The NITROGEN CYCLE

​1. NITROGEN FIXATION: Fixation converts 'free' nitrogen (N2) in the atmosphere into forms that plants can absorb through their root systems.

• A small amount of nitrogen can be fixed when LIGHTNING provides the energy needed for N2 to react with oxygen.

• NITROGEN-FIXING BACTERIA invade the root hairs of plants, where they multiply and stimulate formation of root nodules. Within the nodules the bacteria convert Atmospheric Nitrogen (N2) to ammonia (NH4), which plants use.

​2. DECOMPOSITION: Decay or decomposition is the process where DECOMPOSERS (bacteria and fungi) break down organic nitrogen compounds in dead remains, feces and urine to give ammonia.

• Decomposition produces ammonia, which can then go through the nitrification and denitrification process.

​3. NITRIFICATION: Nitrification is the process that converts ammonia to nitrite and then to nitrate and is carried out by bacteria.

​4. DINITRIFICATION: Denitrification is the process that converts nitrate to nitrogen gas by bacteria, thus removing bioavailable nitrogen and returning it to the atmosphere.

​5. ASSIMILATION: Assimilation is the process by which plants and animals incorporate the nitrates and ammonia formed through nitrogen fixation and nitrification. Plants take up these forms of nitrogen through their roots, and incorporate them into plant proteins and nucleic acids.