Effect of slope position and land use on nitrous oxide (N₂O) emissions (Seine Basin, France)
Vilain, Guillaume | Garnier, Josette | Tallec, Gaëlle | Cellier, Pierre
Nitrous oxide emissions from soils are known to be variable in both space and time. To better understand this variability, this study was conducted to (i) evaluate the landscape-scale patterns and seasonal variations in N₂O emissions, (ii) determine the contribution of the different environmental factors (texture and organic matter content of the soil, crop management, mineral nitrogen content, and fertilizer application) on the estimation of N₂O emissions at the field scale. We used static chamber and gas chromatography methods to measure N₂O emissions in the Orgeval sub-basin (Seine Basin, France), in representative sites selected on the basis of land use: a continuum from an agricultural plateau to the riparian buffer, grassland and a forest site. A consistent landscape-scale pattern of N₂O emissions was observed with higher emissions in the footslope (annual flux of 4.0±2.2kgNha⁻¹ yr⁻¹) than in the slope positions (1.1±0.6 and 1.9±1.2kgNha⁻¹ yr⁻¹) or the shoulder positions (1.1±0.5kgNha⁻¹ yr⁻¹). Nitrous oxide emissions from the riparian buffer were significant with an annual budget of 0.5±0.4kgNha⁻¹ yr⁻¹, while extrapolated emissions from forest and grassland were 0.6±0.2kgNha⁻¹ yr⁻¹ and 0.7±0.2kgNha⁻¹ yr⁻¹, respectively. Topography plays a role mainly in its relation with hydrological processes which, in turn, regulate the soil factors (mainly water-filled pore space) controlling N₂O emissions at the microscale level. The seasonal fluctuations of N₂O emissions were influenced by precipitations (pulses after large rainfall events following fertilization) and thawing.
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