Rotating cereal rye and winter wheat into fields of corn and soy reduces fertilizer loss by 50% in Illinois, without impacting overall yields. These results come from a new study that brings us closer to sustainable intensification in the US Corn Belt, its researchers say.
They went in with a hypothesis that diversifying Illinois’ conventional two-year farm rotation of soybeans and corn would keep the soil covered for longer, and increase the amount of carbon stored in the ground. More soil carbon is an established way to capture and store more nitrogen from fertilizer instead of letting this precious resource flow away with the rain and runoff.
On most largescale farms, this nutrient-rich water is channeled via subterranean pipes called ‘tiles’ that are built to drain excess water out of the soil to avoid flooding. Conveniently, this gave researchers a way to measure the outflow of dissolved nitrate from soils, and compare levels between two types of farms. One set were conventional farms, where corn and soybeans are grown on a two-year rotational basis. These farms acted as a control. Another was an experimental plot, where plantings of soybean and corn were variously interchanged with cereal rye and winter wheat at different points over a three-year period. Altogether, this farmland comparison experiment ran for nine years, from 2015 to 2023.
Over its course, a stark difference between the two farms became clear. Overall, the diverse cropping showed a 50% decline in the nitrogen run off sampled from tiles. This was especially notable for cereal rye, whose presence on the field subsequently led to the largest annual difference in nitrate loads between the two cropping systems, reducing it by 90% compared to the control, in 2019. The winter wheat planting showed a similar capacity to hold nitrogen in the soil.
In both cases, the crop was cut back and left on the field to create thick mats of biomass that covered the soil. According to the study, the more diverse three-year rotation meant the soil was covered with either crops or leftover biomass for 30 out of the 36 months, compared to just 10 out of 24 months in the two-year rotation. It’s thought that the more constant coverage, presence of roots in the soil, and higher quantities of biomass and carbon work together to “immobilize” the nitrate and stop it seeping out of the soil.
This suggests it’s possible to amp up agricultural production with less nutrient pollution. “Two crops in one year is intensification, and simultaneously reducing nutrient loss demonstrates sustainable intensification,” says Lowell Gentry, a researcher in natural resources and environmental sciences at the University of Illinois Urbana-Champaign, who co-authored the study.
How this affected yields is a slightly more mixed picture. Interestingly, the nitrogen-capturing cereal rye seemed to have a negative effect on the productivity of the soybean crop that was planted next. This was likely because wet weather had prevented farmers from cutting the cereal rye crop in time, and so when the soybean plants emerged they grew into standing cereal rye which deprived them of the sunlight necessary for strong growth.
However, there were points in the cycle where yields increased. The researchers noticed that when corn and soybeans were planted slightly earlier in the season, they produced more grain. And, yields of winter wheat were 32% higher on the diverse fields compared to the average production of southern Illinois. Importantly, the researchers found that overall, yields were not reduced on the more diverse farmland.
The three-year rotation also led to an earthworm boom, which can help increase drainage and make nutrients more available in soils. This farm was tilled at a much reduced rate, because tillage is associated with increased nitrate leaching and loss—but it seems this also made it a friendlier environment for these worms, whose middens started appearing all across the untilled land. None were visible on the conventional farms, which by comparison are heavily tilled.
In future research, the team plans to look into how earthworms affect the soil and nitrate leaching: “I would like to quantify worm abundance in diverse rotations because tillage seems to eradicate them,” Gentry says. They’ll also be working on getting the crop timings right which “is very important under an intensified system” with varying and sometimes competing interests between plants, Gentry says—as seen with the soybeans and cereal rye mismatch.
With this fine-tuning, diverse cropping across more farmland could have a striking impact in the wider US Corn Belt and particularly in Illinois: nitrogen pollution in rivers there regularly reaches levels exceeding U.S. Environmental Protection Agency standards for safe drinking water, the study points out.
Gentry et. al. “A diverse rotation of corn-soybean-winter wheat/double crop soybean with cereal rye after corn reduces tile nitrate loss.” Frontiers in Environmental Science. 2025.
Image: ©Anthropocene Magazine
