Cover crops in cereals – better companions than weeds?

Summary

Cover crops have gained popularity in cereal cropping now that they are one of the subsidized options in agri-environmental schemes of the EU. Several studies on cover/catch crops affecting nutrient leaching have been published but less information is available concerning their applicability for weed management. In our opinion, combinations of crop and cover crop types as well as crop sequencing conform IPM principles and optimize weed management. The PRODIVA project (ERA-Net Core Organic Plus Action, www.coreorganicplus.org) aims at identifying weed community associations with most common crop types in organic crop production systems. We will clarify the characteristics and relative competitiveness of cover crops providing strong weed suppression without severely compromising weed species diversity and crop yields. Long-term cropping system experiments in Denmark, Finland and Latvia provide information on weed dynamics both in terms of weed biomass production and weed community associations with cropping factors such as crop type, crop sequencing and mechanical weed control. We aim at understanding the main factors driving weed pressure and weed community assemblies under northern European circumstances. Perennial weed species (e.g. Cirsium arvense, Elymus repens, Sonchus arvensis) are particular important in organic cropping systems because they heavily constrain crop productivity. Cover crop establishment and early growth are key factors for the suppression of weeds. Poorly developed cover crops can cause extensive proliferation of rhizomatous perennials. Clover species (Trifolium spp.) are one of the most applicable cover crops thriving in the Nordic/Baltic agroclimate. Clovers supply nitrogen to the crops to improve both yield and crop competitiveness against weeds and they suppress C. arvense in cropping systems where clover together with grasses acts as a green manure that is repeatedly mown.