The importance of climate, site and management on weed vegetation in oilseed rape in Germany

Data on the occurrence of weed species in 1463 German oilseed rape (OSR) fields were used to multivariately investigate the interactions of management practices and ecological processes with weed species composition. Partial canonical correspondence analysis (pCCA) served to quantify the relative contribution of 25 characteristics of climate, site and crop to weed species composition. According to pCCA the considerable differences in weed species composition of OSR fields were mainly associated with the crop preceding OSR, the tillage intensity and soil quality. Longitude and precipitation were the most important environmental parameters. Factors driving the occurrence of weed species differed for the categories ‘common’, ‘frequent’ and ‘rare’ weed species. Common weed species showed the strongest response to factors acting at the field scale such as crop sowing date or soil quality, while only frequent species were affected by local environment, and the occurrence of rare weeds more than the other groups depended on large-scale geographical position variables as well as cropping intensity. Cluster analyses of thematically grouped explanatory variables resulted in the identification of four farming systems with different soil properties and management, two farming systems differing in the occurrence of OSR cropping, and five ecoregions, each with characteristic and statistically verified OSR weed communities.