Modelling Complex Crop Rotations and Treatments Across Sites in Europe with an Ensemble of Crop Models.

Crop modelling is widely used to assess agricultural production under current or future climate conditions. Recently, uncertainty of crop models became more and more a focus and ensemble modelling is seen as a suitable approach to overcome specific weaknesses of single models using a ensemble mean or median which has turned out to be a better predictor than any single model over a wide range of conditions. Studies on climate change impacts on crop productivity are mainly focussed on single crops. However, the position of crops within a rotation can have significantly influence crop production due to carry-over effects between two seasons. Therefore, the design and management of crop rotations provide an important measure to adapt to changing climatic conditions and to perform sustainable crop production. Within the European MACSUR project, we started a study on crop rotation effects using data from 5 sites across Europe with various treatments/variants which provide data for 201 cropping season at all. In a first step only few data for a rough calibration for each site where provided. Depending on the site different variants were investigated comprising irrigation, N fertilization level, atmospheric CO₂ concentration, tillage, residue management, inserted catch crops and different soils. 14 models participated in this “low calibration run” providing results of single year simulations and/or continuous simulations over whole crop rotation. Comparing both ways of simulation, results were provided slightly better results with lower RMSE between observed and simulated crop yields for the continuous runs compared to the single year runs were achieved. However, distinct differences regarding model performance exist between the different crops showing that cereals are usually better simulated than tuber/beet crops. Regarding the treatment effects irrigation, nitrogen supply and catch crops as well as atmospheric CO₂ concentration showed clearer effects than tillage and crop residue management.