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"Using Cover Crop Mixtures to Achieve Multiple Goals on the Farm" is the Topic of Free Webinar Recording

Posted: January 13, 2015

A team of Penn State researchers studying the agronomic, environmental, and economic benefits and trade-offs of using cover crop mixtures instead of monocultures in organic farming systems recently presented a webinar in which they described their project and shared some preliminary results. The webinar, sponsored by eOrganic and attended by more than 300 people nationwide, is now available online for public viewing.
The Cover Crop Cocktail research project is looking at how cover crop mixtures might help farmers achieve multiple goals. Their test plots at the Agronomy Research Farm are pictured here, circa July 2014.

The Cover Crop Cocktail research project is looking at how cover crop mixtures might help farmers achieve multiple goals. Their test plots at the Agronomy Research Farm are pictured here, circa July 2014.

[Watch the webinar here.]

Project Coordinator Jim LaChance kicked off the presentation with an explanation of the research project informally known as the Cover Crop Cocktails (CCC) project. The research team is testing four different cover crop mixtures against six monoculture species in a corn-soy-wheat crop rotation at its research station, while further on-farm testing is being carried out by three farmer collaborators around the state. The research team is assessing the performance of the cover crop mixtures on several different measures, and the webinar presenters focused on three of these: weed suppression and management, beneficial insect support, and nutrient cycling.

CCC rotation diagram

During the webinar, the researchers discussed the performance of ten different cover crop treatments planted between wheat and corn in a corn-soy-wheat rotation. They encountered difficulties establishing mixtures after corn silage and before soybean because the late-September planting date is too late for successful establishment of most legume and brassica species in the Central PA climate.

The six cover crop mixtures being tested are:

  • red clover + rye + pea
  • radish + rye + oat
  • red clover + rye + oat
  • red clover + canola + rye + pea
  • canola + radish + rye + pea
  • red clover + canola + radish + rye + oat + pea

The four monoculture species being tested are:

  • red clover
  • canola
  • radish
  • rye
  • oat
  • pea

For more detailed information about seeding rates, check out the project's seeding chart (PDF).

Mitchell Hunter, a doctoral candidate in agronomy, discussed the weed management goals that can be addressed using cover crops, including preventing weeds from setting seeds, overcoming weeds so that cover crop benefits are achieved, and drawing down the weed seed bank. He also described how the team measured the weed-suppression performance of the different cover crop mixtures included in the study.

Hunter and his colleagues found that all the mixtures trialed were as effective at weed suppression as the best-performing monoculture cover crops. The strongest predictor of successful spring weed suppression was good fall coverage, which underscores a valuable lesson that emerged from the team’s results: for best weed suppression, choose one or two cover crop species that provide fast ground cover in the fall, and then add species from there to achieve other goals.

Jermaine Hinds, a doctoral candidate in entomology, discussed the economic value of the pollination and pest-suppression services provided by beneficial insects, and explained several ways that cover crop mixtures can influence the status and composition of beneficial insect populations. Hinds also shared some results from research on the number of wild bee visits to the cover crop plots in the study. The researchers found that the plots planted to a monoculture of canola attracted the most bee visits, indicating that floral density is quite important in attracting pollinators. Therefore, to support beneficial insects for pollination or biological control, growers should manage mixtures to include flowers when possible. Hinds also suggested that if including flowering cover crops is not compatible with farm goals, planting insectary strips — strips of flowering plants between cash-crop fields — can be a useful alternative.

Sustainable Agriculture Extension Associate Charlie White explained how the characteristics of the individual species used in a cover crop mixture — like winter hardiness and method of N acquisition — can influence the nitrogen management performance of that mixture. As part of the CCC project, White and his colleagues compared the efficacy of the cover crop mixtures and monocultures at preventing nitrate leaching and at supplying N to the subsequent cash crop. They found that the cover crop mixtures that were most effective at preventing N leaching all contained either a winter-hardy grass or brassica, while legumes (especially slow-growing clover) and winter-killed cover crops were less effective at preventing leaching. On the other hand, the cover crop species that were most effective at supplying N to the subsequent cash crop — primarily the monocultures of pea, radish, and clover — tended to allow more leaching. These results suggest that cover crop mixtures are an acceptable compromise, as they were moderately effective at both preventing leaching and at providing N for subsequent crops, said White. Therefore, the team recommends combining a well-adapted legume with a low seeding rate of a winter hardy grass or brassica to balance nitrogen retention and supply.

The team concluded that cover crop mixtures can help growers achieve multiple goals, and recommended that growers develop a plan that considers the cover crop functions that are most important to them, in addition to a planting schedule that is compatible with their cash crop plantings. They suggested aiming for balanced biomass from all species in the mix in order to benefit from a range of functions. However, because grasses like rye tend to have greater biomass and higher C:N ratios than other cover crop species, the researchers cautioned against allowing grasses to become dominant. When tilled under, their large quantities of residue can interfere with the creation of a seed furrow, thus creating difficulties in subsequent cash-crop establishment. Further, grasses can also suppress cash-crop yields since they tie up N while decomposing. Growers can prevent these problems by incorporating grasses into their mixture at a lower seeding rate, and by terminating the cover crop earlier, when its C:N ratio is lower.

Guidelines for Using Cover Crop Mixtures:

  • Weeds: Include one or two species that provide fast ground-cover in the fall, then add species to achieve other goals.
  • Insects: To support beneficial insects for pollination or biological control, manage mixtures to include flowers.
  • Nitrogen: Combine a well-adapted legume with a low seeding rate of a winter-hardy grass or brassica.
  • Overall: Aim for balanced biomass from all species in the mix to benefit from a range of functions.

At the webinar’s conclusion, the presenters were joined by other project team members, including Professor of Entomology Mary Barbercheck, Associate Professor of Soil Biogeochemistry Jason Kaye, and Professor of Weed and Applied Plant Ecology Dave Mortensen, to field audience questions. The 27-minute question-and-answer session is included in the archived webinar recording available here.

The CCC project is funded by USDA Organic Agriculture Research and Extension Initiative. More information about the project, including a link to subscribe to the project’s newsletter, is available at:
http://agsci.psu.edu/organic/research-and-extension/cover-crop-cocktails.

The webinar was hosted by eOrganic, the organic community of practice at eXtension.org, an Internet-based collaborative environment where Land Grant University content providers exchange objective, research-based knowledge.