Physical, topological and hydraulic properties of an Oxisol under conservation practices: X-ray tomography imaging and pore-network simulation

Pore structure plays an essential role in fluid flow and solute transport in soils. In this study, the physical, topological, and hydraulic properties of an Oxisol under two land uses, i.e., secondary forest (SF) and reduced tillage (RT), were characterized using a combination of X-ray computed tomography (XCT) imaging and pore network simulations. The SF was utilized as a baseline to assess changes in the pore structure of soils under the RT conditions. Tomographic images were obtained under three voxel sizes, i.e., 5.3, 35, and 60 μm. Porosity, surface area, Euler characteristic, and tortuosity were computed using image processing algorithms. The pore network of each soil sample was extracted to determine the pore-body radius, pore-throat radius, pore-throat length, and pore coordination number distributions as well as the absolute permeability. We found that the average pore-body radius, pore-throat radius, pore-throat length, and surface area increased with increasing voxel size for both land uses. No obvious differences in tortuosity and pore coordination number were observed between the 35 and 60 μm voxel sizes for both land uses but differ from those with 5.3 μm voxel size. Regarding pore connectivity, the images with 5.3 and 35 μm voxel sizes were similar, although they differed from the 60 μm images, whose samples were more connected. By analyzing the effect of land use, we found that, in general, there were little differences between the SF and RT at all voxel sizes examined. Exceptions occurred mainly for some of the physical properties determined on the images with the voxel size of 60 μm. The results of this study demonstrated the influence of different voxel sizes on the Oxisol properties. Despite the differences in image voxel sizes, distinctions between land uses were practically not found, which indicates that reduced tillage is an appropriate conservation system strategy to keep the soil physical structure quality.