What do red clover, seabird poop, World War I, the current world population and the Oklahoma City bombing all have in common? Nitrogen, specifically fixed nitrogen. In human hands it has the power to nurture or to destroy. We cannot exist without it. For example, it is nitrogen in the form of an amine group (-NH2) that gives amino acids their name. Amino acids are the building blocks of proteins, and proteins are vital components of the human organism. Nitrogen is also essential to DNA and RNA. In fact, nitrogen is the fourth most common element in the human body, accounting for about 3.2% of your body weight. Multiply that by a world population of over 7 billion, and that’s a lot of nitrogen tied up in humanity.
Fortunately, we are surrounded by nitrogen. Unfortunately, most of the nitrogen with which we come in contact is not, immediately, useful to us. Nitrogen makes up almost 80% of the earth’s atmosphere, so we should just be able to collect it from our breath, like oxygen, right? Well, in a word, no. Atmospheric nitrogen exists in an extremely stable, or inert, form, two nitrogen atoms linked together by a triple bond (N2). Our bodies cannot break that bond in order to harvest usable nitrogen from the air, nor can other animals, nor can plants. So how do we get it? The short answer is that plants can use nitrogen from the soil if it has been “fixed”. Nitrogen fixation means that the two nitrogen atoms have been separated and each combined with another element, like oxygen (e.g. in nitrates -NO3, which are what plants use) or hydrogen (e.g. in ammonia NH3). In these forms the nitrogen atom is reactive, or chemically available for cellular processes. Plants incorporate the fixed nitrogen from the soil, animals eat the plants, and we eat plants and other animals to get nitrogen.
Great, so where does the nitrogen in the soil come from? Well, it happens that although plants and animals cannot fix nitrogen, there are bacteria that can. Some of these bacteria are free-living, and some exist in symbiotic, or mutually beneficial, relationships with plants. So plants get the fixed nitrogen from the soil, animals get the nitrogen from the plants, plants and animals die, and other bacteria (as well as fungi) degrade organic matter, returning some of the nitrogen to the soil and some to the atmosphere. Animals also poop out excess nitrogen, which is why manure can be fantastic fertilizer. This “nitrogen cycle” is an elegant system, but you may have noticed that it is also self-limiting. Nitrogen fixing bacteria can only do so much, and not all plants exist in symbiosis with them. Legumes (e.g. peas, beans, and vetch) contain bacteria which can fix gaseous nitrogen in nodules in their roots. Cereal crops, such as wheat, on the other hand, do not. Early farmers noticed that growing certain crops repeatedly in the same field would “deplete” the soil, and the crops would stop producing well. They had no idea that it was nitrogen that was being depleted, and often dealt with the problem by allowing fields to lie “fallow,” or uncultivated, for a year or two. Human agriculture hummed along for around 10,000 years replenishing soil with compost and manure, or letting it “rest,” but there was an in-built upper limit to how many humans could exist at any one time.
A shift which was to have global consequences occurred in these agricultural practices in the eighteenth century with the introduction of the four field crop rotation system to England. Now the English did not develop this system, they imported it from Flanders where it had long been commonplace, but their implementation of it was pivotal to developments with far-reaching consequences. For centuries, arable land on English manors had been divided into two or three major fields, each of which was then subdivided into strips allotted to lord and tenants. To deal with soil depletion, one, entire field was left fallow every year. This meant that between a third and a half of all English farmland at any given time was devoted to weeds. Not only did this limit plant food for humans, it also limited fodder for livestock. Cattle could not be kept alive through the winter, and it was customary to slaughter many every autumn.
