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Agriculture has an important potential role in mitigating greenhouse gas emissions (GHG). However, practices that reduce CO2 emissions from soils and increase the soil organic C level may stimulate N2O emissions. This is particularly critical in Quebec where heavy soils and a humid climate may limit the adoption of agricultural practices designed to mitigate GHG. The objective of this work was to study the effects of two tillage and N fertilization regimes on CO2 and N2O fluxes and the seasonal variability in emissions of these gases, associated with corn (Zea mays L.) grown in southwestern Quebec. Different seasonal emission patterns of CO2 and N2O were observed. Higher N2O fluxes occurred during the spring and were associated with precipitation events, while higher CO2 fluxes occurred in mid-season and were related to temperature. Conventional tillage (CT) had greater peaks of CO2 emissions than no-till (NT) only after disking in the spring. Once corn was established, differences between tillage systems were small. Peaks of N2O emission occurred in both systems (NT and CT) following N application. Plots receiving 180 kg N ha-1 in both tillage systems had large peak of N2O emission rates during the wettest parts of the season. The CT and NT systems generally had similar cumulative CO2 emissions but NT had higher cumulative N2O emissions than CT. Our findings suggests that changing from CT to NT under the heavy soil conditions of Quebec may increase GHG, mainly as result of the increase in N2O emission. This negative effect of NT could be reduced by avoiding fertilizing when precipitation is more intense. [ABSTRACT FROM AUTHOR]

Abstract: Agricultural soils are an important contributor to greenhouse gas emissions and the size of this contribution can be influenced by tillage practice and crop. The objective of this work was to study greenhouse gas (carbon dioxide—CO2 and nitrous oxide—N2O) emissions associated with N2 fixing soybean (Glycine max) grown under two tillage systems (conventional—CT and no-till—NT). The experiment was organized following a randomized complete block design with four blocks. The CO2 and N2O fluxes were evaluated throughout the growing seasons of 2002 and 2003. The seasonal emission patterns were different for CO2 and N2O. Soil CO2 emissions during the season were associated with soil temperature while the N2O fluxes were mainly associated with precipitation. The CT system generally had greater CO2 fluxes than the NT system, particularly in 2002. In that year the maximum peak, which occurred in the summer, was about 160gm−2 d−1 under CT and 68gm−2 d−1 under NT. N2O emissions were low in the first year but high in the second, and were greater for CT than NT with a maximum peak about 18.1mgm−2 d−1 under CT and 7.4mgm−2 d−1 under NT. Our findings suggests that use of NT in the production of N2 fixing soybean may reduce both CO2 and N2O emissions, in comparison to CT. Soybean residue incorporation increased N2O emissions, leading to greater emissions from the CT production system. [Copyright &y& Elsevier]