History shows that urbanization throughout the western world has been largely fuelled by increases in agricultural productivity, and that the enabling commodities are hydrocarbons. The discovery of how to unlock geological energy beneath our feet has given rise to the mechanization of farm labour and the scalable production of synthetic nitrogen fertilizers.
Unfortunately, urbanization has also created historic levels of agricultural naivety.
With increasing productivity, fewer people are required to produce food for society. As a result, knowledge of how food gets to our dining table is increasingly absent in the metropolitan population.
This article is intended to impress on readers some facts specific to the “green revolution” and the introduction of synthetic nitrogen fertilizers made possible by the invention of the Haber-Bosch process. The Haber-Bosch process is in essence an air separation and natural gas steam reforming plant, which produces and combines purified streams of nitrogen gas (N2) and hydrogen (H2) extracted from hydrocarbons, to synthesize ammonia (NH3).
Figure 1 – Bacterial mediated nitrogen cycle.
The Haber-Bosch process stands as one of humanity’s most transformative inventions, a triumph of science and engineering that reshaped agriculture, fueled global population growth, and redefined our relationship with Earth’s natural systems.
To fully appreciate its significance, we first revisit the agricultural revolutions of the 17th and 18th centuries, which set the stage for the nitrogen crisis of the late 19th century.
From the guano (fertilizer made from excrement of seabirds and bats) trade to the ancient practice of summer fallow, humanity has grappled with the challenge of maintaining soil fertility, a struggle that the Haber-Bosch process would ultimately resolve in a way that revolutionized food production and human progress.
The agricultural revolution of the 17th and 18th centuries marked a turning point in human history. Innovations such as crop rotation, improved plows, and selective breeding boosted yields and laid the foundation for modern farming.
Central to this transformation was the recognition that soil fertility, particularly nitrogen availability, was critical to sustaining agricultural productivity and to enhancing drought resistance in crops. Nitrogen, a key component of proteins and deoxyribonucleic acid (DNA), is essential for plant growth, but it is often scarce in forms that crops can readily use.
One of the earliest solutions to this problem was the guano trade, which emerged as a global phenomenon in the 19th century. Guano was rich in nitrogen and phosphorus, making it an exceptional natural fertilizer that is multiple times more potent per unit mass than cow or horse manure.
By the mid-1800s, guano deposits, particularly from the Chincha Islands off the coast of Peru, became a cornerstone of industrial agriculture in Europe and North America. Farmers relied on guano to replenish depleted soils, boosting crop yields and supporting growing populations.
However, Peru’s White Gold was finite.
Figure 2 – Mid-19th-century Chincha island quano mining operation.
By the late 19th century, the best guano deposits were nearing exhaustion, and the logistical challenges of mining and transporting it across oceans made it increasingly costly and unsustainable.
The guano boom exposed a critical limitation: humanity’s dependence on naturally occurring nitrogen sources was a bottleneck that threatened to cap agricultural growth.
Parallel to and predating the guano trade, farmers employed the ancient practice of summer fallow to restore soil nitrogen. In this method, fields were left unplanted for a season, allowing natural processes such as atmospheric nitrogen oxide deposition and nitrogen fixation by soil bacteria to replenish nutrient levels.
While effective to an extent, summer fallow was inefficient, reducing the amount of arable land in production and limiting yields. For example, in semi-arid landscapes such as Ukraine and the North American Prairies, anywhere from 20-50% of arable landscapes were rotated between summer fallow and active production.
Figure 3 – Croplands under summer fallow.
Summer fallow, which required one or more plowing or harrowing treatments per season to keep weeds from going to seed, had the negative consequence of accelerating the deep oxidation of humic materials (aka carbon content) present in the soil. In the long run, this practice diminished the moisture-retention capacity of the soil and increased the risks of crop failure due to even minor droughts.
Prime examples of such crop failures in the 20th century include the North American Dust Bowl of the 1930s and the Ukrainian Holodomor (aka death by hunger) in 1931-32. Both disasters involved improper farming practices, made worse by a multi-year drought.
As populations grew and urbanization accelerated in the late 19th century, the demand for food outstripped the capacity of these traditional methods. The world faced a looming nitrogen crisis: without a reliable and scalable source of nitrogen, agriculture could not keep pace with human needs.
Enter Fritz Haber and Carl Bosch, two German scientists whose collaboration would change the course of history. In the early 20th century, the scientific community was racing to find a way to synthesize ammonia, a nitrogen-rich compound that could serve as a precursor to fertilizers and explosives.
Nitrogen gas (N₂), which makes up roughly 78% of Earth’s atmosphere, is abundant but chemically inert, requiring immense energy to break its strong triple bond and convert it into usable compounds. The Haber-Bosch process consumes 1-2% of global energy, equating to 6-12 exajoules (EJ) annually, with ~70–75% of this energy derived from hydrocarbons – primarily natural gas for steam methane reforming (SMR).
Earlier attempts to fix nitrogen artificially had been inefficient and impractical for large-scale production. Haber, a brilliant chemist, developed a breakthrough in 1909 by demonstrating that nitrogen and hydrogen gases could be combined under high pressure and temperature, in the presence of a magnetite (Fe₃O₄) – alumina (Al2O3) stabilize catalyst, to produce ammonia (NH₃).
