LONG-TERM TILLAGE AND CROP RESIDUE MANAGEMENT IN THE SUB-ARCTIC - FLUXES OF METHANE AND NITROUS-OXIDE

Methane and nitrous oxide are important radiatively active gases that are influenced by agricultural practices. This study assesses long-ter m tillage, crop residue management, and N fertilization rates on the f lux of these two gases at a high latitude site representing the northe rn fringe of large-scale agriculture. Cumulative methane uptake for th e summer was higher from no-tillage plots than tilled plots. This was associated with lower soil water contents with tillage. Thus, the redu ction in CH4 uptake was attributed to water stress on methane oxidizer s. At planting, soil water contents were near field capacity, and the no-till plots had the lowest uptake which was attributed to restricted diffusion of methane to active sites. A similar pattern of methane up take to soil water content was found with the residue management treat ments. Removing the straw lowered the soil water content and for most of the season methane uptake was also lower than where the straw had b een left on the plots. Nitrogen fertilizer rate had little effect on m ethane uptake over the summer, but high N rates lowered consumption du ring the time of active nitrification early in the season. This corres ponded to the time of maximum efflux of nitrous oxide. Nitrous oxide e fflux was greatest at the high N rate where straw was retained on the plots.