Philippe Rochette1, Devon Worth2, Reynald Lemke2, Brian McConkey2, Raymond Desjardins2, Edward Huffman2, Dan Pennock3, Anthony Brierley2, Jingyi Yang2, Samuel Gameda2, and Julian Hutchinson2. (1) Agriculture & Agri-Food Canada, 2560 Hochelaga Blvd., Ste-Foy, QC G1V 2J3, Canada, (2) Agriculture and Agri-Food Canada, Carling Ave., Ottawa, ON K1A 0C6, Canada, (3) Univ of Saskatchewan, 51 Campus Dr, Saskatoon, SK S7N 5A8, Canada
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 and use a country-specific (Tier II) methodology to produce the inventory of N2O emissions from agricultural soils in Canada. Regional fertilizer-induced emission factors (FIEF) were first determined using available field experimental data. Values for FIEF ranged from 0.0016 kg N2O-N / kg N in the arid brown soil zone of the Prairies to 0.012 kg N2O-N /kg N in the humid eastern provinces. A function relating FIEFs to climate (P/PE; P: precipitations PE: potential evapotranspiration) was developed and used to estimate annual emissions at the ecodistrict scale (avg. area of ecodistrict = 430, 000 ha). Algorithms were also developed to account for the effect of soil texture, spring thaw, topography, conservation tillage, summerfallow and irrigation on N2O emissions. Total direct N2O emissions from agricultural soils averaged 36.8 Gg N /yr between 1990 and 2004 with variations from 32.4 (2001) to 45.2 Gg N/ yr (2004). These estimates are approximately 40% lower than estimates obtained using the Inter-governmental Panel on Climate Change general (Tier I) methodology. Differences in N2O estimates between the two approaches mainly arise from the use of lower emission factors in the Tier II than in the Tier I methodology. Application of mineral N fertilizers was the most important single source of soil N2O with average emissions during the 1990-2004 period of 13.5 Gg N /yr or 36% of direct emissions. Crop residues (9.0 Gg N /yr; 24%), grazing animals (7.6 Gg N /yr; 20%) and manure applied to soils (4.6 Gg N /yr; 12%) were the other major soil N2O sources.
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