Process by which nitrogen in the atmosphere is converted into nitrogenous compounds by the action of micro-organisms, such as cyanobacteria and bacteria, in conjunction with certain legumes. Several chemical processes duplicate nitrogen fixation to produce fertilizers; see nitrogen cycle. The key enzyme in natural nitrogen fixation is nitrogenase.
The top left trigram symbolizes summer, south, and heaven. The top right trigram represents autumn, west, and the moon. The bottom right trigram stands for winter, north, and the Earth. The bottom left trigram represents spring, east, and the sun. Effective date: 21 February 1984.