Impact of tillage on greenhouse gas emissions by an agricultural crop and dynamics of N2O fluxes: Insights from automated closed chamber measurements

Our experiment aimed at studying the impact of long term tillage treatments - reduced tillage (RT) and conventional tillage (CT), on CO2 and N2O emissions by soil and at describing the dynamics of N2O fluxes. Gas measurements were performed from June to October 2015 in a Belgian maize crop, with homemade automated closed chambers, allowing continuous measurement at a high temporal resolution. After 7 years of treatment, CO2 and N2O average emissions were significantly larger in the RT parcel than in the CT parcel. This observation was attributed to the effect of tillage on the distribution of crop residues within the soil profile, leading to higher soil organic C and total N contents and a greater microbial biomass in the upper layer in RT. A single N2O emission peak triggered by a sudden increase of water-filled pore space (WFPS) was observed in the beginning of the measuring campaign. The absence of large emission afterwards was most likely due to a decreasing availability of N as crop grew. N2O background fluxes showed to be significantly correlated to CO2 fluxes but not to WFPS, while the influence of soil temperature remained unclear. Our results question the suitability of reduced tillage as a “climate-smart” practice and suggest that more experiments be conducted on conservation practices and their potent negative effect on environment.