Arable plant communities as indicators of farming practice

The diversity and abundance of the within-field seedbank and emerged weed flora, were measured in over 100 fields from conventional, integrated and organic farms across the arable east of Scotland. Both seedbank and emerged flora showed significant responses to a management intensity gradient from farms with high agrochemical inputs and winter cropping to those with no inorganic inputs, spring cropping and mixed farming practices. The emerged weed flora was more affected by recent agrochemical inputs than was the seedbank, which is buffered by the persistence of weed seeds in the soil. The seedbank was more strongly influenced by soil characteristics, such as % organic carbon and % total nitrogen, than by management. Overall farming approach (categorised here as organic, integrated and conventional) appeared to exert a selection pressure on the species composition of the seedbank, building up different communities under the three farming approaches over time. These effects were scale dependent. At a within-field scale, species richness was greatest in organic farms where there was a greater abundance of weeds. At a regional and landscape scale, species richness was greater in integrated and conventional farms. This was particularly evident in integrated farms which represented a greater range of crop types and cropping practices between fields than either conventional of organic farms alone. Increasing the diversity of cropping practices between fields may offer a complementary approach to reducing agrochemical inputs for enhancing arable biodiversity across landscapes.