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 global 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 study region was stratified according to soil texture and land use types, and we selected seven landscapes (sites) to cover the range of soil texture and land use characteristics in the region. The study sites were, in turn, stratified into distinguishable spatial sampling units (i.e., footslope and shoulder complexes), which reflected the differences in soils and soil moisture regimes within a landscape. N2O emission was measured using a sealed chamber method. Our results showed that water-filled pore space (WFPS) was the variable most correlated to N2O fluxes. With this finding, we estimated the total N2O emissions by using regression equations that relate WFPS to N2O emission, and linking these regression equations with a soil moisture model 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 fluxes for the medium- to fine-textured and sandy-textured areas were 1.40 and 0.04 kg N2O-N ha-1 yr-1, respectively. 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 the regional area but contributed about 98% of the regional flux. We found that in the clay loam, cropped site, 2% and 3% of the applied fertilizer were emitted as N2O on the shoulders and footslopes, respectively.