In the Four Field System, as the name suggests, land was divided into four major fields, which were not subdivided. Each field was planted with a single crop, and no field was left fallow. One field would be planted with wheat, another with turnips (or swede/rutabaga), a third with barley (or oats), and the last with clover. The crops would be rotated each year, so that in the course of four years, each field had grown each crop once. The genius of this system was that not only were all fields productive at all times, but turnips and clover provided winter fodder for cattle, and clover, which exists in symbiosis with nitrogen-fixing bacteria, replenished the soil. Farmers could keep larger herds of livestock, allowing them to experiment with breeding. More food could be produced, which meant more people could be fed, but it also meant an end to individual “peasant” farming and communal fields. As the proportion of the workforce needed for agriculture fell, workers were freed up for (or pushed into, depending on how you view things) labor in service and, critically, industry. This was a complex and multifactorial process, but it is not a stretch to say that clover, with its nitrogen-fixing bacteria, lay at the root of the industrial revolution and budding British hegemony. By 1850, as the British Empire expanded dramatically, only 22% of the British labor force actively engaged in agriculture. This was a smaller proportion than in any other nation in the world at that time.
Crop rotation with cover crops (turnips and clover, in this case) was very much akin to what we would now consider sustainable, organic agriculture. It produced enough food to support the spark of industrial revolution, but not enough to sustain the growing populations of nineteenth century Europe and North America. Even with crop rotation, soils were being depleted, when another source of nitrogen came to the rescue. If the industrial revolution was rooted in clover, global empire rested on bird shit. Europeans first encountered the thick deposits of bird droppings, called guano, in South America at the beginning of the nineteenth century. Rich in accessible nitrogen, as well as phosphates, guano had been used as fertilizer along the Peruvian coast since before the Inca. In 1840-1841 a consortium of Peruvian, French and English businessmen made a huge profit by mining 8000 tons of guano, and exporting most of it to England. By 1858 England was importing more than 300,000 tons of guano a year, and the ammonia scented resource had become Peru’s leading export.
Other countries also imported significant quantities of guano. By the middle of the nineteenth century the USA, France and Germany all relied heavily on it as a nitrogen source. In fact, South American bird poop was so critical that it showed up in American President Millard Fillmore’s 1850 State of the Union address. He declaimed, “Peruvian guano has become so desirable an article to the agricultural interest of the United States that it is the duty of the Government to employ all the means properly in its power for the purpose of causing that article to be imported into the country.” Not surprisingly, enterprising businessmen sought other locations to obtain guano. One result of this was the passage of the Guano Islands Act of 1856, which effectively sanctioned U.S. imperialist expansion in the quest for bird feces. In the following decade the United States would use this act to justify claiming 59 islands, the majority in the Pacific, as overseas territories.
Even as Peru’s economy came to depend on guano export, Europe started to exploit another source of useable nitrogen found in South America. The Atacama Desert along the Pacific coast, west of the Andes Mountains, contains high quality deposits of sodium nitrate (NaNO3). Free living bacteria in shallow salt lakes had fixed nitrogen, forming a band of deposits 30 km wide and 700 km long. You may recognize sodium nitrate from the ingredients list in preserved meats like bacon, salami and hot dogs, but as the nineteenth century progressed the vying world powers had more critical uses for nitrates. By the second half of the century scientists knew that fixed nitrogen was the limiting factor in soil, and that nitrate fertilizer was essential to maintaining agricultural production in countries like Germany and Britain. Of equal interest to industrial nations, nitrates, when combined with sulfur and charcoal, form explosive black powder. By 1868, fueled by European capital, nitrate mining in the Atacama Desert was booming and it would change the political geography of South America.
When the first 700 tons of nitrate left South America in 1830, the nitrate fields were shared by Chile, Bolivia and Peru. As exports increased, so did boundary disagreements, which exploded into the War of the Pacific in 1879. This bloody conflict lasted five years, and ended with Chile victorious and in possession of the vast band of nitrate deposits. Chile profited hugely from the export taxes on nitrates. They accounted for 43% of government income by the late 1880s, and a whopping 68% in 1894, but the nitrate industry, itself, was largely foreign owned. The British Empire, Germany and the United States controlled over three-quarters of Chile’s exports at the end of the first decade of the twentieth century. Of these, Kaiser Wilhelm II’s Germany, with its sandy overused soils and formidable industrial capacity, was the largest importer of Chilean nitrates in the world. This brings us to the eve of the First World War.
