An option for getting an earlier establishment on fall-seeded cover crops is to overseed. This practice requires using a helicopter, airplane or ground rig with high clearance to apply seed over the top of soybeans or corn before harvest.
"Overseeding will allow the cover crop seed more time to become established rather than waiting until after grain harvest," says Alan Sundermeier, a Wood County, Ohio, extension specialist. "However, the risk with this method is that seed-to-soil contact is more difficult and seed may not germinate until after a significant rainfall."
The most adaptable cover crop to use with overseeding is cereal rye, Sundermeier says. It has a denser seed with more weight: therefore, a higher percentage of the seed will fall through crop canopy to make soil contact compared to a lighter seed like annual ryegrass.
Spreading patterns with cereal rye when using aerial application will also be more accurate.
"Overseeding into soybeans or corn should be completed before leaves drop," Sundermeier says. "When leaves yellow and begin to droop down. that's a good time to overseed. Seed will more easily reach the soil and be covered with the dead leaves, which will help retain moisture and aid in germination."
Sundermeier says cereal rye will continue to grow throughout the fall even as temperatures drop into the 40’s. The growth will add organic matter to the soil, help correct soil compaction and could be grazed or harvested for forage in early winter or the following spring.
Oats may also be overseeded, Sundermeier adds. It's best suited for southern Ohio after mid-September application to give enough time before a killing frost. Overseeding oats into corn will provide an excellent grazing option in late fall corn stalks.
The researcher says that overseeding Austrian winter peas into soybeans is a practice that he continues to research. Since winter pea is a larger seed, it needs to be placed into the soil versus a surface seeding.
"Soil heaving through the winter may also damage a winter pea stand that is surface seeded," Sundermeier says. "To improve success, wait until after a significant rainfall and aerial-apply winter peas. The seed may then penetrate the soil enough to improve germination."