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 DA ISY was evaluated using data from one year field trials with and witho ut incorporation of 8 t ha(-1) rape straw into the soil. Periodic meas urements of soil microbial biomass (C and N), mineral N and light part iculate 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 so il 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 bio mass. Metabolic quotients (qCO(2)), turnover rates of microbial biomas s and substrate utilization efficiencies derived from the parameteriza tion of the model were evaluated against literature data. The soil mic robial biomass seems to be associated with the production of temporari ly protected microbial residual products. The production of these resi duals might be responsible for the nitrogen immobilization observed af ter incorporation of rape straw. In the early stage of rape straw deco mposition, measured carbon in light particulate soil organic matter se emed to be represented by one of the added organic matter pools simula ted 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 physiolo gical state of microbial populations in their natural environment. (C) 1997 Elsevier Science B.V.