Effect of topography on nitrous oxide emissions from winter wheat fields in Central France

We assessed nitrous oxide (N 2O) emissions at shoulder and foot-slope positions along three sloping sites (1.6–2.1%) to identify the factors controlling the spatial variations in emissions. The three sites received same amounts of total nitrogen (N) input at 170 kg N ha −1. Results showed that landscape positions had a significant, but not consistent effect on N 2O fluxes with larger emission in the foot-slope at only one of the three sites. The effect of soil inorganic N (NH 4 + + NO 3 −) contents on N 2O fluxes (r 2 = 0.55, p < 0.001) was influenced by water-filled pore space (WFPS). Soil N 2O fluxes were related to inorganic N at WFPS > 60% (r 2 = 0.81, p < 0.001), and NH 4 + contents at WFPS < 60% (r 2 = 0.40, p < 0.01), respectively. Differences in WFPS between shoulder and foot-slope correlated linearly with differences in N 2O fluxes (r 2 = 0.45, p < 0.001). We conclude that spatial variations in N 2O emission were regulated by the influence of hydrological processes on soil aeration intensity. ► Soil inorganic N content was the major factor controlling N 2O emission. ► Soil water content influenced the effect of soil inorganic N content on N 2O emission. ► The position-by-site interactions affected the cumulative fluxes significantly. Spatial variations in N 2O fluxes were in part the result of variations in soil water content.