A comparison of fractal analytical methods on 2- and 3-dimensional computed tomographic scans of soil aggregates

Computed tomographic (CT) images of small (approximately 3 mm diameter) intact aggregates from an agricultural soil of two contrasting management histories were analyzed. Fractal analysis was employed to quantify the heterogeneity of mass and pore space within individual aggregates. Three fractal analytical methods were compared: 1) density scaling fitted to a solid mass fractal model, 2) density scaling fitted to a pore-solid fractal model, and 3) cumulative pore number scaling. Ten aggregates from a continuous corn treatment and another 10 aggregates from a five-year crop rotation treatment were each scanned to obtain a 2-D CT image. Two of these aggregates, one from each treatment, were scanned fully for 3-D reconstructions. The objectives were to 1) demonstrate the utility of industrial quality CT scanning and density scaling for deriving fractal parameters, including the ability of 2-D scans to represent 3-D structures, and 2) compare the three fractal analytical methods to identify which worked best for estimating fractal parameters of individual soil aggregates. The results showed that density scaling methods are compatible with CT scanning and that solid mass fractal models described the 20 aggregates better than pore-solid fractal models. Comparison of the 2-D and 3-D data suggested that some fractal parameters, including the fractal dimension, can be obtained from 2-D slices of a whole soil aggregate. This study demonstrated a non-disruptive approach to quantify internal heterogeneity of individual soil aggregates, which can be used to address scaling issues of soil structure and to predict soil behavior and soil quality.