One of the aims of organic farming systems is to maintain or enhance the agricultural and natural biodiversity in agro-ecosystems. Weeds can contribute to biodiversity but also need to be controlled. Compared to conventional farming the weed density and diversity in organic farming is expected to be enhanced because of reduced fertilisation and low efficacy of control measures. It is also assumed that the diversity of crops, especially alternation of summer and winter crops, results in a greater range of weed species. However, relatively few data are available confirming this benefit of organic farming. Thus, continuous monitoring studies have been started in 1996 on a trial area for organic farming in northern Germany
