N2O and CO2 dynamics in a pasture soil across the frozen period1

Since the process of gas dynamics in agricultural soils is mainly studied during plant growth, only a few studies have focused on these dynamics in frozen soils covered with snow. Nevertheless, gas dynamics during the cold season is important to quantify the yearly mass balance of gas emitted to the atmosphere. Spatiotemporal concentrations of CO2 and N2O have been measured from the prefreezing to the thawing period in a pasture soil during two cold seasons along with soil temperature and other soil properties. The spatial dynamics of these gases differed from each other and depended on the spatial and temporal variability of soil temperature as long as the soil surface temperature was above 0 °C. Two main occurrences of gas release occurred during thawing, one related to trapped gases, similar for both gases, and the other to reactivation of microorganisms, different between both gases. Once the soil was frozen, both gas concentrations increased throughout the frozen period, even during very cold conditions, indicated a gases production faster than the loss. Under frozen condition, their spatial variability was independent of soil temperature during which their correlation was up to 90%. Three periods related to gas dynamics were observed during both cold seasons: freezing with spatiotemporal trends different between both gases, completely frozen with similar trends, and partial to complete thawing with trends different between both gases.