Ammonia oxidisers and their inhibition to reduce nitrogen losses in grazed grassland: a review

Pastoral agriculture is a major source for nitrate (contamination in surface and ground waters and for the greenhouse gas emissions in New Zealand. Advances have been made in recent years in understanding the role of different ammonia oxidisers, including ammonia oxidising bacteria (AOB) and ammonia oxidising archaea (AOA) in nitrification, and in developing nitrification inhibitor (NI) mitigation technologies. Results showed that, in the N-rich soil environment under the animal urine patches in grazed grassland, AOB are the dominant microbes responsible for ammonia oxidation whereas AOA play a less important role. A number of laboratory and field studies have demonstrated conclusively that treating grazed pasture soils with a nitrification inhibitor (NI), such as dicyandiamide (DCD), which inhibits the growth and activity of AOB, is an effective means of reducing NO3- leaching and N2O emissions.