INCREASE IN NITROUS-OXIDE PRODUCTION IN SOIL INDUCED BY AMMONIUM AND ORGANIC-CARBON

We observed that soil cores collected in the field containing relative ly high NH4+ and C substrate levels produced relatively large quantiti es of N2O. A series of laboratory experiments confirmed that the addit ion of NH4+ and glucose to soil increased N2O production under aerobic conditions. Denitrifying enzyme activity was also increased by the ad dition of NH4+ and glucose. Furthermore, NH4+ and glucose additions in creased the production of N2O in the presence of C2H2. Therefore, we c oncluded that denitrification was the most likely source of N2O produc tion. Denitrification was not, however, directly affected by NH4+ in a naerobic soil slurries, although the use of C substrate increased. In the presence of a high substrate C concentration, N2O production by de nitrifiers may be affected by NO3- supplied from NH4+ through nitrific ation. Alternatively, N2O may be produced during mixotrophic and heter otrophic growth of nitrifiers. The results indicated that the NH4+ con centration, in addition to NO3-, C substrate, and O2 concentrations, i s important for predicting N2O production and denitrification under fi eld conditions.