11 oct 2019
Nitrogen is a keystone in the world's food chain, providing billions of humans with the energy to drive human progress forward.
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Stuff of Progress, Pt. 1: Nitrogen
By Tony Morley
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So much time has gone by that people in rich countries have all but lost the ability to imagine the lives of those who toiled on pre-industrial farms, where farm workers struggled to produce enough calories to survive. Pre-industrial agricultural conditions were dirty and cripplingly hard — particularly for the children. Without the capacity to produce and store a significant surplus of foodstuffs, most people were exposed to crop failure, punishingly high food costs and occasional famines. The collective inability of our species to produce, on average, more food per-capita than was required for consumption, dramatically limited our ability to support a higher population. That also limited our potential for a high degree of specialization, trade and an upward march in living standards.

 

Prior to 1900, progress in improving agricultural yields was extremely slow. The food crops that feed modern civilization require fixed nitrogen in the soil in order to grow. Nitrogen, while abundant in the air (it constitutes approximately 78 percent of the air we breathe), is wholly inaccessible to plants, as it is tightly locked in a molecular triple bond. The nitrogen triple bond is a chemical bond in which three pairs of electrons are shared between two atoms. In this configuration, nitrogen cannot be induced to react or be absorbed by plants. It is essentially inert and thus of no use in agriculture. Fixed nitrogen, which is a form of nitrogen that plants can access to foster growth, is produced on a geological timescale by tiny microorganisms in the soil. These unicellular prokaryotes utilize the enzyme nitrogenase to catalyze atmospheric nitrogen (N2) to ammonia (NH3), which plants can then consume. 

 

The natural replenishing process is far too slow to keep pace with the demands of pre-industrial, let alone modern, agriculture. Since the dawn of the agricultural era some 10,000 years ago, each crop harvest reduced the available nitrogen in the soil, thus reducing yields in subsequent harvests. All that changed with the development of fixed nitrogen synthesis — later called the Haber-Bosch process. Between 1909 and 1913, Fritz Haber and Carl Bosch, two prominent chemists working in Germany, drew fixed nitrogen directly from the air. By using natural gas and catalysts under extremely high pressures, Haber and Bosch “cracked” the triple bond, rendering ammonia — a hydrogen-nitrogen compound that can be applied to fields to replace depleted nitrogen from the soil.

 

(The Haber-Bosch process works by combining hydrogen, which is sourced from abundant and relatively inexpensive natural gas, with nitrogen from the air. The mixture is then subjected to 200 atmospheres of pressure and temperatures of 450 °C or 840 °F. The continuous reaction that takes place in a high pressure iron catalyst reactor results in an uninterrupted flow of liquid ammonia.)

 

The Haber-Bosch process currently feeds some 3.5 billion humans annually — the others are fed by less advanced agricultural methods. Ammonia is produced inexpensively at a rate of more than 160 million tons annually and the production rate is expected to grow by more than 6 percent in the next three years combined. The application of ammonia-nitrogen fertilizer allows humans to extract a large and reliable volume of crops across the globe, reducing the risk of food shortages and eliminating famines outside of war zones. Because of a series of key technological advances in agriculture, including but not limited to nitrogen fertilizer, GMO crop utilization, mechanized farming, and pesticide applications, Paul Ehrlich’s predictions never came true. 

 

“The battle to feed all of humanity is over,” wrote the Stanford University biologist in his 1968 book The Population Bomb. “In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate.” That bleak prophecy turned out to be inaccurate, not due to luck, but rather due to the application of agrochemical science and technology. Nitrogen remains a keystone in the world’s food chain, providing billions of humans with the energy to drive human progress forward. 

 

If you want to learn more about nitrogen, the author recommends a 2004 book titled Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production by Vaclav Smil, Distinguished Professor in the Faculty of Environment at the University of Manitoba in Winnipeg, Canada.

Tony Morley is a freelance science writer and progress and growth exponent, based in Sydney, Australia.
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