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Cover Crop Termination and Relay Crop Trials 2020

Article cover photo
Research is underway to determine when to terminate rye cover crops when planting soybeans early. (Photo: Joseph L. Murphy/Iowa Soybean Association)

By Theo Gunther, ISA Research Center for Farming Innovation conservationist

The trend of planting soybeans early has generated questions about management of cover crops with soybeans.

Research, experience, and well-placed intuition tell us that to gain the greatest water quality and soil benefits from cover crop they need to have an opportunity to grow. Early planting of soybeans, while easily done into green rye, raises questions about when to terminate the rye. Does waiting and letting the rye grow while soybeans emerge influence emergence, soybean development, and ultimately final yield?

Several cooperating farmers are executing delayed cover crop termination comparisons with at-planting termination and termination up to ~V1 growth stage. This will provide several weeks of additional growth of cover crops. Experienced cover crop farmers don’t see a detrimental yield effect. Replicated comparisons will inform this in more detail. 2019 on-farm research in Iowa was done by Practical Farmers of Iowa (PFI) farmer cooperators and will be repeated this year at both Iowa Soybean Association (ISA) and PFI trial sites. With a late and widespread frost last week and with soybeans in the ground, it will be interesting to see whether the rye canopy can provide any additional buffer against a cold night sky.

Beyond delayed termination, how about not terminating and harvesting the small grain with soybeans growing in the canopy? Innovative farmers have used this technique in wheat growing regions in the US where double crop soybeans are not consistent. These trials will compare a sole crop soybean crop with soybeans planted into a small grain, the soybeans grow together in the small grain canopy until harvest mid-summer. The soybeans are then released and grow the remainder of the season until harvest in the fall.

Most of the Iowa farmers doing this are seeking to generate their own supply of cover crop seed. These side by side trial comparisons are seeking to build on reports by farmers in the state using this method and achieving ~80% or more of their historic field average soybean yields while generating a second crop of small grains.

Replicated trials should help answer the larger questions about soybean yield tradeoff and economics of using these methods. Seven sites are in place to execute this comparison this season. These trials are being done in partnership with Northeast Iowa Resource Conservation and Development and partially with funds from the Leopold Center/Iowa Nutrient Research Center. This method had great potential to achieve the water quality and soil quality benefits of small grains while still producing soybeans in the same growing season. Look for updates on social media about these trials when we start to get “1000-word pictures” later this spring and summer at these handles @multiIowa; @practicalfarmer; and @iowasoybeans.  Call or email with any questions or thoughts 563-260-9017 or

For media inquiries, permission to republish articles or to request high-res photos, please contact Katie James, ISA Public Relations Manager at © 2020 Iowa Soybean Association. All rights reserved.