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  • Michael J. Kieffer

Greatest 20th Century Innovation and Its Lasting Legacy

As the world’s population has recently surpassed 7 billion, it seems to be a good time to review how that is even possible. At the turn of the 20th century, all arable land was in agricultural use and China was leading the world in recycling all possible waste to naturally fertilize their crops. Even if every country recycled waste as thoroughly as China, the human population growth of the planet was limited if widespread famine was going to be avoided.


Carbon is the structural element of life, making up nearly half of all living matter, but nitrogen is the key. Life requires only small quantities of nitrogen, yet its shortage is often the limiting factor in crop production and human growth. Nitrogen-containing compounds control all of life's phenomena, and within these compounds, the nitrogen atom plays a vital role. Nitrogen is present in every living cell, including chlorophyll, which can be excited by light to energize photosynthesis; DNA and RNA which store and process all genetic information; amino acids which make up all proteins; and enzymes which control the chemistry of life. Nitrogen's importance in plants cannot be overstated. It is the nutrient responsible for vigorous vegetative growth and for the size and protein content of humankind's staple cereals.



Photo courtesy of public.ornl.gov


Commercialized sources of nitrogen in the early 1900’s were limited to guano (mainly from the Chincha Islands off the coast of Peru), recovery of by-product ammonia from the coking of coal, and the exploitation of nitrate fields in Chile. Collectively, these inputs added up to a small fraction of managed nitrogen requirements worldwide, with Europe consuming a disproportionate amount. European countries, mainly Germany, relying on Chilean nitrates in time of volatile global relationships, put growing pressure on a century-long search to take nitrogen and hydrogen and synthesize the most basic nitrogen compound, ammonia. With World War I looming on the horizon, Germany pushed their chemists to synthesize ammonia, fearing the British navy would cut off the Chilean nitrates needed to feed their countrymen (Smil, 2001).


Nitrogen gas is odorless, colorless, nonflammable, non-explosive, nontoxic, and nonreactive under normal environmental conditions. Nitrogen comprises 78 percent of the earth's atmosphere as N2, a triple-bonded molecule. N2 molecules must be split before nitrogen atoms can be incorporated into inorganic and organic compounds, and thus its usable forms are scarce. Lightning is the main physical process that can naturally fix substantial amounts of nitrogen; it splits the tightly bonded molecules and frees the nitrogen atoms to form reactive compounds. Lightning's contribution to the nitrogen cycle, however, falls considerably short of agriculture's needs.


Most usable nitrogen is fixed by nitrogen-fixing microorganisms, which employ the nitrogenase enzyme. The reduction of nitrogen gas to ammonia by nitrogenase at standard atmospheric conditions is an unbelievable evolutionary happenstance. Remarkably, there are only a few kilograms of nitrogenase on the planet at any one time, yet those few kilograms sustained the biosphere for millennia. Biology accomplished what 19th-century chemists could not replicate experimentally, and certainly not commercially, due to the tremendous heat, pressure, and energy consumption a chemical process required.


Arguably the greatest 20th century innovators were two German chemists. Fritz Haber, who demonstrated experimentally the conversion of nitrogen gas (N2) to ammonia (NH3) in 1909 with a bench top model, and Carl Bosch, who scaled it up to industrial production in 1913. This engineering feat cannot be overlooked; even BASF, the chemical company responsible for patenting the Haber-Bosch process of ammonia synthesis, was very skeptical about running continuous catalytic synthetic reactions at the high temperatures and pressures needed. A more efficient process is used today, but it operates very much like the original invention. The Haber-Bosch process was the breakthrough needed to effectively remove the key limit to crop production and to turn world agriculture towards high-yielding cultivars, but the world fertilizer market sat and waited through the first half of the 20th century, as the process was usurped for making munitions.


It took until the end of World War II to begin making fertilizers in quantities that changed how we feed ourselves. Worldwide, and especially in areas experiencing population explosions, much of the protein needed for growth comes from the synthesis of ammonia. This brings up a couple of serious concerns. First it means that the 5 billion people that in a sense were born from ammonia synthesis rely on an energy intensive commercial food production rooted in fossil fuels that are not sustainable. Secondly, synthetic fertilizers have almost doubled the reactive nitrogen in the environment, dramatically altering natural nitrogen flows, often by more than a magnitude. Rivers, lakes, coastal waters, and forests are experiencing many known and unknown effects, and many are alarming. As a global community, we tied our fate to the Haber-Bosch process, as more than half of us rely directly on the production achieved from these nitrogen inputs.


The world has evolved for millions of years with fixed nitrogen as a limiting factor to plant growth. We are loosing many of our synthetic inputs on surrounding natural communities that have never experienced such a deluge. We cannot be sure what will happen, but prudent action would eliminate all unnecessary inputs while making sure all necessary inputs do enter into crops and not natural communities. Nature is not designed to adapt in mere generations to a change in such a fundamentally important nutrient cycle. Next time you think about the importance of landing on the moon or personal computers, remember that only one 20th-century innovation feeds the world. Use it wisely.


Smil, Vaclav, Enriching the Earth: Fritz Haber, Carl Bosch, and The Transformation of World Food Production (MIT Press, 2001). Copyright © 2020 BRMC Publications

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