The rate of carbon change in agricultural soils in Canada at the landscape level

The Century model [a computer simulation of the dynamics of soil organic carbon (SOC)] was used to estimate the rate of SOC change in agricultural soil in Canada. The analysis was carried out on 180 Soil Landscapes of Canada (SLC) polygons, representing 15% of the SLC polygons within agricultural regions. The analysis was stratified into soil zones and into soil textural classes. For each sampled polygon, Century was run for 1 to 5 types of crop rotations under conventional-tillage as well as no-tillage, providing that no-till was used on at least 5% of the land. From the Century simulations, it was estimated that the overall rate of SOC loss from agricultural soils in Canada for 1990 was 39.1 kg ha−1 yr−1 This implies that 1.93 Mt of SOC (7.08 Mt of CO2) was lost from agricultural soils in Canada. Compared to 1990, the SOC loss was estimated to have been greater by 11.9 kg ha−1 yr−1 in 1980 and 9.1 kg ha−1 yr−1 in 1985. The lower loss in 1990 was primarily due to the incorporation of no-till practices and reduction of summer fallow in the mid 1980s. In 1990, at the provincial level, Alberta had the highest rate of SOC loss at 74.5 kg ha−1 yr−1 followed by Manitoba with 66.1 kg ha−1 yr−1 In Ontario, Quebec, and the Atlantic Provinces the average provincial rate of SOC loss was less than 35 kg ha−1 yr−1 Higher SOC loss rates were typically found in soils with coarser texture and greater native SOC content. Key words: Carbon dioxide, greenhouse gas, Century model