Brent Deppe is taking me on a tour of the farm supply business, called Key Cooperative, that he helps to manage in Grinnell, Iowa. We step though the back door of one warehouse, and our view of the sky is blocked by a gigantic round storage tank, painted white.
“This is the liquid nitrogen tank,” Deppe explains. “It’s a million-and-a-half gallon tank.”
Nitrogen is the essential ingredient for growing corn and most other crops. Farmers around here spread it on their fields by the truckload.
“How much nitrogen goes out of here in a year?” I ask.
Deppe pauses, reluctant to share trade secrets. “Not enough,” he eventually says with a smile. “Because I’m in sales.”
For the environment, though, the answer is: Way too much.
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…
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