ABSTRACT
Residue of leguminous cover crops such as hairy vetch (Vicia villosa Roth) on the soil surface in minimum tillage cropping systems contributes to integrated weed management and provides nitrogen for subsequent crops. Research was conducted to determine the role of allelopathy on suppression of weed emergence by hairy vetch residue as the residue decomposes throughout the season. Residue was removed from the field at various times before and after the vetch was killed in spring and assayed for suppression of emergence and growth of selected species in greenhouse assays or Petri dish assays. Results showed that hairy vetch residue that was allowed to decompose in the field or that was subjected to leaching in the laboratory was less suppressive of emergence and/or growth than was residue that was fresh. These results could be explained by the presence of aqueous soluble phytotoxins in fresh hairy vetch residue that were lost during the decomposition process in the field or the leaching process in the laboratory. Aqueous extracts of the upper leaf tissue were more inhibitory of seedling root and hypocotyl growth than the lower leaf or stem tissue. This suggests that phytotoxins are present primarily in the metabolically active upper leaves of hairy vetch and that allelopathy contributes to weed suppression for a relatively short time following cover crop kill until leaf tissue has decomposed.
