Rye-Vetch Cover Crop Species Proportion and Polyethylene Mulch Affect Total Biomass Production, Soil Nitrate Accumulation and Bell Pepper Yield

The unique and often complementary traits of cereal and legume species make cover crop mixtures composed of these two functional groups 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.  In a study conducted on sandy soils in Michigan, a variation of the replacement series experimental design was used to investigate 1) how the relative composition (seeding rates) of a cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) cover crop mixture influenced biomass production and total residue quality, and 2) the interactive effects of residues of these cover crop mixtures and black polyethylene mulch (PM) on bell pepper (Capsicum annuum) performance and soil nitrate dynamics.  Cover crop main plot treatments consisted of a gradient of 7 rye:vetch mixture proportions from 100% rye (94 kg/ha) to 100% vetch (42 kg/ha), in addition to a no cover crop control.  Subplots consisted of bell pepper grown either with or without PM.  Soil nitrate levels were monitored through biweekly soil sampling during the growing season.  Although relative biomass yields of vetch in mixture varied greatly with year and planting date, total residue C:N generally decreased with increasing proportion of vetch. 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 yields were higher following cover crop mixtures with greater proportions of vetch.  However, total yields were uniformly higher for peppers grown on PM.  Our results suggest that PM may be an important tool for maximizing N fertility benefits from incorporated cover crop residues.  Although increasing the proportion of vetch (and the total amount of nitrogen) in the cover crop mixture generally benefitted pepper yields, 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.