Nitrogen Losses Reduced from Perennial Biofuel Crops

E thanol from corn has been the primary biofuel for liquid fuels in the United States, but perennial cellulosic biofuels are on the horizon. Intensive corn production with large fertilizer inputs leads to large losses of nitrogen into the environment, both through gas emissions of nitrous oxide and leaching losses of nitrate to ground and surface (through tile systems) waters. Nitrous oxide is an important greenhouse gas, and nitrate can contaminate drinking water supplies and leads to coastal ocean problems. The hypoxic zone that forms each summer in the Gulf of Mexico is a result of nitrate losses from the tile-drained Corn Belt of the midwestern United States. There are few measurements of nitrogen losses on large, tile-drained fi elds planted with perennial biofuels in the Midwest of the United States, a likely location for biofuel production. Nitrogen budgets (to assess balances and need for fertilization) and loss measurements are needed to fully understand the response of the nitrogen cycle to the production of biofuel crops on tile-drained fi elds. This allows for a more complete assessment of the long-term sustainability of biofuel production systems compared with corn and soybean production. In the January–February 2013 issue of the Journal of Environmental Quality, researchers report on four years of measurements of nitrogen losses during the establishment phase of perennial biofuel crops compared with conventional corn and soybean production in east-central Illinois. The biofuel crops, planted on rich Mollisols, were miscan-thus, switchgrass, and mixed prairie species, all compared against a typical corn–corn–soybean rotation. Miscanthus is a highly productive grass, planted from rhizomes, that is being evaluated as a biofuel crop. Harvested biomass and nitrogen, nitrous oxide emissions, and nitrate leaching in the mid-soil profi le and through tile drainage lines were all measured. The authors found that perennial crops quickly reduced nitrate leaching in the mid-soil profi le as well as from tile lines, so that by Year 4, each of the perennial crops had small losses. Nitrous oxide emissions also were much smaller in the perennial crops (including switchgrass, which was fertilized with nitrogen, unlike prairie and mis-canthus). Overall nitrogen balances (inputs minus outputs) were positive for the corn and soybean treatment as well as switchgrass but were negative for prairie and miscanthus. Prairie and miscanthus balances were negative due to harvest of the plant biomass (and nitrogen) each winter, with no fertilizer nitrogen additions to replace it, as occurred in …