Where is Nitrogen Found?
Nitrogen and oxygen make up most of the air, and the nitrogen cycle controls its use in the vital processes of life.
Nitrogen and oxygen are the two most abundant gases in the air. Oxygen makes up about 21 percent and nitrogen, about 78 percent, leaving just one percent to be shared between carbon dioxide, the noble gases, and other gases. Oxygen is reactive and is involved in many reactions, in fact, it is the constituent of the atmosphere that makes the earth habitable by living creatures. Nitrogen, on the other hand, is very unreactive as the gas that we find in the atmosphere.
Nitrogen is Not Reactive
Living things cannot live in pure nitrogen, and neither can combustible materials burn in it. These facts lead to the use of nitrogen to provide a non-reacting atmosphere for welding, glass-making, and other processes where oxidation would be a problem in normal air. The gas is also used for flushing out oil pipelines and tanks to remove flammable or explosive vapor, for food packaging to prevent food from being spoiled by reaction with oxygen, and in corn silos to prevent dust explosions.
Nitrogen Is Indispensable for Life
Nitrogen, however, is actually indispensable for life to succeed. Plant, animals, and humans would not be able to live without nitrogen, but the nitrogen in the air is unusable, it needs to be chemically bonded with other elements to form useful compounds for life. Important molecules like amino acids, proteins, and nucleic acids (e.g. DNA) all contain nitrogen. We obtain most of our nitrogen from eating plants and animals, but they are only able to obtain the element from either nitrate (NO3-) or ammonium (NH4+) compounds.
The nitrogen cycle is the name given to the way nitrogen travels between different locations in nature. So, nitrogen in the air is ‘fixed’ by bacteria or by lightning, turning it into nitrate or ammonium compounds in water or soils, which are used by plants to grow. The plants are then eaten by animals. Nitrogen is returned to the soil through dead animal or plant matter, and the cycle continues.
Human beings have discovered the importance of nitrogen in growing plants, and so add to the nitrogen cycle by fixing nitrogen industrially, by means of the Haber Process, which turns nitrogen from the air into ammonia which is then used to make nitrogen fertilizers, encouraging plants to grow stronger and faster. Unfortunately, overuse of nitrate fertilizers can have a detrimental effect on the environment, through entry into groundwater and drinking water, which can cause health problems, especially to new-born babies.
As with many natural processes, the nitrogen cycle is a very finely balanced system that humankind has tinkered with at our peril. The use of fertilizers seems to be vital in a day of increasing population and the necessity for huge quantities of food, but overuse must be avoided.
- Dr. Michael Pidwirney: Introduction to the Biosphere: The Nitrogen Cycle, PhysicalGeography.net
- Scott C. Killpack and Daryl Buchholz: Nitrogen Cycle, University of Missouri Extension