Greenhouse gas budget ( CO 2 , CH 4 and N 2 O) of intensively managed grassland following restoration

The first full greenhouse gas ( GHG ) flux budget of an intensively managed grassland in Switzerland (Chamau) is presented. The three major trace gases, carbon dioxide ( CO 2 ), methane ( CH 4 ), and nitrous oxide (N 2 O) were measured with the eddy covariance ( EC ) technique. For CO 2 concentrations, an open‐path infrared gas analyzer was used, while N 2 O and CH 4 concentrations were measured with a recently developed continuous‐wave quantum cascade laser absorption spectrometer ( QCLAS ). We investigated the magnitude of these trace gas emissions after grassland restoration, including ploughing, harrowing, sowing, and fertilization with inorganic and organic fertilizers in 2012. Large peaks of N 2 O fluxes (20–50 nmol m −2  s −1 compared with a <5 nmol m −2  s −1 background) were observed during thawing of the soil after the winter period and after mineral fertilizer application followed by re‐sowing in the beginning of the summer season. Nitrous oxide (N 2 O) fluxes were controlled by nitrogen input, plant productivity, soil water content and temperature. Management activities led to increased variations of N 2 O fluxes up to 14 days after the management event as compared with background fluxes measured during periods without management (<5 nmol m −2  s −1 ). Fluxes of CO 2 remained small until full plant development in early summer 2012. In contrast, methane emissions showed only minor variations over time. The annual GHG flux budget was dominated by N 2 O (48% contribution) and CO 2 emissions (44%). CH 4 flux contribution to the annual budget was only minor (8%). We conclude that recently developed multi‐species QCLAS in an EC system open new opportunities to determine the temporal variation of N 2 O and CH 4 fluxes, which further allow to quantify annual emissions. With respect to grassland restoration, our study emphasizes the key role of N 2 O and CO 2 losses after ploughing, changing a permanent grassland from a carbon sink to a significant carbon source.