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

We assessed nitrous oxide (N(2)O) 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 170kgNha(-1). Results showed that landscape positions had a significant, but not consistent effect on N(2)O 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(2)O fluxes (r(2)=0.55, p<0.001) was influenced by water-filled pore space (WFPS). Soil N(2)O 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(2)O fluxes (r(2)=0.45, p<0.001). We conclude that spatial variations in N(2)O emission were regulated by the influence of hydrological processes on soil aeration intensity.