Five-Year Cover Crop Mixtures Study: Significant Nitrate Reduction and Unchanged Crop Yields

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The results of a five-year study conducted by the Iowa Learning Farms, Iowa State University Extension and Outreach and Practical Farmers of Iowa, reinforced that cover crops added to a corn-soybean rotation have no negative effect on yield and result in statistically significant reductions in nitrate concentration in subsurface water. The details of the study are included in a brand new infographic now available for download.

Throughout the 22 site-years of yield data, there was no significant difference in cash crop yields between control strips without cover crops and those planted with cover crops. Is it important to note that planter settings may impact yield if not properly managed to accommodate residue from the cover crops.

yield results

Iowa soils are highly vulnerable to nitrate losses between April and June when natural nitrate production exceeds typical crop demands. The analysis of water samples from those three months, showed a statistically significant reduction in nitrate concentration in the cover crop strips.
nitrate reduction

We are really excited to see this significant reduction in nitrate concentration when cover crops are present, as addressing nitrate levels is a key component to reaching our Iowa Nutrient Reduction Strategy goals.

Project MapSince this project had locations located throughout the state, we were able to see how the different cover crop species performed in different soil regions and weather patterns. We observed consistent establishment and biomass production of the rye and oats at all sites and gained the largest reduction in nitrate concentration from those single species treatments. Rye and oats provided the most biomass and had the lowest cost of establishment, helping make them the top choice for cover crops in Iowa!

The infographic is available online at the ILF website. Funding for this study was provided by NRCS Conservation Innovation Grant and Leopold Center for Sustainable Agriculture.

-Liz Juchems