Nitrous Oxide Emissions from Agricultural Toposequences in Alberta and Saskatchewan

Nitrous oxide fluxes from soils are inherently variable in time and space. An improved understanding of this variability is needed to make accurate estimates of N 2 O fluxes at a regional scale. The objectives of this work were to (i) characterize the influence of soillandscape combinations and N application rates on N 2 O emissions and to (ii) determine the contribution of these influences on the estimation of N 2 O emissions at the field scale. We used static chambers and gas chromatography methods to measure N 2 O fluxes and collected ancillary data (mineral N, water soluble C, soil water content, soil temperature) in Canada at Mundare (AB) in the aspen parkland ecoregion and at Swift Current (SK) in the short-grass prairie ecoregion. At Mundare, measurements were taken in 1995 and 1996 by landscape position and land use. At Swift Current, data were collected in 1999 and 2000 by landscape position and N rate. At Mundare, landscape position affected N 2 O emissions but the pattern varied seasonally. During a 46-d period in summer 1995, a flux of 430 g N 2 O-N ha -1 measured in a backslope was greater than the 60 g N 2 O-N ha measured on average in shoulder and depressional areas. The flux pattern changed during a 43-d spring thaw of 1996 when fluxes from depressional areas were greatest (1710 g N 2 O-N ha -1 ). Nitrous oxide emissions from natural areas were small. The emission pattern during summer 1996 was similar to that of 1995 but the fluxes were an order of magnitude larger. At Swift Current, N 2 O fluxes in summer 1999 were affected by topography and N rate. Fluxes were greatest in depressional areas receiving N at 110 kg ha -1 (3140 g N 2 O-N ha -1 ). Use of the area fraction occupied by each landscape position to calculate N 2 O flux increased the estimates of N 2 O fluxes at the field scale in five out of six cases. Further research of N 2 O fluxes in variable landscapes should help elucidate factors controlling N 2 O fluxes from pedon to field scale and thus translate into improved flux estimates at regional scales.