Overfertilizing Corn Undermines Ethanol

Joanna Schroeder

In a new paper published online in American Chemical Society’s Journal Environmental Science and Technology when it comes to growing corn for ethanol and using fertilizer – less may be more. Postdoctoral researcher Morgan Gallagher led the research team as part of her dissertation at Rice and discovered that corn, and its stalks and leaves, responded differently to nitrogen fertilizer.

The team 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 to be converted into cellulosic ethanol. They also found that when the corn is used for food and the cellulose is processed for biofuel, increasing the rate of nitrogen actually makes it more difficult to extract the cellulose, or lignin, which is converted to sugars and ultimately ethanol, from the corn stover and stalks. This is the case because surplus nitrogen fertilizer speeds up the biochemical pathway that produces lignin.

Carrie Masiello, an assistant professor of Earth science at Rice and Gallagher’s adviser believes that the findings of this research are an important next step in building a sustainable biofuel economy. While some nitrogen fertilizer is needed for plants to grow and function, she noted that for some crops, a little is enough.

We already know too much fertilizer is bad for the environment. Now we’ve shown that it’s bad for biofuel crop quality too,” Masiello said. 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.”

The research showed that although increasing nitrogen improves the plant’s cellulose content, grain yield quickly hits a plateau. “The kilograms of grain you get per hectare goes up pretty fast and peaks,” Masiello said. At the same time, the researchers found only a modest increase in plant and stem cellulose, the basic component used to produce cellulosic ethanol.

The implicit assumption has always been that the response of plant cellulose to fertilizer is going to be the same as the grain response, but we’ve showed this assumption may not always hold, at least for corn,” Gallagher said.

These are just a few of the findings of the research and the team hopes that their methods can be transferred to other energy crops. Click here to read the full release.

Cellulosic, Ethanol, Research