We burn through more of it per capita than any other country; and our appetite for it can only be sated with massive imports.

No, not oil-I’m talking about nitrogen fertilizer. With only 5 percent of the world population, the U.S. consumes nearly 12 percent of the globe’s annual synthetic nitrogen fertilizer production. And we’re producing less and less of it at home-meaning that, as with petroleum, we’re increasingly dependent on other nations for this key crop nutrient.

In a sense, the answer to the question of where our food comes from is not some vast Iowa cornfield or teeming North Carolina hog factory. It’s places like the Port Lisas Industrial Estate on the Caribbean island nation of Trinidad and Tobago, where 10 natural gas-sucking ammonia plants produce about a quarter of the nitrogen fertilizer used by American farmers.

Nitrogen fertilizer production is tied directly to natural gas, the energy source used in the United States to synthesize nitrogen-rich ammonia from thin air. So you could also imagine our food coming from some vast natural gas deposit in the Gulf of Mexico or off of Trinidad. Nearly as much as grain elevators or supermarkets, off-shore gas rigs count as vital food-system infrastructure.

But as U.S. natural gas prices began rising early this decade, the domestic nitrogen fertilizer industry went into crisis. Producers either scaled up to gain efficiency, moved to countries with cheaper natural gas sources like Trinidad and Tobago, or simply shuttered plants.

The industry has flirted with the idea of switching to gasified coal as the energy source for N fertilizer. “Recent advances in using coal to produce ammonia have increasingly made this technology economically feasible, especially at high natural gas prices,” USDA analyst Wen-yuan Huang wrote in a 2009 paper [PDF]. “Domestic ammonia production based on coal may play a larger role in the U.S. nitrogen supply if economic conditions and environmental considerations are favorable.”