Nitrogen is the basis of fertility. It’s the base of the amino acids that make up our DNA and the proteins in our bodies. Nitrogen is a common limiting nutrient in nature, and agriculture, meaning that naturally it is in the shortest supply and limits growth. Humanity used to face global food shortages due to a fixed amount of Nitrogen in circulation. However, since scientists in the early 20th century learned to synthesize, human population has grown rapidly. Today we have more than enough Nitrogen in our biosphere to feed everyone.
Like the elements of carbon and hydrogen, nitrogen also has global cycles that it moves through on the planet. While water and carbon are relatively more simple, stable cycles Nitrogen is dynamic and moves through several pathways as it journeys around the biosphere. Nitrogen has traditionally moved out of the air (N2 makes up 78% of our atmosphere) and into the biosphere through a process called nitrogen fixation. Fixation happens when lightning strikes the ground or through bacteria in the soil working with leguminous plants (like alfalfa and peas). Legumes and soil bacteria convert N2 into ammonia, a form of nitrogen that's usable by plants. When animals eat the plants, and humans eat the plants and animals we acquire protein. Manures from plants, animals and humans have been utilized throughout human history to recycle that nitrogen supplying fertility to agricultural fields.
Perhaps even more so than water and carbon humans have substantially changed the global nitrogen cycle by synthesizing atmospheric N2 into ammonia in the early 20th century through what is known as the Haber Bosch process. German scientists Fritz Haber and Karl Bosch achieved the alchemical feat of creating bread from air when they figured out how to “fix” nitrogen through chemical and electrical processes. Prior to this invention the global population had been limited to under 2 billion. Since the synthesis of Nitrogen global population has more than tripled to 7.8 billion meaning that most of us alive today are made in large part, by ammonia that was synthesized in the Haber Bosch process.
Resources:
Vaclav Smil, Enriching the Earth
The Global Nitrogen Cycle in the 21st Century
