Opportunities for Reducing GHG Emissions in Canada through Increased C Input to Cropland.

One important option for mitigating greenhouse gases is to accomplish soil sequestration by increasing C input to the soil. We undertook a high-level modelling study of whole of Canada to investigate the effect on carbon sequestration of changing crop types, increasing crop yields, increasing use of cover crops, and increasing soil application of currently underutilized organic materials such as municipal biosolids and composted organic wastes, etc. The study included both changes to soil carbon and effects on N use and fate including emission of N₂O. The carbon sequestration opportunities of increasing soil application of underutilized materials is not large nationally although could be large locally. However, use of legume crops, N-fixing cover crops, and crops that return more C to the soil, particularly canola, will increase soil C. Due to generally unfavorable weather for plant growth after annual crop harvest throughout most of Canada, cover crops did not have a major effect on C input and hence did not greatly increase soil C. Nevertheless, where are some C sequestration opportunities with cover crops after early maturing crops, especially in regions with favourable (warm + moist) fall and early spring weather. The better understand the overall mitigation benefits of increasing C input through changing crop types and yield, the associated effects on GHG emissions for N fertilizer manufacture and from direct and indirect soil N₂O emissions need to be included; generally legumes reduce N-related GHG emissions while increasing C input through non-legume crops increased them. The study did not consider the economic ramifications although these would be important for actual large shifts in types of production. This study is useful to understand the potential magnitude of the GHG mitigation opportunities from major shifts in cropland management to increase C input.