Bacteria in the soil are responsible for several transformations within the nitrogen cycle. Ammonium (NH4+) is converted to nitrite (NO2-) and then to nitrate (NO3-). This process is known as nitrification.
Other processes that occur in the soil are mineralisation and denitrification. Mineralisation is the decomposition of litter in soil and the release of nitrogen into forms that plants can take up. Denitrification is the conversion of nitrate to nitrous oxide (N2O) and gaseous nitrogen (N2).
IMAGE: © The University of Waikato Te Whare Wānanga o Waikato