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 NH4+ and C substrate levels produced relatively large quantities of N2O. A series of laboratory experiments confirmed that the addition of NH4+ and glucose to soil increased N2O production under aerobic conditions. Denitrifying enzyme activity was also increased by the addition of NH4+ and glucose. Furthermore, NH4+ and glucose 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 NH4+ 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 NO3- supplied from NH4+ through nitrification. Alternatively, N2O may be produced during mixotrophic and heterotrophic growth of nitrifiers. The results indicated that the NH4+ concentration, in addition to NO3-, C substrate, and O2 concentrations, is important for predicting N2O production and denitrification under field conditions.