Corn growers are looking between the rows for ways to incorporate cover crops into their traditional crop rotations. Interseeding cover crops between those rows is drawing more interest and has innovators exploring this unique production practice.

“An increasing number of growers are integrating cover crops into their cropping systems with goals of reducing erosion, increasing soil health, adding or capturing nitrogen, providing livestock grazing or suppressing weed growth,” says University of
Nebraska extension educator Jenny Rees.

Rees says planting cover crops after corn or soybean harvest has had mixed results, so there’s interest in interseeding into those crops before canopy closure. “The hope is the cover may produce more biomass after harvest since it’s already established.  Studies have shown minimal impact on corn yield if interseeding occurs during the V5-V7 growth stages.”

Farmers are trying various methods of interseeding including aerial and broadcast seeding, commercial and homebuilt interseeding units, sidedress and cultivator adaptations and even planters and grain drills.

“Generally, methods that provide good seed-to-soil contact have been most reliable in establishing good cover crop stands,” says Dean Krull, technician with Nebraska’s Central Platte Natural Resources District.

Henderson, Nebraska, farmer Jay Goertzen used row units borrowed from a grain drill to seed a pair of 12-inch spaced cover crop rows between his 36-inch corn rows. “We mounted the units on a 12-row toolbar and delivered seed with an air system. We planted two seed mixtures that included sweet and red clover, rapeseed, turnips, annual rye, and several other species. They got very spindly in the shade, but still provided a mat about six inches thick,” says Goertzen.

The dilemma. The biggest challenge to interseeding is to maximize cover crop biomass without damaging corn yields. Farmers and researchers are trying to do that by interseeding earlier and by using wider corn rows that let sunlight into the canopy.

Western Illinois University researchers Joel Gruver and Andy Clayton are testing various corn row spacings as a possible solution. So far they’ve found planting corn in 60-inch rows provides a five to tenfold increase in cover crop biomass, but has also reduced corn yields by 20%.

“We think we can close that yield gap by selecting more suitable corn hybrids and by manipulating row spacings. We’re testing ideas like skipping every third or fourth 30-inch row to leave a 60-inch gap for cover crops. This may maintain grain yield while providing the increased grazing and soil health benefits from more cover crop growth,” says Gruver.

He is also testing a forage soybean as the cover crop in that blank row. “We think these could be planted at the same time as the corn so they’ll have a full season to fix nitrogen, yet won’t produce seed in our area. To interseed, all you’ll do is change planter plates on a few rows,” he says.

Clayton says the initial approach of interseeding into 30-inch rows has also shown promise. “In our first year, there was no yield loss from interseeding at corn’s V4 stage, and last year there was a 8.6 bushel yield increase,” (See more results at www.wiu.edu/cbt/agriculture/farms/organic/).

Beat the weeds. Interseeding plays a role in Cody Nelson’s soil health consulting efforts. “My clients interseed into 22, 30, 44 and 60-inch rows, and have found interseeding early is important, especially in the narrower rows. The cover crop could even be seeded with a grain drill just as the corn is emerging,” says Nelson, whose SoilRX company (www.soilrx.net) is located in Belview, Minnesota.

“We like the wider rows because species like rye—which dies out in the shade of narrower rows—survives so we can plant soybeans into the green seedbed. We’ve rarely seen a yield difference for 60-inch rows, and any shortfall  is more than offset by the weed suppression and other benefits with more cover crop growth,” he adds.

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