Read the full story at NPR.
The problems with nitrogen fertilizer start at its creation, which involves burning lots of fossil fuels. Then, when farmers spread it on their fields, it tends not to stay where it belongs. Rainfall washes some of it into streams and lakes, and bacteria in the soil feed on what’s left, releasing a powerful greenhouse gas called nitrous oxide.
There have been lots of attempts to control renegade nitrogen. Most have focused on threats to water and wildlife. Maryland, Virginia and Pennsylvania, for instance, have spent billions of dollars keeping nitrogen (and other forms of fertilizer runoff) out of the Chesapeake Bay.
Reducing nitrogen’s contribution to global warming, though, is even more difficult. Philip Robertson, a researcher at Michigan State University who’s studied those greenhouse emissions, says that “ultimately, the best predictor of the amount of nitrous oxide emitted to the atmosphere is the rate at which we apply nitrogen.” Essentially, the only proven way to cut heat-trapping emissions from nitrogen fertilizer is to use less of it. Most farmers haven’t been willing to do this, because it could cut into their profits.