The nitrogen cycle is the processing of nitrogen through different chemical and organic states in nature. This is one of the most important biological cycles on Earth. Nitrogen is a gas, which combines with carbon, hydrogen and oxygen to form the basis of most organic molecules. The process is broadly described as Nitrogen > compound > assimilation > release of nitrogen.

The nitrogen cycle is a common process in plants, which use nitrogen for foliage, which is then released as the leaves fall and are replaced. The leaves decay through the action of denitrifying bacteria, and release nitrogen into the atmosphere, and the cycle repeats.