A long-term study shows diverse crop rotations improve yields.
Yet many farmers today grow strictly corn and soybeans, which has caused a decline in crop diversity and that is a major concern for Ontario producers.
“It (corn-soybeans) is not really a crop rotation, it’s just an alternating crop sequence,” says Dave Hooker, assistant professor in plant agriculture at the University of Guelph, Ridgetown Campus.
Why it matters: The addition of a cereal into a corn-soybean rotation can improve soil quality and the yield of corn and soybeans.
A long-term trial, ongoing since 1995 at the University of Guelph, Ridgetown campus, shows the addition of a cereal, such as winter wheat, improves yield in corn and soybeans.
The trial studied seven different rotations: corn on corn, soybean on soybean, corn-soybean, corn-soybean-wheat, corn-soybean-wheat under-seeded with red clover, soybean-wheat and soybean-wheat under-seeded with red clover.
As well, there are four different rates of nitrogen added to these trials with two tillage systems in place — moldboard plow and no-till.
When looking at a continuous corn rotation, corn yields 173 bushels per acre, a corn-soybean rotation yields similarly and a corn-soybean-wheat rotation yields about nine bushels more at 182 bushels per acre.
As wheat is included in the rotation, the yields vary from an increase of nine to 17 bushels per acre, depending on which treatment is used in the comparison.
“This is significant because wheat often does not get the credit for increased corn yields and increased soybean yields,” says Hooker.
As well, including wheat provides an opportunity to incorporate a cover crop or under-seeded red clover into the rotation, more so than a corn-soybean rotation.
The trials that used wheat under-seeded with red clover provided an additional six bushels per acre, says Hooker, with a nitrogen credit of 70 pounds per acre.
“The contribution of red clover we are thinking is because of enhanced soil structure and other soil quality factors that the red clover is contributing.”
Some producers who have had difficulties establishing a red clover stand have avoided the problem by planting a cover crop following a wheat crop.
When looking at soybean yield, the incorporation of wheat improves this as well by about four to six bushels per acre.
Soybean yield during different weather scenarios is more consistent within the corn-soybean-wheat rotations to that of the corn-soybean rotation.
The effect is even greater in the no-till system than the tilled system.
“This is where we see the biggest rotational responses. As a farmer, I want my income to be as stable as possible. I don’t want fluctuation from one year to the next.”
When producers decide whether to plant wheat, they typically look at market price, says Hooker, but they should also consider the benefits of adding it into a proper rotation.
“When we factor in higher corn yields, higher soybean yields, along with an additional nitrogen credit, there’s a lot of value there. We add that value to the wheat enterprise and it’s extremely competitive, sometimes exceeding the profitability of corn and soybeans.”