The exploits of the Dakota Lakes Research Farm, near Pierre, S.D., and its farm manager, Dwayne Beck, are well-documented. According to numbers from 2014, the research farm has helped increased crop production in the surrounding area by $1.6 billion compared with production in 1986.

"We achieved this success not because we set out to improve yields. That wasn't our goal," Beck told a room full of farmers and conservationists at a recent Cover Crop Management Day in Columbus, Neb. "Our goal was to better manage the ecosystem, make the water go in the ground, do a better job of harvesting the sunlight. We used native prairie as our model."

This involves what Beck refers to as a "brain transplant" in thinking about the long-term resiliency of the land and how native vegetation has evolved and adapted to local growing conditions — and mimicking Mother Nature by adding diversity to the rotation.

"Weeds and diseases are Mother Nature's way of adding diversity to a system that lacks diversity,” Beck says. “Mother Nature is an opportunist. Nature's efforts to add diversity to the system can be countered by adding beneficial diversity of your own."

For Dakota Lakes, this increased diversity has resulted in no need for applying broadcast insecticides for 17 years — including on a field that's been continuous corn since 1990.

However, Beck notes it also is useful for knocking back weeds.

While a two-year rotation such as corn-soybeans or wheat-peas every other year might sound like a better rotation than a continuous crop, Beck notes that it still leaves a lot to be desired from a weed suppression standpoint.

With longer rotational intervals (the amount of time in a rotation before coming back to the same crop or same herbicide mode of action), weed seed populations have less opportunity to grow or develop herbicide resistance.

Beck cites a long-term study (from 1990 to 2002) at Dakota Lakes evaluating different rotations and their effect on weed populations: winter wheat-chickpeas; winter wheat-corn-chickpeas; and a more diverse rotation of chickpeas-winter wheat-corn-soybeans.

"Where we had wheat-chickpea for 12 years, we had 94 weeds per square meter. Where we had wheat-corn-chickpea we had 40," Beck says. "Where we did a more diverse rotation, which isn't a good rotation from a carbon standpoint, but a good rotation from a weed standpoint, we had 7."

While tillage often is brought up as a last resort for controlling resistant weeds, Beck says tillage often leads to more weed seeds being brought to the soil surface. In that same study, using tillage in the two-year rotation led to 225 weeds per square meter after 12 years. This means the no-till, four-year rotation had 97% weed control.

In a separate study using green foxtail seeds buried at different depths — 0, 2 and 4 inches — only 11% still were alive on the soil surface after two years. Of those buried at 2 inches, 28% were alive, and 55% of those buried at 4 inches were alive.

"If you till it again, they'll come back to the surface and start to grow," Beck says.

However, bringing diversity to the rotation also benefits yield and profitability, Beck says.

At Dakota Lakes, expanding to a rotation of corn-corn-soybeans-winter wheat-soybeans, with a cover crop seeded after winter wheat, resulted in a yield benefit not only for corn but soybeans as well.

By comparison, a continuous corn rotation resulted in an irrigated corn yield of 203 bushels per acre — with 1,015,000 bushels when spread out over 5,000 acres. With a corn-soybean rotation, that increased to 217-bushel corn, with 62.9-bushel soybeans — or 542,500 and 157,240 bushels, respectively, at 2,500 acres each.

Expanding to the five-year rotation raised corn yields to 235 bushels and soybean yields to 78.8 bushels — or 470,000 and 157,600, respectively, at 2,000 acres each — with the addition of 120,000 bushels of wheat.

"I get more total bushels of soybeans on 2,000 acres than I would on 2,500 acres in corn-soybean,” Beck says. “Plus, I get 120,000 bushels of wheat. So, I lose 72,550 bushels of corn to gain 120,000 bushels of wheat and 350 bushels of soybeans. That's a pretty good trade. Then I get a chance to grow cover crops better, and get weed control, disease control and insect control."