Last year Britain began commemorating the hundredth anniversary of its involvement in The Great War. Among the familiar names we are hearing, like Ypres, Gallipoli, Verdun and Somme, is the less well known Battle of Coronel which opened on 1 November 1914. One of the earliest naval battles of the war, it happened off the coast of Chile, as British and German fleets vied to control the region’s critical trade routes. The Germans destroyed the smaller British fleet and, briefly, cut off essential nitrate shipments to the allies. The British responded by dispatching a huge naval force which defeated the German fleet at the Battle of the Falkland Islands in December and reversed the situation. From 1915 the British, in association with the U.S., controlled Chilean nitrate supplies, cutting off the Germans completely. So how did Germany keep going until the eleventh hour of the eleventh day of the eleventh month of 1918? As is often the case with historical questions, the answer depends on a confluence of events, not a single factor, but, once again, nitrogen proved a key ingredient.
It is impossible to overstate the degree to which European nations had come to depend on fixed nitrogen, not only for munitions, but, quite simply, to feed their people. Sir William Crookes, President of the British Association for the Advancement of Science, had devoted his address to the scientific community in 1898 to the issue of nitrogen fixation. He pointed out that, even with massive nitrate imports, Britain was able to produce only 25% of the wheat which it consumed, making it reliant on other countries for the remainder. As he saw it, “England and all civilized nations stand in deadly peril of not having enough to eat.” Crookes believed that the solution lay with the sort of people in his audience. He exhorted them, “It is the chemist who must come to the rescue of the threatened communities. It is through the laboratory that starvation may ultimately be turned into plenty.” His words were to prove prophetic, but it would be Germany, not Britain, which first implemented the fixation of nitrogen on a meaningful industrial scale.
By the time he gave the 1898 address in Bristol, Crookes had first-hand experience with nitrogen fixation from air. He had “put the air on fire” with an electric arc, oxidizing nitrogen into nitrates in a process similar to that which occurs in nature in the presence of lightning. Meanwhile, in 1892 a Canadian inventor working in the United States had produced calcium carbide, which will react with atmospheric nitrogen, by combining lime (calcium oxide, not the fruit) and coal tar in a high temperature electric-arc furnace. The amount of electricity needed to produce useful amounts of fixed nitrogen by either process proved problematic. Crookes proposed hydroelectric power as a source, and the Spectator article which reported on Crookes’ address joked that “Niagara alone can supply the required energy.” In fact, Norway had sufficient hydroelectric power, and did construct a nitrogen-fixation plant. The nitrogen it produced scarcely supplied domestic needs. This state of affairs brings us to the complicated figure of Fritz Haber, the man who won the 1918 Nobel Prize in chemistry for developing the process that feeds the world.
Born to Jewish parents in 1868 in what is now Wroclaw, Poland, but was then Breslau, Prussia, Haber renounced his Judaism for practical reasons. Academic opportunities for Jews were limited in most European countries at the end of the nineteenth century. In 1898, the year Crookes was calling for chemists to solve the issue of industrial nitrogen fixation, Haber was appointed professor extraordinarius at the Karlsruhe Institute of Technology and published a textbook on Electrochemistry. In the preface to the book he made it clear that one of his goals was to apply his chemical research to industry. He set himself (among other things) to finding the correct combination of pressure, temperature and catalyst which could convert atmospheric nitrogen to ammonia by reacting it with hydrogen. In 1909 he succeeded, and was able to produce about half a liter of ammonia in an hour using a process which, critically, required relatively little energy (and no waterfalls). Initially Haber used osmium for the catalyst, although he noted that there was another possibility which was obscure, cheap, and otherwise commercially useless, uranium.
Haber demonstrated the process to two scientists, Alwin Mittasch and Carl Bosch, from the company Badische Anilin-& Soda-Fabrik (you may be more familiar with it as BASF). It took a few years to scale up the system, making it commercially viable, but by 1912 the Haber-Bosch Process had been refined. By 1913 Carl Bosch, who was awarded his own Nobel Prize in Chemistry in 1931, had opened the first factory to produce synthetic ammonia, the Stickstoffwerke (nitrogen-works) in Oppau, Germany. If you have been keeping track, you will have noted that this was a year before the Battle of Coronel. Germany already knew that it had the capacity to produce nitrogen for fertilizer and explosives, two absolute necessities if it was to wage war, by the time that Gavrilo Princip assassinated Archduke Franz Ferdinand of Austria in Sarajevo on 28 June 1914. It was this supply that kept Germany going for as long as it did in World War I.
