Improving Weed Suppression with Cover Crops in Organic Grain Production.

            Organic grain producers often heavily rely on tillage for mechanical weeding, creating compacted areas that generate ideal conditions for weedy species, and create a vicious cycle of tillage, compaction and increasing weed populations. With the collaboration of three private certified organic farmers from Illinois, we explored the effect of cover crops and compaction on weed populations and yields. The experimental design was at four locations around Illinois in a split-plot design with two replications per location.  The main plot treatments were compacted (CP) versus non-compacted areas (NCP), and the sub-plot was four rotations of cover crops. Four species of cover crops were used, forage radish (Raphanus sativus L.), hairy vetch (Vicia villosa), cereal rye (Secale cereale L.), and buckwheat (Fagopyrum esculentum), and the four cover treatments were included, control that was left fallow (C), forage radish (FR), forage radish and buckwheat (FRbw) and forage radish, hairy vetch and cereal rye (FRhvr). Soybean (Glycine max L. Merr.) was planted in 2012, and corn (Zea mays) followed in 2013. Cover crop counts were conducted every fall prior to winterkill and spring before termination by tillage, weed counts, biomass, and identification were collected prior to cash crop planting and during the growing season, and cash crop yields were determined every fall.  Our findings suggest the rotations with cover of forage radish/hairy vetch/rye can significantly suppress weed populations but can potentially decrease yields in dry years.