The need for models of soil organic matter (SOM) turnover is similar to the need for many models of environmental processes: they are used to better understand processes; extrapolate or interpolate experimental results in time, space and to different environmental conditions; and to investigate scenarios and hypotheses that are beyond the realm of experimental work. As a result of this, a wide variety of SOM models have been developed, differing in their formulation and purpose. There are a number of approaches to modelling SOM turnover including process-based multi-compartment models, models that consider each fresh addition of plant debris as a separate cohort that decays in a continuous way, and models that account for carbon and nitrogen transfers through various trophic levels in a soil food web. This chapter aims to give a broad overview of currently available SOM models, highlighting areas of model application, identifying strengths and weaknesses and future directions for model development. We focus on two of the most widely used SOM models, RothC and CENTURY, to provide detailed case studies of model formulation, development and application.
SOIL ORGANIC MATTER MODELS
There are several sources of metadata and information on SOM models. CAMASE (Plentinger and Penning de Vries, 1996) contains 98 agro-ecosystems models having soil components, and the Global Change and Terrestrial Ecosystems Soil Organic Matter Network (GCTE-SOMNET) database (Smith et al., 1996a, 1996b: online at http://saffron.rothamsted.bbsrc.ac.uk/cgi-bin/somnet/) contains metadata on over 30 current operational SOM models. Several authors have previously reviewed SOM models extensively.