Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2006
Publication Date: 1/15/2007
Citation: Clark, A.J., Meisinger, J.J., Decker, M.A., Mulford, R.F. 2007. Effects of a grass-selective herbicide in a vetch-rye cover crop system on nitrogen management. Agronomy Journal. 99:36-42. Interpretive Summary: A cover-crop of hairy vetch, rye, or a vetch-rye mixture can affect the next crop by adding nitrogen through fixation or by conserving residual soil nitrogen. Data are needed on spring management of vetch-rye cover crop mixtures, compared to pure stands, in order to optimize cover crop management and to estimate fertilizer nitrogen equivalents of the cover. This research was conducted on the Eastern Shore of Maryland and studied spring dry matter and nitrogen accumulation for the above cover crops and the nitrogen uptake of the following corn crop as affected by: corn fertilizer nitrogen rates, and the application of a grass selective herbicide to the rye cover in the late March which killed the rye early, but allowed the vetch in the mixture to grow until May. This early kill of the rye was compared to pure stands of vetch and rye, to a late kill of the vetch-rye mixture, and to a no-cover control. There was no difference in corn N uptake for late- versus early-kill date of pure rye, or of the vetch-rye mixture. Corn N uptake was largest following pure vetch, was lowest following rye or the no-cover control, and was intermediate after the vetch-rye mixture. The nitrogen content of the rye was affected by the fertilizer N rate applied to the previous years’ corn. High residual soil nitrogen produced greater rye growth and corresponding less vetch growth in the mixtures than if residual soil nitrogen was low. These results are important to extension and soil conservation agents and show that a vetch-rye cover crop mixture can function as a “dual purpose” cover by conserving fall residual nitrogen and by supplying greater nitrogen to the succeeding corn crop than pure rye.
Technical Abstract: Cover-crop kill date affects N fixation by hairy vetch (Vicia villosa Roth), N uptake by cereal rye (Secale cereale L.), residue C:N ratio, and subsequent N availability. Data are needed on spring management of vetch-rye cover crop mixtures, compared to pure stands, to estimate fertilizer nitrogen (FN) equivalents. A two-year study evaluated spring-kill dates of hairy vetch (HV), rye, a vetch-rye mixture, and a no-cover check on N accumulation and subsequent no-till corn N uptake following corn FN rates of 0, 45, 90, 180 and 270 kg/ha. A grass-selective herbicide was applied in late March to the pure rye cover and the vetch-rye mixture, leaving HV to accumulate N until early May. These treatments were compared to same covers killed in early May. The cover crop N uptake were lowest for rye, intermediate for the mixtures, and highest for HV. The N content in the pure rye and in the vetch-rye mixture were significantly increased if the previous year’s corn had received excess FN. The cover-crop mixture produced greater rye growth following high fall soil nitrate-N, while low soil nitrate-N produced greater HV. There was no difference in corn N uptake for the late- vs. early-kill pure rye, or of the rye component in the vetch-rye mixture. A vetch-rye cover-crop mixture functions like a "dual purpose" cover by conserving fall residual N, by producing a lower C:N ratio residue than pure rye, and by supplying more N to the succeeding corn than pure rye; although the N supplied is still less than pure vetch.