SU MMARYAs agriculture contributes about 0 . 08 of Canada's greenhouse gas (GHG) emissions, reducing agricultural emissions would significantly decrease total Canadian GHG output. Evaluating mitigation practices is not always easy because of the complexity of farming systems in which one change may affect many processes and associated emissions. The objective of the current study was to compare the effects of selected management practices on net whole-farm emissions, expressed in CO 2 equivalents (CO 2 e) from a beef production system, as estimated for hypothetical farms at four disparate locations in western Canada. Whole-farm emissions (t CO 2 e) per unit of protein output (t) of 11 management systems (Table 2) were compared for each farm using a model based, in part, on Intergovernmental Panel on Climate Change (IPCC) equations. Compared with the baseline management scenario, maintaining cattle on alfalfa-grass pastures showed the largest decrease (0 . 53-1 . 08 t CO 2 e/t protein) in emissions for all locations. Feeding lower quality forage over winter showed the greatest increase in emissions per unit protein on the southern Alberta (S.AB) and northern Alberta (N.AB) farms, with increases of 1 . 36 and 2 . 22 t CO 2 e/t protein, respectively. Eliminating the fertilization of forages resulted in the largest increase (4 . 20 t CO 2 e/t protein) in emissions per unit protein on the Saskatchewan (SK) farm, while reducing the fertilizer rate by half for all crops showed the largest increase (11 . 40 t CO 2 e/t protein) on the Manitoba (MB) farm. The findings, while approximate, illustrate the importance of considering all GHGs simultaneously, and show that practices which best reduce emissions may vary among locations. The findings also suggest merit in comparing emissions on the basis of CO 2 e per unit of protein exported off-farm, rather than on the basis of total CO 2 e or CO 2 e per hectare.

No abstract

. 2008. Estimation of carbon dioxide production and energy expenditure of grazing cattle by the sulphur hexafluoride (SF 6 ) tracer gas technique. Can. J. Anim. Sci. 88: 651Á 658. The purpose of the study was to explore the suitability of the sulphur hexafluoride (SF 6 ) tracer gas technique to estimate CO 2 production and energy expenditure (EE) for grazing animals on pastures typical of western Canada. During each year of a 3-yr study, CO 2 emissions were collected from 60 yearling steers on grass pastures receiving one of three fertility treatments: no manure, liquid hog manure applied as a split application (74 kg available N ha(1 ) in the spring and fall, and a single application of liquid hog manure applied at a rate of 155 kg available N ha(1 each spring. The mean CO 2 production estimate across all treatments was 542492218 L d(1 (mean9SD) with a range of 1099 to 11548 L d(1. When compared across three grazing periods in June, July and August, steers produced more (PB0.05) CO 2 in June than in either July or August. Metabolic body weight (BW 0.75 ), average daily gain (ADG), standing forage biomass, and forage neutral detergent fibre (NDF) and crude protein (CP) contents explained 33% of the variation in CO 2 production. Energy expenditure (EE) was estimated from CO 2 production by adopting an energetic equivalent of 22 kJ L(1 CO 2 and EE was calculated for animals that were not losing body weight at time of measurement. The average EE estimate was 1.290. . Energy expenditure declined as ADG and forage biomass declined, but EE was not influenced (P0.05) by fertility treatment. The EE estimate was higher (P B0.05) early in the grazing season (June) and declined as the grazing season progressed. The SF 6 tracer gas technique was able to estimate EE of individual animals without interfering with herd dynamics. The technique was also able to show differences in EE in response to pasture conditions. The results of this study suggest that the SF 6 tracer gas technique shows potential as a simple and non-invasive method of estimating CO 2 production and EE for grazing animals. Further validation under different grazing conditions and with animals undertaking different degrees of activity is required. Comparisons with other field techniques of estimating EE are also important.Key words: Energy expenditure, carbon dioxide, sulphur hexafluoride, grazing animals Stewart, A. A., Undi, M., Wilson, C., Ominski, K. H. et Wittenberg, K. M. 2008. Estimation de la production de dioxyde de carbone et de la de´pense d'e´nergie par les bovins en paissance par de´tection de l'hexafluorure de soufre (SF 6 ). Can. J. Anim. Sci. 88: 651Á658. L'e´tude devait e´tablir si la de´tection de l'hexafluorure de soufre (SF 6 ) permet d'estimer la production de CO 2 et la de´pense d'e´nergie des animaux mis a`l'herbe dans les paˆturages caracte´ristiques de l'Ouest canadien. Chaque anne´e pendant trois ans, les auteurs ont recueilli les e´missions de CO 2 de 60 bouvillons d'un an mis a`l'herbe sur des paˆturages bonifie´s de trois fac¸on...

2014. Whole-farm greenhouse gas emissions from a backgrounding beef production system using an observation-based and model-based approach. Can. J. Anim. Sci. 94: 463Á477. Backgrounding, raising weaned beef cattle in preparation for finishing in a feedlot, is a common practice in western Canadian beef production systems. The objectives of this study were: (i) to assess the whole-farm greenhouse gas (GHG) emissions from a pasture-based backgrounding system using an observation-based and model-based approach and (ii) to compare model-based estimated emissions with observation-based emissions from the key components of the farm, in order to identify the knowledge gaps that merit further study. For the observation-based approach, emissions were garnered from a multi-disciplinary field study that examined three fertility treatments applied to the pasture grazed by beef cattle: (i) no liquid hog manure application (control); (ii) split application of liquid hog manure, half applied in fall and half in spring (split) and (iii) single spring application of liquid hog manure (single). The model-based approach used a systems-based model, adapted from Intergovernmental Panel on Climate Change algorithms, to estimate annual net farm GHG emissions from the three fertility treatments and a hypothetical synthetic fertilizer treatment. Total farm emissions included methane (CH 4 ), nitrous oxide (N 2 O) emissions from farm components and carbon dioxide (CO 2 ) emissions from energy use. Net farm GHG emissions using the observation-based approach ranged from 0.4 to 2.2 Mg CO 2 eq ha (1 and from 4.2 to 6.5 kg CO 2 eq kg (1 liveweight gain exported; the model-based approach resulted in net farm emissions ranged from 0.6 to 3.7 Mg CO 2 eq ha (1 and from 7.0 to 12.9 kg CO 2 eq kg (1 liveweight gain exported. Except in the control treatment, both enteric CH 4 and soil N 2 O emissions were the major contributors to total farm emissions. Emissions intensity for the hypothetical synthetic fertilizer treatment (9.4 kg CO 2 eq kg (1 liveweight gain) was lower than for the split and single scenarios. Although individual GHG emission estimates varied appreciably, trends in emissions intensity were similar between the two approaches. Efforts to reduce GHG emissions should be directed towards components such as enteric CH 4 and soil N 2 O, which have larger impacts on overall system emissions.