Nitrogen Cycle

Like water and carbon, nitrogen is continuously recycled through the biosphere in a process called the nitrogen cycle, moving nitrogen between the atmosphere, soil, plants, and animals.

Although nitrogen gas makes up 78% of Earth’s atmosphere, it must be converted into usable forms for plants and animals to take up, which involves several steps.

The nitrogen cycle begins with nitrogen fixation, a process in which special bacteria in the soil and plant roots turn nitrogen gas into ammonia, which plants can absorb.

Next, two different types of bacteria convert ammonia into nitrates through a process called nitrification. Plants absorb nitrates through their roots, turning them into organic compounds that animals consume.

When plants and animals die or release waste, decomposer bacteria break down their remains. This process, called ammonification, converts nitrogen back into ammonia, returning it to the soil.

The final step in the cycle is denitrification. In this process, specific bacteria convert nitrates back into nitrogen gas, releasing it into the atmosphere and completing the cycle.