Temporal variation of C and N turnover in soil after oilseed rape straw incorporation in the field: simulations with the soil-plant-atmosphere model DAISY

The Soil Organic Matter submodel of the soil-plant-atmosphere model DAISY was evaluated using data from one year field trials with and without incorporation of 8 t ha−1 rape straw into the soil. Periodic measurements of soil microbial biomass (C and N), mineral N and light particulate soil organic matter in the top 15 cm of the soil, and of soil CO2-evolution were made. The simulation of the temporary pattern of soil microbial biomass and mineral N was improved markedly by systematic modification of the default turnover rate coefficients, the substrate utilization efficiencies and the initial levels of soil microbial biomass. Metabolic quotients (qCO2) turnover rates of microbial biomass and substrate utilization efficiencies derived from the parametrization of the model were evaluated against literature data. The soil microbial biomass seems to be associated with the production of temporarily protected microbial residual products. The production of these residuals might be responsible for the nitrogen immobilization observed after incorporation of rape straw. In the early stage of rape straw decomposition, measured carbon in light particulate soil organic matter seemed to be represented by one of the added organic matter pools simulated in the DAISY model. We propose that turnover rate coefficients of microbial biomass and added organic matter obtained by fitting a model to measured values may be used as a tool to characterize the physiological state of microbial populations in their natural environment.