ARS | Publication request: THE POTENTIAL FOR ALLELOPATHY DURING DECOMPOSITION OF HAIRY VETCH RESIDUE

Submitted to: Proceedings of Northeastern Weed Science Society
Publication Type: Abstract
Publication Acceptance Date: November 2, 2005
Publication Date: January 3, 2006
Citation: Teasdale, J.R., Abdul Baki, A.A., Park, Y.B., Rosecrance, R.C. 2006. The potential for allelopathy during decomposition of hairy vetch residue [abstract]. Proceedings of Northeastern Weed Science Society. 60:58.

Technical 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. Rapid decomposition is a recognized characteristic of hairy vetch residue, but there has been little research to document the change in allelopathic potential of this residue during decompostion. Hairy vetch above-ground vegetation was harvested from the field one day before desiccation with paraquat, five days after desiccation, and one month after desiccation and brought to the greenhouse for assay. Emergence of several annual weed species was assessed as a function of various rates of hairy vetch residue placed on the soil surface. There was no significant difference between live or recently killed vetch in suppressing weeds when compared at equivalent biomass. However, vetch harvested just before or just after desiccation suppressed all species more than vetch residue that remained in the field for one month. The I50 values were approximately doubled when residue remained in the field for one month. In a second experiment, fresh hairy vetch was used intact (unleached) or was leached in a container overnight with a circulating pump. A similar greenhouse assay was conducted as that previously described for assessing weed emergence suppression by residue. Stems of leached residue were similar in diameter to those of unleached residue, averaging 1.8 mm. However, unleached hairy vetch residue had intact leaves whereas leached residue had shriveled or missing leaves. Unleached hairy vetch residue inhibited emergence of all weed species more than a comparable amount of leached residue. In a petri-dish assay, aqueous extracts of living hairy vetch shoots harvested before the cover crop was killed were more toxic to lettuce roots than extracts of desiccated hairy vetch residue. By 3 weeks after kill, extracts of hairy vetch residue had lost 23 to 51% of activity relative to the activity of extracts from live hairy vetch tissue. By 6 to 9 weeks after kill, extracts of hairy vetch residue had little activity left. In addition, aqueous extracts of upper leaf tissue were more inhibitory of root and hypocotyl growth than were lower leaf or stem tissue. All of these results could be explained by the presence of aqueous soluble allelopathic compounds in fresh hairy vetch residue that were lost during the decomposition process in the field or the leaching process in the laboratory. Higher inhibition of seedling growth by aqueous extracts of upper leaves compared to lower leaves or stem tissue is consistent with the findings that fresh and unleached tissue were more inhibitory than decomposed and leached tissue. Generally, decomposed and leached material had lost most leaf tissue and was composed primarily of stems. This suggests that allelochemicals are present primarily in the most metabolically active upper leaves of fresh hairy vetch residue and that allelopathy contributes to weed suppression for a relatively short time following cover crop kill until leaf tissue has decomposed.