MOUNT CARROLL, Ill. – Researchers from the University of Illinois Agroecosystem Sustainability Center (ASC) and the College of Agricultural, Consumer and Environmental Sciences (ACES) may have unlocked the science beyond why the time-honored corn-soybean planting rotation followed by farmers continues to pay benefits through soil health and yield boosts

After using a sophisticated agroecosystem model known as ecosys to explain why corn yield is higher after soybean at normal nitrogen fertilization rates, the researchers also sought answers as to how corn-soy rotation impacts soil greenhouse gas emissions and nitrogen leaching, and when corn-soy rotation is most economically advantageous.

“We found that while corn-soy rotation can boost corn yields and reduce nitrogen fertilizer needs, the benefits come with nuanced environmental and soil carbon trade-offs,” said study leader Kaiyu Guan, founding director of the ASC and ACES and Levenick Professor in the U of I Department of Natural Resources and Environmental Sciences.

Corn grown after soybeans consistently yielded around 6.4 percent more than corn grown following corn, the researchers found, at standard N rates of 151 kilograms per hectare. This is due to the lower biomass and faster breakdown of soybean plant matter during spring planting season for corn. This natural fertilizer effect may lead to more beneficial growing conditions.

The research also suggested that the more N added throughout the growing process, the less the yield benefit. “In some cases, the yield boost nearly disappears,” said Ziyi Li, the study’s first author and research scientist at ASC.

While the corn-soy rotation helped reduce nitrous oxide and ammonia emissions from soils, the study suggested that fast-decomposing soybean residues led to an overall reduction in soil organic carbon compared to continuous corn. Nitrogen leaching was found to increase in subsequent corn years when decomposed soybean residues released N into the soil.

“The results underscore a key trade-off,” according to Guan. “Rotation improves some sustainability metrics while compromising others, especially under typical fertilization practices.”

A key takeaway from the study: using historical commodity prices, the researchers found that corn-soy rotation offered higher economic returns – up to $458/acre ($1,133/hectare) more than continuous corn – at low nitrogen fertilizer rates (45 pounds/acre) and under typical market conditions (soybean: $11/bushel, corn: $4.50/bushel, and N fertilizer: $193/Mg ($175/short ton) UAN). Under higher nitrogen input prices and market scenarios with elevated corn prices, however, the advantage was significantly reduced or even reversed.

“These are market factors that are definitely affecting what farmers are doing” in regard to crop rotation, agreed Ellen Hopkins, a soil health expert and board member of the Illinois Corn Growers Association from Mount Carroll, Ill. Hopkins is a seed retailer and co-owner of a business, R&H Seed Solutions, that helps farmers maintain optimal soil health through an array of management tools.

“Market factors also affect the usage of cover crops, in my opinion,” Hopkins said. “The way pricing is, our markets are low and our inputs are high; it’s hard to make a dollar.”

Hopkins feels that many Midwest farmers may have opted for continuous corn in 2025 due to current market conditions that favor corn over soybeans in terms of profitability.

“There is more profitability, I believe, if you look at corn this year than if you look at soybeans,” she said. “The inputs going into corn are high, and the market is low. But the yields we are able to get off our corn crop here in the Midwest have increased significantly over the past 10 years, and even over the last five years. Our soybean yields have increased but not like our corn crop has, and you don’t have as much input cost with soybeans, but at the end of the year the yields that you are getting for corn during this market pricing year point to a more profitable corn crop.”

Profitability for soybeans could be enhanced if the crop was planted into a no-till or limited-till field, according to Hopkins. Ranchers can also typically afford to be more flexible in their crop selection due to lower input costs for fertilizers, though cattle producers historically prefer corn for silage, she added.

A U of I ASC and ACES news release states that their recent study underscores the importance of tailoring nitrogen management to balance profitability and sustainability. “Lower fertilizer rates in corn-soy rotation compared with continuous corn can maximize economic return while mitigating some environmental impacts, but farmers must weigh these benefits against potential declines in soil organic matter and greater nutrient leaching,” the researchers concluded.

The study, “Comparing continuous-corn and soybean-corn rotation cropping systems in the U.S. central Midwest: Trade-offs among crop yield, nutrient losses, and change in soil organic carbon,” is published in Agriculture, Ecosystems and Environment (DOI: 10.1016/j.agee.2025.109739).