Biomass and nitrogen accumulation of hairy vetch-cereal rye cover crop mixtures as influenced by species proportions

Authors: POFFENBARGER, HANNA - Former ARS Employee; Mirsky, Steven; Maul, Jude; WEIL, RAYMOND - University Of Maryland; Kramer, Matthew; SPARGO, JOHN - Pennsylvania State University; Cavigelli, Michel

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2015
Publication Date: 6/9/2015
Citation: Poffenbarger, H.J., Mirsky, S.B., Maul, J.E., Weil, R.R., Kramer, M.H., Spargo, J.T., Cavigelli, M.A. 2015. Biomass and nitrogen accumulation of hairy vetch-cereal rye cover crop mixtures as influenced by species proportions. Agronomy Journal. doi: 10.2134/agronj14.0462.

Interpretive Summary: Cover crops are nonmarket crops that are used as multi-functional tools to provide agro-ecosystem services. The extent to which a service is provided will vary by cover crop species. Combining species into a cover crop mixture is a useful approach to maximize multiple services. Our research focused on combining grass and legume mixtures to optimize weed and fertility management. Legumes are useful in providing nitrogen to the subsequent cash crop while grasses provide good weed control as a mulch, slow nitrogen release rates for better synchrony with crop uptake, and scavenge soil nitrogen. To understand how mixtures optimize these services, it is important to understand how best to combine species to target a specific service. Therefore we conducted an experiment at two locations for two years to assess how sown proportions and initial state conditions influence cover crop mixture composition, the total above ground biomass, nitrogen content, and the extent to which nitrogen fixed from the legume transfers nitrogen to the grass. Cover crop biomass tended to be higher in mixture or similar to the greatest yielding monoculture. Nitrogen content was maximized in the cover crop when 50% of the cover crop was composed of the legume. This work provides a decision framework for farmers when considering how to combine grass and legume cover crops and how management and initial soil fertility levels can influence cover crop composition.

Technical Abstract: The performance and suitability of a legume-grass cover crop mixture for specific functions may be influenced by the proportions of each species in the mixture. The objectives of this study were to: 1) evaluate aboveground biomass and species biomass proportions at different hairy vetch (Vicia villosa Roth.):cereal rye (Secale cereale L.) sown proportions, 2) characterize aboveground N content and biologically fixed N across a gradient of hairy vetch:cereal rye biomass proportions, and 3) quantify the transfer of biologically fixed N from hairy vetch to associated cereal rye. A gradient of six sown proportions ranging from 100% hairy vetch to 100% cereal rye was drilled in fall 2011 and 2012 at two sites in Beltsville, MD. The following spring, the cover crops were sampled, separated by species, dried, ground, and analyzed for N concentration and biologically fixed N. In three of four site-years, cereal rye was the dominant species in mixtures, and biomass levels were similar between the cereal rye monocultures and mixtures. Nitrogen content increased from 63 to 180 kg ha-1 as hairy vetch biomass in mixture increased, and was estimated to plateau when hairy vetch reached approximately 50% of the total biomass. Biologically fixed N made up 69-97%, and 19-81% of hairy vetch N in mixture and monoculture, respectively. We found no evidence that hairy vetch biologically fixed N was transferred to cereal rye. While a wide range of sown proportions produced > 8 Mg ha-1 biomass, maximum N content was most reliably achieved with a hairy vetch:cereal rye seeding rate of 27 kg ha-1:34 kg ha-1.