Kariyapperuma, K. A., Furon, A. and Wagner-Riddle, C. 2012. Non-growing season nitrous oxide fluxes from an agricultural soil as affected by application of liquid and composted swine manure. Can. J. Soil Sci. 92: 315-327. Agricultural soils have been recognized as a significant source of anthropogenic nitrous oxide (N₂O) emissions, an important greenhouse gas and contributor to stratospheric ozone destruction. Application of liquid swine manure (LSM) has been reported to increase direct N₂O emissions from agricultural soils. Composting of LSM with straw under forced aeration has been suggested as a mitigation practice for emissions of N₂O. In cold climates, up to 70% of total annual soil N₂O emissions have been observed during winter and spring thaw. Non-growing season soil N₂O emissions after field application of composted swine manure (CSM) versus LSM have not been directly compared in past studies. A 2-yr field experiment was conducted at the Arkell Research Station, Ontario, Canada, as a part of a larger study to evaluate composting as a mitigation strategy for greenhouse gases (GHGs). The objectives were to quantify and compare non-growing season N₂O fluxes from agricultural soils after fall application of LSM and CSM. Nitrous oxide fluxes were measured using the flux-gradient method. Compared with LSM, CSM resulted in 57% reduction of soil N₂O emissions during February to April in 2005, but emissions during the same period in 2006 were not affected by treatments. This effect was related to fall and winter weather conditions with the significant reduction occurring in the year when soil freezing was more pronounced. Compared with LSM, CSM resulted in a reduction of 37% (CO₂-eq) of estimated N₂O emissions per liter of treated manure and of 50% in the emission factor for the non-growing season.