Ten-year study shows corn, soybean yields not affected by cover crops

Iowa Learning Farms, a hands-on education and outreach program for Iowa landowners and agricultural producers based at Iowa State University Extension and Outreach, and Practical Farmers of Iowa, a statewide organization working to equip farmers to build resilient farms and communities, have published the final results of their 10-year, field-scale study of the effects of winter rye cover crops on corn and soybean yields.

With consistent results across the full decade of recording and measurements, the final report notes no significant improvement or decline in cash crop yields attributable to the use of cover crops.

“The cooperating farmers in the study were asked to plant full field length contiguous strips with and without the cover crop to provide a valid comparison at field scale,” said Jaqueline Comito, director of Iowa Learning Farms. “While five farms stayed the course for the full 10 years, other participants saw enough value or improvement to convince them to plant cover crops in the entire field, thereby removing themselves from the study. It was a good problem to have and a testament to the value of cover crops, but it did reduce the number of data points in later years.”

The study included 39 site-years with corn crops and 31 site-years for soybean crops. All farms included in the study were using a corn-soybean rotation. In corn, three site-years showed yield increases and five saw reductions. With soybean, 10 site-years had improvements and two had yield reductions. Cooperating farmers indicated reductions were primarily attributed to planter settings that were adjusted to account for additional biomass for subsequent plantings.

“While the yields did not show significant changes, the cooperating farmers noted significant increases in biomass and reduced erosion and washouts in fields with cover crops,” said Stefan Gailans, PFI project lead. “Keeping the rich Iowa soil and nutrients in the fields not only helps maintain productivity on the farms, it also keeps it out of the state’s waterways, thereby contributing to improved water quality for all. PFI is pleased with the results of this study and eager to share the results and cover crop best practices with the farming community.”

The project was funded by the State Soil Conservation Committee, the Iowa Department of Agriculture and Land Stewardship and the Leopold Center for Sustainable Agriculture. The final report is available on the Iowa Learning Farms website at https://www.iowalearningfarms.org/files/page/files/winter_rye_effect_on_... and Practical Farmers of Iowa website at https://practicalfarmers.org/wp-content/uploads/2020/01/Winter_Rye_Effec....

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