By Alan Kraus, Conservation Program Manager, Cannon River Watershed Partnership

Many agronomists and farmers agree that planting cover crops to keep farm fields covered with vegetation during the fall, winter, and spring can prevent soil erosion and keep soil and fertilizers from washing into area rivers and lakes. A concern, however, for farmers can be that a cover crop might compete with a corn crop and reduce the yield. The Cannon River Watershed Partnership (CRWP) just completed a two-year study in cooperation with eight farmers in Rice, Goodhue, and Waseca Counties to examine methods of interseeding cover crops into standing corn early in the growing season and the impact on corn yields. Those farmers were pleased to find that rather than seeing a yield reduction in interseeded cover crop fields, they actually found an average 1.3 bushel/acre yield increase compared to control areas.

Most often, farmers who use cover crops to protect their soil and capture excess fertilizer, plant them after they harvest corn in the fall. But with Minnesota’s short growing season, sometimes fall-planted cover crops don’t establish well. Interseeding a cover crop earlier in the season into standing corn can give that cover crop a chance to grow and fully cover the soil at the time of year when the soil is most susceptible to erosion and nutrient leaching.

The results, on average, showed a 1.3 bushel/acre increase in areas of the fields that were planted with cover crops compared to control areas (with no cover crops). These results were gathered at the field level and although the study did not determine the statistical significance of the results, the farmers were pleased to see this outcome. While weather, herbicide carryover, and planting equipment were found to be key factors affecting success, 7 out of the 8 participating farmers stated they will continue to plant cover crops on their farms using the interseeding method. All of the 8 farmers stated they will continue to plant cover crops by some method.

Want to try this on your farm?

  • The earlier you plant a cover crop, the better – corn may grow rapidly or wet soils may persist and then you can lose the opportunity to interseed.
  • Drilled planting is the best method to establish a cover crop – it achieves good seed to soil contact necessary for seeds to germinate quickly.
  • Air seeding with direct row placement and shallow incorporation of the cover crop seed also works well.
  • Interseed annual ryegrass – it germinates quickly and maintains vigor for fall regrowth after corn harvest.
  • Do not broadcast seed annual ryegrass – the seed has very little weight; wind and rain can blow or wash seeds away.
  • Do not interseed cereal rye – the seed germinates and then loses vigor under the corn canopy and is unable to regrow after corn harvest.
  • Plan the cover crop seeding as thoroughly as you plan the corn planting – it takes planning and management to be successful.
  • Plan the herbicide application in advance to include the cover crop planting at V4-V7 corn growth stage.
  • Start with single species cover crop – drilled in annual ryegrass.
  • Gain experience and then add more species of cover crops to the mix. Experience has shown that the more plant species a farmer uses in a cover crop mix, the more effective the cover crop is at protecting the soil and capturing excess fertilizer in a wide range of growing conditions.

The Minnesota Department of Agriculture and the McKnight Foundation funded this study. For more information about using cover crops in southern Minnesota, contact your county Soil and Water Conservation District, or contact CRWP at