Flawed Logic: Would 4 Billion People Die Without Nitrogen Fertilizer?

This graph implies that it's impossible to feed the world with organic farming. But what data is it really based on?

“Without the Haber-Bosch synthesis of ammonia about two-fifths of the world’s population would not be around,” Vaclav Smil wrote in his 2001 book Enriching the Earth. Others estimate that anywhere from 30 to 50 percent of the nitrogen in food was fixed by the Haber-Bosch process. From there, it’s only a small extrapolation to claim, as Hannah Ritchie does, that two to four billion people are only alive because of synthetic nitrogen fertilizer. And from there it’s only another small extrapolation to claim that switching to organic farming would mean mass murder by starvation of up to half the world’s population!

But is that really true? The tricky thing here is that, since both synthetic and biological nitrogen come from the atmosphere, we can’t accurately measure what percentage of nitrogen in our food (or bodies) was fixed using the Haber-Bosch process. A closer look at how Smil, Ritchie, and others derive their calculations shows that they aren’t based on any kind of direct measurements at all. They look at a different set of statistics—yields of grain crops, the amount of nitrogen fertilizer applied, and global population. All three graphs show a sharp upward increase after World War II. Therefore, they conclude, fertilizer increased crop yields, which allowed the population to increase. So really, the nitrogen “statistics” go back to the yield question. It has nothing to do with trying to figure out the source of the nitrogen molecules in any given food product.

There are two things to consider here. One is how much of that yield increase was due to nitrogen fertilizer. There were a lot of other improvements in agriculture during that time—improved varieties, closer row spacing, soil conservation, and abandonment of marginal land all played a role in raising yields. Also, there are other ways to raise yields than applying synthetic nitrogen. Organic farmers in the 1940s and 1950s consistently had double the yields of their neighbors. Organic crop yields have risen since 1945, too, following the same general curve—and have always been much higher than average American yields were in the 1930s.

Another common argument is that the human population has somehow outstripped the capacity of biological nitrogen fixation, making it impossible for biological processes to support the world’s current population of 8 billion. But there’s no set limit on the amount of nitrogen that can be fixed by bacteria. They fix as much as is needed. If the soil is already rich in nitrogen, legumes don’t grow as many nitrogen-fixing nodules. Since even biological nitrogen fixation is an energy-intensive process, plants only allocate as much carbohydrate to their bacterial nitrogen-fixers as they need to. Applying nitrogen fertilizer shuts down biological nitrogen fixation. But without the fertilizer, biological fixation starts back up.

To show why this logic is flawed, consider this scenario: According to the USDA, Americans get about 30 percent of the calories they eat from restaurant food. Does that mean that, if all restaurants closed, 100 million Americans would die of starvation? Of course not! Long before they would starve, people would cook their own food at home, and they’d still get just as many calories as they needed. Claiming that 4 billion people would die without nitrogen fertilizer is just as illogical. The argument sounds convincing—but it’s not supported by any solid data. The reality is that it’s impossible to accurately measure the amount of nitrogen fixed by biological processes, that amount is not static, and careful management of the biological nitrogen cycle through organic farming can raise yields just as much as the Haber-Bosch process.