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a USDA Sustainable Agriculture Network, Beltsville, MD 20705-2351
b USDA-ARS, Animal and Natural Resources Inst., Beltsville, MD 20705
c Dep. of Natural Resource Sciences and Landscape Architecture, Univ. of Maryland, College Park, MD 20742
d Lower Eastern Shore Research and Education Center, Salisbury, MD 21801
* Corresponding author (aclark{at}sare.org)
Received for publication December 30, 2005. 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 vetchrye cover crop mixtures, compared to pure stands, to estimate fertilizer nitrogen (FN) equivalents. A 2-yr study evaluated spring management of hairy vetch (HV), pure rye, a vetchrye 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 ha1. A grass-selective herbicide (GSH) was applied in late March to the pure rye and the vetchrye mixture, leaving HV to accumulate N until early May. These treatments were compared to the same covers killed in early May. Cover crop N uptake was lowest for rye, intermediate for the mixtures, and highest for HV. The N content in the pure rye and vetchrye mixture was significantly increased if the previous year's corn had received excess FN. The cover crop mixture produced greater rye growth if fall soil nitrate N was high, while low soil nitrate N resulted in greater yield of HV in the mixture. There was no difference in corn N uptake for the late- vs. early kill pure rye, or of the rye component in the vetchrye mixture. A vetchrye mixture functioned like a "dual purpose" cover by conserving fall residual N, producing a lower C/N ratio residue than pure rye, and supplying more N to the succeeding corn than pure rye, although the N supplied was still less than pure vetch.
Abbreviations: CKL, no-cover check DM, dry matter FN, fertilizer N GSH, grass selective herbicide HV, hairy vetch LSD, least significant difference MXL, late-killed vetchrye mixed cover MXP, early killed rye in vetchrye mixed cover RCB, randomized complete block RYL, late-killed pure rye cover RYP, early killed pure rye cover VTL, late-killed vetch cover
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