Crop type and management are key filtering factors of functional traits in the weed communities of regions with contrasting soils and climates

Abstract

Questions: Weed community composition responds to the interactions between environmental and management factors at different scales. The aim of this study was to disentangle the relative contributions of factors defining the composition of weed communities through crop type and agronomic management at the field scale, and climate and soil factors at the regional scale. Location: The study was carried out in croplands in the phytogeographic provinces of Espinal and Pampas in central Argentina. Methods: The floristic and functional compositions of weed communities in maize and soybean crops were characterized and compared using permutational multivariate analysis of variance and non-metric multidimensional scaling in the two regions. The Espinal and the Pampas differ in soil and climatic characteristics, but crops are grown with similar management strategies due to the widespread use of no-tillage and agrochemicals. Results: Years of continuous cropping, previous crop and sowing date were the most important factors modulating the species composition of both crops at field scale. Perennials and exotics were more abundant in the Pampas, whereas natives were more abundant in the Espinal. Moreover, mechanically dispersed species were more abundant in maize crops in the Pampas. Annuals and barochoric species were closely related to the years of continuous cropping in maize. In soybean, more monocotyledonous species were observed in fields previously cropped with maize, whereas more dicotyledonous and C3 species were observed in fields previously cropped with soybean. Conclusions: Differences in species composition depend mainly on climatic and biogeographical factors. In contrast, the functional composition of the weed communities in maize and soybean is mostly determined by local factors at field level, which are mostly related to crop identity and agronomic management. The effects of farming practices determine the functional composition of weed communities, which makes crop rotation and thorough cleaning of harvester machines key strategies in the development of weed management.