What is meant by nitrogen cycle?

The nitrogen cycle is the continuous process by which nitrogen moves through the atmosphere, soil, plants, animals, and back to the air.

Nitrogen is essential for making proteins and DNA. Though the atmosphere contains 78% nitrogen, plants and animals cannot use it directly. The nitrogen cycle converts it into usable forms through biological and chemical processes. It includes several steps:

• Nitrogen fixation: Bacteria and lightning convert N₂ into ammonia (NH₃).
• Nitrification: Ammonia changes into nitrites (NO₂⁻) and nitrates (NO₃⁻).
• Assimilation: Plants absorb nitrates to make proteins.
• Ammonification: Decomposers convert dead matter into ammonia.
• Denitrification: Bacteria return nitrogen gas to the atmosphere.

This cycle maintains soil fertility and balances atmospheric nitrogen levels.