While there are many known benefits of adding cover crops to your crop rotation, species selection, seeding method and timing, and termination are not always straightforward. In the Northern U.S. especially, winter weather shortly after corn and soybean harvest limits the ability of most cover crop species to establish, and farmers are often left with few options to include a cover crop.
One potential solution to this problem is to interseed cover crops early in the corn growth stage, allowing for the cover crops to establish prior to corn canopy closure, then take off in the fall as the corn senesces and is harvested. Still, many of the same questions arise when considering this practice, such as which species to interseed, when to interseed, and how to interseed (broadcast or drill)? Additionally, there is concern over whether or not cover crops will compete with corn and if herbicides with residual activity can be used when planning to interseed a cover crop. A recent research project conducted at Michigan State University (MSU) aimed to answer some of these questions.
Dr. Aaron Brooker, SHP Research Fellow and recent graduate of the Department of Plant, Soil and Microbial Sciences at MSU, conducted this research in collaboration with other MSU scientists and farmers throughout the state of Michigan. The goals of this research were to determine cover crop species and interseeding timings that would establish in corn, cover crop seeding rates that would not be competitive with corn, preemergence (PRE) and postemergence (POST) the soil health benefits of interseeding cover crops, and if remote sensing can be used to detect cover crops and corn health in an interseeded system.
The research evaluated broadcast interseeding of three cover crop species: annual ryegrass, oilseed radish, and crimson clover. Maximum seeding rates evaluated for each species were 30, 20, and 40 lb/acre, respectively; additionally, half and quarter rates were used. The V1-V7 corn growth stages were evaluated for interseeding timings. Nearly every PRE and POST herbicide option in corn in Michigan was evaluated for use with interseeded cover crops. Additionally, the soil health and nitrogen cycling effects of interseeding cover crops were determined. Finally, remote sensing was used to detect cover crop establishment and corn health throughout the season.
Below is a summary of the results:
- Annual ryegrass and oilseed radish were the most successful species, while crimson clover was successful when there was average or above average rainfall.
- Cover crops can be broadcast interseeded at the V1-V7 corn growth stages without competing with corn, but summer annual weeds must be controlled to prevent corn yield loss.
- Increasing seeding rates did not cause competition with corn, and the highest rates used in this experiment were beyond what farmers would spend to seed a cover crop. So, farmers should feel comfortable seeding at rates that are within their budgets.
- Cover crops can be interseeded following the application of a variety of PRE and POST herbicides. Herbicide selection should be based on weed control needs, and this may determine what cover crop species can be interseeded. Also, be aware of label restrictions for planting cover crops following the application of certain herbicides. Here is a factsheet for herbicide options.
- Annual ryegrass was the only species that overwintered, and reduced soil nitrate levels in the spring compared with the other two cover crops tested. This nitrogen could be available to the following crop depending on its release from the terminated cover crop.
- Other soil health indicators were not impacted by one year of interseeding; however, further research is being conducted to determine the effects of multiple years of interseeding on soil health.Remote sensing is a powerful tool that can be used to detect changes in corn health at a large scale. Remote sensing was able to detect cover crop emergence prior to corn canopy closure. Since cover crops did not affect corn grain yield, remote sensing did not detect differences in corn health.
These results were also discussed on the most recent Soil Session, titled: Interseeding Cover Crops in Corn.
