Crop modelling based analysis of site-specific production limitations of winter oilseed rape in northern Germany

Winter oilseed rape production is typically characterised by low nitrogen (N) use efficiency. Defining site-specific fertiliser strategies based on field trials and crop modelling may help to improve the ecological efficiency of this crop. However, no model has been evaluated for winter oilseed rape that simulates the growth of the plant as limited by the interaction of water and N. In this study, the APSIM canola model which was originally developed for the temperate regions of Australia, was adapted for conditions in Germany and tested against measured data (total biomass, grain yield, leaf area index, N-uptake andsoil mineral N) at three sites near Göttingen (northern Germany). In the second part of the study, the evaluated model was used in a simulation experiment to explore site-specific climate and soil related production limitations to match fertiliser rates to yield targets. Historical weather data from four sites across northern Germany and a fertile loamy soil with different rooting depths, implicating different plant available water capacities, were used. Model results showed large differences in yield (up to 1000 kg/ha) and N-balance (>30 kg/ha) for 200 kg N-fertiliser rate per ha between restricted (50 cm) and unrestricted rooting depths. Simulated yields for such high N-fertiliser rate were lower for sites with continental climate than for sites close to the coast, reflecting different rainfall patterns. Results indicate that water supply plays a critical role when maintaining high N use efficiency and reaching simultaneously grain yields of 4000 kg/ha.