The effect of tile-drainage on nitrous oxide emissions from soils and drainage streams in a cropped landscape in Central France

Tile drainage may have contrasting effects on soil nitrous oxide (N2O) emission. Because drainage decreases anoxic periods in soils, it could reduce N2O production via denitrification and also limit the reduction of N2O into nitrogen gas (N2). Moreover, drainage accelerates the discharge of water enriched in dissolved N2O and mineral nitrogen. Thus, nitrogen losses and N2O releases from discharged surface water need to be quantified to assess the total effect of drainage on N2O emissions. Thus, the objectives of this study were two-fold: (1) to assess the effect of tile-drainage on soil N2O emissions in an agricultural area in Central France (direct emissions) and (2) to compare emissions from soils and from the stream draining the area (indirect emissions). The emissions of N2O by soils were measured using static chambers in two drained and two undrained cereal plots over two growing seasons. A rule-based model was fitted to identify the influence of drainage and ancillary variables. Stream N2O emissions were measured with a floating chamber during one growing season. The mean direct N2O emissions were 0.071mgNm−2h−1 and were larger in the undrained plots than in the drained plots in both growing seasons (p<0.001). The rule-based model showed that the drainage effect on N2O emissions was dominant over the permanent soil variables. The mean stream N2O emissions were 0.190mgNm−2h−1. The surface water emissions represented 31kgN during the flow period (7 months) while direct emissions were 1846kgN during the same period. Thus, indirect emissions accounted for <2% of the total N2O emissions in the study site. While tile-drainage did not result in significant indirect emissions at this local site scale, it was identified as the dominant factor controlling the direct soil N2O emissions. Thus, drainage should be taken into account in greenhouse gas emission inventories for larger areas.