Long-term weed community dynamics in Swiss organic and integrated farming systems

In 1991, a farming-system comparison was established on Burgrain Farm (Alberswil) to investigate the longterm sustainability of farming systems in Switzerland. In this study, the impacts of the three farming systems [organic (ORG), and integrated (IF) with an extensive (IFext) and an intensive (IFint) variant] on weed dynamics and diversity in six fields planted with winter wheat, maize, summer/winter barley, potatoes/oilseed rape and temporary grassland are examined. Altogether, 51 plant species were recorded from 1999 to 2006 in the maize and winter wheat crop. Total weed ground cover prior to harvest was seven times higher for wheat and 15 times higher for maize in ORG than in IFint, but grain yields were not negatively affected. Weed diversity was higher for ORG than for IF. In the temporary grassland, Taraxacum officinale and Rumex obtusifolius increased with time and dominated the weed community in the maize which followed. Chenopodium and Polygonum species dominated in the wheat, especially in ORG. We conclude from this study that an optimal combination of direct and indirect means for controlling weeds would allow organic farming at this site, provided that problematic weeds (e.g. Elytrigia repens) can be kept at the low level observed at the end of 2006.