By Jason Tetrick

Cover crops help farmers reduce soil erosion and nutrient loss. The most common and versatile cover crop — cereal rye — is planted near corn and soybean harvesttime and overwinters until it’s terminated, either mechanically or chemically, near planting time the next spring. But is this ultimately the best way of seeding cover crops?

Some Iowa farmers who have experience with growing cereal rye are coming up with creative ways to get cover crops seeded other than planting rye in the fall. Over the past three years, more farmers have begun planting (interseeding) cover crops earlier in the season — just a month after corn is planted. They plant the cover crop around V4 corn growth.

But when cover crops are seeded into corn planted in 30-inch-row spacing, the cover crops can’t consistently survive the summer because the corn blocks sunlight from reaching the soil surface under the crop. So in their quest to make cover crops work during the corn year, farmers are now testing wide-row, 60-inch corn.

Interseeding into wider rows
Interseeding into 60-inch-row width corn allows a cover crop to more easily survive during the cash-crop season. Because wide rows allow sunlight to penetrate to the surface between the rows, cover crops like cowpeas or other leguminous cover crops cannot only survive, but also thrive. This allows farmers to reap some of the benefits of a diverse cover crop mix while growing corn.

The 60-inch-row width corn is still planted at the same population per acre as the 30-inch planting, but within each row the plants are much more densely spaced to ensure similar plant populations per acre that are common in the 30-inch spacing.

Interseeded cover crops add much-needed plant diversity and potential economic diversity. Interseeded cover crop mixes typically include a warm-season legume like cowpeas, but a mix of species could include buckwheat or annual ryegrass depending on the farmer’s goals.

For cattle producers, diverse cover crops interseeded into corn can be grazed by cattle gleaning fields in the fall or even baled up with cornstalks destined for feedlots. This green material is high in protein and results in a more balanced ration for the ruminant when fed with cornstalks. Cattle producers can then save on stored feed costs, one of the largest annual expenses for their operation. If certain herbicides are used, the cover can’t be grazed or used for animal feed. Always read and follow label instructions.

Will corn yield suffer?
Yield loss is a common concern when farmers think about interseeding cover crops into a corn crop. However, recent research published by South Dakota State University in the journal Crop Management showed no yield loss when interseeding cover crops at V5 corn growth stage.

The researchers say the key to avoiding yield loss depends heavily on when the cover crop is interseeded. If the interseeded cover crops are planted too early, corn plants could suffer a yield loss. Planted between V4 and V6, interseeded cover crops should not negatively affect yield if the cover isn’t planted too densely.

“You must be careful when interseeding,” says Sharon Clay, a researcher who helped conduct the SDSU studies. “Make sure you understand which species in a mix will be dominant and which will survive residual herbicides.”

Weeds are another player in potential yield loss. Once cover crops are interseeded, farmers no longer have a full toolbox of herbicides at their disposal because the chemicals can also terminate the interseeded crop along with the weeds. Again, the key is timing when the last application occurs, and type of chemical program used.

Testing it out
To see whether these practices work in the field, Practical Farmers of Iowa members Fred Abels, Jack Boyer, Brian Kessel and Chris Teachout interseeded cover crops into standing corn in early June. To address the issue of cover crop survivability, they evaluated interseeding into corn planted in 60-inch-wide rows to see how the cover crops would thrive compared to 30-inch rows.

For the on-farm trial, corn was planted into a terminated winter small-grain cover crop in four separate replications, each one including paired strips of corn in 30-inch rows and 60-inch rows. Strips were as wide as at least one combine pass, running the length of the field. In early June, the cover crop mix was interseeded in the corn. Though many different species could be used, in this study the mix included cowpeas, buckwheat and annual ryegrass.

Farmers in PFI’s Cooperators’ Program conduct on-farm research on a wide variety of topics, including soil management practices like interseeding cover crops. In 2018, a total of 54 farmers conducted 77 research projects as part of the program. Knowledge from these projects helps equip farmers to be more profitable, to be better environmental stewards, and ultimately, to make their farms and communities more resilient.

The findings were shared at PFI’s recent annual cooperators’ meeting where Boyer presented on this research. To find research reports on topics you are interested in, visit practicalfarmers.org/research.

Wide rows provide more light
Boyer, farming near Reinbeck in east-central Iowa, is finding that most cover crop species can survive in the wider row spacing. He was able to grow more than 10 times the amount of biomass compared to the typical 30-inch rows. “The cover crop gets so much more light. In the 30-inch-row spacing, when corn gets 12, 13 or 15 feet tall, it’s just so dark down there, not much can survive in a 30-inch row.”

Boyer knows there’s always room for improvement, but on his farm, things looked pretty good in the 60-inch rows. “I may try another small plot to evaluate weed control strategies,” he says.

Boyer doesn’t have cattle, but he sees the opportunity for those who do, and he knows the added benefit this year’s interseeded cover crop will have on future years’ corn. But losing the option to spray herbicides after interseeding makes weed control a challenge. “Unless you’re trying to build soil health or graze, it’s probably not worth it,” Boyer says. “Those who have livestock are certainly interested in grazing, and I know I’m certainly interested in soil health.”

Learning how to make it work
Fred Abels farms near Holland in east-central Iowa. His results showed a much higher corn yield in the 30-inch rows, which he attributes to weed control. He thinks he didn’t have a high enough herbicide rate before the mix was sown, giving weeds a head start over the interseeded cover crop mix.

However, Abels still sees potential in interseeding in 60-inch rows. “We need to learn more about the best way to manage this. Things just need to get ironed out,” he says.

Abels also ran his cattle in areas last fall where he had interseeded cover crops, but he didn’t keep track enough to really know how much forage they were getting. He initially got excited about doing research with 60-inch rows because of grazing opportunities in the fall, which could reduce labor after a long farming season.

“If I could plant 10 to 20 acres and harvest the corn, and the cows had it for grazing, that would add roughly two weeks of them being out of my hair,” Abels says.

In 2018, Abels saw the buckwheat and the cowpeas come up, but his annual ryegrass never had noticeable emergence.

Tetrick writes for Practical Farmers of Iowa, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.