Keith Hartmann

Keith Hartmann standing in front of his research plot at the AgRevival site in Gibbon, Minn. Keith is studying the effects inter-seeded cover crops have on corn yields when planted around V6.

GIBBON, Minn. – Cover crops continue to grow in popularity and use. For the shorter growing season in the upper Midwest, getting an established cover crop before the winter freeze and after harvest is a challenge. This has led to more growers inter-seeding a cover crop with their corn crop.

“The most common question I was getting asked was aren't you seeding weeds out there and that is what my trial has been about, testing to make sure I'm not competing with the corn, I'm not hurting corn yield and I'm not taking nutrients away,” said Keith Hartmann during an interview at AgRevival.

Hartmann received a Sustainable Ag Demonstration grant from the Minnesota Department of Agriculture and a Conservation Innovation grant from the Minnesota Corn Growers Association to conduct his research.

“When the corn is V6, I'm putting in about 15 pounds of cover crop seed, annual ryegrass and kale I've had the most success with, and I'm seeding those right behind my side dressing unit,” said Hartmann. “I'm putting a band of nitrogen 4 inches deep and broadcasting the cover crop seed right in front of our firming wheel.”

This is the third year of Hartmann’s research program. As part of his MDA grant, he must present his findings to farmers.

By partnering with AgRevival, he was able to place a demonstration plot at their Gibbon location. He then made his presentation part of AgRevival’s 2018 crop tour, held on Sept. 13, and reached a larger audience.

His method of inter-seeding with the side-dress unit ensures good seed to soil contact and emergence, roughly 85 percent.

“Guys are broadcasting seed in August, but they're getting 50/50 success rate using about 30 to 40 pounds of seed, that’s about $50 per seed cost,” he said. “That's hard to justify, where I'm doing about $15 to $16 and I am getting the establishment.”

Getting an established cover crop was only part of the research, the main focus is how does that early planted crop affect the corn crop.

“This is the third year of the study and, on corn yield, there has not been any statistical difference,” he said. “The first year, it showed the cover crop as 0.9 bushels (corn) better and last year, it showed that with the cover crop was 1.1 bushes (corn) less, which isn't statistically different across the whole field.”

Hartmann explains that the cover crop gets established early in the year. At this point, both the corn crop and the cover crop are too small to be competing for nutrients. Once the cornfield has canopied over, the cover crop is shaded and goes dormant. At this point, the cover crop is only about 4 inches tall.

“Middle of August, it's yellow, it's pale and just very spindly, so the corn doesn't even know it's there,” he said.

Later in the season, as the corn plant finishes its growth cycle and starts to dry up, the sun is able to reach those cover crop plants again. They green back up and start growing.

“It doesn't put seed on, that's a big thing too,” said Hartmann. “With weeds, you get a little water and they’ll put seed on, but these aren't going to produce seeds to be an issue down the road.”

As that cover crop grows through October and November, before the winter kill, it is taking nitrogen from the soil that would otherwise have the potential to be lost. It is now locked in plant form, in organic matter, stored for the next season.

“One of the biggest things I saw when I first started digging roots in the fall, I would see a 10:2 ratio of earthworms,” he said. “In my strip of cover crop, I had 10 earthworms and in the check strip where there's nothing, there would maybe be two.”

In the very first year, the cover crop fields showed better water infiltration. The need for fall tillage was reduced because there was a living root pushing through the dirt.

When those fields are harvested in the fall, Hartmann’s combine is driving on green cover crop versus black dirt. In a wet year, he is able to get into his fields sooner and his combine stays cleaner.