Nitrogen, as any farmer or gardener knows, is essential to plant life. But there's a limited amount available naturally, so 100 years ago, chemists developed a way to turn inert nitrogen gas in the atmosphere into reactive, biologically available nitrogen in the form of ammonia. The widespread use of this chemical nitrogen fertilizer to boost crop production has resulted in food to feed the world. It has also resulted in too much nitrogen getting into waterways and our air, essentially adding unwanted, unneeded fertilizer to our natural systems — with disastrous results. The combustion of fossil fuels adds even more reactive nitrogen to our environment. A single atom of reactive nitrogen can contribute to aquatic dead zones, smog, acid rain, climate change and ozone depletion as it moves through the air, water and soil.