In the study, funded by the Energy Biosciences Institute, miscanthus, switchgrass, and mixed prairie species were compared against a typical corn-corn-soybean rotation. Harvested biomass and nitrogen, nitrous oxide emissions, and nitrate leaching in the mid-soil profile and through tile drainage lines were all measured.

The researchers found that the perennial crops quickly reduced nitrate leaching in the mid-soil profile as well as from tile lines. “By year four each of the perennial crops had small losses,” Smith said. “Nitrous oxide emissions also were much smaller in the perennial crops–including switchgrass, which was fertilized with nitrogen, while prairie and miscanthus were not. Overall, nitrogen levels were higher for the corn and soybean treatment as well as switchgrass, but were lower for prairie and miscanthus. Prairie and miscanthus levels were lower due to harvest of the plant biomass (and nitrogen) each winter, with no fertilizer nitrogen additions to replace it, as occurred in corn and switchgrass,” she said.