Nitrogen is essential to living organisms however it cannot be used in its natural state and must be converted to mineral form for use. It must first be "fixed", that is pulled from the air and converted into an inorganic compound such as ammonium (NH4) and nitrate (NO3). It can then be used and recycled through the food chain. .
The two sources of "fixing" are nitrogen-fixing organisms like algae and bacteria and lightning. The standard measurement for analyzing the global nitrogen cycle is the teragram (Tg), which is equal to a million metric tons of nitrogen. Worldwide lightning production is about 5-10 Tg. Terrestrial organisms account for 90-140 Tg per year. The astonishing fact is that humans, on an average just in fertilizer alone, produce 80 Tg per year! During the past century, humans have accelerated the nitrogen on this Earth, and it's almost safe to say that we have doubled it! But, is there a problem with this? The answer is an unequivocal, "Yes!".
We are changing the chemical makeup of the atmosphere. One result of our over usage of fossil fuels, and harvesting of legumes and other plants that host bacteria for the nitrogen into plant friendly forms, is that we are increasing the amount of nitrous oxide, nitric oxide and ammonia (NH3) into the atmosphere. Automobiles produce nitric oxide, a very-effective, heat-trapping gas which leads to greenhouse warming by absorbing and reradiating the heat back toward the Earth. It also can trigger reactions that deplete and thin the ozone layer, the layer that shields us from damaging ultraviolet rays.
Phosphorus (P) is "a natural element found in rocks, soils and our own bodies!" (Phosphorus Pollution). It is essential for animals and plants and is a common ingredient, as is nitrogen, in fertilizers. Some sources of phosphorus are eroded soil, leaves and grass clippings, garbage, human and animal waste, lawn fertilizer and pesticides.
