There are three things on which the mighty engine of U.S. agriculture depends: water, fuel, and synthetic nitrogen. Like water, nitrogen is elemental to life. It's the essential building block of the plants we eat. Farmers remove it from the soil when they harvest the year's crop, and they must replenish it for the following year's.
Compared with water and fuel, nitrogen is actually in one sense quite plentiful: it makes up about 80 percent of the air we breathe. Yet for all that ubiquity, it's also in a sense scarce: its extremely strong chemical bond -- it exists in the air in triple-bonded pairs of nitrogen known as N2 -- makes it difficult for plants to use.
The N of the world as we know it
Less than 100 years ago, we learned -- in the process of perfecting bomb-making technology -- how to create readily available nitrogen on a vast scale. The introduction of mass-produced synthetic nitrogen fertilizer revolutionized agriculture, freeing farmers from the burdens of nitrogen fixation and allowing them to grow more food than ever before. Synthetic nitrogen revolutionized society, too: the explosion in crop yields that it helped drive made food cheaper and more plentiful than ever, setting the stage for the 20th century's population boom.
This series has explored how the annual cascade of synthetic nitrogen fertilizer isn't just helping farmers grow tremendous quantities of food; it is also generating serious problems for soil quality, public health, the climate, and more. As my article on the geopolitics of our N dependency showed, the process of generating synthetic nitrogen requires massive amounts of increasingly scarce natural gas. (In China, the situation is even worse; that nation, the globe's largest consumer of nitrogen, uses coal, a fuel source significantly dirtier than natural gas, to produce 70 percent of its N supply.)
And because of the physiology of plants and the pressure to maximize yields, farmers routinely over-apply nitrogen. According to Peter Vitousek, a professor of biology at Stanford and a leading scholar on the nitrogen cycle, under optimum conditions and using best practices, plants take up only "50 or at best 60 percent" of the nitrogen laid on by farmers. So if so much of their fertilizer is going to waste, why do farmers apply so much? Vitousek explained that plants take up different amounts of nitrogen at different points in the growing cycle. To ensure that crops have sufficient N when they need it most, farmers essentially have to over-apply.
Globally, "about two-thirds of the nearly $100 billion of nitrogen fertilizer spread on fields each year is wasted," estimates The Economist. That's a lot of cash down the drain and a lot of nitrogen bleeding out of fields in various forms, wreaking all manner of havoc: Exhibit A, the 8,000-square-mile dead zone that blooms every year in the Gulf of Mexico, as Krysta Hozyash covered.
America's Nitrogen Dilemma - and What We Can Do About it
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The N of an era: America’s nitrogen dilemma—and what we can do about it
By Tom Philpott
Grist, March 4, 2010
Straight to the Source
