PhD thesis defense of Florian POINCOT (INRA UR Sols, Orléans)
Control of N2O emissions by the structural state of soils
April 05, 2019 at 10:30 at the INRA Orleans – Salle Dominique King
Nitrous oxide (N2O) is a powerful greenhouse gas, and the third gas responsible for the anthropogenic greenhouse effect. Agricultural soils account for nearly 66% of N2O emissions from human activities. The variability of emissions measured in the field is high. The soil structure impacts both the production and transport of N2O in the soil profile. The objective of this thesis was to understand the role of the soil structural state on the spatial variability of N2O emissions. The approach used combines two types of experiments in the laboratory (on a scale of 0.3 m² x 0.1 m and on a farm plot of 10 m² x 0.3 m in bare soil) and a modeling work integrating physical, chemical and biological processes in the soil profile and runoff, all at a fine temporal resolution.
This work has highlighted a hierarchy between production and transport processes, which evolves with time and environmental conditions: under favorable conditions for denitrification, the production of N2O increases with the density in connection with an increase of the portion of porosity filled with water, up to a certain limit. The deterministic model has shown that rainfall and runoff dynamics modify the intensity and dynamics of N2O emissions according to the hydrodynamic properties of the soil. Finally, this work confirmed the complexity of N2O emission determinism and highlighted the interest of characterizing soil structure and emissions at high spatial resolution to improve the quality of predictive models.