Individual and interactive effects of crop type and management on weed and seed bank composition in an organic rotation

We investigated the effects of organic and conventional pest and fertility management on weed cover and the seed bank community in an organic rotation. The study was conducted during the 4th and 5th years of an organic rotation on part of a long term organic-conventional comparison trial. Results showed that although crop type (potato vs. cabbage) in a single year significantly affected weed functional group and cover of individual species, it did not change weed functional group and composition in the seed bank in the following year. Five years of organic crop protection management increased weed species that depend on regeneration from seed and increased Ellenberg light, reaction and nitrogen values and a seed bank persistence index in comparison with conventional crop protection management. Three species (Chenopodium album L., Poa spp. L. and Stellaria media (L.) Villars) that is important for biodiversity of arable fields were more prevalent in organic protection plots. Fertility management had no significant effects on weed seed bank composition and functional group. The additive effect of organic practices on perennial ratio and competitor radius value was an important finding. Organic fertility management and crop protection acted together to increase these two aspects of the soil seed bank in comparison with other treatment combinations and a similar effect was seen on Poa spp. L. Keywords: Additive effect; Weed cover; Weed functional group; Crop protection; Fertilizer.