America’s nitrogen dilemma—and what we can do about 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.

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.

But what to do about this genuine N dilemma? Our food system has become reliant on an input that appears to be unsustainable at current levels of use, while our population is growing. How can we maintain a robust, plentiful, growing food supply while also using less synthetic N?