Coupling X-ray microtomography and mercury intrusion porosimetry to quantify aggregate structures of a cambisol under different fertilisation treatments

The description of soil structure is primordial to determine the effects of management practices on soil environment. Different techniques were developed to determine the pore structure, each with its own limitations. In this study mercury intrusion porosimetry (MIP) and X-ray microtomography (micro-CT) were used to study the total porosity and pore size distribution of soil aggregates (5-6 mm) treated with different fertilisations (organic, mixed and mineral). The network model Pore-Con was applied to pore distribution curves to highlight subtle structural properties affecting the aggregates. The combination of these techniques highlighted that: (1) MIP was fundamental to reveal the small pores that were not detected by micro-CT and that represented up to 70% of total porosity; (2) micropores (30-6.25 mu m) detected by MIP were underestimated with respect to micro-CT (-9.4%) probably due to the "ink bottle" effect, whereas meso- and macropores were overestimated; (3) only micro-CT highlighted the effects of organic amendants on pore morphology. These outcomes were compared with modelling results of the network model Pore-Cor that proved its ability to predict the pore structure organisation and the differences between fertilisations. Further improvement of micro-CT will allow to cover a wider range of pores, but at present the integration with different techniques is still fundamental