International initiatives such as the United Nations Framework Convention on Climate Change and the Kyoto Protocol require that countries calculate national inventories of their greenhouse gas emissions. The objective of the present study was to develop a country-specific (Tier II) methodology to calculate the inventory of N₂O emissions from agricultural soils in Canada. Regional fertilizer-induced emission factors (EFreg) were first determined using available field experimental data. Values for EFreg were 0.0016 kg N₂O-N kg^-1 N in the semi-arid Brown and 0.008 kg N₂O-N kg N^-1 in the sub-humid Black soil zones of the Prairie region, and 0.017 kg N₂O-N kg^-1 N in the humid provinces of Quebec and Ontario. A function relating EFreg to the "precipitation to potential evapotranspiration" ratio was determined to estimate annual emission factors (EFeco) at the ecodistrict scale (≈ 150 000 ha) in all agricultural regions of Canada. Country-specific coefficients were also developed to account for the effect of several additional factors on soil N₂O emissions. Emissions from fine-textured soils were estimated as being 50% greater than from coarse- and medium-textured soils in eastern Canada; emissions during winter and spring thaw corresponded to 40% of emissions during the snow-free season in eastern Canada; increased emissions from lower (wetter) sections of the landscape and irrigated areas were accounted for; emissions from no-till soils were 10% greater in eastern, but 20% lower in western Canada than from those under conventional tillage practices; emissions under summerfallow were estimated as being equal to those from soils under annual cropping. This country-specific methodology therefore accounts for regional climatic and land use impacts on N₂O emission factors, and includes several sources/offsets that are not included in the Intergovernmental Panel on Climate Change (IPCC) default approach. Key words: Nitrous oxide, soils, greenhouse gases, inventory

Considerable evidence of climate change associated with emissions of greenhouse gases (GHG) has resulted in international efforts to reduce GHG emissions. The agriculture sector contributes about 8% of GHG emissions in Canada mostly through methane (CH₄) and nitrous oxide (N₂O). The objective of this paper was to compile an integrative review of CH₄ and N₂O emissions from livestock by taking a whole cycle approach from enteric fermentation to manure treatment and storage, and field application of manure. Basic microbial processes that result in CH₄ production in the rumen and hindgut of animals were reviewed. An overview of CH₄ and N₂O production processes in manure, and controlling factors are presented. Most of the studies conducted in relation to enteric fermentation were in dairy and beef cattle. To date, research has focussed on GHG emissions from the stored manures of dairy, beef cattle and swine; therefore, we focus our review on these. Several methods used to measure GHG emissions from livestock and stored manure were reviewed. A comparison of methods showed that there were agreements between most of the techniques but some systematic differences were also observed. Additional studies with comprehensive comparisons of methodologies are needed in order to allow for comparison of results obtained from studies using contrasting methodologies. The need to standardize measurement methods and reporting to facilitate comparison of results and data integration was identified. Prediction equations are often used to calculate GHG emissions. Various types of mathematical approaches, such as statistical models, mechanistic models and estimates calculated from emission factors, and studies that compare various types of models are discussed herein. A lack of process-based models describing GHG emissions from manure during storage was identified. A brief description of mitigation strategies focussing on recent studies is given. Reduction in CH₄ emissions from ruminants through the addition of fats in diets and the use of more starch was achieved and a transient beneficial effect of ionophores was reported. Grazing management and genetic selection also hold promise. Studies focussed on manure treatment options that thave been suggested to reduce gas fluxes from manure storage, composting, anaerobic digestion (AD), diet manipulation, covers and solid-liquid separation, were reviewed. While some of these options have been shown to decrease GHG emissions from stored manure, different studies have obtained conflicting results, and additional research is needed to identify the most promising options. GHG emissions from pasture and croplands after manure application have been the subject of several experimental and modelling studies, but few of these have linked field emissions to diet manipulation or manure treatments. Further work focussing on the entire cycle of GHG formation from feed formulation, animal metabolism, excreta treatment and storage, to field application of manure needs to be conducted. Key words: Greenhouse gases, enteric methane, nitrous oxide, manure management

Risk, N., Snider, D. and Wagner-Riddle, C. 2013. Mechanisms leading to enhanced soil nitrous oxide fluxes induced by freeze–thaw cycles. Can. J. Soil Sci. 93: 401–414. The freezing and thawing of soil in cold climates often produces large emissions of nitrous oxide (N₂O) that may contribute significantly to a soil's annual greenhouse gas emission budget. This review summarizes the state of knowledge of the physical and biological mechanisms that drive heightened N₂O emissions at spring melt. Most studies of freeze–thaw N₂O emissions have concluded that denitrification is the dominant process responsible for the large thaw fluxes. Soil moisture, availability of carbon and nitrogen substrates, and freeze temperature and duration are the major factors identified as controlling freeze–thaw cycle (FTC) N₂O emissions. Two mechanisms are proposed to lead to enhanced N₂O emissions at thaw: (1) the physical release of N₂O that is produced throughout the winter and trapped under frozen surface layers and/or within nutrient-rich water films in the frozen layers, and (2) the emission of newly produced (de novo) N₂O at the onset of thaw, which is stimulated by increased biological activity and changes in physical and chemical soil conditions. Early studies implicated the physical release of N₂O from subsurface soil layers as the main mechanism contributing to spring thaw emissions, but most current studies do not support this hypothesis. Mounting evidence suggests that most of the emitted N₂O is produced de novo. This may be fueled by newly available denitrification substrates that are liberated from dead microbes, fine roots, and/or the disintegration of soil aggregates. The release of N₂O trapped in shallow surface layers may represent a small, but important contribution of the total emissions. Application of new techniques to study microbial communities in their natural environments, such as metagenomics and stable isotope studies, have the potential to enhance our understanding of the soil N cycle and its linkages to FTC N₂O emissions. Future field studies of N₂O emissions ought to quantify both overwinter accumulation/release and the de novo production of N₂O so that the contribution of each mechanism to the annual emission budget is known.