CN-SIM—a model for the turnover of soil organic matter. I. Long-term carbon and radiocarbon development

A novel computer model is presented which describes the flow of C and N in the soil. It employs a structure with conceptual compartments. Organic matter is represented by seven different compartments, two for added matter, two for soil microbial biomass, one for microbial residues, one for native (‘humified’) organic matter, and one for inert organic matter. The latter pool represents both truly inert matter, and matter with negligible turnover in a time-span of decades to a century. This paper describes the parameterisation and performance of this model on selected long-term field carbon and radiocarbon data from United Kingdom, Sweden and Denmark. Previously unpublished radiocarbon data series from Denmark are included. Statistical methods were employed to estimate parameters, and obtain proximate confidence intervals for these parameters. Simulations in good agreement with measured values could be achieved, using the same set of parameters on all sites. It was demonstrated that the inert pool might constitute any amount between approx. 10 and 50% of total soil C, so that modelling cannot be used as a tool to obtain narrow estimates for this pool.