Extraction of three-dimensional soil pore space from microtomography images using a geometrical approach

Abstract

This paper presents a geometrical model of soil pore space based on the quantitative analysis of synchrotron X-ray microtomography data. Our model calculated the minimal set of balls that recovered the skeleton of the pore space using Delaunay tessellation, and the simply connected sets of balls that could be considered as potential pore channels. This model (DTM software) was then applied to three-dimensional tomography reconstructions of soil aggregates (~ 5 mm diameter) from two management systems (conventionally tilled soil, namely CTT and grassland soil, namely GL) with a voxel edge length of 3.2 μm and 5.4 μm, respectively. Geometric characteristics such as the frequency distribution of pore radius, length, and tortuosity as well as the retention curve were calculated using our model. The organic matter decomposition was also simulated using DTM approach. The results were compared with pore space statistics obtained during a previously published study on the same data using algorithms based on the medial axis and throat computation ( 3dma software). The same tendency on the geometrical statistic was obtained using both methods, with more pores of smaller length and diameter calculated for the aggregate from the conventionally tilled site compared to the grassland aggregate. However, the 3dma method generated a larger quantity of voxels (385,673 and 189,250 for CTT and GL, respectively) compared to the amount of balls in DTM (170,250 and 64,273 for CTT and GL, respectively) and shorter channels because of the presence of throats.