Nitrogen fixation can be done by

Nitrogen fixation is a process through which the nitrogen present in the air is converted to nitrogenous compounds that are used by the plant. It can be done by the blue-green algae, Rhizobium, lightning, nitrogen-fixing bacteria in the soil, etc. The nitrogen fixing bacteria either lives freely in the soil or in the root nodules of leguminous plants. They convert the nitrogen in the air to make it usable for plants and they also help in increasing the fertility of the soil.