A stage in the nitrogen cycle in which nitrates in the soil or in dead organic matter are converted into nitrite, nitrous oxide, ammonia, or (primarily) elemental nitrogen. The process is made possible by certain types of bacteria, known as denitrifying bacteria. Denitrification is a reduction reaction and occurs, therefore, in the absence of oxygen. For example, flooded soil is likely to experience significant denitrification since it is cut off from atmospheric oxygen. Although denitrification is an important process for the decay of dead organisms, it can also be responsible for the loss of natural and synthetic fertilizers from the soil.