Biogeochemical Cycle - Nitrogen Cycle

The nitrogen cycle is the continuous circulation and recycling of nitrogen gas in the atmosphere into different nitrogen compounds through various biotic (living) and abiotic (non-living) processes. Nitrogen makes up 78% of the atmosphere and is vital for life as it is a key component of proteins and nucleic acids. However, most organisms cannot use nitrogen in its free form, so it must be converted into usable compounds.

The important processes involved in the nitrogen cycle are:

1. Nitrogen Fixation: Free nitrogen in the atmosphere is converted into usable forms like nitrates and nitrites. This process occurs through atmospheric (lightning), industrial (fertiliser production), and biological (nitrogen-fixing bacteria in soil or plant roots) methods.
2. Ammonification: Decomposition of dead organisms and excretory waste by decomposers releases ammonia into the soil. This ensures nitrogen is recycled back into the ecosystem.
3. Nitrification: Ammonia is converted into nitrites (NO₂⁻) and then into nitrates (NO₃⁻) by nitrifying bacteria in the soil. Nitrates are absorbed by plants to synthesise proteins and nucleic acids.
4. Denitrification: Denitrifying bacteria convert nitrogen compounds like nitrates back into nitrogen gas (N₂), which is released into the atmosphere. This completes the nitrogen cycle by returning nitrogen to the air.

The Nitrogen Cycle