U.S. corn yields have been increasing steadily in recent years at a much higher rate than soybean yields. Concern over aphids, nematodes and diseases that attack soybean fields, plus the corn yield trends, have led some producers to consider changing from a corn-soybean rotation to either continuous corn or two years of corn followed by one year of soybean.
One benefit of a corn-soybean rotation is it helps control diseases and pests that bother each crop. "Producers are really taking a chance if they don't rotate," said Palle Pedersen, Iowa State University soybean extension agronomist. "Diseases and pathogens build up in the soil and rotation helps manage them."
"Research shows the most profitable rotation in the Corn Belt is the corn-soybean rotation," he said. "The nitrogen provided by soybean for growing corn is a major reason for this profitability."
Pedersen was involved in a 15-year research project at the University of Wisconsin that studied corn and soybean yields based on rotation sequence and tillage systems. " First-year corn and corn rotated annually with soybean yielded higher than continuous corn," Pedersen said. "In addition, first-year soybean yields were 12 percent higher than the other six soybean rotation sequences studied."
Not only do yields increase with a corn-soybean rotation, so do profits. "In this study, both first-year corn and soybean produced the highest returns. We concluded that first-year corn or soybean and alternating corn and soybean were the most profitable rotation sequences over the last 15 years in Wisconsin," Pedersen said.
Pedersen believes the same is true in Iowa. But to provide scientific proof, he has launched a similar research project at three ISU research farms. Various rotations combined with two tillage methods – no-tillage and chisel plow – will be studied in this long-term experiment.
"In Wisconsin, we found that conventional tillage increased corn yield by an average of 8 percent, but did not affect soybean yield. We also found producer returns were higher for corn in a conventional tillage system, but there was no effect on soybean returns," Pedersen said.
Another benefit of crop rotation is that with different planting and harvest dates, producers spread out their workload. "Farming is a business. Producers need to consider everything, and keep an eye on the bottom line," Pedersen said.
Pedersen knows bean prices have been low in recent years. But he thinks the strong uptrend in new-crop soybean prices, higher anhydrous fertilizer costs and research that shows the value of a corn-soybean rotation will help Iowa producers make better decisions.