Overfertilizing Corn Undermines Ethanol
Tuesday, March 8th, 2011
When growing corn crops for ethanol, more means less.
A team of researchers from Michigan State University and Rice University shows how farmers can save money on fertilizer while they improve their production of feedstock for ethanol and alleviate damage to the environment. The results are featured in the current issue of American Chemical Society’s journal Environmental Science and Technology.
The research has implications for an industry that has grown dramatically in recent years to satisfy America's need for energy while trying to cut the nation's reliance on fossil fuels, according to Sieglinde Snapp, a crop and soil scientist at MSU’s Kellogg Biological Station.
“In an era of increasing reliance on corn production for food and fuel, it is important to quantify the full impact of corn nitrogen management on the environment and on the crop biochemistry,” she said.
The team discovered that corn grain, one source of ethanol, and the stalks and leaves, the source of cellulosic ethanol, respond differently to nitrogen fertilization. The researchers found that liberal use of nitrogen fertilizer to maximize grain yields from corn crops results in only marginally more usable cellulose from leaves and stems. And when the grain is used for food and the cellulose is processed for biofuel, pumping up the rate of nitrogen fertilization actually makes it more difficult to extract ethanol from corn leaves and stems.
This happens, they discovered, because surplus nitrogen fertilizer speeds up the biochemical pathway that produces lignin, a molecule that must be removed before cellulosic ethanol can be produced from corn stems and leaves.
The findings are an important next step in building a sustainable biofuel economy. While farmers have a clear incentive to maximize grain yields, the research shows a path to even greater benefits when corn residues are harvested for cellulosic ethanol production.
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.
The research was supported in part by the National Science Foundation and MSU’s AgBioResearch.
Michigan State University Extension