Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 1 2010 10.5194/bg-7-27-2010 http://www.biogeosciences.net/7/27/2010/ http://www.biogeosciences.net/7/27/2010/bg-7-27-2010.html http://www.biogeosciences.net/7/27/2010/bg-7-27-2010.pdf 27 41 2010-01-05 Measuring and modeling continuous quality distributions of soil organic matter S. Bruun sab@life.ku.dk G. I. Ågren B. T. Christensen L. S. Jensen Plant and Soil Science Laboratory, Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark Department of Ecology, Swedish University of Agricultural Sciences, P.O. Box 7044, 750 07 Uppsala, Sweden Department of Agroecology and Environment, Faculty of Agricultural Sciences, Aarhus University, 8830 Tjele, Denmark An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution approaches the underlying continuum. Continuous distributions lead to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods will have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help generate the interest needed to accommodate this. % vor jede Referenz Ågren, G. and Bosatta, E.: Theoretical ecosystem ecology: understanding element cycles, Cambridge University Press, Cambridge, 1996a. 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