How many people does synthetic fertilizer feed?

Predictions of a global food crisis — that the world's food production would not be able to keep pace with population growth — have a long history. In the 18th century the English cleric Thomas Robert Malthus hypothesized that gains in per capita resources would inevitably be outstripped by population until food supplies finally acted as a barrier to further growth.1

Such predictions have continued well into the 20th and 21st centuries; in his controversial 1968 book The Population Bomb, Paul Ehrlich argued that global population would continue to grow until the point of mass starvation.2

Both Malthus and Ehrlich should be surprised to see the current state of the world. Today, we can support a global population of around 7.4 billion (and growing), with many consuming far in excess of requirements.3

There are a number of scientific and technological innovations which have allowed for rapid growth in crop productivity, particularly in the second half of the 20th century. None of these had a more dramatic impact than the ability to produce synthetic nitrogen fertilizer.

In fact, it's estimated that nitrogen fertilizer now supports approximately half of the global population. In other words, Fritz Haber and Carl Bosch — the pioneers of this technological breakthrough — are estimated to have enabled the lives of several billion people, who otherwise would have died prematurely, or never been born at all.4

It may be the case that the existence of every second person reading this attributes back to their 20th century innovation.

Atmospheric alchemy: making fertilizer from air

Understanding the significance of nitrogen fertilizer requires a brief explanation of its role in global crop production. In addition to water and sunlight, crops need three key nutrients to grow: nitrogen, phosphorous and potassium. Nitrogen is often the nutrient that is limiting to further crop production, despite Earth's atmosphere containing more than 78 percent. This is because in the atmosphere, nitrogen exists in its largely unreactive Nform, rather than in a reactive form which plants can utilize.

For millennia, agricultural crop had to rely on the limited quantity of reactive nitrogen which was naturally occurring in soils and ecosystems.5

This remained the case until 1908 when the German chemist Fritz Haber developed a process by which atmospheric N2 could be converted into ammonia (NH3) – a form of reactive nitrogen which plants can use.6

Carl Bosch, another German chemist and engineer, was able to take Fritz Haber's laboratory-scale process and develop it at an industrial scale. The combined "Haber-Bosch process" remains the primary industrial method for the production of synthetic nitrogen fertilizer.

How many people does nitrogen fertilizer feed?

In simple terms, crops typically respond positively to nutrient inputs. As we explore in detail in our entry on Crop Yields, crop yields and fertilizer application typically show a strong positive relationship. Fertilizer application, combined with other productivity factors such as improved crop varieties, genetic breeding, irrigation and mechanization led to a significant inflection in crop yield trends across the world in the 20th century. It should be noted that this growth in agricultural output — from both industrial and organic farming — has undoubtedly  resulted in important ecological and resource pressures. However, as we cover in detail in a recent blog post, organic farming (that is, agriculture without synthetic inputs) can often have a greater environmental impact than conventional agriculture.

So, how many people does synthetic nitrogen fertilizer actually feed? Below we draw upon several published estimates, which tend to converge on a similar share of the global population. Results published by Erisman et al. (2012) in the scientific magazine Nature are shown in the chart.7

These results also tie closely with Vaclav Smil's widely-quoted estimates, which we discuss later.8

Click to open interactive version

How can we estimate the number of people fed?

Firstly, it's important to note that these estimates are understandably difficult to derive with a high degree of certainty. This difficulty arises for several reasons. Notably there have been a number of additional contributors to productivity gains in agriculture throughout the 20th and 21st centuries, including crop breeding, irrigation, mechanization, and farm management techniques — untangling the individual role of nitrogen fertilizers alone is challenging. Secondly, the global food system is complex and geographically highly unequal: high-income countries have moved beyond the stage of aiming to meet basic nutritional requirements from food production, and now dedicate a large share of food production to meat (which is a much less efficient nitrogen converter) and bioenergy production.9

Nonetheless, general estimates tend to converge on a figure in the range of 40-50 percent of the population. Let's look at three widely cited estimates:

The complexities of the global food system make it challenging to provide a firm figure, however, it's likely that just under half of the global population is dependent on synthetic nitrogen fertilizers. This is further shown in the chart. As a result, the Haber-Bosch process will likely have enabled the lives of at least 3 to 3.5 billion people today.

Click to open interactive version

Could we have achieved the same without synthetic nitrogen?

If Fritz Haber had not discovered how to make synthetic nitrogen, would we have found alternative solutions to support a population as large as today's?

Addressing this question partly relies on retrospective guesswork about whether, in the absence of synthetic nitrogen fertilizer, we would have managed to supply nitrogen via other methods. If Fritz Haber or Carl Bosch (or any scientist to follow) hadn't developed a method for transforming inert atmospheric nitrogen into reactive nitrogen plants could utilize, what is the likelihood that other solutions would have filled the gap?

