In his book Enriching the Earth: Fritz Haber, Carl Bosch and the Transformation of World Food Production, Vaclav Smil pointed out that "there is no way to grow crops and human bodies without nitrogen." Before Haber's invention, the sheer amount of life earth could support—the size of crops and therefore the number of human bodies—was limited by the amount of nitrogen that bacteria and lightning could fix. By 1900, European scientists had recognized that unless a way was found to augment this naturally occurring nitrogen, the growth of the human population would soon grind to a very painful halt. The same recognition by Chinese scientists a few decades later is probably what compelled China's opening to the West: after Nixon's 1972 trip, the first major order the Chinese government placed was for 13 massive fertilizer factories. Without them, China would have starved.
This is why it may not be hyperbole to claim, as Smil does, that the Haber-Bosch process for fixing nitrogen (Bosch gets the credit for commercializing Haber's idea) is the most important invention of the 20th century. He estimates that two of every five humans on earth today would not be alive if not for Fritz Haber's invention. We can easily imagine a world without computers or electricity, Smil points out, but without synthetic fertilizer billions of people would never have been born. Though, as these numbers suggest, humans may have struck a Faustian bargain with nature when Fritz Haber gave us the power to fix nitrogen.
Fritz Haber? No, I'd never heard of him either, even though he was awarded the Nobel Prize in 1918 for "improving the standards of agriculture and the well-being of mankind." But the reason for his obscurity has less to do with the importance of his work than an ugly twist of his biography, which recalls the dubious links between modern warfare and industrial agriculture: during World War I, Haber threw himself into the German war effort, and his chemistry kept alive Germany's hopes for victory, by allowing it to make bombs from synthetic nitrate. Later, Haber put his genius for chemistry to work developing poison gases—ammonia, then chlorine. (He subsequently developed Zyklon B, the gas used in Hitler's concentration camps.) His wife, a chemist sickened by her husband's contribution to the war effort, used his army pistol to kill herself; Haber died, broken and in flight from Nazi Germany, in a Basel hotel room in 1934.
His story has been all but written out of the 20th century. But it embodies the paradoxes of science, the double edge to our manipulations of nature, the good and evil that can flow not only from the same man but from the same knowledge. Even Haber's agricultural benefaction has proved to be a decidedly mixed blessing.
When humankind acquired the power to fix nitrogen, the basis of soil fertility shifted from a total reliance on the energy of the sun to a new reliance on fossil fuel. That's because the Haber-Bosch process works by combining nitrogen and hydrogen gases under immense heat and pressure in the presence of a catalyst. The heat and pressure are supplied by prodigious amounts of electricity, and the hydrogen is supplied by oil, coal or, most commonly today, natural gas. True, these fossil fuels were created by the sun, billions of years ago, but they are not renewable in the same way that the fertility created by a legume nourished by sunlight is. (That nitrogen is fixed by a bacterium living on the roots of the legume, which trades a tiny drip of sugar for the nitrogen the plant needs.)
Liberated from the old biological constraints, the farm could now be managed on industrial principles, as a factory transforming inputs of raw material—chemical fertilizer—into outputs of corn. And corn adapted brilliantly to the new industrial regime, consuming prodigious quantities of fossil fuel energy and turning out ever more prodigious quantities of food energy. Growing corn, which from a biological perspective had always been a process of capturing sunlight to turn it into food, has in no small measure become a process of converting fossil fuels into food. More than half of all the synthetic nitrogen made today is applied to corn.
From the standpoint of industrial efficiency, it's too bad we can't simply drink petroleum directly, because there's a lot less energy in a bushel of corn (measured in calories) than there is in the half-gallon of oil required to produce it. Ecologically, this is a fabulously expensive way to produce food—but "ecologically" is no longer the operative standard. In the factory, time is money, and yield is everything.
One problem with factories, as opposed to biological systems, is that they tend to pollute. Hungry for fossil fuel as hybrid corn is, farmers still feed it far more than it can possibly eat, wasting most of the fertilizer they buy. And what happens to that synthetic nitrogen the plants don't take up? Some of it evaporates into the air, where it acidifies the rain and contributes to global warming. Some seeps down to the water table, whence it may come out of the tap. The nitrates in water bind to hemoglobin, compromising the blood's ability to carry oxygen to the brain. (I guess I was wrong to suggest we don't sip fossil fuels directly; sometimes we do.)
It has been less than a century since Fritz Haber's invention, yet already it has changed earth's ecology. More than half of the world's supply of usable nitrogen is now man-made. (Unless you grew up on organic food, most of the kilo or so of nitrogen in your body was fixed by the Haber-Bosch process.) "We have perturbed the global nitrogen cycle," Smil wrote, "more than any other, even carbon." The effects may be harder to predict than the effects of the global warming caused by our disturbance of the carbon cycle, but they are no less momentous.
The flood of synthetic nitrogen has fertilized not just the farm fields but the forests and oceans, too, to the benefit of some species (corn and algae being two of the biggest beneficiaries) and to the detriment of countless others. The ultimate fate of the nitrates spread in Iowa or Indiana is to flow down the Mississippi into the Gulf of Mexico, where their deadly fertility poisons the marine ecosystem. The nitrogen tide stimulates the wild growth of algae, and the algae smother the fish, creating a "hypoxic," or dead, zone as big as New Jersey—and still growing. By fertilizing the world, we alter the planet's composition of species and shrink its biodiversity.