Nitrogen oxides and ozone fluxes following organic and mineral fertilisation of a growing oilseed-rape
Auteurs
R. M. Vuolo, B. Loubet, N. Mascher, J. C. Gueudet, B. Durand, P. Laville, O. Zurfluh, R. Ciuraru, and I. Trebs
Référence
Biogeosciences, vol. 14, no. 8, pp. 2225-2244, 2017
Description
This study reports NO, NO2 and O3 mixing ratios and flux measurements using the eddy-covariance method during a 7-months period over an oilseed rape field, spanning an organic and a mineral fertilisation event. Mean NO emissions during the whole period were in agreement with previous studies and showed quite small emissions of 0.26 kg N ha−1 with an emission factor of 0.27 %, estimated as the ratio between total N emitted in form of NO and total N input. The NO emissions were higher following organic fertilisation in August due to conditions favouring nitrification (soil water content around 20 % and high temperatures), while mineral fertilisation in February did not result in large emissions. The ozone (O3) deposition velocity was significantly larger following organic fertilisation. We argue that reaction of O3 with emitted NO or reaction of O3 at the surface did not explain this finding, but we propose that reactions of O3 with VOCs emitted by the slurry were the main reason. The analysis of the chemical and turbulent transport times showed that reactions between NO, NO2 and O3 below the measurement height occurred at all time during the 7-months period. Following organic fertilisation, the NO ground fluxes were 30 % larger than the NO fluxes at the measurement height (3.2 m) , while the NO2 fluxes changed sign during some periods, being negative at the surface and positive at the measurement height. This phenomenon of "apparent NO2 emissions" reveals to be important during strong NO emissions and high O3 ambient mixing ratios, even on a bare soil during August.
