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Cover crops growing with a sunflower crop. (Abbey Wick/Special to Agweek)

Soil Health Minute: Cover crops with sunflower

Farmers are working on fitting cover crops into every phase of their rotation to achieve multiple goals. One practice, which is of interest but is not well evaluated, is growing cover crops along with sunflower. In this case, cover crops could provide the following benefits:

• Flowering throughout the growing season to attract beneficial insects and possibly reduce insecticide applications.

• Diverse root structures to build soil health properties.

• Competition with weeds in a crop where herbicide options are limited.

As farmers try this approach on test strips, we are helping to evaluate the practice. This year, we are working with farmers in southeastern North Dakota to learn more about how planting a cover crop mix at the same time as sunflower can help and/or hurt the system. We're not sure what will happen, so we will follow the data.

On two separate farms, we have a total of four fields with three replicates of (1) cover crop and (2) non-cover crop. Pre-emerge herbicides were applied to all fields. Sunflower were seeded on 30-inch row spacing and cover crops were seeded right after the sunflower on 7.5-inch spacing with a drill. The cover crop mix included buckwheat, crimson clover, flax, oats, winter peas and yellow mustard. This mix costs around $18 per acre and was seeded at a 24-pound-per-acre rate. We are taking cover crop and soil measurements throughout the growing season and will assess yield at harvest.

How did we select the cover crop species? We were looking to achieve the above three goals of flowering to attract beneficial insects, diverse roots and competition with weeds — we selected cover crops accordingly. We also considered the comfort level of the farmers with the different cover crops and their next crop in rotation on these fields.

The Sustainable Agriculture Research and Education program has a publication titled: Cover Cropping for Pollinators and Beneficial Insects (www.SARE.org). In this publication, buckwheat and mustard receive high ratings for value to honey bees, wild bees and natural enemies of crop pests. Crimson clover and flax have moderate to high ratings while oats and winter peas have low ratings for these categories. We chose species effective for pollinators and beneficial insects along with species that provide a function for the soil like fixing nitrogen (crimson clover, winter peas), increasing phosphorus availability (buckwheat and flax) and fibrous root systems for improving aggregation (oats). The sunflower crop also provides deep tap roots that benefit soil function. Weed suppression occurs by having the cover crops growing and filling spaces where weeds could grow.

Incorporating cover crops based on goals and selecting species around function is a great way to use cover crops in rotation. Though we don't have many answers now, we will continue to evaluate this approach and post findings on the NDSU Soil Health webpage: ndsu.edu/soilhealth. You can also get information by following us on Twitter: @NDSUsoilhealth and @ckgasch.

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