How many people does synthetic fertilizer feed?

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.12

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.13

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.


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