Soil samples of an Oxisol collected from the soil A horizon under forest or grassland, and the oxic horizon (B) were used for the study of cation movement. The A-forest and A-grassland samples were treated with calcium carbonate, calcium sulphate or with a combination of both, with the objetive of evaluating the electrochemical changes of the soil, mainly in relation to the sulphate. Afterwards, the A horizon samples were packed in pots over the B horizon samples and incubated. After incubation the samples were leached with seven pore-volumes of destilled water, weekly. After this, exchangeable calcium, magnesium, potassium and aluminium, pH in water, pH in 1 mol L-1 KCl, potencial acidity and the zero point of salt effect (ZPSE) were evaluated. With sulphate application the A horizon presented a decrease in exchangeable aluminium, without changes in the effective CEC, CEC at pH 7.0, and ZPSE. Sulphate was probably precipitated by aluminum. In relation to the B horizon, sulphate application resulted in alterations of the ZPSE, effective CEC and CEC at pH 7.0, without a decrease in the exchangeable aluminum. In this layer, chemical adsorption of sulphate might wave occurred. Calcium carbonate was more efficienty in decreasing soil acidity. The combination of carbonate with calcium sulphate was similar to the addition of carbonate only in the decrease of soil acidity.
adsorption; zero point of charge; saline effect; gypsum
