Intercrop no “home run” but has potential

The first formal study on mixed oat-pea intercropping suggests both advantages and disadvantages to growing the two together.

Project lead Luke Struckman said the practice of intercropping has increased in the last 10 years but little research has been done beyond grower experience.

This study, funded by General Mills and supported by in-kind contributions from Agriculture Canada and South East Research Farm at Redvers, Sask., included test plots, small plots and farm-scale work in collaboration with farmers. Twenty-five farmers in Canada, the United States and the United Kingdom contributed information and there were 12 on-farm test plots in Saskatchewan, Manitoba and North Dakota, as well as 200 small test plots.

Struckman said the research found that growers should experiment before they go farm-scale.

“What’s most important to me is this understanding that if a farm operation wants to incorporate this mixed intercrop combination it’s not going to be a home run,” he cautioned.

One of the biggest challenges is separation after harvest since the seeds are similar in size and peas can’t take a lot of handling, but some see advantages during the growing season.

“The advantage we have with the oat-pea is that growers would be able to cut back on nitrogen use if that’s something that interests them,” Struckman said. “As well, it’s a way to grow high-value lodge-prone pea varieties. You’d be favouring peas in the stand.”

Many growers participating in the research favoured oats in terms of seeding rate, he said, but that comes at the detriment of the peas.

Cutting back the oat seeding rate to 60 percent of normal will enable the peas to grow properly; the oats won’t crowd them out and the peas will stand until harvest.

Many field pea varieties are quite short, he noted.

Some taller and lodge-prone types, such as 4010 forage peas or Austrian winter peas offer small but high value markets. Growing them as an intercrop will improve standability.

“You don’t have to worry about scraping peas off the ground with a combine header,” he said.

While oat seeding rates can be cut back, the peas should be seeded at standard monocrop rates or slightly below, the study said.

The economic results were wide-ranging.

“While we cannot discern a clear economic advantage to inter-cropping, the incredible variation ($113 per acre loss to $128 per acre gain) implies potential for oat-pea mixed grain intercropping to improve financial outcomes in certain contexts,” says the study summary.

Oat yields are likely to be lower in the intercrop due to the lower seeding rate and less nitrogen, but the higher value of harvested peas will most likely cover the oat losses, the study found.

General Mills conducted quality testing on the 12 on-farm trials and found that intercropping did not affect yield, oat test weight, kernel plumpness, beta-glucan, protein and fat content, or groats.

Struckman said one concern is the lack of herbicide labelled for simultaneous use in both crops. Anyone contemplating growing this mix should make sure to have a clean field from the previous growing season and use a pre-emergent herbicide.

“If you have a really weedy field, an oat-pea intercrop is not a good way to clean it up,” he said.

There is no research being done in this regard, Struckman said, perhaps because many farmers interested in intercropping are also interested in cutting back on synthetic inputs from both financial and environmental perspectives.

Some weed suppression will come from the canopy, providing the crops can get to mid-season and develop a thick canopy to keep the weeds down.

Struckman believes variable rate seeding is a valuable tool for intercroppers.

Farmers can adjust for different parts of the field and, for example, favour the oats where it is wet and the peas where it is dry, to improve returns, he said.

Variable rate seeding is still relatively new when compared to variable rate fertilizer application.

“Variable rate seeding is a little bit more difficult just because … if you don’t want to do a double-seeding pass, which most farmers don’t want to do … with a mixed intercrop you have to have two or three separate tanks on your seeders as well as openers that can put two or three things in the ground at the same time at different rates,” he said. “Those that have adopted it are seeing a lot of success.”

It’s unknown how many farmers are actually growing two or more crops together with the intention of harvesting them for separate grain crops.

Saskatchewan Crop Insurance Corp. in 2019 estimated that about 100,000 acres were insured as mixed intercrops, Struckman said.

“That excludes people that don’t use insurance, or a lot of the mixed intercroppers will plant it as a mixture but insure it as a monocrop,” he said.

For some farmers, intercropping is a way to self-insure. For example, if it hails on an oat-pea crop the peas might not recover well but the oat yield might not be affected much.

Struckman added that interc-ropping is an old practice with a long history but is cutting edge in many ways.

“This growing two or three crops together with the intention of separating them after harvest and marketing them separately as a cash crop is kind of a new thing,” he said.

He also observed it is more prevalent on the Prairies, perhaps as part of the movement since the 1970s to diversify away from wheat, followed by the mass adoption of no-till and now precision farming.

Some farmers in the study said they wouldn’t continue inter-cropping because of issues related to separating the crops and marketing.

“There are some processors that are still a little bit reluctant to accept a mixed grain intercrop that’s been separated, whether it’s potential allergen issues or even milling issues,” said Struckman.

Mixes can be sold as livestock feed, however, and that’s an advantage.