Weed and arthropod communities in soyabean as related to crop productivity and land use in the Rolling Pampa, Argentina

P>In the Rolling Pampa, Argentina, changes in crop management caused changes in weed and arthropod communities and reductions in weed diversity in soyabean. Loss of landscape heterogeneity, caused by an increase in the area planted to soyabean, and herbicide treatment of field margins, may affect weed and arthropod assemblages and reduce species richness. This study focused on the effect of land use in neighbouring fields, weed management of field margins and crop productivity and history on weed and arthropod communities and their richness inside soyabean fields. Weeds and arthropods were surveyed in a total of 60 soyabean fields in 1999, 2001 and 2002. Neighbouring land use was determined in concentric circles of 500 and 1500 m radius around each field using LANDSAT images, and field margin management (sprayed or non-sprayed) was recorded. Data was analysed using regression and canonical correspondence analysis. Cropping history (number of years of cropping) and percentage of soyabean in concentric circles of 1500 m explained 23% of the variation in weed assemblages, whereas management of field margins and soyabean productivity (mean summer Normalised Difference Vegetation Index) explained 23% of the variation in arthropod assemblages. Perennial, dicotyledon and exotic weed richness and non-herbivore arthropod richness decreased with increasing percentage of soyabean in the surrounding landscape. Results show that weed and arthropod communities respond to different production and landscape variables and that increasing the area planted to soyabean and spraying field margins will put weed and arthropod species and functional groups at risk of extinction.