What is nitrogen fixation?

Nitrogen fixation is one stage of the nitrogen cycle. The nitrogen cycle describes the different transformations of the forms of nitrogen in nature. The nitrogen cycle is important because plants need nitrogen to form proteins and other compounds for their function and survival and because nitrogen is a limiting factor to plant growth.

Nitrogen fixation involves the conversion of nitrogen gas in the air (a form which cannot be used by plants) in to usable forms of nitrogen in the soil (such as nitrate and ammonium). Several processes can contribute to nitrogen fixation. One process is the fixation of nitrogen gas in the air to nitrate in the soil by lightning. Another process is the production of fertilisers to be added to soil, which involves the conversion of nitrogen gas to ammonia by the Haber Process. Finally, nitrogen gas can be fixed to usable forms by bacteria. This includes bacteria in the root nodules of leguminous plants and also different types of bacteria in the soil which produce usable forms of nitrogen either from nitrogen gas, organic nitrogen-containing compounds or ammonia.