Nitrogen Cycle

-         - Nitrogen not used directly by living organisms

-         -  Nitrogen gas constitute 78% of the air

Nitrogen fixation

This describes how nitrogen gas from the air is converted into nitrates. Plants use the nitrates as fertilizer. This occurs by two methods

1.      Lightening : Lightening causes N2 gas to react with H2O molecules in the atmosphere and form ammonia and nitrates

2.      Nitrogen fixing bacteria: some plants, especially leguminous plants, have bacteria living in their root nodules. These bacteria convert the atmospheric nitrogen to nitrates. E.g. of bacteria: Rhizobia

Nitrification

Animals and plants produce waste. Also, when they die, their body starts to decompose. Ammonia is released, which is then converted to nitrites. The Nitrifying bacteria, such as Nitrosomanas, convert the ammonia to nitrites, and the nitrites to nitrates, which can then be used by plants for growth

Denitrification

In this process, the nitrates and nitrites in the soil are converted back into nitrogen gas by the denitrifying bacteria such as Pseudomonas.