|Dead zone off La Jolla, CA*|
What's so bad about excess nitrogen? Increased nitrogen entering our watershed promotes algae growth which in turn reduces dissolved oxygen in the water which aquatic animals and fish require, creating dead zones. Imagine the effect fertilizer run off has on an algae-choked pond and then expand that picture to oceans. Also, excess nitrogen may contribute to climate change. Nitrous oxide may be "the single most important ozone-depleting substance (ODS) emission and is expected to remain the largest throughout the 21st century."**
Ordinarily, bacteria in plant roots and soil "fix" atmospheric nitrogen, converting it to usable forms for plants and animals. A "nitrogen cycle" has occurred with fluctuations for billions of years, first by natural energy such as volcanoes and lightning and later by the introduction of oxygen and life.
A big change occurred in the last 100 years with the increase in nitrogen fertilizers. From 1960 to 2000 the use of nitrogen fertilizer has increased 800 percent! The addition of excess phosphorus in fertilizer increases algae growth even further. Needless to say, the need for fertilizer use is expected to continue growing with the world's expanding population's need for more food. Like turning a battleship, any change in this pattern will take lots of time while the nitrogen load continues to increase.
What else can we do? Just as we encourage proper fertilizer use to maintain stream health, the answers lie in intelligent use of fertilizers. By increased use of crop rotation and modifying the over use and badly time application of nitrogen fertilizer, we may eventually reduce the nitrogen burden on our planet. Also, new strains of crops can be developed to better utilize the microbial community in the soil.
A continued challenge will be the global increase in meat consumption by traditionally less prosperous societies. Meat requires much more plant production per calorie than traditional vegetarian predominate diets and therefore more fertilizer. Also the growth of bio fuels such as corn that require heavy fertilization adds to the burden. I am not quite ready to give up beef, but I would be willing to pump a load of switchgrass fuel into my tank if the opportunity arises. More to come in the next decade.
* The picture above and more on dead zones are at Wikipedia.