. 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 (CH 4 ) and nitrous oxide (N 2 O). The objective of this paper was to compile an integrative review of CH 4 and N 2 O 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 CH 4 production in the rumen and hindgut of animals were reviewed. An overview of CH 4 and N 2 O 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 CH 4 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 have 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. attribua...

No-tillage (NT), a practice that has been shown to increase carbon sequestration in soils, has resulted in contradictory effects on nitrous oxide (N 2 O) emissions. Moreover, it is not clear how mitigation practices for N 2 O emission reduction, such as applying nitrogen (N) fertilizer according to soil N reserves and matching the time of application to crop uptake, interact with NT practices. N 2 O fluxes from two management systems [conventional (CP), and best management practices: NT 1reduced fertilizer (BMP)] applied to a corn (Zea mays L.), soybean (Glycine max L.), winter-wheat (Triticum aestivum L.) rotation in Ontario, Canada, were measured from January 2000 to April 2005, using a micrometeorological method. The superimposition of interannual variability of weather and management resulted in mean monthly N 2 O fluxes ranging from À1.9 to 61.3 g N ha À1 day À1 . Mean annual N 2 O emissions over the 5-year period decreased significantly by 0.79 from 2.19 kg N ha À1 for CP to 1.41 kg N ha À1 for BMP. Growing season (May-October) N 2 O emissions were reduced on average by 0.16 kg N ha À1 (20% of total reduction), and this decrease only occurred in the corn year of the rotation. Nongrowing season (November-April) emissions, comprised between 30% and 90% of the annual emissions, mostly due to increased N 2 O fluxes during soil thawing. These emissions were well correlated (r 2 5 0.90) to the accumulated degree-hours below 0 1C at 5 cm depth, a measure of duration and intensity of soil freezing. Soil management in BMP (NT) significantly reduced N 2 O emissions during thaw (80% of total reduction) by reducing soil freezing due to the insulating effects of the larger snow cover plus corn and wheat residue during winter. In conclusion, significant reductions in net greenhouse gas emissions can be obtained when NT is combined with a strategy that matches N application rate and timing to crop needs.

. Estimation of N 2 O emissions from agricultural soils in Canada. I. Development of a country-specific methodology. Can. J. Soil. Sci. 88: 641Á654. 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 N 2 O 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 N 2 O-N kg(1 N in the semi-arid Brown and 0.008 kg N 2 O-N kg N(1 in the sub-humid Black soil zones of the Prairie region, and 0.017 kg N 2 O-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 N 2 O 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 N 2 O emission factors, and includes several sources/offsets that are not included in the Intergovernmental Panel on Climate Change (IPCC) default approach. For personal use only.

The use of N fertilizer in agriculture is considered an important source of atmospheric N2O and NOx. Choice of fertilizer type and management has been considered a method for mitigating these emissions. Micrometeorological methods were used to study the effect of inorganic N fertilizers urea (U), slow‐release urea (SRU), and ammonium nitrate (AN) on fluxes of N2O, NO, and NO2 from turfgrass field plots during three seasons, from 1995 to 1997 (total of 353 d of measurement). Daily average fluxes after fertilizations reached a maximum of 2091 ng N2O‐N m−2 s−1 after the first fertilization with AN in 1996. The fertilized plots had significantly higher emissions (P < 0.05) than the control plot, and the highest N2O emissions were from AN in 1995 and 1996, and from SRU in 1997. Daily fluxes of up to 186 ng NO‐N m−2 s−1 were measured within 1 wk following fertilization in 1997. The U plot had significantly higher NO emissions during all seasons compared with other fertilized plots. Fluxes of NOx during 1996 and 1997 were consistently downward, indicating that turfgrass was acting as a sink for NOx. NO2 uptake seemed to be directly related to NO emissions, and the U plot presented the highest NO2 uptake. Urea‐based fertilizers seem to minimize N2O emissions, although long‐term effects of SRU still need to be studied. The higher NO emissions from U‐based fertilized plots do not seem to be a problem, since NOx uptake occurred at higher rates than NO emission.

Increasing atmospheric carbon dioxide (CO2) and nitrous oxide (N2O) levels have prompted research on management of the soil C and N pools. The impact of C and N fertilizer addition on N2O and CO2 field emissions is not clear. We determined N2O and CO2 fluxes from a 1‐ha bare soil plot using micrometeorological methods with the objective of evaluating the effect of management practices (cultivation, irrigation, fertilizer, and sucrose applications) on the relative importance of both trace gases. Research was conducted at the Elora Research Station (Typic Hapludalf) in Ontario, Canada, over 7 mo. The N2O concentration gradients were measured using a Tunable Diode Laser Trace Gas Analyzer and the CO2 gradients using an Infra‐Red Gas Analyzer. The transport coefficients were calculated using a Bowen Ratio Energy Balance and two wind profile approaches. These three approaches resulted in similar hourly fluxes. Daily N2O fluxes for nonevent periods were 12 ng m−2 s−1 in 1991, and 2 ng m−2 s−1 in the summer of 1992, while CO2 fluxes before treatments in 1991 were 0.18 mg m−2 s−1. Sucrose addition (420 kg C ha−1) resulted in the highest N2O and CO2 daily emissions measured during the experiment at 3100 ng m−2 s−1 and 0.5 mg m−2 s−1, respectively. Peak emissions of 250 ng N2O m−2 s−1 were measured after wetting of dry soil (WFP < 0.4) through irrigation in 1991, and rain in 1992. Application of ammonium sulfate (100 kg N ha−1) and irrigation increased N2O emissions to 75 ng m−2 s−1, with a smaller effect caused by two subsequent irrigations on wet soil (WFP > 0.6). Carbon dioxide fluxes varied between 0.01 and 0.5 mg m−2 s−1 being the predominant gas contributing to an equivalent CO2 global‐warming potential, but addition of sucrose increased the contribution of N2O to twice the contribution of CO2. The combined effect of C and N additions (e.g. manure and legume) on the N2O emissions in irrigated or high rainfall areas should be considered in the efforts of atmospheric C sequestering.