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AIPROPX ReportFortune · 2h ago
The Strait of Hormuz isn’t fertilizer’s first starring role — and 1856 law still defines U.S. overseas territory
The closure of the Strait of Hormuz, through which roughly one-third of the world’s fertilizer normally passes, has made clear that access to nutrients for crops remains as strategically important in the 21st century as access to oil.
As an environmental historian , I study how fertilizer transformed the modern world. That history is about more than scientific innovation or agricultural progress. It also reveals the hidden costs of modern food production, including the brutal treatment of workers and the expansion of imperial power.
Even before the Iran war began, Russia’s invasion of Ukraine had disrupted natural gas markets and the global trade in nitrogen fertilizers ; sanctions on Belarus had unsettled global markets for potash , one of agriculture’s principal sources of potassium; and China had restricted phosphate exports in an effort to stabilize domestic prices.
Even further back, long before synthetic fertilizers transformed farming in the 20th century, farmers increasingly relied on a scarce and geopolitically contested resource: seabird guano. Here is how bird droppings reshaped global agriculture and helped build an overseas empire for the United States.
The first Green Revolution
During the 19th and early 20th centuries, fertilizer companies shipped millions of tons of dried bird excrement from islands in the Pacific and Caribbean to farms across Europe and North America. Rich in nitrogen and phosphorus, guano transformed agricultural productivity at a time when expanding populations and industrializing societies demanded more food than traditional farming systems could produce.
Guano became the first fertilizer commodity traded on a truly global scale. For centuries, farmers had sustained soil fertility by recycling locally available nutrients , including animal manure, crop residues and human waste. Those nutrients circulated within largely closed ecological systems linking soils, crops, livestock and people.
As industrialization accelerated during the 19th century, the local nutrient cycles that had sustained farming for centuries began to unravel. Expanding cities drew food from increasingly distant farms but returned few nutrients to the countryside. Instead, material that used to fertilize farms accumulated in urban streets, rivers and sewers , while rural soils grew steadily poorer with each harvest. Farmers searched for new ways to replenish depleted fields as they struggled to feed rapidly growing populations.
For millennia, millions of seabirds, including guanay cormorants , Peruvian boobies and pelicans , had nested on rocky outcrops along South America’s arid Pacific coast. With almost no rainfall to wash away their nutrient-rich droppings, guano accumulated in towering layers. Islands that appeared barren were, in fact, among the world’s richest natural sources of fertilizer.
And since at least the 13th century, Indigenous farmers along Peru’s Pacific coast had understood the extraordinary resource stored on the Chincha Islands 13 miles offshore.
European scientists began to appreciate this fact only after 1804, when Alexander von Humboldt carried samples of Peruvian coastal guano to Europe, where scientists demonstrated its unusually rich nitrogen content. Commercial interest in guano surged in the 1840s after agricultural chemists – most notably Justus von Liebig – demonstrated that crop growth depended on replacing nutrients removed from the soil. Peruvian guano suddenly appeared not as an exotic curiosity but as an extraordinarily concentrated natural fertilizer.
An early 20th-century ad for Navassa guano touted its soil-enriching characteristics. Navassa Guano Company via Science Photo Library
European and North American agricultural journals hailed guano as a miraculous remedy for exhausted soils . Wheat farmers in Britain, sugar beet growers in central Europe, tobacco planters in Virginia and cotton cultivators across the American South all embraced the new fertilizer. Farmers who had long relied primarily on local sources of fertilizer increasingly depended on nutrients transported thousands of miles across the world’s oceans.
This new global trade in agricultural nutrients marked the first Green Revolution. Decades before synthetic ammonia transformed agriculture , millions of tons of naturally accumulated nitrogen and phosphorus crossed oceans from remote ecosystems to the world’s farms. For the first time, agricultural fertility itself became a globally traded commodity, laying the foundations for the chemically intensive agriculture that emerged after World War II.
The hidden costs of fertilizer
Chinese workers stand on a hill of guano on Peru’s Chincha Islands, circa 1865. Henry de Witt Moulton, Alexander Gardner and Philp & Solomons, via Library of Congress
Contemporary observers commonly compared the guano deposits on the Chincha Islands to cliffs or small mountains. When commercial extraction began in the 1840s, workers were not simply shoveling loose bird droppings. Centuries of accumulated guano had been compressed by its own weight into a dense, cementlike mass that had to be hacked apart with picks, crowbars and iron bars before it could be shoveled into sacks.
As the global abolition movement brought the Atlantic slave trade to an end, employers increasingly turned to debt peonage and indentured labor, systems that occupied the uncertain terrain between slavery and freedom. Agricultural productivity in Europe and North America depended not only on the long-distance transfer of nutrients but also on the equally consequential transoceanic movement of workers around and across the Pacific Ocean .
Peru’s Chincha Islands became notorious for the brutal exploitation of Chinese indentured laborers recruited through the so-called “coolie trade .” Thousands worked beneath an unforgiving sun, hacking hardened guano into pieces while breathing caustic clouds of ammonia-laden dust that burned their eyes and lungs. In 1854, after...
The StraitHormuzU.SCongressGuano Islands ActStraitEvenIranRussia’sUkraineBelarusChina
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