Winter fluxes of greenhouse gases from snow‐covered agricultural soil:intra‐annual and interannual variations

Abstract

Despite the length of winter in cold temperate climates, few studies refer to greenhouse gas emissions from soils during the nongrowing season. In this study, N 2 O and CO 2 fluxes from agricultural and forest soils in southeastern Quebec (Canada) were measured during winter and spring from 1994 to 1997, and the influences of climate, soil, and snow properties on the gaseous emissions were examined. N 2 O fluxes were far greater from the agricultural soil (2‐187 ng N 2 O m −2 s −1 ) than from the forest soil (< 3 ng N 2 O m −2 s −1 ), but CO 2 fluxes were equivalent for both soil systems (2‐102 μ CO 2 m −2 s −1 ). The higher N 2 O concentrations in the lower soil horizons could be explained by positive temperature gradients with depth and concomitant negative gas solubility gradients. However, the higher N 2 O concentrations could also be explained by variations in the expression of N 2 O reductase with depth, which can modify the N 2 /N 2 O ratios in relation to the availability of O 2 . Calculated N 2 O‐N fluxes showed that N losses by gaseous emissions from soils during winter and spring were comparable to, or exceeded, similar reported N losses during the growing season. The highest winter fluxes observed in 1997 were interpreted to be due to favorable meteorological conditions that prevailed for denitrification through high soil water content in summer and fall of 1996. Although interannual and nterseasonal variations of fluxes are important, this study shows that wintertime losses of N 2 O from agricultural soil can be up to 2 to 4 times greater than emissions measured during the growing season in similar agroecosystems.