Since the origins of agriculture, people have sought to produce more food using fewer resources. Enhancing soil fertility through the addition of fertilizers is one way in which they have done that. Beginning at the dawn of agriculture with trial-and-error attempts to naturally amend soil, fertilizer use has progressed to today's giant fertilizer producers using the best that science has to offer to squeeze every bit of productivity from an acre.
"Organic agriculture is the oldest form of agriculture on earth," writes the Iowa State University Extension. Early farmers used fertilization methods that, today, you would recognize as organic. They applied natural substances like manures and decaying plant matter to supplement their soils. Observing that productivity declined after planting the same crop in the same space year after year, early farmers also practiced crop rotation to boost soil fertility.
During ancient Greece and Rome, scholars such as Aristotle and Plato documented the agricultural practices being used to feed their ever-growing empires. The ancients continued to rely on manures and crop rotation to restore nutrients. New fertilizer technology would not develop until the 19th century.
One reason for centuries of reliance on ancient methods is that, until the 19th century, people didn't understand exactly what made soil fertile. They knew what worked and what didn't without knowing why. Chemist Baron Justus von Liebig, in 1840, demystified soil fertility when he revealed nitrogen, phosphorus and potassium as the most important elements, or macronutrients, in fertile soil. His discovery directed future fertilizer advancements focusing on those three elements.
Despite new insights into soil fertility, however, farmers were limited to naturally occurring supplies of the three macronutrients. During the early 20th century, German chemists developed processes for synthesizing nitrogen needed for munitions during the World Wars. After the wars had ended, munitions plants switched to producing fertilizers using the same process, called the Haber process, as explained by Raymond Zmaczynski of Princeton University.
The evolution of fertilizers has led to more, easier and cheaper food, but it has also contributed to environmental degradation. As shown by the U.S. Department of Agriculture, in 1940, before the widespread use of the Haber process, one farmer fed just over 10 people. That number leaped to an estimated 100 people in 1990. The cost of such efficiency has been fertilizer pollution and increased reliance on fossil fuels to power the energy-intensive production of synthetic fertilizers.