Daniel H. Smith, Nutrient and Pest Management Program, Matt Ruark, Soil Science Extension Specialist, Department of Soil Science, University of Wisconsin-Madison
Cover crop establishment
Cover crop establishment following wheat, silage corn, and canning crops can be relatively easy. Corn and soybean production practices allow for a short window for cover crop establishment in the fall and this may not be enough time for some cover crop species to establish and provide agronomic benefits. Corn and soybean growers interested in using cover crops following corn and soybean crops may look to interseeding to establish a cover crop earlier in the season. Interseeding is defined as planting a cover crop during the vegetative growth stage of a crop, whereas overseeding typically occurs near harvest.
Goal of Cover Crop
A goal is needed to achieve maximum cover crop success. Cover crop species often have common benefits but each species may contribute more of one benefit over another. Several cover crop goals include reducing soil erosion, scavenging for nutrients, nitrogen source, forage quality, or winter kill. It is also important to consider interseeding cover crops a long-term strategy for soil improvement. One year of interseeding will have little effect on soil health. It is the long-term and continual use of cover crops that lead to improvements in the soil condition.
Cover Crop Species
Wisconsin research has demonstrated red clover interseeded into V5 growth stage corn successfully the past three years with no significant difference in grain yield when compared to a non-interseeded plot. Red clover was seeded with a modified no-till drill at university recommended rates and depths. Many cover crop species may work in an interseeding system, however, experimentation in any unproven species may result in reduction in yield, future cover crop management issues, and lack of desired cover crop performance.
The herbicides previously applied on the desired field for interseeding may dictate whether interseeding is possible or not. In general, residual herbicides may reduce cover crop growth. Interseeding and using residual herbicides is not impossible but is challenging. Herbicide resistant weed management should be considered when planning herbicide applications. The field should be weed free prior to interseeding. The cost of herbicide program, cover crop benefits, and resistance management should all be considered. More information on cover crop interseeding and herbicides is available through Penn State Extension: http://extension.psu.edu/plants/crops/soil-management/cover-crops/interseeder-applicator/improving-the-success-of-interseeding-cover-crops-in-corn
For crop insurance purposes, overseeding and interseeding are defined as planting one or more cover crop species into an existing crop. If the cover crop and insured grain crop are established in such a way that separate agronomic practices and management cannot occur, then the cash crop is not insurable. Overseeding and interseeding a conservation cover crop does not affect the insurability of the grain crop as long as the cover crop is established in a way that does not affect harvest and yield of the cash crop. Any damage or yield loss to the grain crop caused by interseeding or overseeding a cover crop will not be covered by crop insurance and will be applied to appraised value of cash crop, thus reducing any insurance indemnity that may be paid. Finally, note that for crop insurance purposes, interplanting is defined as planting multiple species that are grown together with no distinct row pattern and in this case, separate agronomic practices are not possible and so the grain crop is not insurable. Always talk with your crop insurance agent before interseeding any cover crops.
Recent Wisconsin research has focused on interseeding using a modified no-till drill. However, there are many ways of interseeding cover crops. Cover crops can be interseeded using specialized commercially made equipment commercially, fertilizer spinner, or an air spreader. Larger growers have relied on overseeding cover crops in late summer via aerial applications or using specialized high clearance seeding equipment that often mounts onto a high clearance sprayer. Cover crop seeding rate, soil moisture levels, and environmental conditions should be considered prior to seeding the cover crop with a cash crop. Cover crop seeding rate can be reduced when drilling a cover crop vs. overseeding.
Cover Crops for Forage Use
A crop is classified as a cover crop when no biomass is harvested. A cover crop becomes a forage crop when biomass is harvested for feed. A cover crop can be used for forage, however, most pesticide labels do not provide the plant back restriction time required from pesticide application to grazing or harvest for cover crops, only forage crops. If a cover crop will be planted later this cropping season, consider the rotational restrictions for any herbicides used in the field the past few seasons
For more information on Wisconsin cover crop interseeding research:
For more information on cover crops and cover crop species selection: