Stacked rotation an unpredictable, resilient system

Ask a room full of agronomists what's significant about the year 1993, and the word "fusarium" ripples through the crowd.

It was a memorable year. Much of the wheat in the Red River Valley was infected with the yield-robbing fusarium head blight disease, which can create toxins damaging to human and animal health. The disease is now endemic on the Prairies, and farmers routinely use fungicides to reduce its effects.

Another significant year is 2003, which will be remembered as the year the soil-borne disease clubroot first surfaced in an Alberta county. In 2012, it was found for the first time in Saskatchewan.

Blackleg, another fungal disease, became endemic to the canola-growing regions of the Prairies in the mid-1970s, forcing a quick search for varieties that offered genetic resistance.

And 1988 was when the industry first acknowledged herbicide-resistant weeds were a reality that has only worsened with time.

After dramatic expansion in soybean acres in the past few years, extension agronomists are asking whether 2013 will be the year marking the official arrival of soybean cyst nematode.

These dates of dubious distinction in the Prairies' agronomic history now number in the dozens. But they are all linked by a common thread.

"Weeds and disease are Mother Nature's way of adding diversity to a system that lacks it," says Dwayne Beck, a leading proponent of no-till farming and manager of the Dakota Lakes Research Farm, affiliated with South Dakota State University.

Beck was at a recent agronomists conference in Winnipeg to discuss the role crop rotation plays in managing agricultural ecosystems. He offers an alternative view, but one that seems to be working on his commercial-scale farm.

He stresses farmers need to better manage both the sequence and interval of their rotations if they want to build a resilient cropping system that doesn't require the heavy use of pest-control products.

"Remember those two words, sequence and interval," he told his audience. "The goal is to be inconsistent."

Beck isn't a fan of organic agriculture; he likes to keep his options open. That said, he's consciously backing away from what he calls the escalating "arms race" between farmers and pests.

"We have not used a grass-control herbicide in wheat since the 1980s and we do not have wild oats and cheatgrass and goat grass that my neighbours have," he says.

Nature is balanced by inconsistency. Spring never comes on exactly the same day every year; when that first frost will hit is anybody's guess.

Humans, on the other hand, prefer routine. Farmers' crop rotations typically rotate between three or four crops in the same sequence, cycle after cycle. It may be diverse, but in a predictable fashion.

It's only a matter of time before nature figures out human routines and responds.

"If you have a problem weed or disease or something, Mother Nature is an opportunist. If you've got a problem, you've created an opportunity," he said.

He cited corn rootworm in the U.S. as an example.

"The normal habit of corn rootworm is the beetles feed on the silks. The females drop down and lay their eggs at the base of the corn plant and if you plant corn there the next year, the babies eat the roots," Beck says.

Rotation

So, farmers went to a corn-bean rotation. In the western Corn Belt, the rootworm eggs now hatch out every two years. In the eastern Corn Belt, the female flies to the soybean field to lay her eggs.

"The first case is because the interval is only two years; the other case is because the corn always follows the soybeans."

Beck's approach to crop sequencing would be considered heresy in some agronomic circles. He frequently grows the same crop back to back for two years. But then he doesn't come back to that crop for several years.

The so-called stacked rotation gives the farmer more flexibility in how weed-control products are used, and it doesn't allow disease pressure to build up.

"You have a clean system and you come back and go boom, boom and Mother Nature sees what you are up to and then you switch to something else," he says. "It keeps pest populations diverse and confused because of diversity in sequence and interval."

The beauty and the beast of it, though, is it's unique to each farm and it's constantly changing.

"Whenever I get asked what rotation should I use, I ask, 'Who chose your wife?' I can tell you a lot of things that are important, but I can't choose the rotation for you," he says.

Laura Rance is editor of the Manitoba Co-operator. She can be reached at 204-792-4382 or by email: laura@fbcpublishing.com.

Republished from the Winnipeg Free Press print edition February 16, 2013 B9