Remember the Guano Wars

A Response to Breakthrough’s Essay on the Hidden Footprint of Making All Farms Organic

In their essay on the necessity of synthetic nitrogen in agriculture, Dan Blaustein-Rejto and Linus Blomqvist do an excellent job of running us through the arithmetic, biology, and physics that inexorably lead to the necessity of synthetic nitrogen. As they mention, in the mid-19th century British and American farmers got a major reprieve from soil exhaustion and a boost to yields thanks to the importation of guano from South America. The history of that period is largely forgotten, but it brings the centrality of nitrogen to civilization into sharp relief. And while we struggle today to manage over-application of nitrogen, it’s easy to take access for granted. It’s worth remembering that countries once went to war to secure nitrogen for their farmers.

In 1804, the Prussian geographer Alexander von Humboldt, working in Peru, noticed the brisk trade in seabird guano that had passed beneath the radar of Europeans in search of shinier treasures.1 He immediately recognized the value for farmers back home, who struggled even then to maintain soil fertility to feed growing populations. He brought home samples with him for testing. Top chemists of the day confirmed the guano to be a major discovery.

After the establishment of Peruvian independence, the guano export trade to Europe and the United States set off a frenzy of resource exploitation that ran from around 1840 until the invention of the Haber-Bosch process of nitrogen fixation in 1909.

In 1864, war broke out between Spain and Peru. Spain, demanding repayment of debts arising from Peru’s war of independence, took control of the guano-rich Chincha Islands. They occupied the islands from 1864 to 1866.2 The islands were so crucial that a war that started first with Peru came to include Chile, and then Bolivia and Ecuador.

A guano war broke out again in 1879, this time between Bolivia, Chile, and Peru in a series of border and guano tax disputes. The War of the Pacific roiled the region for another 5 years, leaving as many as 18,000 dead. By the end of that war, the US population had grown to 50 million and the European population to more than 200 million, making South American guano all the more valuable.

The essential nature of guano had long been understood in the region. Guano powered the farms that supported the complex Inca civilization. Those farms produced the potatoes and quinoa that fed what had possibly been the largest empire in the world in the early 16th century. Before the conquistador Francisco Pizarro showed up in Peru, the Inca carefully managed their guano reserves. Hunting the cormorants and boobies that turned anchovetas and sardines into agricultural gold was punishable by death. Supplies were guarded by stewards tasked with doling out each citizen’s proper share. The growth of the great Inca Empire was propelled by its proximity to the guano islands.

In addition to the wars that attest to the absolute necessity of access to nitrogen, consider the 19th century logistics of the trade. Guano was transported from Peru to Britain, a distance of 10,000 nautical miles; the trip would have taken 40-50 days. The US was unable to import guano directly from Peru due to a British/Peruvian treaty. In his 1850 State of the Union Address, President Millard Fillmore spent a full paragraph on tough talk, committing to do anything necessary to make Peruvian guano available to American farmers.3 In 1856, the US Congress passed the Guano Islands Act, allowing any US citizen to take possession of unclaimed islands containing guano deposits and committing US war ships to their security.

Mind you, California had become the 31st state just months before Fillmore’s sabre-rattling on guano trade. The full lower 48 was available for cultivation, and yet soil fertility was already a challenge. US agriculture is currently tasked with feeding 325 million citizens while exporting $150 billion worth of food. But in the 1850s, with just 25 million citizens to feed and hundreds of millions of acres of some of the most fertile soil in the world, on farms where manure-producing cattle, hogs, and poultry were well-integrated with crop production, US presidents were promising to get tough on guano prices and US business interests were verging on war in the Caribbean over fertilizer.

The invention of the Haber-Bosch process changed everything. Blaustein-Rejto and Blomqvist mention that the Romans understood the role of legumes in maintaining soil fertility. And yet, the Roman Empire was largely defined by imperial expansion, in search of fresh sources of nitrogen. They found it in the form of soil which had not yet been exhausted. The whole Mediterranean basin became tasked with feeding the city-state at the heart of the empire.4 All this is to say that this is not an industrial agriculture problem; clearly, it’s been a central obstacle of civilization for thousands of years. If the problem of nitrogen scarcity could be solved by cover crops and manure, it would have been solved long ago.

There is no getting around it. The nutrients taken off the farm must be replaced. The guano era of the 19th century was a brief reprieve from what had previously been a geographically-bounded limitation. Access to plant-available nitrogen had been the primary limiting factor in the growth of civilizations until the invention of Haber-Bosch in 1909. The history of agriculture in the 20th century was the story of learning to take advantage of nitrogen without the limits of nature. The history of agriculture in the 21st century may turn out to be the story of learning to manage that freedom.


1. “When The Western World Ran on Guano” Cara Giaimo, Atlas Obscura - October 14, 2015

2. “The Cincha Island Wars” Wikipedia

3. “1850 State of the Union Address” Millard Fillmore - December 2, 1850

4. “Empires of Food: Feast, Famine, and the Rise and Fall of Civilizations” Andrew Rimas and Evan Fraser 2010