Reintroduction of rare arable weeds under various farming practices and their influence on ecosystem services and yield

Agricultural intensification and changing landscape structure led to decreasing numbers of arable flora and fauna during the last decades. To counteract these declines, weed diversity needs to be supported. It is important to promote regional weed communities including endangered species to ensure adoption to agricultural landscapes, restore their ecosystem services (e.g., pollination, weed and pest control, soil fertility) and mitigate biodiversity loss. To reintroduce rare weed species, two experiments in spring cereals were started in Renningen in 2019 and in Hirrlingen in 2021. In the first experiment, variations of weed control intensity, fertilization and row spacing were compared in regard to their influence on crop yield and biodiversity. Two different mixtures containing rare weed species were used for reintroduction: one commercially available, one self-composed regarding the former occurrences of the species in these regions. Treatments with sown rare species had on average the twice the number of weed species occurring compared to treatments without any sown weeds. Yield was significantly lower in treatments with wider row spacing, reduced fertilization, reintroduction of weed species and no herbicide use. Mechanical and chemical weed suppression did neither differ significantly in yield nor species richness in 2019. Additionally, an on-farm experiment, which started in spring 2021, examines the reintroduction success by different approaches (sowing and topsoil translocation). Besides reintroduction success the pollinator community, ground-dwelling carabid beetles and yield were investigated. The reintroduction of rare weeds was successfully accompanied by an increasing floral diversity.