What is a definition of the nitrogen cycle?
The nitrogen cycle is the biogeochemical cycle describing how nitrogen moves through the biosphere and atmosphere.
The nitrogen cycle is the biogeochemical cycle describing how nitrogen moves through the biosphere and atmosphere. Like the carbon cycle or the water cycle, the nitrogen cycle describes how nitrogen is converted into different forms as it moves through the cycle.
The complete cycle is shown below:
The majority of nitrogen on Earth is actually stored in the atmosphere. Atmospheric nitrogen is not not readily available for most organisms to use though.
Conversion of atmospheric nitrogen is called nitrogen fixation and is largely done by certain bacteria, although it nitrogen can also be converted through the Haber-Bosch Process. After this conversion process, nitrates and ammonia from the Haber-Bosch Process can be used by plants. When living organisms die, nitrogen returns to the soil through ammonification. Nitrification by bacteria transforms ammonia in the soil into nitrates so that it is available for plants to use again. There is also denitrifying bacteria which transform nitrates in the soil into atmospheric nitrogen again.
You can read about the nitrogen cycle in more detail here.