Weed vegetation of organic and conventional dryland cereal fields in the mediterranean region

Summary

Weed abundance, species richness and diversity in conventional and organic dryland cereal fields in Catalonia (NE of Iberian Peninsula) were compared to assess the effect of intensification on the floristic composition and structure of weed vegetation and to evaluate the role of organic farming in preventing the continued loss of biodiversity caused by intensive farming practices. Between 1 and 3 closely paired fields (blocks) were selected at 10 agricultural sites. Each pair contained one long-established organic farm and one conventional farm. Weed abundance, taking into account the spatial pattern, was surveyed in spring 2003 and 2004 by means of a relative abundance index for each species, ranking from one to six. Results show that abundance, species richness and diversity were higher in organic than conventional fields. Low tolerance to herbicides and the dense crop swards of conventional fields may explain the lower abundance of broad-leaved weeds, while the increase in legumes in organic fields may be related to the absence of chemical fertilization. Species richness was higher at the crop edges than mid-field in both organic and conventional fields, whereas weed abundance was higher at field margins than mid-field in conventional fields.