Characterization of organo-mineral association by thermal analysis of density fractions

The degree of association of soil organic matter with the mineral matrix is considered a major control on organic matter stability. Fractionation of soils by density separation separates organic matter more or less associated with mineral matter, where the lighter fractions have generally been found to be more C-enriched with higher C/N ratios while heavier fractions have less C and narrower C/N ratios. The objective of this study was to characterize density fractions ranging from < 1.65 g cm-3 to > 2.55 g cm-3 isolated from an Oregon andic soil using thermogravimetry and differential scanning calorimetry to assess the quality and stability of the organic matter associated with these fractions. Preliminary results suggest lighter fractions exhibit large exothermic regions at lower temperatures, while heavier fractions exhibit a greater proportion of organic matter oxidized at higher temperatures. The results further support a potential link between thermal stability and long-term soil organic matter stabilization.