UC Davis

The reduction of nitrate (NO3-) to gaseous products in aerated environments (oxic denitrification) has been reported sporadically in the past, mostly in pure culture studies, but the extent to which it occurs in soil is not known. We investigated the emission of nitrous oxide (N2O) due to oxic denitrification in bulk soil under continuous aeration in a soil slurry experiment. Out of 19 soils assayed, a subset of five, representing both cultivated and natural or unmanaged ecosystems, showed emissions of N2O-N derived from NO3- ranging from 0.02 to 1.14 ng per gram of soil per hour. This emission occurred immediately after rewetting and continued during the 8 hour observation period. Although much less attention has been given to oxic denitrification compared to its anaerobic counterpart, our study indicates that the phenomenon, specifically the emission of N2O, is active in a variety of soils. The periods during which denitrification in soils can occur may be far more extensive if both aerobic and anaerobic activities are considered, especially in soils that remain moist (but not necessarily anoxic) for long periods.