
TY  - JOUR
A1  - Alves, M. E. 
A1  - Lavorenti, A. 
T1  - Potassium&#8211;calcium exchange in electropositive oxisols: description of exchange sites
JF  - Soil Research
JO  - Soil Res.
Y1  - 2003
VL  - 41
IS  - 8
SP  - 1423
EP  - 1438
KW  - caesium-adsorption method, Dufey&#8211;Delvaux multisite model, Gaines&#8211;Thomas, permanent negative charges, Rothmund&#8211;Kornfeld formulation.
UR  - https://doi.org/10.1071/SR03010 
N2  - 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. 
ER  -

