Denitrification

Along with dinitrogen fixation, ammonification, and nitrification, denitrification is a major component of the nitrogen cycle. Estimates of nitrogen fluxes from terrestrial and marine ecosystems to the atmosphere as a result of microbial denitrification range from 90 × 10¹² to 243 × 10¹² grams per year for terrestrial systems and 25 × 10¹² to 179 × 10¹² grams per year for marine systems. Scientist generally agree that less than 10% of these fluxes occur with nitrogen as a component of nitrous oxide. The range in these estimates reflects the difficulty researchers face in measuring denitrification and extrapolating the measurements to a global scale.

Humans are primarily interested in denitrification because this process is responsible for fixed nitrogen being removed from sewage and lost from cropland. Environmentally harmful nitrate concentrations in sewage discharge can be reduced by storing wastes under denitrifying conditions before releasing them into the environment. Although denitrification is a beneficial process in sewage treatment, it is considered a problem in agriculture. Farmers increase their crop yields by applying nitrogen containing fertilizers to their land. As a result of denitrification, crop yields may be reduced because much of the added nitrogen is lost to the atmosphere. This loss of fixed nitrogen may have global consequences. Increased denitrification from cropland is responsible for increased amounts of nitrous oxide in the atmosphere. Although nitrous oxide is not the major end product of denitrification, it is highly reactive and may contribute to the depletion of ozone in the stratosphere.