Inventories of methane and nitrous oxide emissions from animal and crop farms of 69 municipalities in Alberta, Canada

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 ha⁻¹. 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 yr⁻¹ and 23.5 Gg N₂O yr⁻¹, 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 yr⁻¹ (7.70% of total CH₄ of entire Alberta) and 1.26 Gg N₂O yr⁻¹ (5.40% 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 yr⁻¹ (4.80% of total CH₄ of entire Alberta) and 1.14 Gg N₂O yr⁻¹ (4.80% of total N₂O of entire Alberta), respectively.