Nitrogen Cycle

The nitrogen cycle consists of several major steps. In nitrogen fixation, specialized bacteria in soil, as well as blue-green algae (cyanobacteria) in aquatic environments, combine gaseous N2 with hydrogen to make ammonia (NH3). The bacteria use some of the ammonia they produce as a nutrient and excrete the rest into the soil or water. Some of the ammonia is converted to ammonium ions (NH4+) that plants can use as a nutrient.