Measurement of soil porosity and pores connectivity by different physical approaches and support volumes

The detailed geometrical description of the natural environment at different scales(i.e. from satellite images to micromorphology) is one of the key factors for the understandingof the physical processes affecting soil functioning. This work deals with theanalysis of one very important component of the soil system: the porosity, analysedfrom the microscopy scale to the macroscopy scale which is the scale of a representativesample taken from a soil horizon.The representation of the pore network of soil samples through these scales enable,for instance, the study of very different processes such as biologic processes (differentmicro habitats inside soil aggregates) and physical processes such as water and solutetransport in a soil core.This study has been produced using very different approaches in terms of boththe physical methodology employed and the support volume of the measurements.The following methods have been used: high resolution X ray microtomography(SKYSCAN 1072), a mechanical serial sectioning based tomography (developed atCNR ISAFOM) and hydrological analysis such as water retention and hydraulic conductivitymeasurements.The techniques have enable the analysis of the pore system with scale range of thesupport volume from cubic millimeter (mechanical serial sectioning based tomography)to cubic decimeter (hydrology).The samples analysed consist of 3 soil horizons (Apg, EBtg, Btg) of a soil from a ricepad classified as Aeric Endoaquent (USDA) o Hydragric Anthrosol (WRB) and a manmade sample having an homogeneous particle size (about 70 microns).The results from the particle size distribution and pore connectivity obtained using imageanalysis approaches based on mathematical morphology algorithms have shownthe relevance of the two tomography based techniques which integrate the classical hydrologybased approach enabling a better understanding of the transport phenomena atthe core scale. Differences between the techniques have also been clearly shown bothin terms of the quality of the results obtained (resolution, maximum sample size, etc.)and sustainability (cost, time, etc.). Of course these discrepancies must be related tothe differences between the physics behind the methods and technologic restrictions.