A novel approach for optimizing the benefits of cereal-­legume cover crop mixtures in vegetable cropping systems under organic management

Graduate Student Final Report – Ceres Trust Research Grant

Graduate Student: Zachary D. Hayden

Major Professor and Collaborator:  Dr. Mathieu Ngouajio and Dr. Daniel C. Brainard, Michigan State University Department of Horticulture

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The unique and complementary traits of cereal rye (Secale cereale L.) and the legume hairy vetch (Vicia villosa Roth) make winter annual cover crop mixtures of the two species promising for vegetable cropping systems. Informed management of the relative species proportions in the mixture could provide an important means of optimizing performance to serve various farmer goals. A variation of the replacement series experimental design was used to investigate 1) how relative species proportions (seeding rates) influence biomass characteristics of cover crop mixtures, and 2) the interactive effects of mixture residues and the use of black polyethylene mulch (PM) on cover crop mixture performance in bell pepper and slicing cucumber cropping systems. Although relative biomass yields of vetch in mixture can vary greatly with planting date, total residue C:N generally decreased with increasing proportion of vetch. All cover crop mixtures

provided significant winter weed suppression, but incorporated residues exhibited little effect on subsequent summer weed communities. Cover crop mixtures with higher proportions of vetch generally resulted in higher soil nitrate concentrations during the growing season, but both the magnitude and duration of the increases in soil nitrate following cover crop incorporation were greater under PM than without. In general, total bell pepper and cucumber yields were higher following cover crop mixtures with greater proportions of vetch. However, total yields were uniformly higher for vegetables grown on PM. Our results suggest that PM may be an important tool for maximizing N fertility benefits from incorporated cover crop residues, but evaluations of overall mixture performance must ultimately be based on a systems level consideration of the numerous services that cover crops can provide, as well as their relative costs.