Estimation of annual nitrous oxide emissions from a transitional grassland-forest region in Saskatchewan, Canada

The increasing atmospheric N2O concentration and the imbalance in its globa l budget have triggered the interest in quantifying N2O fluxes from various ecosystems. This study was conducted to estimate the annual N2O emissions from a transitional grassland-forest region in Saskatchewan, Canada. The st udy region was stratified according to soil texture and land use types, and we selected seven landscapes (sites) to cover the range of soil texture an d land use characteristics in the region. The study sites were, in turn, st ratified into distinguishable spatial sampling units (i.e., footslope and s houlder complexes), which reflected the differences in soils and soil moist ure regimes within a landscape. N2O emission was measured using a sealed ch amber method. Our results showed that water-tilled pore space (WFPS) was th e variable most correlated to N2O fluxes. With this finding, we estimated t he total N2O emissions by using regression equations that relate WFPS to N2 O emission, and linking these regression equations with a soil moisture mod el for predicting WFPS. The average annual fluxes from fertilized cropland, pasture/hay land and forest areas were 2.00, 0.04, and 0.02 kg N2O-N ha(-1 ) yr(-1), respectively. The average annual duxes for the medium- to fine-te xtured and sandy-textured areas were 1.40 and 0.04 kg N2O-N ha(-1) yr(-1) r espectively. The weighted-average annual flux for the study region is 0.95 kg N2O-N ha(-1) yr(-1). The fertilized cropped areas covered only 47% of th e regional area but contributed about 98% of the regional flux. We found th at in the clay loam, cropped site, 2% and 3% of the applied fertilizer were emitted as N2O on the shoulders and footslopes, respectively.