Short term fluctuation of soil organic carbon can mask the long-term trends in C storage. Different fractionation techniques have been developed to distinguish between a more persistent mineral associated fine/heavy fraction and a more labile coarser/lighter particulate organic matter fraction. It has been suggested that the mineral-associated fraction reaches an upper limit as a result of saturation of the mineral organic adsorption complex. As data on C fractionation becomes available from a number of research groups and inter-comparison of fractionation methods has been tested, the theoretical saturation concept can be demonstrated with field data. In order to use the mineral-associated fraction as an indicator for the C sequestration potential, a consensus on a simple yet robust fractionation technique and a technique to establish the baseline and upper limit of persistent C for a region or a country should be reached. Lastly, the throughput of fractionation techniques, that is currently low, should be addressed for its use in routine soil analysis. Vis-NIR or MIR spectroscopy is one of the techniques for decreasing the analysis costs.

Invited Talk:
Dr. Axel Don
"What can we learn from soil organic carbon fractions -analytical options and limitations"