Avoiding another year of ‘snirt’

North Dakota farmers and researchers are finding success in controlling soybean field erosion by planting cover crops

“Snirt” became a buzzword in Prairie agricultural journalism in 2017 and 2018, and for good reason: the dirty snow lining ditches along highways was a telling indicator that there had been a soybean field there last season.

It’s a problem across the Red River Valley region in particular, where soybean producers are used to tilling to manage heavy clay soils. Because soy is a low-residue crop there’s little left on the surface to anchor the topsoil.

“Tillage is a big problem and in these dry years we get especially concerned,” says Cassandra Tkachuk, a production specialist for Manitoba Pulse and Soybean Growers Association.

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Tkachuk says that following the second dry year in a row, the association is challenging soybean growers to reduce tillage as much as possible to minimize erosion.

“You want to conserve the moisture that’s already there because there’s no guarantee we’ll get a lot of snow this winter, or rain next year,” she says. “Less tillage is not an easy answer but it’s an answer I would like farmers to consider.”

Interseeding

There is another answer being considered south of the border by North Dakota State University researchers.

Marisol Berti, a professor in forages, cover crops and biomass production at NDSU, conducts annual field trials interseeding cover crops into standing soybeans to minimize erosion.

Berti says wind erosion in soy fields is a huge problem in North Dakota and the reason she started the trials in 2016.

“In the spring, the soil starts freezing and then thawing and that change of volume makes the topsoil particles vulnerable to detachment from the soil structure, especially in high-clay soils,” she explains. “It forms a layer of loose particles. So you can lose soil by wind when it’s not covered by residue.

“For every inch of soil you’re losing through erosion you’re losing productivity.”

Berti’s objective is to determine cover crop biomass, yield and per cent cover when interseeded at two soybean reproductive stages, R4 and R6, and to assess any impacts on soybean yield and quality.

In 2016, four cover crops were tested, including a winter camelina, a winter pea, a winter rye and a forage radish.

Cover crops after soybean harvest that were flown on into standing soybean prior to leaf drop.
photo: Abbey Wick

The study found that soybean quality and yield were not affected by cover crops interseeded into soybeans at the R4 or R6 stages. It also found that interseeding cover crops such as winter peas, rye or radish after R4 is possible because soon after cover crop planting the soybeans begin to drop their leaves, allowing enough light into the canopy for cover crops to become established before winter.

“Interseeding cover crops during the later soybean reproductive stages is a viable solution for North Dakota producers to mitigate soil erosion after soybean harvest when there is not time for a cover crop to have enough growth to cover the soil before a hard frost,” Berti concluded in a report on the 2016 trial.

No-till systems plus cover cropping works best, Berti says, and if winter-hardy cover crops are used, producers can get on the land sooner for spring planting.

“Soils with a live cover crop in the spring dry faster,” she explains. “You reduce erosion because of ground cover and you have the advantage of moving water off the soil faster.”

In North Dakota, because of strong weather fluctuations in the spring, producers have fewer choices for winter-hardy cover crops than Manitoba growers — even though use of cover crops as an erosion management strategy is more common in the U.S. than it is north of the border, and seed is easier to find.

Berti says the Red River Valley is a difficult place to convince people of the utility of cover crops — farmers have been told that no till will make their soils wet and cold. But her team has worked with a farmer using no till and cover crops in the valley who typically seeds five to seven days before his neighbours.

“When other farmers see that, they get interested,” she says.

Managing moisture

Abbey Wick, an extension soil health specialist with NDSU, works with producers on tackling erosion. She says soybean producers across the state are losing productivity due to erosion in April and after the crop comes off — in the so-called “shoulder seasons.”

Her program is attempting to help producers establish cover crops on the “front end” and also the “back end” of the crop year. For producers planting soybeans after corn, Wick’s program recommends interseeding the beans with cereal rye so the rye will overwinter and offer erosion control right into the spring.

They’re also helping some farmers fly on cover crop seed just before soybean leaf drop, which allows the cover crop to take off after the beans are harvested.

Flying on seed can be hit or miss, says Wick, particularly if soils are hot and dry in August. But in heavy clay soils, some farmers have had a lot of luck with the strategy if there’s enough moisture, she says.

Cereal rye seeded after soybean harvest growing the following spring on high-clay soils.
photo: Abbey Wick

“The alternative is to build up residue with cornstalks and cereal rye. I encourage farmers to go that route. If they can interseed cereal rye into their corn or seed it after wheat, they’ve got something to help them manage the moisture and plant their soybeans into it.”

In the Red River Valley, moisture control, not erosion, is the primary reason many producers plant cover crops, according to Wick, so when producers can accomplish both goals with one cover crop “it’s pretty outstanding,” she says.

North Dakota producers are finding that cover crops require more management, but for many of them it’s worth it.

“The benefits outweigh the risks,” says Wick. “They’re learning how to manage their cover crops and get the right species in the mix.”

Berti cautions that the use of cover crops doesn’t come with an automatic return on investment, at least not in the traditional sense.

“Cover crops don’t increase yield in general. They’ll increase soil health and soil organic matter, but you don’t see that in dollars,” she says.

“But they (growers) need to start protecting their soils because they’ll have to invest more and more in fertilizers and other inputs to keep the crop’s productivity. You never get the eroded soil back. Organic matter takes a long time to build.”

This article was originally published in the Oct 2018 issue of the Soybean Guide.

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