Effects of factor reduction in energy crop rotations on weed flora Einfluss der Faktorreduktion in Energiefruchtfolgen auf die Beikrautflora

Opportunities for reductions of fertilization and weed control efforts in energy cropping are frequently posed and contrarily discussed. Beside effects on biomass yields weed flora, increments and increased weed control requirements in subsequent years are in the focus of the discussion. As part of the research project “Site-adapted Cropping Systems for Energy Crops ” (EVA), the effects of factor reductions have been analysed in a crop rotation context. The trial consisted of three different crop rotations with three levels of factor reduction: 1- no reduction, 2- reduced nitrogen application by 30 kg/ha per crop, 3- reduced nitrogen application and no weed management. The whole trial was replicated with one year time difference. In order to show effects of input reduction on subsequently grown cash crops, the last crop in the rotation was winter wheat for grain production in which no input reduction was performed over all plots. The field trial has been investigated regarding the effects of: Levels of fertilization and weed control, crop rotation, crop species and year of investigation on weed cover and species composition as target variables. The results suggest that the reduction of weed control efforts showed the main effect on the weed flora. Energy crops, like maize and sorghum, seemed to be highly sensitive to reduced weed control especially during early development stages; they showed the greatest differences between the factor levels. The reduction in fertilization resulted in no or only slight differences in the weed flora. Despite strong effects in single years and crops, there were no or only little cumulative effects observed in the final crop of the crop rotations (winte