The Nitrogen Cycle
Author: Theresa Lynn Ford
Created: Monday, 2/14/2005 3:49 PM
(Modified: Monday, 2/14/2005 3:52 PM EST)

The Nitrogen Cycle

First, we'll take a bottle of liquid nitrogen and poor it on the bank vault's lock one night, and then we'll take a sturdy hammer and shatter the frozen lock. And then we take all the money and buy more liquid nitrogen, so we can go to the next lock. The nitrogen cycle according to cartoons! The real nitrogen cycle is actually a little different than this as you might suspect but is generally as simple.

Nitrogen exists mostly in the air (78% of the air). To be used, the nitrogen gas must undergo a process called nitrogen fixation which converts it to an ammonia form. Nitrogen fixation can be done by bacteria (living with legumes), lightning, and the Haber-Bosch process (manufacturing fertilizer), or through burning fossil fuels which creates nitrogen oxide in the air and comes down as acid rain. (Wright, 2005, p. 74-76)

Plants and animals then use the nitrogen which eventually returns to the soil. Soil bacteria returns the nitrogen to the atmosphere through a process called denitrification. Denitrification is the decomposition process of microbes using nitrates (the "returned to soil" nitrogen) for oxygen. (Wright, 2005, p. 74-76)

Unfortunately, just as the bank-robbing cycle can be interrupted by a frowning policeman, our nitrogen cycle is being interrupted by active humans. Through edible plant choice and quantity (more producers and fertilizers) and fossil fuel combustion, we have exceeded the natural nitrogen fixation amount by 1 and a half times. This "nitrogen saturation" causes other mineral deficiencies and kills plants and allows too much algae to grow in estuaries and oceans which negatively impacts those biomes. (Wright, 2005, p. 74-76)


Wright, R. (2005). Environmental Science, Ninth Edition. New Jersey: Pearson Prentice Hall.

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