Winter fluxes of greenhouse gases from snow-covered agricultural soil: Intra-annual and interannual variations

Despite the length of winter in cold temperate climates, few studies refer to greenhouse gas emissions from soils during the nongrowing season. In thi s study, N2O and CO2 fluxes from agricultural and forest soils in southeast ern Quebec (Canada) were measured during winter and spring from 1994 to 199 7, and the influences of climate, soil, and snow properties on the gaseous emissions were examined. N2O fluxes were far greater from the agricultural soil (2-187 ng N2O m(-2) s(-1)) than from the forest soil (< 3 ng N2O m(-2) s(-1)), but CO2 fluxes were equivalent for both soil systems (2-102 mu g C O2 m(-2) s(-1)). The higher N2O concentrations in the lower soil horizons c ould be explained by positive temperature gradients with depth and concomit ant negative gas solubility gradients. However, the higher N2O concentratio ns could also be explained by variations in the expression of N2O reductase with depth, which can modify the N-2/N2O ratios in relation to the availab ility of O-2. Calculated N2O-N fluxes showed that N losses by gaseous emiss ions from soils during winter and spring were comparable to, or exceeded, s imilar reported N losses during the growing season. The highest winter flux es observed in 1997 were interpreted to be due to favorable meteorological conditions that prevailed for denitrification through high soil water conte nt in summer and fall of 1996. Although interannual and interseasonal varia tions of fluxes are important, this study shows that wintertime losses of N 2O from agricultural soil can be up to 2 to 4 times greater than emissions measured during the growing season in similar agroecosystems.