I mentioned above that Haber was a complicated figure in history. If you read his official biography on the Nobel website you will find, in among a truly phenomenal list of achievements, one, particular (almost) innocuous sentence. “When the First World War broke out he was appointed a consultant to the German War Office and organized gas attacks and defenses against them.” A staunch German patriot, he is considered by many to be the “father of chemical warfare.” He personally supervised the release of 168 tons of chlorine gas on Allied troops in Ypres on 22 April 1915, killing over 5,000 by asphyxiation in a matter of ten minutes. For this Haber was given the rank of captain, and in May he attended a party, given in his honor, in Berlin. After the party his wife, Clara Immerwahr, a brilliant chemist who vehemently opposed Haber’s involvement with weapons research, shot herself in the heart with her husband’s Army pistol, purportedly dying in the arms of their thirteen year old son. Haber left the next day to oversee gas attacks against Russian forces on the Eastern Front.
Of course the story of humanity’s fixation with nitrogen (I resisted as long as I could!) doesn’t end with Fritz Haber and World War I. The high explosives and bombs of World War II required a steady supply of reactive nitrogen. During the 1930s, the United States government had already invested millions of dollars in researching and building nitrogen plants, many of them near the hydroelectric dams of the Tennessee Valley Authority, to provide fertilizer. From the advent of the Second World War, they added ten new large-scale plants in the country’s interior, this time expressly to produce ammonia for munitions. By the time President Truman marked the end of the war by declaring 2 September 1945 to be V-J Day, all of these plants combined were producing 730,000 tons of ammonia, and they had the capacity to produce 1.6 million tons. What could be more natural than to turn all of that nitrogen-rich ammonia to fertilizer, now that it was no longer needed for bombs? Crop yields rose, and with a plentiful, and reliable, supply of nitrogen, farmers could focus on one or two major cash crops in all of their fields, year after year, without fear of depletion. Now that nitrogen was no longer a limiting factor, new, hybrid strains of commercially valuable cultivars, like corn, could be developed. These depended on increased fertilizer applications, but, in return, provided extremely high yields.
As the production and use of nitrogen fertilizers skyrocketed in the following decades, so did the world population. Estimates vary (as always), but most researchers agree that, without synthetic nitrogen, between a half and a third of the world’s people could not exist. That’s somewhere in the neighborhood of 3.5 billion people. Now it’s always tempting to turn numbers like that into “other” people, other lives, so let’s rephrase a bit. Some writers like to say that about half of the nitrogen in your body comes from fertilizer, but let’s face it, if you live in a “developed” nation, that percentage is likely to be much higher, even if you buy organic. Without nitrogen fertilizer we, you and I, would not be here.
At the same time, humanity’s relationship with nitrogen is genuinely problematic. The spectacular explosive potential of ammonium nitrate fertilizer tends to garner the most press. The explosion of the West Fertilizer Company facility outside of Waco, Texas on 17 April 2013, not only obliterated the entire plant, but also destroyed or damaged nearby buildings including homes, a school, and a nursing home. The West, Texas, explosion may be freshest in our collective memory, but it is by no means unique. Remember Carl Bosch’s original BASF plant in Oppau, Germany? It exploded on 21 September 1921, killing 561 people, outright, and leaving 7,500 people homeless. It is not only in production and storage, but also in transport, that ammonium nitrate has the potential to be dangerous. On 16 April 1947, in Texas City, Texas, the SS Grandcamp, loaded with over 2000 tons of ammonium nitrate caught fire. The resulting explosion triggered a chain reaction of explosions on other ships and at oil storage facilities, leaving 581 people dead.
