Spatially explicit, accurate inventories of greenhouse gas (GHG) emissions are of primary importance when calculating the carbon footprint, identifying sources and sinks, pricing carbon pollution, and creating policy that is effective in reducing emissions. However, there are few reports available on methane and nitrous oxide emissions from each type of livestock and crop in all counties of the province due to a lack of statistical data of sub-categories, such as the different fertilizer quantities used in each crop in the county. Because fertilizer input is the most significant factor for N2O emissions from agricultural soils, how to best distribute the total fertilizer mass to a crop-specific fertilizer rate for each county is a major challenge in agricultural management. In this study, authors developed a crop-specific method correlating the recommended fertilizer rate and planted area of each crop for a reasonable distribution of total fertilizer mass to fertilizer rate. This is based on a balance between the sum of fertilizer used in all crops and the total fertilizer mass used by each municipality. Using this method, our calculations in 69 municipalities in the province of Alberta, Canada showed that the fertilizer rate for each crop was reasonably distributed from the total fertilizer mass of a municipality: less than 170 kg-N ha۱ . The obtained fertilizer rates for each crop in 69 municipalities were used in GHG inventories using IPCC 2006 tier 1 and 2 methods. The total CH4 and N2O emissions from agriculture in all of Alberta in 2011 were 328 Gg CH4 yr۱ and 23.5 Gg N2O yr۱ , respectively. The southeastern municipalities generally emitted more CH4 and N2O than northwestern municipalities. The southern municipality of Lethbridge emitted the largest amount of CH4 and N2O of all municipalities (25.3 Gg CH4 yr۱ (۷٫۷۰% of total CH4 of entire Alberta) and 1.26 Gg N2O yr۱ (۵٫۴۰% of total N2O of entire Alberta), respectively). This was due to its largest cattle population (414,627 head) and larger synthetic fertilizer input (32,111 ton-N) and planted area (206,077 ha). The second largest CH4 and N2O emission source was also located at the south. The Taber municipality emitted 15.8 Gg CH4 yr۱ (۴٫۸۰% of total CH4 of entire Alberta) and 1.14 Gg N2O yr۱ (۴٫۸۰% of total N2O of entire Alberta), respectively.
Since the industrial revolution, human activities have increased greenhouse gas (GHG) concentrations in the atmosphere, resulting in climate change with severe consequences for human life and economic development. It has been determined that the main GHGs include carbon oxide (CO2), methane (CH4), and nitrous oxide (N2O). Their concentrations in the atmosphere are heavily affected by human activities, such as combustion of carbon fuels (coal, oil and natural gas), agricultural production of both livestock and crop farms, land use changes and deforestation. The contribution of each GHG to climate change is expressed by its Global Warming Potential (GWP) according to IPCC (Stocker, 2014), which indicates a gas’ capacity to absorb radiation and its lifetime in the atmosphere based on CO2 capacity (Eilers, 2010). Thus, GWPs of CH4 and N2O are, respectively, 25 and 300 of CO2 equivalents for the first 100 years of their lifetime in the atmosphere, based on GWP as one of CO2. While CO2 emissions can partially be offset by CO2 uptake in plants, CH4 and N2O are not subject to photosynthesis or other direct biological offsets. Therefore, CH4 and N2O emitted from agriculture, such as livestock, managed agricultural soils, rice cultivation, burning of savanna, and returned crop residues are GHG net sources (Eggleston et al., 2006). Agricultural soils are estimated to contribute about 65% of global N2O emissions (Reay et al., 2012). Therefore, it is a challenge to reduce GHG emissions as well as maintaining affordable food prices. In Canada, although the combustion of fossil fuels is a major source of GHG emissions, the agricultural activities also result in a relatively large percentage (8%) of CO2, CH4 and N2O emissions (with an additional 3% agricultural fossil fuel and energy use) of Canada’s total GHG emissions in 2006 (Janzen, 2008; Weldemichael and Assefa, 2016).