INTERFERENCE BY ORGANIC COMPLEXATION OF FE AND AL ON THE SO4(2-) ADSORPTION IN SPODIC-B HORIZONS IN SWEDEN

The relations between pH, different fractions of Fe and Al and Na4P2O7 -soluble C and the amount of adsorbed SO42- were assessed by analysing 63 soil samples from 14 podsolized soils in Sweden. The amount of ads orbed SO42- was significantly better correlated with the calculated am ount of the inorganic fraction of Fe and Al oxides obtained by subtrac ting Na4P2O7-soluble Fe and Al from oxalate-soluble Fe and Al than wit h the oxalate extraction alone. There was a close correlation between C and organically-bound S in the Na4P2O7 extract which shows that the C:S ratio of the extracted fulvic acids is about constant in the soils studied. It was found that, as the proportion of organically-complexe d Fe and Al increases, the ability of the soil to adsorb SO42- decreas es. The amount of adsorbed SO42- expressed on the basis of the amounts of oxalate-soluble Fe and Al was generally smaller in areas with low S deposition (<60 mmol m-2 a-1). The ratio between pyrophosphate-solub le C and oxalate-extractable Fe and Al was negatively correlated with pH in water. It was concluded that Fe and Al associated with organic m atter cannot adsorb SO42- and that the degree of this association is p H dependent. These observations have important implications regarding the effects of anthropogenic acidification.