One solution would have been to greatly increase the production of nitrogen-fixing legume crops. As noted earlier, leguminous crops (i.e. peas, beans and other pulses) possess a unique ability to transform (or 'fix') atmospheric nitrogen into reactive nitrogen in the soil. Growing these crops can therefore increase soil nitrogen sources over time. Whilst this might have credibly increased the total availability of reactive nitrogen to some extent, it's unlikely to have been a widely-scalable solution for several reasons.

Firstly, legumes tend to be lower-yielding relative to cereals and other staple crops. This is true of yields today, but also true of historical yields — in the late nineteenth century, Western European legume yields were typically less than half that of staple cereals.8

Farmers in the 19th and early 20th century would have had little incentive to widely adopt these crops. Secondly, despite the many nutritional and environmental benefits of legumes, they form only a small component of most peoples' diets. Furthermore, preferences for pulses and legumes tend to decline as incomes rise and food choices widen. The overall appetite for legumes — both from a farmer's and dietary preference perspective means it would have been high unlikely that they would have been able to supply nitrogen at a scale close to that of the Haber-Bosch process throughout the 20th century.

Another potential nitrogen source is that of organic wastes — nitrogen is supplied in many organic farming systems today in the form of animal manure. Couldn't we have relied on these non-synthetic nitrogen sources instead? In fact, we did; prior to Haber-Bosch and the creation of synthetic nitrogen inputs, most agricultural systems relied on the recycling of manure, wastes and other biomass back into the soil to maintain nitrogen balance. The issue is that these existed in limited supply: recycling nutrients, by definition, means you have a limited supply. This allowed societies to sustain moderate levels of nitrogen but did not allow them to create more. As Smil (2004) discusses in detail, previous societies could typically support only small numbers of domesticated animals, and as a result, had very limited supplies of manure and animal wastes.8

Synthetic nitrogen not only increased crop yields, but also enabled an expansion in livestock numbers. Increased productivity and excess crops allowed farmers to allocate an increasing share of output to livestock — particularly grain-fed animals. Overall, this has increased the amount of reactive nitrogen which can be recycled through our agricultural systems; with more livestock, we also have more manure to recycle. But it's important to recognise that such levels of organic nitrogen sources are only available because of previous synthetic nitrogen inputs. The creation of synthetic nitrogen delivered reactive nitrogen to the soil which could then be recycled in the form of organic wastes and biomass. If organic nitrogen could today support a large share of the global population then it is because synthetic nitrogen has enabled it to do so by adding reactive nitrogen to our agricultural systems. Without Fritz Haber's discovery, this would never have been a possibility.


  1. Malthus (1798). An Essay on the Principle of Population: Or, A View of Its Past and Present Effects on Human Happiness; with an Inquiry Into Our Prospects Respecting the Future Removal Or Mitigation of the Evils which it Occasions. J.Johnson. London. Later edition available online.

  2. Ehrlich, P. R. (1997). The Population Bomb (1968). New York: Sierra Club/Ballantine.

  3. It is also true that around 815 million people were undernourished in 2016. However, as is often the case with food insecurity and famine, this is largely attributed to sociopolitical, stability and economic factors rather than an inability to produce enough food.

  4. See also this BBC programme.

  5. Legumes are the one exception to this condition. Legumes — such as peas, beans and other pulses — have the unique ability of being able to convert atmospheric N2 into reactive nitrogen, which can then be used for crop growth.

  6. Reay, D. (2015). Nitrogen and Climate Change: An Explosive Story. Palgrave Macmillan. ISBN 978-1-137-28696-3.

  7. Erisman, J. W., Sutton, M. A., Galloway, J., Klimont, Z., & Winiwarter, W. (2008). How a century of ammonia synthesis changed the world. Nature Geoscience1(10), 636-639. Available online.

  8. Smil, V. (2004). Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production. MIT Press. ISBN: 9780262194495.

  9. A global estimate therefore hides these inequalities; it may be the case that less than 48 percent of the population in high-income countries rely on nitrogen fertilizer to meet basic food requirements, whereas this share is higher in lower-income nations.

  10. Stewart, W. M., Dibb, D. W., Johnston, A. E., & Smyth, T. J. (2005). The contribution of commercial fertilizer nutrients to food production. Agronomy Journal97(1), 1-6. Available online.

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    author = {Hannah Ritchie},
    title = {How many people does synthetic fertilizer feed?},
    journal = {Our World in Data},
    year = {2017},
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