INTERACTIONS OF ORGANIC MATTER AND ALUMINUM IONS IN ACID FOREST SOIL SOLUTIONS

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Abstract
Using F potentiometry, we analyzed samples of ultrafiltered organic material obtained from lysimeter solutions during a growing season in two forest soils of different acidity. F potentiometry is a newly developed technique that allows the speciation of Al in the presence of complexes of unknown thermodynamic characteristics. The samples were analyzed for the amount of bound Al after known amounts had been added. All samples were separately studied with gel chromatography, to quantify the occurrence of precipitation and flocculation phenomena. These were performed after buffering the samples to the pH ranges usually occurring in the soil solution during a growing season. The original pH of the samples and the Al content were also measured. Results regarding the intensity of Al binding and the formation of precipitates in 62 samples are shown. The variance of the variable describing the intensity of precipitation was significantly split among the different factors affecting it, namely the pH of the treatment, the amounts of bound and free Al, and a covariant representing unspecified site differences. One can conclude that all these factors are important in defining the precipitation and mobility of the organic matter in the solution of the upper forest soils studied. These have implications for the interpretation of processes related to organic matter turnover and Al mobility in the upper soil.