- Agronomic: rye, grass (misc. perennial), hay
- Vegetables: cucurbits, peppers
- Animal Production: feed/forage
- Crop Production: cover crops, nutrient cycling, tissue analysis
- Education and Training: demonstration, display
- Pest Management: allelopathy, mulches - killed, mulching - plastic, physical control, weed ecology
- Production Systems: transitioning to organic
- Soil Management: green manures, nutrient mineralization, soil analysis, soil microbiology
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 composition (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, based on a systems-level investigation of agro-ecological services that cover crops can provide. Results show that cover crop mixture proportion and the use of PM affect weed communities, soil chemical and biological characteristics, and crop productivity.
Multi-species cover crop mixtures can provide a means of combining the strengths of different plant functional groups in a single field while also moderating their individual weaknesses. Cereal-legume cover crop mixtures are of particular interest because they provide the opportunity to effectively suppress weeds, control erosion, and scavenge leachable nitrate while also fixing atmospheric nitrogen.
Winter annual cover crop mixtures of cereal rye (Secale cereale L.) and the legume hairy vetch (Vicia villosa Roth) have shown promise in previous studies, and their winter hardiness makes them well suited for production in the North Central region. Alone, the notable ability of rye to suppress weeds, scavenge residual nitrate, and control erosion is often tempered by the high C:N ratio of its residues and the threat of subsequent yield losses due to nitrogen immobilization (Allison 1966, Wagger et al, 1998). Rye-vetch mixtures, however, have exhibited moderation of the total C:N ratio of residues without sacrificing benefits characteristic of rye, all while contributing significant amounts of fixed nitrogen to the system (Clark et al., 2007a, 2007b, 2007c; Ranells and Wagger, 1996, 1997a, 1997b; Teasdale and Abdul-Baki, 1998). In addition, total dry matter yields in rye-vetch mixtures can be greater than yields of either species in monoculture, and total N release from mixture residues can approach the amount released from vetch monocultures (Rannells and Wagger, 1996).
The performance of any 2-species cover crop mixture with respect to traits of interest (e.g. total biomass production and residue quality, weed suppression, nitrogen recycling and mineralization dynamics, and yields of subsequent crops) will theoretically vary along a continuum from 100% species A to 100% species B. For certain environmental conditions and farmer goals, an optimum mixture rate should exist somewhere between the two extremes, where the respective strengths of each species are balanced to provide maximum benefit. Few studies to date (Clark et al, 1994) have evaluated rye-vetch cover crops based on more than a single mixture proportion, and more thorough research on the relationship between mixture proportion and cover crop performance could ultimately lead to more-informed seeding rate recommendations that consider growing conditions, farmer goals, and crop management practices.
The replacement series is an experimental design where treatments consist of a pure stand of each component species and a gradient of species mixtures, allowing the researcher to observe how species proportions influence interspecific competition and mixture performance. The design has been applied in agricultural contexts most often to evaluate crop-weed interactions and the performance of cash crop bicultures, but with appropriate interpretation, the design is also suited for investigating cover crop mixtures (Jolliffee, 2000).
Furthermore, the use of black polyethylene mulch (PM) is an industry standard for large-scale commercial organic and conventional production of bell peppers and slicing cucumbers. By distinctly altering the soil microclimate through increasing soil temperatures and alteration of soil moisture dynamics, PM may have a substantial effect on the relative performance of cover crop mixtures, particularly with respect to nutrient mineralization and leaching (Clarkson et al, 1960; Tarara, 2000). Because many smaller scale organic growers reject the use of PM based on economic and environmental grounds related to its use and disposal, results for cover crop performance derived under both management practices can provide for broader applicability across the spectrum of vegetable producers.
The overall objective of this study was to improve our understanding of how species proportions (based on seeding rates) of a mixture of cereal rye and hairy vetch influence cover crop performance in a vegetable production system with respect to crop grown and plastic mulch use. Performance was evaluated based on a systems-level approach to data collection, encompassing the following specific objectives:
- Quantify trends in cover crop establishment and total residue quantity and quality across rye-vetch mixture rates.
Study the effect of mixture rate on winter annual and summer annual weed populations.
Quantify trends in soil inorganic N dynamics across mixture treatments and PM use.
Evaluate the effects of mixture rate and PM use on soil microbial biomass and community functional diversity.
Evaluate the effects of mixture rate and PM use on vegetable yield and fruit quality.