Overfertilization also increases the decomposability of corn residue plowed back into the fields. This implies that soil carbon storage becomes less efficient—another minus for the environment because storing additional carbon in soil can reduce the atmospheric concentration of carbon dioxide and help crops access soil water.
Issues associated with the runoff of nitrogen from fertilizer into streams and leaching into groundwater are common knowledge, Masiello said. She noted the well-established link between nitrogen fertilizer use in the Mississippi Valley and a "dead zone"—defined as a lack of life-supporting oxygen—in the Gulf of Mexico. Nitrate runoff and leaching into drinking water supplies has also been linked to a number of health problems, the researchers wrote.
Finally, Gallagher noted that improving the yield of feedstock for cellulosic ethanol leaves more corn for food. “There's a billion people who are malnourished, so it's ethically questionable to use corn grain for fuel rather than food,” she said.
The researchers hope their methods can be transferred to other crops grown for ethanol. Gallagher, who recently earned her doctorate at Rice and is starting a joint postdoctoral stint between Masiello's lab and the NSF agricultural research station at Michigan State, plans to quantify the effects of nitrogen fertilization on switchgrass, which is growing in importance as a biofuel feedstock.
Co-authors of the paper include Sieglinde Snapp, an associate professor at MSU and a soils and cropping system ecologist at the W.K. Kellogg Biological Station; Claire McSwiney, a postdoctoral researcher at the Kellogg Biological Station; and Jeffrey Baldock, a researcher at Australia's Commonwealth Scientific and Industrial Research Organization.
The National Science Foundation and its Long-Term Ecological Research Program at the Kellogg Biological Station and MSU's AgBioResearch supported the research.
Read the abstract at http://pubs.acs.org/doi/abs/10.1021/es103252s
See a video of Masiello and Gallagher discussing their research here: http://www.youtube.com/watch?v=32BS7kpSeIs
A high-resolution photo of Masiello and Gallagher is available for download at: http://media.rice.edu/images/media/NewsRels/0217_ETHANOL.jpeg