Soil nitrous oxide emissions from winter wheat cropland at landscape scale

An improved understanding of how variables such as soil type, water content or temperature, interact to control N2O emissions at the landform scale is needed for scaling up emissions to regional/national scales. In this study, N2O emissions were measured along three sloping sites (1.6 - 2.1%) cropped to winter wheat within a 10-km2 area in Central France by non steady-state chamber technique. The objectives were to measure N2O emissions at the shoulder and foot-slope landform positions and to identify the factors controlling their variations. Fluxes of N2O ranged from 0 to 0.11 mg N m-2 h-1, increased exponentially with soil mineral nitrogen (N) concentrations (r2 = 0.57, p < 0.001) and correlated with soil denitrification potential rate. The soil mineral N content explained 31% (p < 0.05) of the variations in N2O fluxes when the Water-Filled Pore Space (WFPS) was 60%. Landform positions had a significant, but not consistent effect upon N2O fluxes with greater emission in the foot-slope position at only one of the three sites. The differences in WFPS between shoulder and foot-slope positions correlated linearly with the differences in N2O fluxes (r2 = 0.47, p < 0.001). While soil water content could not explain a large proportion of the variation in N2O fluxes, it modulated the effect of soil mineral N content. Our results therefore suggest that in this agricultural landscape, the spatial variations in N2O emission were regulated by the influence of hydrological processes on soil aeration and denitrification intensity.