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The element nitrogen was first identified in 1772 by the Scottish physician Daniel Rutherford. It wasn’t until 1840 that Justus von Liebig (1803–1839), one of the pioneers in agricultural chemistry, identified nitrogen as essential to plant health. One of Liebig’s most important contributions was the “Law of the Minimum” which stated that plant growth is limited by the least available (or scarcest) essential nutrient, not by the total available nutrients. That meant that if an essential nutrient was lacking, providing more of other nutrients would not help.

Liebig’s research revealed that nitrogen, being the most essential, was typically the least available nutrient. Therefore, Liebig recommended nitrogen-based (nitrate rich) fertilizers for gardens and agriculture. This was not the start of man’s use of fertilizer, but it did give it scientific footing. Without understanding the precise chemistry involved, farmers had learned long before that some additions to the soil improved production.

As humans spread across the globe and human agricultural activities leached nutrients from farm lands, available nitrates from decomposition of organic matter and the work of nitrogen-fixing bacteria were unable to keep up with demand. Egyptians, Babylonians, Greeks and Romans all made contributions to the use of manure to enhance farm productivity. Nitrate-rich manure from farm animals was regularly collected and spread out over crop fields.

As farming grew, manure and other local amendments were unable to keep up with the depletion of soil nutrients. Farmers needed to find additional sources of nitrates.

In the early 17th century, the Spanish chronicler Garcilaso del la Vega reported that seacoast Peruvians used the guano of sea birds as fertilizer. These seabirds dropped their waste on coastal islands, which, in time, were covered with what appeared to be snowy mountain ranges of guano often 50 or more feet deep. Records indicate that the Inca, over centuries, had also used this guano as fertilizer and placed such a value on it that they managed the harvesting of guano with military ruthlessness.

Alexander von Humboldt was the first European scientist to encounter guano (on a field trip Peru in 1802), and he began investigating its chemical properties. His subsequent writings popularized guano as a fertilizer. Soon Peruvian seabird guano was all the rage in Europe, and there was a stampede to procure it. British merchants formed a joint venture with the Peruvian government, cornering the market by giving them exclusive rights to harvest and distribute the guano. From 1840 to 1870 Peru exported over 12 to 20 million tons of seabird guano at an estimated value of 500 million to two billion American dollars.

Peruvian seabird guano was not only a rich source of nitrogen but of phosphorus and potassium and was marketed as a super fertilizer. The cold Antarctic waters of the Humboldt Current along the Peruvian coast teemed with anchoveta and the sky above teemed with their predators, cormorants, pelicans and boobies. Island seabird guano commanded a premium in the global fertilizer market, and soon enterprising explorers were staking claims to other guano deposits on Caribbean atolls, islands off Oman, Namibia, Patagonia and even Baja, California.

The United States was not immune from guano fever or the lure of empire. In 1850, President Millard Fillmore pledged in his first State of the Union address to negotiate a fairer price for guano, which then cost $76 a pound. Soon after, William Seward — who later convinced the Senate to buy Alaska—proposed the Guano Islands Act, which allowed for any American citizen who found guano on an unclaimed island to claim it for the U.S. Fillmore’s successor, Franklin Pierce, signed the act into law in 1856. This was America’s first foray into imperialism. Around 60 to 200 islands, mostly in the Caribbean and Pacific, ended up being acquired under this act, some of which remain U.S. territories today.

By the 1870s, the guano deposits were largely exhausted and were being replaced by exploitation of nitrate deposits from the high deserts of northern Chile. Nitrates, needed for fertilizer, were also needed for explosives. Military victory often depended on steady access to nitrates. As the human population grew and Europe moved from frequent regional wars toward world war, the scramble for nitrates was intense and total nitrate deposits were nearing exhaustion. With a foreseeable crash in agricultural production, scientists contemplated a Malthusian die-off of the human population. The stage was set for Fritz Haber and the intervention of science.

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