Emissions of N2O from Sonoran Desert and effluent-irrigated grass ecosystems

Nitrous oxide (N 2 O) is a radiatively and photochemically important atmospheric trace gas whose concentration is increasing annually by about 0·25%. The cause of this increase is not fully known but may be related to land cover changes in terrestrial ecosystems. N 2 O emissions from Arizona Upland Sonoran Desert and effluent-irrigated turf grass (golf course) were measured by a closed chamber method at weekly intervals during a 10-week period from 18 June to 20 August 1991. Fluxes at three turf grass sites ranged from 7 to 275 ng N 2 O-N m −2 s −1 , while fluxes at three desert sites ranged from −1·6 to 7·3 ng N 2 O-N m −2 s −1 . The mean (±1 SE) flux over the 10-week period at the grass location (40·2 ± 48·7 ng N 2 O-N m −2 s −1 ) was almost 17 times larger than the mean flux at the desert location (2·4 ± 2·2 ng N 2 O-N m −2 s −1 ). Additional measurements during November 1991 and April 1992 indicated nearly negligible fluxes during cooler months at both locations. The estimated annual flux of 6·4 kg N 2 O-N ha −1 from grass was similar to, but slightly larger than, emissions reported for most other intensively managed ecosystems. The estimated annual flux of 0·4 kg N 2 O-N ha −1 indicates that the Sonoran Desert may emit more N 2 O-N per unit land area than other dry regions such as grassland steppe and sagebrush steppe. More measurements are needed over longer periods to fully assess the contribution of the Sonoran Desert to the atmospheric budget of N 2 O. Results indicate, however, that land use change from desert to irrigated grass can markedly increase N 2 O emissions.