Interactions between mineral phases in the preservation of soil organic matter

Given appropriate management, soils may serve as a sink for carbon, and thereby play a potentially important role in helping countries meet CO2 emission reductions as agreed to under the Kyoto Protocol. To fully judge the capacity of soils to store carbon, however, gaps regarding the mechanisms of organic carbon (OC) stabilization need to be filled. A number of studies have demonstrated the significance of oxides in the preservation of soil OC. Although oxides are known to strongly bind with clay minerals, potential interactions between these minerals in OC preservation in soils are often overlooked. The goal of this study was to, thus, examine possible interactions between clay minerals and oxides in the storage of soil OC. For this, we analysed how the OC, clay content, clay mineralogy and dithionite-extractable Fe (Fed) and oxalate-extractable Fe (Feo) and Al (Alo) concentrations of several sampled soils are statistically related. Samples from two Umbrisols, a Stagnic Acrisol, an Anthrosol/Vertisol/Gleysol-Chernozem and a Gleysol (FAO terminology) from profiles located in Hesse, Germany were analysed. Clay content exhibited a strong significant relationship with the OC concentrations of only two soils. Feo and Alo were found to be strongly related to the OC concentrations of most profiles. Some clay minerals such as chlorite displayed very strong relationships with OC and Feo and Alo concentrations. The results suggest that oxides interact with clay minerals in at least two of the soils examined, forming complexes or aggregates which may play an important role in stabilizing organic material. Future studies should also consider potential mineral interactions in the sequestration of OC in soils.