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• Nitrogen fixation
• Words to Know
• Ammonification, nitrification, and denitrification

The term nitrogen cycle refers to a series of reactions in which the element nitrogen and its compounds pass continuously through Earth's atmosphere, lithosphere (crust), and hydrosphere (water component). The major components of the nitrogen cycle are shown in the accompanying figure. In this diagram, elemental nitrogen is represented by the formula N₂, indicating that each molecule of nitrogen consists of two nitrogen atoms. In this form, nitrogen is more correctly called dinitrogen.

Nitrogen fixation

Nitrogen is the most abundant single gas in Earth's atmosphere. It makes up about 80 percent of the atmosphere. This fact is important because...