In a 2013 on-farm trial, we evaluated cover crop species for their ability to germinate and grow when overseeded in late summer into a corn crop. Here are the main conclusions:
- There are many cover crop species that will germinate well when overseeded into standing corn in the Columbia Basin. However, most do not do well when shaded more than 2-3 weeks.
- Planting 2-3 weeks before harvest may improve plant survival, although crushing by harvest equipment can then become a problem. This is in agreement with Midwest recommendations to plant 2-3 weeks before silage harvest, or for grain harvest, when corn plant is dried to the ear. However, in contrast to the Midwest, we generally field dry grain corn, and so following the latter timing would allow very little growing time for cover crops after grain harvest. This makes overseeding cover crops into corn being harvested for dry grain impractical.
- The short growing season after corn harvest, even after earlier harvested high moisture corn, probably rules out using warm season and slower growing species, like legumes, as overseeded cover crops, unless they can overwinter AND are allowed to grow to at least early May the following year.