In one of history’s fascinating coincidences, on the 80th anniversary of the explosion in Oppau, 21 September 2001, ammonium nitrate stored in the AZF factory in Toulouse, France exploded, leaving a crater 200 m across and at least 20 m deep and damaging buildings within a radius of over 700 m. Staggering as this explosion was, the terrorist attacks of 11 September overshadowed it in much of the news coverage outside of France. This reminds us that not all explosions are accidents. Neither do they all require planes or foreign zealots. American citizens Timothy McVeigh and Terry Nichols used two tons of ammonium nitrate fertilizer, combined with racing fuel and a blasting cap to destroy the federal building in Oklahoma City on 19 April 1995, killing 168 people.
Despite their headline and heart grabbing nature, nitrate explosions do not pose a major threat to most of us. The real problems with nitrogen fertilizer are much more mundane and accretionary. One of the biggest issues is that nitrogen is a nutrient, but it does not all end up nourishing crops. Agricultural run-off in rain or irrigation water carries available nitrogen into lakes, rivers, oceans and public reservoirs, and can change entire ecosystems. Algae thrive in this nitrogen bath. The famous “red tide” is the result of an algae proliferation which produces chemical toxins killing fish, impacting commercial fisheries, and sickening people who eat tainted shellfish. Even non-toxic algal blooms can be devastating, as they deprive other organisms of oxygen. “Dead zones” produced by these nitrogen-fed algae proliferations occur worldwide with real consequences for humans. The collapse of the Baltic cod fishery in the early 1990s was one result. The Gulf of Mexico Dead Zone at the mouth of the Mississippi River is one of the most famous. It varies in size each year, but can easily cover 6,000 to 7,000 square miles, or about half of Belgium. Reactive nitrogen doesn’t just show up in water, it can also enter the air as nitric oxide (NO), where it is a component of smog. As nitrous oxide (N2O) in the atmosphere it is a greenhouse gas, and nitrogen oxides contribute to the acidity in acid rain.
This all seems incredibly bleak, and if, like me, you once had a soft spot for 1970s dystopian sci-fi, you may find your thoughts turning in that direction now. Should we balance population and consumption a la Logan’s Run, by killing off everyone as soon as they turn 30? Are we doomed to the world of Soylent Green, where all but the privileged few live in overcrowded, polluted and stagnant poverty, munching on our fellow humans in the form of “high nutrient” green wafers? I rather hope not. This is the point in the article where the author usually tells you all of the research that is being done on new methods of agriculture, responsible fertilizer use and groundbreaking chemistry. And I could certainly do that, because people out there are involved in all of those. Instead, I’d like to point out that humans, while often slow to see problems, nevertheless like to try to solve them. I’m not a believer in progress, in the sense that things inevitably get better, but, realistically, we cannot go back. Whatever is done is, irrevocably, done. People (like me!) who enjoy looking back in time aren’t always the best prognosticators, but I think that it is probably safe to say that whatever new solutions we develop will have drawbacks and unforeseen complications, and we will debate long and hard about whether the good outweighs the bad.
Resources are linked in the text, for space reasons.
– Success Manure Spreader, ca. 1870-1900
– Purple Vetch by AgriLife Today
– Basic Nitrogen Cycle
– Clover Root with Nodules
– Four Field Crop Rotation
– Orchilla Guano AA, from the Boston Public Library
– Orchilla Guano, ca. 1870-1900, from the Boston Public Library
– guano mining
– abandoned Humberstone nitrate mine, Chile, by rewbs.soal
– The Anglo-Chilean Nitrate Co, January 1937 by Alan
– “Sir William Crookes 1906″ by George Charles Beresford (1864-1938)
– “Lightning NOAA” by C. Clark – NOAA Photo Library (direct), NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL)
– photos of Fritz Haber and Clara Immerwahr
– Chlorine Gas at Somme, 1916
– BASF Plant in Oppau Germany, After Explosion
– Nitrogen Cycle in the Modern World
– Aftermath of Texas City Disaster, 1947
– Logan’s Run
– Soylent Green
– World Population
– Phillips 66 Agricultural Ammonia, Adrian, Oregon by Allen