It’s colorless, odorless and gets no respect, but it’s vital to the cycle of life— and we may be using too much

Common and yet limited, nitrogen is a conundrum of the biosphere. Plants, animals and humans all need it, as it's an essential part of food cycles. And it makes up almost 80 percent of the air.

Yet, to be used by living organisms, nitrogen must be "fixed" — that is, combined with other elements. In nature, only specialized bacteria (as well as lightning) fix nitrogen. Today, however, humans fix as much nitrogen as all natural processes on land combined. Scientist James Trefil looks at how our activities have changed the nitrogen cycle and what those changes mean.

Humans fix and release nitrogen in three important ways: in factories for use as fertilizers, by planting legumes (which host bacteria that fix nitrogen), and by burning fossil fuels. As the world's population grows, commercially fixed nitrogen fertilizers are essential for agriculture. But runoff pollutes groundwater and overloads streams and lakes with nutrients. Biodiversity plummets when nitrogen fertilizers are added to grassy fields. And nitrogen compounds created by the burning of fossil fuels lead to smog and acid rain.

Seeking answers to these and other problems of our nitrogen use, Trefil talks with researchers experimenting with the efficient use of fertilizers as well as using wetlands for balancing our nitrogen use. "For better or worse," notes one researcher, "the world is in our hands."

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