Free nitrogen is released to the atmosphere by

Free nitrogen is released to the atmosphere by denitrifying bacteria. Denitrifying bacteria convert nitrates in soil back into gaseous nitrogen and release it into the atmosphere, thereby completing the nitrogen cycle. Nitrogen fixation is the process by which atmospheric nitrogen is converted into organic compounds, such as ammonia and amino acids, by nitrogen-fixing bacteria. Nitrifying bacteria convert ammonium into nitrates. Saprophytic bacteria break down dead organic matter and recycle nutrients, but they do not release free nitrogen to the atmosphere.