Flora and seed bank during and after set-aside

Wildflower strips are sown with species-rich wildflower seed mixtures and stay at the same place between two and six years. After this period wildflower strips are tilled and reintegrated in the crop rotation. In a five-year field experiment in Hüttwilen (canton of Thurgau) we examined flora and seed bank in the soil during and after wildflower strip, natural regeneration, and grass-clover ley. Wildflower strip plots had the highest species diversity (17 to 28 species), in particular compared to the grass-clover ley. Seeds especially accumulated in the soil of wildflower strip and natural regeneration plots. After ploughing two years old set-aside plots, numerous and endangered species appeared in the subsequent crop. Within two years, the seed densities generally decreased to the level before the installation of the experiment. The cover of agronomic problem weeds in the crop was similar than during set-aside and the density of the flora in the crop could generally be reduced to small levels by ploughing and applying herbicides.