Getting Our Nitrogen Fix

: Image via Wikipedia

Our ability to pull nitrogen from the air fed a growing human population.

Can 21st century biotechnology refine the process while reducing environmental impact?

In 1968 the entomologist Paul Ehrlich published a foreboding manifesto called The Population Bomb, in which he argued that the explosive growth of the human population would lead, within the next decade, to mass starvation and the death of hundreds of millions of people. It was the old Malthusian trap: Population increases tend to be exponential, while increases in the food supply are linear. The tragedy was simple math.

But Ehrlich was wrong. There were plenty of horrific famines in the 1970s, especially in Sub- Saharan Africa, but there was no global food shortage. In fact, over the next few decades, the growth of the food supply consistently outstripped population growth; it was Malthus in reverse. While a long list of variables drove this trend, from the increased use of pesticides to new varieties of corn, wheat, and rice, one of the most important factors was the introduction of synthetic fertilizer. Plants thrive on nutrients in the soil, and these mass-produced fertilizers led to the doubling of crop yields between 1950 and 1990. We learned how to feed ourselves because we learned how to feed plants.

The story of modern fertilizer is really the story of nitrogen, and how humans learned to make plant food out of air and energy. Fritz Haber was there first. A German industrial chemist, he developed a method for “fixing” nitrogen around the turn of the 20th century. Although nitrogen is abundant, accounting for more than 78 percent of the Earth’s atmosphere, it is also highly inert: The gas is defined by its triple covalent bonds, which are extremely difficult to sever. Haber achieved his breakthrough by heating a mixture of nitrogen and hydrogen gas in the presence of the chemical catalyst iron oxide. When this concoction was heated to 500°C and 200 atmospheres of pressure, the result was a brick of ammonia, or NH₃. With Haber, the sky was rendered solid.

Before the Haber process was perfected, fixed nitrogen, usually in the form of sodium nitrate, or “Chile saltpeter,” was a crucial natural resource. In addition to being valuable as fertilizer, it was an essential component of military ammunition?—?nitrogen provides the explosive lift inside the gun chamber?—?so controlling access to nitrogen meant controlling the ingredients of war. Indeed, the first major deployment of Haber’s chemical process had nothing to do with agriculture. Rather, it provided Germany with a seemingly infinite supply of ammonia, which meant that it could fight a world war even if the British Navy cut its access to saltpeter.