Quantification and simulation of nitrous oxide emissions from agroecosystems in the Boreal and Parkland regions of Alberta

The concentration of atmospheric nitrous oxide (N{dollar}sb2{dollar}O) is increasing rapidly. Nitrous oxide, a "greenhouse gas", contributes to global warming. It is also involved in the catalytic destruction of stratospheric ozone. Best estimates indicate that the increase is almost exclusively attributable to agricultural activities. These contributions need to be accurately quantified to reduce uncertainties in global N{dollar}sb2{dollar}O budgets and facilitate the development of mitigation strategies. The objectives of this study were to: (1) quantify the seasonal and annual N{dollar}sb2{dollar}O emissions from selected field plots in the Boreal and Parkland regions of Alberta; (2) identify the principle controls regulating N{dollar}sb2{dollar}O emissions; (3) compare total N{dollar}sb2{dollar}O emissions from plots under zero and conventional till managements; (4) evaluate the extent to which urea fertilizer, pea residue, manure and fallow promote N{dollar}sb2{dollar}O emissions and; (5) test the ability of the DNDC model to simulate N{dollar}sb2{dollar}O emissions under conditions prevailing in the Boreal and Parkland regions. Nitrous oxide emissions were measured from spring thaw to fall freeze-up at six sites over a three year period. Vented soil covers were placed on the soil surface for one hour. A gas sample was drawn from the headspace and transferred to pre-evacuated vacutainers. Gas samples were analyzed using a gas chromatograph equipped with a {dollar}sp{lcub}63{rcub}{dollar}Ni electron capture detector. Measurements of soil temperature, soil water content, mineral N and water-soluble organic C were taken periodically at some of the sites. Estimates of annual N{dollar}sb2{dollar}O-N losses ranged from 0.5 to 4.0 kg N ha{dollar}sp{lcub}-1{rcub}.{dollar} Up to 70% of this loss occurred during and just following spring thaw. There were significant differences in the magnitude of estimated annual N{dollar}sb2{dollar}O-N losses among the sites. More than 90% of this variation could be explained by differences in soil clay content. When the spring thaw event was considered individually, variability was better explained by differences in the concentration of soil mineral N. Summer fallowing and additions of urea fertilizer and pea residue increased N{dollar}sb2{dollar}O-N losses compared to control plots. Losses of N{dollar}sb2{dollar}O-N were significantly lower from zero compared to conventional till plots during spring thaw, but differences were not significant on an annual basis.