Although the 11-by-44-foot hole on Ethan Koehler’s farm could be mistaken for a swimming pool, it’s actually a woodchip bioreactor under construction.
The 5-foot-deep pit, showcased during the Marshall-Putnam Nutrient Stewardship Field Day Aug. 19, will soon begin capturing nitrogen from about 16 acres of tile-drained cropland in Marshall County. While smaller than some of the other bioreactors installed through partnerships with the Illinois Land Improvement Contractors Association (ILICA) since 2017, the system is expected to make a measurable environmental impact.
“I’m really just out here trying to take care of the land and do the right thing,” said Koehler, who has also implemented other edge-of-field practices on his farm, such as buffer strips, pollinator habitats and filter strips.
Koehler first learned about bioreactors when the practice was still relatively new. Intrigued by the concept, he worked with Illinois Farm Bureau staff to explore the idea and bring the project to life. Having access to trusted experts, he said, made it easier to try “newer, cooler ideas.”
Inside a woodchip bioreactor, microbes convert nitrate into inert nitrogen gas, which safely escapes into the air. This process usually happens in low-oxygen conditions and relies on a carbon source like woodchips to fuel microbial activity.
“The bioreactor itself is a cool way to take some of that nitrate out of the water supply. We’ve got an initiative as a state and a nation to work on that, so I’m trying to do my little part,” Koehler told FarmWeek.
Ryan Arch, ILICA executive director, said the slight slope of Koehler’s field made it a great location for a bioreactor, allowing tile drainage to flow efficiently into the system.
“It’s just really the ideal site when you think of woodchip bioreactor sites,” Arch said, adding Koehler’s system is also capped, allowing for easier access and maintenance, such as mowing, without interfering with its function.
Since the start of the bioreactor partnership involving ILICA, IFB, University of Illinois, Illinois Nutrient Research and Education Council (NREC) and the Environmental Quality Incentives Program, Arch said research has shown an average nitrate load reduction of 27% across installations. That figure aligns with goals outlined in the Illinois Nutrient Loss Reduction Strategy (NLRS), which aims to reduce nitrogen and phosphorus runoff statewide.
Julie Hewitt, executive director of Illinois NREC, said bioreactors are part of a broader system of nutrient management practices. While the “4Rs” — right source, right rate, right time and right place — guide nutrient application, edge-of-field practices like bioreactors help mitigate environmental impacts when excess nutrients remain.
“The bioreactor would come sort of after the four Rs have had their opportunity to work,” Hewitt said.
“The excess nitrates that get taken up by this wood chip bioreactor, those nitrates are now gone,” she said. “They’re no longer available to a growing crop. But the good news is they’ve been captured in this system and have not made their way into a nearby waterway.”