What are the main stages of the nitrogen cycle?

The nitrogen cycle describes the circulation of nitrogen through nature. While these stages are not strictly sequential, they are classified as follows:

• Nitrogen fixation: Atmospheric nitrogen gas is converted into inorganic compounds, such as ammonia, primarily by bacteria and blue-green algae. This can also occur through abiotic means like lightning or the Haber-Bosch process.1
• Nitrogen assimilation: Plants and algae absorb nitrates and ammonia to build tissue compounds. Animals subsequently ingest these plants, incorporating the nitrogen into their own bodies.12
• Ammonification: Microorganisms decompose the remains and waste products of living organisms, releasing ammonia and ammonium back into the environment.1
• Nitrification: Nitrifying bacteria transform soil ammonia into nitrates, which are then available for plant uptake.1
• Denitrification: Denitrifying bacteria metabolize nitrates, particularly in anaerobic soil conditions, converting them back into free atmospheric nitrogen.1