Nitrogen is extremely important to living material. Plants, animals and humans could not live without it. The major source of nitrogen is the atmosphere. It exists as a colorless, odorless, nontoxic gas and makes up about 78 percent of the atmosphere. In its liquid form, nitrogen is also colorless and odorless, and looks similar to water.

Liquid Nitrogen is non-toxic. Liquid Nitrogen melts at -210 degrees Celcius or ?346 F.

Nitrogen is also found in the Earth's crust as part of organic matter and humus. Nitrogen compounds are present in organic materials, foods, fertilizers, explosives and poisons. Nitrogen is crucial to life, but in excess it can also be harmful to the environment.

The nitrogen gas in our atmosphere exists as a molecule composed of two atoms of nitrogen. Plants cannot directly use this form of nitrogen. Nitrogen must be converted into other forms before it can be used by plants. Plant uptake of nitrogen is largely in the form of nitrate (NO3-), and to a lesser degree ammonium (NH4+).