Tenuta, M. and Sparling, B. 2011. A laboratory study of soil conditions affecting emissions of nitrous oxide from packed cores subjected to freezing and thawing. Can. J. Soil Sci. 91: 223-233. A series of laboratory experiments using a packed core soil assay was carried out to test several soil conditions affecting the emission of N₂O (nitrous oxide) during thawing of soil. The assay consisted of a sandy loam soil packed to 1.1 Mg m^-3, moistened to 80% water-filled pore space, and temperature treated to 4 or -20°C for 2.5 d; the emissions from thawing soil were then determined as the differences in N₂O release rates of the temperature-treated soils when placed at 15°C. Nitrate addition to surface soil (0-10 cm) enhanced thaw emission. Thaw emissions, averaged for deeper collected soil (10-30 and 30-60 cm), was 0.3% with NO₃^- treatment and 1.2% without NO₃^- treatment of that for surface soil treated similarly. Higher thaw emission for surface soil was related to greater organic matter and microbial biomass C contents and denitrifying enzyme activity than deeper collections of soil. Increasing the bulk density of soil from 1.1, 1.2, and 1.25 Mg m^-3 decreased thaw emission. A second freeze-thaw cycle of the highest compaction treatment resulted in an emission of 2.3% of the first freeze-thaw cycle. Acetylene increased thaw emission of N₂O and more so for NO₃^- untreated than treated soil. Using the acetylene inhibition method, the N₂O:N₂ ratio of gas produced was higher for frozen (0.17) than cold (0.07) treated soil, respectively, without the addition of NO₃^-. The addition of NO₃^- increased the N₂O:N₂ ratio of gas produced with the ratio being 2.45 and 0.53 for frozen and cold-treated soil. The results are consistent with biological denitrification being a source of N₂O with conditions promoting N₂O production rather than consumption enhancing thaw emissions.