Abstract
Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) monocultures and mixtures in the maritime Pacific Northwest USA. The study included four seed mixtures (100% hairy vetch, 25% rye-75% hairy vetch, 50% rye-50% hairy vetch, and 100% rye by seed weight), two planting dates, and two termination dates, using a split-split plot design with four replications over six years. Measurements included winter ground cover; stand composition; cover crop biomass, N concentration, and N uptake; and June soil NO3 --N. Rye planted in mid-September and terminated in late April averaged 5.1 Mg ha-1 biomass, whereas mixtures averaged 4.1 Mg ha-1 and hairy vetch 2.3 Mg ha-1. Delaying planting by 2.5 weeks reduced average winter ground cover by 65%, biomass by 50%, and cover crop N accumulation by 40%. Similar reductions in biomass and N accumulation occurred for late March termination, compared with late April termination. Mixtures had less annual biomass variability than rye. Mixtures accumulated 103 kg ha-1 N and had mean C:N ratio <17:1 when planted in mid-September and terminated in late April. June soil NO3 --N (0 to 30 cm depth) averaged 62 kg ha-1 for rye, 97 kg ha-1 for the mixtures, and 119 kg ha-1 for hairy vetch. Weeds comprised less of the mixtures biomass (20% weeds by weight at termination) compared with the monocultures (29%). Cover crop mixtures provided a balance between biomass accumulation and N concentration, more consistent biomass over the six-year study, and were more effective at reducing winter weeds compared with monocultures.
Highlights
Farmers have renewed interest in cover crops that have been shown to improve nitrogen (N) management, enhance crop productivity, suppress weeds, reduce erosion, and improve soil and water quality
This study explores seeding ratio and planting and termination date effects on rye-hairy vetch cover crops planted after fall harvest
Research questions include: 1) How does planting and termination timing affect cover crop production and characteristics, including ground cover, species composition, biomass, N accumulation, and C:N ratio? 2) How do ryehairy vetch mixtures compare with monoculture rye and hairy vetch plantings for cover crop production and characteristics across planting and termination dates? 3) How much do cover crop biomass and characteristics vary from year to year, and what are the likely causes of this variability?
Summary
Farmers have renewed interest in cover crops that have been shown to improve nitrogen (N) management, enhance crop productivity, suppress weeds, reduce erosion, and improve soil and water quality. Studies in the eastern USA showed an increase in monoculture hairy vetch biomass of 35 to 61% by delaying the termination date 2 wk from late April to early-mid May, [16,17]. Rye-hairy vetch winter cover crops were evaluated over six years for their ability to provide winter ground cover, produce biomass, accumulate N, suppress winter weeds, and increase plant available N in soil. This study explores seeding ratio and planting and termination date effects on rye-hairy vetch cover crops planted after fall harvest. Research questions include: 1) How does planting and termination timing affect cover crop production and characteristics, including ground cover, species composition, biomass, N accumulation, and C:N ratio? Research questions include: 1) How does planting and termination timing affect cover crop production and characteristics, including ground cover, species composition, biomass, N accumulation, and C:N ratio? 2) How do ryehairy vetch mixtures compare with monoculture rye and hairy vetch plantings for cover crop production and characteristics across planting and termination dates? 3) How much do cover crop biomass and characteristics vary from year to year, and what are the likely causes of this variability?
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