Modelling dynamic interactions between soil structure and the storage and turnover of soil organic matter

Abstract. Models of soil organic carbon (SOC) storage and turnover can be useful tools to analyze the effects of soil and crop management practices and climate change on soil organic carbon stocks. The aggregated structure of soil is known to protect SOC from decomposition, and thus influence the potential for long-term sequestration. In turn, the turnover and storage of SOC affects soil aggregation, physical and hydraulic properties and the productive capacity of soil. These interactions have not yet been explicitly considered in modelling approaches. In this study, we present and describe a new model of the dynamic feedbacks between SOM storage and soil physical properties (porosity, pore size distribution, bulk density and layer thickness). A sensitivity analysis was first performed to understand the behaviour of the model. The identifiability of model parameters was then investigated by calibrating the model against a synthetic data set. This analysis revealed that it would not be possible to unequivocally estimate all of the model parameters from the kind of data usually available in field trials. Based on this information, the model was tested against measurements of bulk density and SOC concentration, as well as limited data on soil water retention and soil surface elevation, made during 63 years in a field trial located near Uppsala (Sweden) in three treatments with different OM inputs (bare fallow, animal and green manure). The model was able to accurately reproduce the changes in SOC, soil bulk density, surface elevation and soil water retention curves observed in the field. Treatment-specific variations in SOC dynamics caused by differences in OM input quality could be simulated very well by modifying the value for the OM retention coefficient e (0.37 for animal manure and 0.14 for green manure). The model approach presented here may prove useful for management purposes, for example, in an analysis of carbon sequestration or soil degradation under land use and climate change.