If you go into Mammoth Cave National Park, among all the flowstone draperies and crystal-encrusted formations, there’s one notable feature of decidedly non-natural origins. It’s a saltpeter mine. Saltpeter (chiefly potassium nitrate) was gathered from the mine in great quantities during the 19th century, as it was from many other caves around the world. It was used in making gun powder (the War of 1812 consumed a good deal of the production), but it had a broader and even more important use: fertilizer.
For fields being used regularly in crop production, nitrogen in the soil can easily be depleted. To replace it, farmers since antiquity have used fertilizers. For most of that time, those fertilizers were of the organic variety (i.e. manure) but the discovery that nitrogen chemicals can give a big boost to soil production was known long before there was a reliable source of nitrogen. Then in the early days of the 20th century a pair of German chemists, Fritz Haber and Carl Bosch, developed a process to produce ammonia from atmospheric nitrogen.
That process made possible the wealth of chemical fertilizers that helped power the “Green Revolution,” which massively increased food production around the world between the 1930s and the 1960s. The Haber-Bosch process is, in a very real sense, how the world feeds itself today. It’s one of the most important chemical processes ever discovered.
But there's a problem.
… what seemed ingenious 100 years ago is running into problems in 2016. The Haber-Bosch process burns natural gas (3 percent of the world's production) and releases loads of carbon (3 percent of the world's carbon emissions). If relying on fossil fuels to give the world electricity and heat is unsustainable, so is relying on fossil fuels to grow its food.
The energy consumption of Haber-Bosch has always been a problem. While the nitrogen in the process comes from the air, and the hydrogen can come from water, the need for large amounts of energy in the process is one of the chief reasons that fertilizers are often shipped to regions rather than made on the spot. So the search for an alternative that can be effective in areas without regular supplies of natural gas has been there for a long time. It’s just that, now that we understand the relationship between that energy and making the world warmer (and, incidentally, affecting the growing regions of many crops that depend on Haber-Bosch fertilizers) that the search for an alternative is getting more deliberate.
So in the search for new ways to make ammonia, scientists have turned to imitating nature. "Biology does this reaction in fairly simple way compared to Haber-Bosch," says Paul King, a photobiologist at the National Renewable Energy Laboratory. For one, it happens at room temperature, since any living thing would be cooked and crushed at Haber-Bosch conditions. Nitrogen-fixing bacteria have enzymes that grab N2 molecules and H+ ions, orienting them just the right way so they form ammonia, or NH3.
Right now, alternative processes aren’t cost competitive, but they have some of the same advantages as renewable energy: chiefly that they can be done “in place” producing fertilizer where it’s needed, so that transportation costs (and energy) can be factored out.
And just as with renewable energy sources, there’s a single action governments could take to move fertilizers away from Haber-Bosch.
Funding interest from the top levels of government is one thing. Making fossil fuel-free ammonia synthesis commercially viable is another. King thinks what will ultimately set the industry off is a carbon tax. Humanity doesn't need to recognize value in nitrogen; it needs to see danger in carbon.
Not-so-fun fact: Fritz Haber drew an enormous amount of praise and international recognition for his role in solving this equation and became something of an international chemical rock star. In 1918, he was awarded the Nobel Prize for Chemistry. There was almost no area of chemistry in the first two decades of the 20th century where he wasn’t a driving force.
When World War I began, Haber wasn’t revolted by the carnage—he was energized. He was one of the names on the Manifesto of the Ninety-Three, a statement from German scientist and philosophers in support of the war.
Haber put his expertise to work in creating chemical weapons. His team put chlorine gas in the air at the Second Battle of Ypres, where it formed hydrochloric acid in the nose, throat, and lungs of soldiers unfortunate enough to breath it in. Haber was enthusiastic about the results, and continued to develop explosives and chemical weapons as part of a special chemical warfare team.
After the war, Haber became the first director of Degesch, a German chemical company, where he helped to developed pesticides. He also held positions in several academic and governmental organizations. He became increasingly worried about the rise of nationalism. Haber’s family was Jewish, though he had converted to Christianity. By 1933, hounded and turned into a symbol of Jewish influence in the sciences, he left Germany.
Haber was offered a role as director at the Sieff Research Institute in Palestine. But on his way to Palestine, he died of a heart attack.
The Haber-Bosch process outlived him. So did something else. Among the products that came out of Haber’s time at Degesch was a pesticide made from hydrogen cyanide. They called it Zyklon.