N 2 O fluxes of a bio‐energy poplar plantation during a two years rotation period

Nitrous oxide emissions are of critical importance for the assumed climate neutrality of bio‐energy. In this study we report on the N 2 O fluxes from a bio‐energy poplar plantation measured with eddy covariance for 2 years, after conversion of agricultural fields to few months after harvesting of the plantation. A pulse peak of N 2 O was detected after the land use change and in the wake of the first heavy rainfall. The N 2 O ‐ N emission during just a single week was 2.7 kg N 2 O ‐ N  ha −1 which represented approximately 42% of the total N 2 O ‐ N emitted during the 2 years of measurements. After this peak emission, N 2 O fluxes were constantly rather low, not increasing after rainfall events any longer. Lowest emissions (and even N 2 O sink) occurred mostly during the end of the second growing season with maximum canopy development, and water table deeper than 80 cm. Gross primary production ( GPP ) explained 68% of the monthly averaged variability in N 2 O emission from August to December 2011. Probably N uptake by vegetation during the peak of the second growing season limited N 2 O emission, which in fact increased again after the plantation was coppiced. For the majority of the measuring period, N 2 O fluxes did not present a well‐defined diurnal pattern, with the exception of two periods: (1) from 19–22 August 2010 and (2) from September–November 2011. In both cases wind speed played a major role in controlling the diurnal pattern in these fluxes (explaining up to 80% of the diurnal variability in N 2 O fluxes on 19–22 August 2010), whereas at the end of the second growing season (September–November 2011), GPP explained 73% of the diurnal pattern in N 2 O fluxes.