Chemists call this process of taking atoms from the atmosphere and combining them into molecules useful to living things "fixing" that element. Until a German Jewish chemist named Fritz Haber figured out how to turn this trick in 1909, all the usable nitrogen on earth had at one time been fixed by soil bacteria living on the roots of leguminous plants (such as peas or alfalfa or locust trees) or, less commonly, by the shock of electrical lightning, which can break nitrogen bonds in the air, releasing a light rain of fertility...
...It has been less than a century since Fritz Haber's invention, yet already it has changed earth's ecology. More than half of the world's supply of usable nitrogen is now man-made. (Unless you grew up on organic food, most of the kilo or so of nitrogen in your body was fixed by the Haber-Bosch process.) "We have perturbed the global nitrogen cycle," Smil wrote, "more than any other, even carbon." The effects may be harder to predict than the effects of the global warming caused by our disturbance of the carbon cycle, but they are no less momentous.
The key to reducing our dependence on synthetic nitrogen is to build a more diversified agriculture—rotating crops and using animals to recycle nutrients on farms—and give up our vast, nitrogen-guzzling monocultures of corn. Especially as the price of fossil fuels climbs, even the world's most industrialized farmers will need to take a second look at how nature, and those who imitate her, go about creating fertility without diminishing our world.
Read more here
