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Effects of Cover Crop in Sunflower

Monday, February 5, 2018
filed under: Rotation

This photo, taken on July 28, shows some of the cover crop species (buckwheat, oats, flax, peas and yellow mustard) interseeded in one of grower Doug Toussaint's 2017 souithern Red River Valley sunflower fields.

Grower experience to date affirms that cover crops and sunflower can co-exist quite well. But does interseeding a cover crop with one’s sunflower actually result in a quantifiable impact, positive or negative, on the final yield and oil quality of the sunflower crop? That’s among the questions being studied by North Dakota State University soil scientists Abbey Wick and Caley Gasch. Wick is NDSU assistant professor of soil health-extension, and Gash is assistant professor of soil health-research.
In 2017, Wick and Gasch cooperated with Richland County, N.D., producer Doug Toussaint* in attempting to provide some answers to the above question. In establishing their study, they foresaw three potential benefits from a cover crop/sunflower crop interseeding:

Plant flowering would occur across the growing season, thus helping attract beneficial insects and possibly reduce insecticide applications.
The diverse plant root structures throughout the field would help build soil health properties.
Competition with weeds from the cover crop would aid a cash crop (sunflower) whose herbicide treatment options are limited.

The NDSU researchers focused on three Toussaint fields, planting three replicates of (1) cover crop and (2) no-cover crop in each field. Pre-emerge herbicides were applied to all fields. Sunflower was planted on 30” row spacing, and the cover crop mix was seeded immediately afterward with a drill on 7.5” spacing.
The cover crop mix consisted of buckwheat, crimson clover, flax, oats, winter peas and yellow mustard. “This mix cost around $18 per acre and was seeded at a 24-lb/ac rate,” Wick and Gasch note. Why that particular mix? “We were looking to achieve the above three goals of flowering to attract beneficial insects, diverse roots and competition with weeds, [and] we selected cover crops accordingly,” they explain, adding that they “also considered the comfort level of the farmers with the different cover crops and the next crop in rotation on those fields.”

NDSU soil health scientists Abbey Wick (left) and Caley Gasch are shown with Dough Toussaint in one of his southeastern North Dakota sunflower fields in late July 2017. Seven cover crop species were interseeded into the field.

      Wick and Gasch reference a publication of the Sustainable Agriculture Research and Education program (www.SARE.org) titled Cover Cropping for Pollinators and Beneficial Insects. “In this publication, buckwheat and mustard receive high ratings for value to honey bees, wild bees and natural enemies of crop pests,” they state. “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 taproots that benefit soil function. Weed suppression occurs by having the cover crops growing and filling spaces where weeds could grow.”
       As of early January 2018, Wick, Gasch and colleagues were still processing soils from the Richland County fields for aggregate stability (a soil quality/health measurement). They also had yet to process soil cores for root biomass measurements. Those two efforts will reveal whether there was a benefit to soil health properties from the 2017 crop crop/sunflower combination.
       As to the sunflower crop itself, there were no significant differences in yield or oil quality between the “cover crop” and “no-cover crop” portions of any of the three fields evaluated. “So, at the least, there was not a competition problem with the cover crops this year in the sunflower,” Gasch points out. “The remaining soil analyses will tell us if there was a soil health gain from them.”

* The sunflower production system of Doug Toussaint and his sons was profiled in an article titled ‘Red River Valley No-Till ’Flowers & Cover Crops’ in the January 2017 issue of The Sunflower.