Revisiting no-till's impact on soil organic carbon storage in Canada

Accurate estimates of soil organic carbon (SOC) stock change as influenced by tillage practices are prerequisites to quantify, the impact of mitigation measures on greenhouse gas emissions associated with crop production. In this study, we compiled SOC stock change data as influenced by tillage practices, i.e. no-till (NT) versus conventional tillage (CT), on agricultural soils in Canada. We determined the rate of C change as a function of soil texture and climate stratified by time since the management change. In the cool and humid climates of Eastern Canada, the impacts of NT were inconsistent and resulted in a decline in C storage rate in the years shortly following management change, but SOC recovered over time. Carbon losses were particularly high on fine and coarse textured soils, whereas in medium textured soils NT tended to increase SOC. On the Canadian prairies NT consistently increased SOC. The rate of gain in SOC under NT decreased over time with higher rates in the 3-10 years following a change to NT at a rate of 740 kg C ha(-1) yr(-1) or 1.3 % yr(-1). Rates declined to 260 kg C ha(-1) yr(-1) or 0.87 % yr(-1) for periods from 11-20 years after tillage change, and to 95 kg C ha(-1) yr(-1) or 0.23 % for periods longer than 20 years. The results of this work clearly show climate, soil texture and duration of management as main drivers of SOC change under NT in Canada and key factors that must be considered in the development of either national or regional SOC models. The results of this study suggest that more detailed stratification of soil texture, climate and duration of NT adoption is required for more accurate estimates of SOC storage rates associated with NT for Canada.