothmund&#8211;Kornfeld formulation of the Gaines&#8211;Thomas approach, and the permanent and variable surface negative charges were measured using the caesium-adsorption method. For both soils, no appreciable involvement of permanent negative charges was observed in the potassium&#8211;calcium exchange, which, in turn, seemed to occur solely on the variable negative charges. The preference for potassium over calcium exhibited by both soils was well described by the Rothmund&#8211;Kornfeld formulation of the Gaines&#8211;Thomas approach. It was hypothesised that the exchange sites could be divided into 2 groups with different potassium selectivities. The proportions and selectivities of these exchange site groups were estimated combining the Rothmund&#8211;Kornfeld formulation with the Dufey&#8211;Delvaux multisite model. For both soils, there was excellent agreement between experimental and modelled data and it was possible to estimate the amounts of exchange sites (cmolc/kg) presenting greater and lower potassium selectivity. The existence of variable negative charge pools more accessible to K than to Ca ions but not evenly accessible to the former was considered as a possible cause of the non-ideal behaviour of the studied soils in relation to the potassium&#8211;calcium exchange. 
