Multi-scale study of soil structure in relation to nitrous oxide emissions

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Maillet, Emile | Lacoste, Marine | Grossel, Agnès | Cousin, Isabelle

Edité par CCSD -

International audience. Nitrous oxide (N2O) is a potent GHG and a dominant ozone-depleting substance. Currently, more than half of global anthropogenic N2O emissions come from cultivated soils and are mostly linked to nitrogen fertilizer use.Soils N2O emissions is a multifactorial phenomenon, with a large spatio-temporal variability whatever the scale. To explain this variability, many deterministic studies focus either on the soil microstructure scale, i.e. the scale of microorganism habitat and N2O production (Schlüter et al., 2018) , or on the macrostructure scale, to focus on fluids transfers (water, N2O) (Rabot et al., 2015). However, the multiscale influence of soil structure on N2O emissions is still poorly understood, and consists in the objective of our work. In this study, we assessed a multiscale approach to gain a more detailed understanding of the N2O emissions determinism. The field-scale variability of N2O emissions has been estimated during a snap-shot campaign in soils with contrasted structure, induced by different agricultural practices (4 soil modalities crossing strip-till and tillage with compacted or uncompacted areas). 24 soil cylinders were collected in low and high N2O emission zones and were then scanned by using both X-ray macro- and micro-tomography; the soil structure was then described at macro and micro-scale by using quantitative morphological tools. Associated relevant soil properties were analyzed (mineral nitrogen, soil texture, pH, C/N, etc.). The 4 different soil modalities showed highly contrasting macrostructures and N2O emissions. The ongoing work is intended to clarify the relationships between other soil factors, microstructure and N2O emissions.

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