Chemically Dependent

Atmospheric nitrogen is converted to the usable forms by lightning or by the action of nitrogen fixing bacteria in the soil or in plants. Nitrogen in living matter is converted back to ammonia by decomposition. Some nitrogen is released by the erosion of nitrate-rich rocks. At the same time, bacteria in anaerobic conditions (without oxygen) in bogs, lakes, and at the bottom of oceans, returns nitrogen to the atmosphere as N2. This biogeochemical cycle dictates the amount of nitrogen available in soil for plants. This movement of nitrogen between the atmosphere and soil, water, and living things is a biogeochemical cycle, and the rates of movement dictate the amount of nitrogen available to plants.

Until the turn of the century, the nitrogen actually available for plant growth limited farm productivity to an amount sufficient to feed 5 people per hectare. Then Fritz Haber and Carl Bosh invented a method of converting N2 to NH3 by combining nitrogen and hydrogen gases at a pressure of 200 atmospheres and a temperature of 500¡ C. Between the 1940s and the 1990s consumption of ammonia fertilizer increased from 10 million to nearly 80 million tons per year. This artificial fertilizer doubled the amount of nitrogen available to plants, and significantly increased the productivity of the average farm. Countries whose population densities had been relatively stable for 100 years (Netherlands, Java, China, Egypt) tripled their populations. And of course, once populations increased, so did our dependence on nitrogen. Presently one third of the protein in our diets comes from the Haber-Bosch process.

Unfortunately, only about half of the fertilizer applied to fields is actually taken up by plants. The remainder is wreaking havoc on the planetary ecosystem. The most well known effect is algal blooms in rivers and lakes. When fertilizer is not taken up by plants, it is washed off of fields into waterways where it increases the growth of algae. When the nitrogen is used up, the algae die, and their decomposition uses up the oxygen in the water, leading to the suffocation of fish and crustaceans. The effect is not just local either. The Gulf of Mexico has a dead zone of 18,200 square km which appears to be linked to the thousands of tons of nitrate flowing in daily from the Mississippi. Fertilizers can also migrate into water wells and make the water undrinkable, they can acidify the soil so that it actually becomes less productive, and they can be converted to nitrous oxides (NO, NO2) that destroy ozone and are 200 times as potent as carbon dioxide in trapping heat.

Barring stabilization of population growth and mass conversion to a vegetarian diet, the most promising way to deal with our nitrogen dependence appears to be using it more efficiently. When farmers monitor soil nitrogen to find the optimal time for fertilizer applications, runoff is significantly reduced. So, could farmers save the planet -- and save money and time -- by reducing fertilizer applications?

Read more about it: Global Population and the Nitrogen Cycle. Vaclav Smil. Scientific American July 1997 A Distant Death. Jason Effman. Columbia Missourian September 23, 1997

BioRegional Quiz: What climatological event usually occurs during the middle of October?

Three Gorges Dam - September Environmental Issues Seminar

Fall Environmental Issues Series

Wed Nov 12 2:40 Man and the Biosphere, a UN Plan for Nature
S206 UNION Roger Soles (U.S. State Depart.) invited

Wed Dec 10 2:40 Thoreau, Muir, Leopold - American Environmental Writers
KETCHAM AUD (Engineering ) Hank Ottinger (Westminster English)

2nd Annual Conference on Environmental Education "Hands On the Environment"

Solid Waste Management Planning for Wichita Kansas -- A Case Study

MU Meetings and Events (call to confirm times and places)

Organization Meetings and Events (call to confirm times and places)

Answer to BioRegional Quiz: The average day of first frost in Missouri is October 20.

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