Biofuel crops have been widely promoted as a sustainable energy source by reducing carbon emissions, yet greenhouse gas emissions for these crops have not been well documented. Traditionally fertilized agricultural systems can emit large amounts of nitrous oxide, a powerful greenhouse house gas. While the leaching of nitrate from agricultural systems has been shown to contribute to the eutrophication of receiving waters and ultimately the Gulf of Mexico hypoxia, little is known about nitrous oxide emissions from streams draining agricultural lands. The goal of this research was to examine the direct and indirect emissions of nitrous oxide from biofuel feedstock crops. A side-by side comparison of four biofuel feedstock crops (corn, Miscanthus x giganteus, switchgrass and restored prairie) was established in 2008 to examine various aspects of biofuel production, including environmental consequences. To quantify direct N2O emissions from biofuel crops, static vented chambers were sampled weekly or biweekly throughout the growing season and monthly the remainder of the year. Indirect emissions were determined using dissolved N2O concentrations from tile drainage and nearby streams combined with emissions from floating chambers deployed in the streams.
Results/Conclusions
The loss of nitrogen through nitrous oxide emissions and tile drainage was greatest in the corn plots following spring fertilization. Nitrate leaching and nitrous oxide emissions were significantly reduced in all three perennial crops (Miscanthus, switchgrass and restored prairie) compared to the fertilized corn treatment. Preliminary data show that dissolved nitrous oxide concentrations from tile drainage did not significantly differ among crops. However, dissolved nitrous oxide concentrations in streams correlated with nitrous oxide emissions from the floating chambers. Both direct and indirect measurements of nitrous oxide emissions from biofuel feedstock crops are needed to determine the effect that biofuel feedstock crops have on global greenhouse gas budgets. Results from this study highlight the need for direct comparisons of biofuel crop biogeochemical cycling and the need to quantify environmental consequences both on and off agricultural fields.