His laboratory-scale process was a proof of concept, but it was Carl Bosch, an engineer at the chemical company BASF, who transformed Haber’s discovery into an industrial reality. Bosch overcame formidable technical challenges, including designing reactors capable of withstanding extreme conditions and developing cost-effective catalysts.
By 1913, the first commercial Haber-Bosch plant was operational, marking the dawn of industrial ammonia production.
Figure 4 – Haber-Bosch process flow diagram.
The irony of the Haber-Bosch process lies in its original purpose. Developed in the context of early 20th-century geopolitics, the process was initially driven by the need for nitrogen-based explosives, such as ammonium nitrate, to fuel military ambitions.
Germany, in particular, sought to secure a domestic source of nitrates for munitions, reducing reliance on imported Chilean saltpeter (sodium nitrate). Yet, what began as a tool for warfare became a cornerstone of human progress. The ability to produce ammonia on an industrial scale revolutionized agriculture by providing a virtually limitless supply of synthetic nitrogen fertilizers, fundamentally altering humanity’s relationship with the natural world.
The Haber-Bosch process is nothing short of a modern miracle, because it allowed humanity to bypass the limitations of the natural nitrogen cycle. In 2024, ammonia stood as the second most manufactured chemical, with annual production estimated at 195 million tonnes.
In nature, nitrogen is fixed primarily by certain bacteria and lightning strikes, which convert atmospheric nitrogen into compounds such as ammonia and nitrates that plants can absorb.
This natural process is slow and insufficient to meet the demands of intensive agriculture. Before Haber-Bosch, farmers were constrained by the availability of organic fertilizers such as manure or guano and the inefficiencies of practices such as summer fallow.
Figure 5 – First Haber-Bosch plant – BASF plant in Germany 1913.
By synthesizing ammonia from atmospheric nitrogen, the Haber-Bosch process decoupled agriculture from these natural constraints. Synthetic fertilizers could now be produced in vast quantities and applied directly to fields, dramatically increasing crop yields. For example, the application of nitrogen fertilizers enabled some farmers to grow multiple crops per year on the same land, eliminating the need for summer fallow and maximizing arable land use.
Crops including wheat, corn, and rice, which are staples for billions, saw unprecedented productivity gains. Between 1900 and 2000, global food production increased by several orders of magnitude, largely due to the widespread adoption of Haber-Bosch-derived fertilizers. The impact extended beyond agriculture to adjacent ecosystems. Wetlands, forests, and grasslands benefited indirectly as agricultural expansion reduced pressure on marginal lands.
Figure 6 – United States wheat production and cultivated land under wheat production.
The positive impact of the Haber-Bosch process became widespread, especially in the post-World War II era. Figure 6 shows this influence on wheat production in the United States. Note that there is more than a 200% increase in production by 2020 relative to 1920, yet land allocated to wheat production decreased by 20 million acres.
By intensifying production on existing farmland, the Haber-Bosch process helped preserve natural habitats that might otherwise have been converted to agriculture to meet food demands.
This is not to say that all environmental outcomes were positive, but the process’s ability to concentrate productivity on smaller land areas was a significant achievement in the context of a growing global population, while helping preserve wild spaces.
The Haber-Bosch process is often credited with enabling the global population to grow from 1.6 billion in 1900 to over 8 billion today. Of course, some see population growth as a negative development that carries with it myriad environmental challenges.
However, without synthetic fertilizers, it is estimated that nearly half the world’s population would face starvation, as natural nitrogen sources could not sustain modern agricultural yields.
The Haber-Bosch process has been a linchpin of the Green Revolution, which introduced high-yield crop varieties and modern farming techniques in the mid-20th century, further amplifying food production.
The process also democratized access to food.
By making fertilizers affordable and widely available, it empowered farmers in developing regions to increase yields and improve livelihoods. Countries including India and China, which faced chronic food shortages in the early 20th century, transformed into agricultural powerhouses, in large part due to their production of synthetic nitrogen.
This productivity boost not only reduced hunger but fueled economic growth, as surplus food production freed up specialized labour, supporting urbanization and industrialization. Moreover, the Haber-Bosch process exemplifies human ingenuity solving existential challenges. At a time when the world faced a nitrogen crisis, science and engineering delivered a solution that transcended natural limits.
The collaboration between Haber’s theoretical brilliance and Bosch’s practical engineering underscores the power of interdisciplinary innovation. Their work laid the foundation for modern chemical engineering, influencing industries far beyond agriculture, from pharmaceuticals to materials science.
The Haber-Bosch process remains a cornerstone of modern civilization.
Today, humans produce more than 200 million tonnes of ammonia annually, supporting roughly 50% of global food production. Its impact is so profound that it has been described as the most important invention of the 20th century.
By liberating agriculture from the constraints of the nitrogen cycle, it has enabled humanity to thrive in ways previously unimaginable.
From the guano trade and summer fallow to the industrial synthesis of ammonia, humanity’s journey to overcome nitrogen scarcity reflects our capacity to adapt and innovate. It is a legacy of progress, feeding billions, while transforming and preserving ecosystems. The Haber-Bosch process is not just a scientific achievement; it is a modern miracle that continues to shape the world for the better.
(Joseph Fournier, BIG Media Ltd., 2025)
