Increase in nitrous oxide production in soil induced by ammonium and organic carbon

We observed that soil cores collected in the field containing relatively high NH _inf4 ^sup+ and C substrate levels produced relatively large quantities of N₂O. A series of laboratory experiments confirmed that the addition of NH _inf4 ^sup+ and glucose to soil increase N₂O production under aerobic conditions. Denitrifying enzyme activity was also increased by the addition of NH _inf4 ^sup+ and glucose. Furthermore, NH _inf4 ^sup+ and glocose additions increased the production of N₂O in the presence of C₂H₂. Therefore, we concluded that denitrification was the most likely source of N₂O production. Denitrification was not, however, directly affected by NH _inf4 ^sup+ in anaerobic soil slurries, although the use of C substrate increased. In the presence of a high substrate C concentration, N₂O production by denitrifiers may be affected by NO _inf3 ^sup- supplied from NH _inf4 ^sup+ through nitrification. Alternatively, N₂O may be produced during mixotrophic and heterotrophic growth of nitrifiers. The results indicated that the NH _inf4 ^sup+ concentration, in addition to NO _inf3 ^sup- , C substrate, and O₂ concentrations, is important for predicting N₂O production and denitrification under field conditions.