Plot and border effects on herbicide-resistant weed seed consumption by rodents in corn and soybean crops of central Argentina

Biological control of weeds is a key ecological function of agriculture production. Our aim was to determine how border quality, distance to border, crop type and phenology, affect the consumption of herbicide-resistant weed seeds by rodents in the agroecosystems of central Argentina. We used seeds of four commonly problematic weeds and two crops in a consumption experiment with three exclusion treatments. We studied seed consumption at three distances of the border in 20 crop plots (10 soybean and 10 maize) associated with borders of different quality in spring and summer. We measured nine environmental variables and determined the abundance of rodents for each site. Seed consumption varied greatly among seed species, Amaranthus hybridus and Zea mays had the highest mean consumption rate, followed by Sorghum halepense and Digitaria sp., Ipomoea purpurea and Glycine max were rarely consumed. Our model predictions show seed consumption rates above 20 % for Digitaria sp, and 40 % for A. hybridus with the increase of border vegetation volume. On the other hand, Z. mays consumption reaches more than 30 % in summer. This high weed seed consumption would modify the population and community dynamic of the weeds by impeding seed entrance to the seed bank. Our results highlight that rodents could perform biological control of herbicide-resistant weeds. The positive effect that habitats with high vegetation cover have on rodent species suggests that appropriate management strategies like maintaining high-quality field borders and establishing natural and semi-natural patches can enhance weed biological control in industrialised agroecosystems.