The first step when starting an interseeding program is to set goals.
“Start with what you are intending to accomplish by interseeding cover crops,” said Daniel Smith, University of Wisconsin Nutrient and Pest Management Program southwest Wisconsin regional specialist. “Some goals may include controlling weeds, scavenging for residual nitrogen, or holding the soil in place over the winter.”
Smith has been involved with interseeding cover crops since 2013, when he started doing experiments as a grad student. He spoke during a presentation at the Soil Heath Seminar Farmers and the Land: Cover Crops meeting, organized by the Winnebago-Boone Farm Bureau, Illinois Farm Bureau, Winnebago County Soil and Water Conservation District and the University of Illinois Extension — Winnebago, Stephenson and Jo-Daviess counties.
Farmers can use interseeding or overseeding to plant cover crops in their fields.
“Interseeding is done when corn is at the knee-high growth stage from V4 to V8,” Smith said. “Overseeding is done by an airplane or high-clearance equipment to broadcast the seed.”
He also has interseeded cover crops into soybeans with mixed results.
“I’ve had really nice stands of cover crops in soybeans and some complete failures,” he said.
Smith prefers to use a no-till drill to interseed cover crops.
“I can do 15 acres per hour while planting three rows of cover crops and getting good seed-to-soil contact,” he said.
Farmers can utilize equipment they already may own.
Smith uses a 1984 Tye drill that is 8 feet, 6 inches wide.
“I take off four row units and the no-till coulters off the drill in about an hour,” he said. “I used it to interseed three rows at 7.5-inch spacings, which allows 15 inches for the corn plant.”
Smith also has used a 2016 Great Plains drill that can be modified in about 15 minutes.
However, he said, there are some reasons a farmer may not choose to use a no-till drill for interseeding cover crops.
“If you have rolling topography or contour strips, the drill won’t track on the hills, so that’s where we go to broadcast spreading,” he said.
The accuracy of planting really shows up when doing interseeding, Smith said.
“You can mow down four to six rows of corn really quick if you’re off a half of inch,” he said.
Herbicide carryover can be an issue when interseeding cover crops.
“We’re using great residual herbicides to control waterhemp and giant ragweed, but those herbicides can stick around a little longer than desired,” Smith said.
“When interseeding four to six weeks after herbicide application, there is a chance to come in contact with the residual herbicide, which will injure the cover crop and potentially reduce the stand,” he said.
If the herbicide injury reduces the cover crop stand by 5% to 10%, Smith said, farmers probably won’t even notice it.
“It is a problem if the residual knocks out 85% to 90% of the stand,” he said.
Before interseeding a cover crop, Smith stressed the need for a weed-free field.
“Because once we get that cover crop out there, you won’t be able to spray weeds,” he said. “And if it is an organic field, you should plant your cover crop after the last row cultivator pass.”
Interseeding red clover at 12 pounds per acre has been successful for Smith.
“I’ve also had success with annual rye grass and cereal rye, but they are highly dependent on the year,” he said. “I’ve had cereal rye that looks great and cereal rye that has died out in July and decreased corn yield by 80 bushels per acre.”
Smith interseeded the cereal rye a little too early at V4 the year he experienced a decrease in yield.
“And we got rain for four days with 85- to 95-degree weather,” he said. “The rye took off, they out competed each other and there was nothing left of the rye at the end of the season.”
Berseem and crimson clover have not worked for interseeding.
“They germinated and died under the canopy pressure,” Smith said. “Oats and peas don’t work well in the shaded canopy.”
Weather will impact the success of interseeding a cover crop, and Smith said since 2013 there has not been a drought year.
“In a drought year, I think this system will struggle,” he predicted.
“If it’s dry at the time you’re going to interseed, I don’t think I would do it unless there is a 90% chance it’s going to rain in the next week or so,” Smith said. “If it’s been dry all season, I don’t think I would take the risk.”
The goal during the growing season, he said, is for the cover crop to look tough and the corn to be thriving.
“The cover crop should be struggling to get light,” he said. “It should be small and focusing on root growth, not focused on putting on above-ground biomass.”