THE SORPTION OF ORGANIC MATTER IN SOILS AS AFFECTED BY THE NATURE OF SOIL CARBON

Abstract

Recent studies have shown that soil organic carbon (OC) may either hinder or favor the sorption of dissolved organic matter (DOM) in soils. Our concept was that the nature of soil OC determines these contrasting findings. To test this hypothesis, we compared the DOM sorption in soils with OC derived from biomass decomposition with that in soils with OC more likely derived from charred materials (black carbon). All the mineral soil samples in the study were from Spodosols, and the DOM was from an aqueous extract of a mor forest floor layer. Sorption was determined in batch experiments. The sorption in soils that contain large amounts of black carbon was, in general, less than the sorption in soils with decomposition-derived OC. When the DOM sorption parameters of the soils were correlated to the OC content, the black carbon soils showed a positive effect of the OC content on the DOM sorption. In the soils lacking the features of black carbon residues, the DOM sorption was negatively influenced by OC. These results lead us to assume that the nature of soil OC is a soil property that needs to be considered in the DOM sorption of soils, especially when soils have large amounts of highly aromatic OC.