Nitrogen Cycling in Four Biofuel Feedstock Crops During Establishment.

The development of clean and affordable renewable energy continues to be of interest, especially in light of recent environmental damages.  While biofuel crops have been promoted as a sustainable energy source by reducing carbon dioxide emissions, different feedstock crops have differential impacts on the environment.  Additionally, nitrogen may play a larger role in global climate change than once thought.  Nitrate leached from fields contributes to the Gulf hypoxia and nitrous oxide, a powerful greenhouse gas, is produced both in field and drainage waters.  In 2008, a side by side comparison of four biofuel feedstock crops (corn/soybean rotation, Miscanthus x giganteus, switchgrass and restored prairie) was established to determine the production and sustainability of each crop.  Our objective was to compare the pools and fluxes of nitrogen in each biofuel feedstock crop for evaluation of environmental consequences and sustainability.In their third year of growth, nitrogen leaching in all three perennial crops has decreased.  However, Miscanthus continues to release elevated amounts of nitrogen compared to prairie and switchgrass. The first year of soybean in the corn-corn-soybean rotation showed reduced nitrate leaching compared to fertilized corn.  Nitrous oxide emissions (using static vented chambers) were elevated in the perennial crops compared to the previous year due to an unusually warm and wet growing season.  While nitrous oxide emissions were highest in the soybean treatment, emissions were significantly reduced from the previous year’s fertilized corn.  Switchgrass was fertilized the first year in this study (56 kg/ha with urea), but did not produce higher nitrous oxide emissions or nitrate leaching.  Results from this study highlight the importance of perennial crops for reducing negative environmental impacts and the need for direct comparisons of biogeochemical cycling in different feedstock crops.