Seasonal distribution of nitrous oxide emissions from soils in the Parkland region

The temporal variability of soil-derived N2O emissions presents a major challenge to the accurate quantification of N2O-N losses from agroecosystems. We characterized the seasonal distribution of N2O emissions from two agricultural sites in the Parkland region of Alberta during 1993 and 1993. Treatments studied were fallow, and spring wheat (Triticum aestivum L.) with and without urea fertilizer, under conventional till management. Gas samples were collected from vented static soil chambers and were analyzed for N2O with a gas chromatograph equipped with a Ni-63 electron capture detector. Soil water content and concentrations of NO3--N, NH4+-N, and water-soluble organic C (WSOC) were measured several times during the season. A brief burst of N2O emission was recorded at both sites during and immediately following spring snow melt. A second period of activity occurred between mid-June and mid-July. Between 16 and 60% of estimated annual N2O-N loss occurred during spring thaw, while >80% of cumulative annual N2O-N Loss had occurred by mid-July. Mean soil NO3--N concentration explained up to 65% of the temporal variability in geometric mean N2O emissions. A multiple regression model that included fall soil concentrations of NO3-N, NH4+-N, and WSOC explained 94% of the variability in estimated cumulative N2O-N loss during the following spring thaw. Most N2O-N losses in the Parkland region appear to occur during spring thaw and early summer; therefore, sampling schedules need to focus on these time periods. Management practices that minimize N availability during spring thaw may be an effective mitigation strategy for this region.