The United States grows a lot of corn and soybeans. Some researchers think it’s a good idea to add wheat into that mix. A new study shows that including wheat once every four years in rotations with corn and soybean can have many benefits. The research was recently published in Agronomy Journal.
Farmers across the United States harvested corn from 81.5 million acres of farmland in 2019. That’s a bit smaller than the areas of Nebraska and Iowa combined. More than half the corn harvested in the United States came from just four states in the Northern Corn Belt – Iowa, Nebraska, Illinois and Minnesota.
The Northern Corn Belt also extends into Canada. The province of Ontario produced more than 350 million bushels of corn in 2020. Across most of the Northern Corn Belt, farmers typically rotate between growing corn and soybean. But occasionally growing wheat could help those farmers. Corn and soybean yields were greater when crop rotations included wheat.
For the study, researchers grew winter wheat once every three or four years with corn and soybean. They found that longer-term corn-soybean rotations that contain winter wheat can be more profitable. The greatest yield increases occurred in rotations that included winter wheat once in four years.
Farmers tend to focus on corn and soybean because those crops typically have higher financial returns than wheat. But the study made a key financial discovery. The increase in corn and soybean yields when those crops are grown in rotation with wheat more than offset the lower sale returns associated with winter wheat.
Farmers would need to continue to grow wheat every four to five years. The increased corn and soybean yields associated with including wheat in rotations disappear over time if wheat is dropped from rotations.
Rotating wheat with corn and soybean crops also has other benefits. Soils tend to be healthier and have better structure when crop rotations include small grains or forages in addition to corn and soybean.
Good soil health and structure can have far-reaching consequences. Inferior soil structure increases soil erosion and runoff risk. In turn that increases the risk of surface water pollution. On the other hand, good soil structure and health may increase water availability for crops.
As global climate changes, water availability may become unreliable. Limited water could even limit crop yields. Improving soil structure by including winter wheat in crop rotations could help address both these issues.
There will probably be even greater benefits of more complex crop rotations in the future. The researchers observed the highest increases in corn and soybean yields in the later years of the study.
The crop rotation studies were carried out in two study sites in Ontario, Canada. At one of the sites near Elora, Ontario, the trial has been ongoing for more than 36 years.
The researchers observed continued increase in soybean yields over time when winter wheat was included in rotations throughout the trial. However, the largest yield increase was recorded in the past two years.
Researchers are exploring more ways farmers can benefit economically from wheat crops. When markets exist, straw sales can increase revenue associated with wheat.
Wheat straw was baled at the Elora trial. Removing the wheat straw did not reduce subsequent corn or soybean yields. That demonstrates that retention of straw is not needed to obtain greater corn and soybean yields when in rotation with wheat.
Ken Janovicek is a researcher at the University of Guelph in Canada. The work was supported by Grain Farmers of Ontario and the Ontario Ministry of Agriculture, Food and Rural Affairs through the Ontario Agri-Food Innovation Alliance.