There are opportunities for farmers to save money by switching from wood to agricultural residue materials —like straw and corn cobs— to remove nitrates from drainage water. That is the conclusion of a new study published by the Agricultural Utilization Research Institute (AURI), in partnership with USDA‐Agricultural Research Service (USDA‐ARS), Minnesota Corn Research & Promotion Council (MCRPC) and the University of Minnesota.

The study “Optimization of Denitrifying Bioreactor Performance with Agricultural Residue-Based Filter Media” examined the performance of agriculturally‐derived residue materials in denitrifying bioreactors compared to traditional wood-based bioreactors.

USDA-ARS scientists measured nitrate removal, microbial abundance and dissolved nitrous oxide gas, comparing wood chips with stover, straw and corn cobs. The residue materials had greater rates of nitrate removal when compared the wood chips, an encouraging sign for farmers looking to save money and reduce costs. Bioreactors powered by residue materials have the potential to be smaller and cheaper to install, maintain and operate than wood-based bioreactors, while producing the same results. Further, this research could spur new developments in bioreactor design to account for agricultural residue materials.

For instance, in comparing the costs for installation of a denitrifying bioreactor designed to treat 50 acres, the study found that installation costs of a residue‐based reactor may be 70 percent of those of a traditional wood‐based bioreactor.

”This report provides Minnesota’s agricultural community with new, yet readily available on-farm mediums to help remove nitrates in their drainage systems. The potential cost savings and enhanced performance benefits from the research, which can help clean water flowing through tiled drainage systems, presents new possibilities to solve challenging problems. While more research is necessary in this area, this report provides an important first step to implementing applicable solutions that take advantage of the availability of on-farm agricultural residues.”