Get used to a new term in corn production — “solar corridor.” The idea is to provide a wide enough row spacing to allow sunlight to reach intercrops such as clover and hairy vetch. How wide? How does 60 inches sound?

Intercropping is attracting more interest from straight grain as well as livestock producers. Grain corn growers get a boost in soil health, and livestock producers get the bonus in feed and protein.

“There are a lot of synergies to learn from corn intercropping for grazing and for grain,” says University of Manitoba researcher Yvonne Lawley, who together with colleague Emma McGeough, has been doing some research into intercropping in corn.

Paired rows

Joe Breker at Havana, North Dakota, has been growing cover crops for about 20 years, but 10 years ago he began experimenting with seeding mainly a winter rye cover crop into standing corn with the aim of having green cover to plant soybeans into the following spring. But he had a lot of problems getting consistent cover crop establishment.

He started interseeding into corn on 30-inch rows and got a fairly consistent establishment. Some years, though, the corn would outcompete and kill the cover crops, so he decided to see if wider rows could solve the problem, although he was naturally concerned about yield drag with wider-row corn.

Joe Breker built a custom frame for his planter so that he could plant twin rows of corn on both 60-inch and 30-inch rows, and with different spacings between the pairs to test what worked best.photo: Joe Breker

Last season, Breker decided to approach the wide rows a little differently, and built a custom frame for his planter so that he could plant twin rows of corn on both 60-inch and 30-inch rows, and with different spacings between the pairs to test what worked best.

After harvesting, he found the wider-paired rows outyielded a single wide row. The 60-inch twin row on two-inch and four-inch spacings yielded 180 bu./ac., and on six-inch and eight-inch spacings yielded 184 bu./ac. compared to 176 bu./ac. on a single 60-inch row.

“The twin row does seem to have a yield advantage over the single row at the same plant population, and for the cover crop there was enough light getting down to have a nice establishment,” Breker says. “It’s only one year, but every field, everything did just great. I’ve never had this kind of cover crop establishment going into winter at this stage, so I’m excited about it.”

High plant population

Plant population is a key factor in going to wider rows, says Michael Ostlie, a research agronomist with North Dakota State University (NDSU), who has been conducting research comparing corn intercrops on 30-inch and 60-inch rows.

“One thing that became clear at both our research sites is we can’t cut back on plant population,” Ostlie says. “Whatever a grower is using on their farm for a narrow row, and what they have found to be the best population, just keep doing that on the same area — make sure it’s the same population.”

In Ostlie’s trials, at an equal plant population of 32,000 per acre, the 60-inch rows yielded about five to seven per cent less than 30-inch rows. But when the population was reduced to 24,000 per acre the corn yields were reduced by 10 per cent, and by 20 per cent at a plant population of 16,000 per acre.

The trials also showed better cover crop establishment in the wider rows. Roughly 40 per cent of the expected cover crop stand grew in the wide rows, but only around 14 per cent in narrower rows.

Breker also saw good cover crop establishment and growth and thinks it may be due to cover crops making use of nitrogen later in the season.

“In wider rows where I had no cover crop, I had a five to eight per cent higher corn yield, and where I had cover crops, I had a little less yield, so the cover crop was impacting the yield in some way,” he says. “The cover crop did grow enough biomass to use some nitrogen, so it could have used that 30 or 40 pounds of nitrogen that the corn could have used to pack that last five to eight per cent yield.”

Joe Breker at Havana, North Dakota, has been experimenting with seeding mainly a winter rye cover crop into standing corn with the aim of having green cover to plant soybeans into the following spring.photo:Joe Breker

Identifying synergies

These are some of the questions that Lawley and McGeough hope to answer with their next collaborative, Prairie-wide project for which they are seeking funding. It would build on their preliminary research into intercropping for grazing and soil health.

In 2019, they interseeded four different species — hairy vetch, Italian ryegrass, clover and radish, as well as a mix of all four. They went into a 30-inch row of herbicide-tolerant corn at around the V6 stage, with low and high nitrogen rates to see how they would perform in a corn canopy.

Although dry conditions in 2019 limited growth of both the corn and the intercrops, they did learn some things that will shape future research into the relationship between intercrop biomass and corn yields. Questions include planting timing, row spacing, corn population, N fertilization regime and intercrop species.

Lawley’s preliminary research showed there was no drag on corn yield despite the stressful conditions. At one site on lighter loam soils, the corn with an intercrop of a legume like clover or hairy vetch gave higher yields than a corn crop alone.

“That has piqued my curiosity about what is going on with these plants under the ground,” Lawley says. “Are things like mycorrhizae helping to facilitate nitrogen or even water transfer between plants?”

Because a corn canopy takes a long time to close, there may also be potential for cover crops to help with issues such as soil erosion or herbicide-resistant weeds. Researchers at Laval University in Quebec are also looking at the potential residual benefits to soybeans after intercropping corn in an organic system.

Extended grazing

McGeough took feed samples at several dates to test nutritional quality throughout the fall grazing period. Because corn is high in energy but low in protein, producers often use it for grazing mature or open cows whose nutritional requirement is less. McGeough says the aim is to create a more complete ration for extended grazing by increasing the protein content through intercrops so producers can also graze bred heifers and weaned calves.

“The protein quality of these intercrops was very high. That is exciting,” McGeough says. “Now we have to figure out what agronomic management strategies we can do to increase the biomass of the intercrops to provide that additional nutrition, and combine that with an economic analysis.”

Many positives

Breker is convinced that twin rows on a wider spacing are key to making the system successful.

“I am going to stick with the twin row,” he says, adding that he saw many other benefits with this system.

“It harvested nicely, and there was lots of room to run sprayers down the rows and to plant down between the rows. The corn will yield very close to 20-inch and 30-inch rows, and we can still get good cover crop establishment and growth on the cover crop for soil health purposes throughout the growing season. We also have the potential to have blooming crops and pollinators in there in the summertime. The positives about it are many.”