The Nitrogen Paradox: Is Feeding the World the Real Issue?

Biological nitrogen fixation fed the world until the end of the nineteenth century. What changed?

Is it possible to feed the world’s current population of 8 billion people without synthetic nitrogen fixation? Although it’s more common to frame the organic/conventional agriculture debate as being about chemical fertilizers in general, the main controversy is about nitrogen. Nitrogen is different from the other mineral element used as fertilizers, which are derived from rock formations. All nitrogen on earth comes, originally, from the atmosphere, which is 78 percent nitrogen. Atmospheric nitrogen is chemically inert—held together with a powerful triple bond, one of the strongest chemical bonds in nature. In order for plants to use nitrogen to build amino acids and proteins, it first needs to be fixed into a plant-available form—ammonium or nitrate. And plants can’t fix their own nitrogen.

That’s where the bacteria come in. Several different species of bacteria have the ability to fix atmospheric nitrogen into ammonium. Some of them live freely in the soil, but the most productive ones can only live in a symbiotic relationship with certain plants, mostly in the legume family (Fabaceae). This fixed nitrogen is recycled from one organism to another in a very complicated cycle and eventually ends back up in the atmosphere through denitrification—another bacterial process. Nitrogen is always closely linked with organic matter, and good farmers all over the world knew that soils rich in organic matter would grow healthy plants.

There was no talk about a nitrogen shortage until agronomists in the late nineteenth century started encouraging farmers to use chemical fertilizers instead of manure. Since nitrogen is biological in origin and is usually associated with organic matter, it was hard to find an inorganic source of fixed nitrogen. Finally, they found one—deposits of sodium nitrate in the Atacama Desert of Chile. These nitrates were fixed by free-living bacteria, and the only reason they piled up instead of being denitrified was because the climate was extremely arid. This natural oddity made it possible to separate nitrogen from organic matter for the first time in history.

Of course, the supply of Chilean nitrates was limited—they could never fully replace organic nitrogen sources. Sir William Crookes, the president of the British Association for the Advancement of Science, misunderstood the nature of the problem. Dismissing the biological nitrogen cycle that had supported all of life since the beginning of the world as “absolutely dependent on difficult and capricious natural phenomena,” he predicted mass starvation when the Chilean nitrates were exhausted. “The only “way out of the colossal dilemma” was for scientists to develop a mechanical and chemical way to fix atmospheric nitrogen, circumventing natural processes. “It is through the laboratory that starvation may ultimately be turned into plenty,” he predicted.

At face value, this sounds like a heartwarming humanitarian sentiment. But what Crookes only briefly alluded to in his speech was that the impending nitrate shortage wasn’t merely an agricultural problem. He explained that the exhaustion of the Chilean nitrates, in addition to causing “a catastrophe little short of starvation for the wheat-eaters,” might also lead to “the extinction of gunpowder!” The huge surge in demand for nitrates wasn’t just for agriculture; it was also for explosives. And while properly managed biological nitrogen fixation could provide enough nitrates for all the world’s organisms, it could never produce enough for the explosives that characterized modern warfare. Though it sounded a lot better to put the emphasis on growing food, the real push for developing synthetic nitrogen fixation was for weapons.