Anybody who’s walked the streets of the Farm Progress Show knows there’s a whole lot of wood chips out there. Turns out, they have life after the show.
Folks at the University of Illinois have put them to work following the 2021 FPS, using them to fill six wood chip bioreactors on Eric Miller’s farm in Piatt County, Ill.
These wood chip bioreactors are also a part of research being done to study the performance of bioreactors in relation to nutrient loss reduction, funded by the Illinois Nutrient Research and Education Council (NREC).
“Bioreactors are essentially a trench or a pit full of wood chips that we route tile drainage through, and the tile drainage has nitrate in it,” says Laura Christianson, U of I crop scientist. “The biological process we’re trying to get to happen in bioreactors is the process of denitrification. This is the conversion of nitrate in soil, or in this case water, to harmless nitrogen gas.”
And the wood chips help make it happen.
“Denitrification is a natural part of the nitrogen cycle that’s been happening for millions of years,” Christianson says. “We are simply enhancing the process of denitrification by adding an extra carbon source, which comes from carbon that’s in the wood chips.”
But there’s more than wood chips in a bioreactor.
Denitrification is completed by denitrifying bacteria, which live on the wood chips and eat the carbon from the wood chips as their food source, Christianson says. So, as nitrate in the water flows by these denitrifying bacteria, the bacteria convert the nitrate to nitrogen gas, which cleans the water.
But why use wood chips sourced from the Farm Progress Show?
Since 2015, Eric Miller has been using wood chip bioreactors, says Lowell Gentry, agronomist and U of I research specialist who has been a part of the study from the start six years ago. From the beginning, NREC has continued to fund this study, which includes a whole-systems approach of corn, soybeans, wheat rotation, cover crops and the bioreactors. The goal is to look at the effect management has in combating tile nitrates.
It just so happened that his bioreactors needed to be recharged and refilled with wood chips during an Illinois Farm Progress Show year. It all fell into place, he says.
“Use of the wood chips for the bioreactor from the FPS landscape strengthens our partnership with the local farmer and Xylem,” says Rick Wild, Farm Progress farm show manager. “It also avoids these leftover wood chips hitting landfills.”
Xylem, the FPS wood chip supplier company, is also a go-to source of wood chips for bioreactors in Iowa and Illinois, Christianson says. The wood chips meet specifications for working in the bioreactor: 1 to 2 inches in size, free of debris and containing less than 50% oak.
Studying bioreactor performance
A new research model was designed during recharging to further understand bioreactor performance, Gentry says.
In 2015, the bioreactors were filled with wood chips and left uncovered, he says. This time, two bioreactors are filled with wood chips and left uncovered like the initial study. Two more bioreactors contain wood chips and are covered with a soil cap, while the remaining two bioreactors are filled with corncobs.
If findings show performance from corncob usage in bioreactors, then this could be a more accessible way for farmers to implement tile nitrate fixation practices, Gentry says. However, he won’t know until more time has passed and more research is done.
But bioreactors are not the complete answer to nutrient loss reduction, he says.
“From U of I research, bioreactors are credited with a 25% loss reduction, which means bioreactors keep a quarter of nitrogen from going downstream,” Christianson says. “But bioreactors are an edge-of-field practice. Edge-of-field practices won’t do anything for soil health or improve yields. But even with some of our best soil health practices, there’s many years where we still wouldn’t meet our nutrient loss reduction goals.”
Instead, think about a combination of practices.
“It’s really going to take all of the practices that we have, spread widely across all of our acres,” Christianson says. “Tile drainage is such a big way of how we do agriculture here. So, something like pairing an in-field practice like cover crops with an edge-of-field practice like bioreactors could really go hand in hand.”