Rl. Peyton et al., FRACTAL DIMENSION TO DESCRIBE SOIL MACROPORE STRUCTURE USING X-RAY COMPUTED-TOMOGRAPHY, Water resources research, 30(3), 1994, pp. 691-700
The size, shape, and arrangement of structured voids 1-10 mm in size p
lay an important role in the transport of water and solutes through so
il. However, these characteristics are complex and difficult to quanti
fy. Improved methods are needed to quantify the characteristics of the
se voids to better understand and predict the behavior of water and so
lutes passing through them. This study applied fractal analysis to soi
l bulk density data measured by X ray computed tomography (CT), a rela
tively new tool for nondestructively measuring macropore-scale density
in soil cores. Studies were conducted using undisturbed soil cores (7
.6 cm ID) from forested and cultivated sites in the A horizon of a Men
fro silt loam soil containing macropores and using two groups of soil
cores which were uniformly packed with Menfro aggregates from 1-2 mm i
n diameter for one group and < 1 mm in diameter for the other group. S
amples were probed using CT to produce a 512 by 512 digital matrix of
CT pixel values corresponding to bulk density. Pixels above a specifie
d CT ''cutoff'' value were designated as occupied. A box-counting meth
od was used to find the fractal dimension of the perimeters between oc
cupied and unoccupied pixels and of the areas formed by the unoccupied
pixels. For length scales from 1 to 10 mm, perimeters and areas of th
ese regions appeared to be fractal systems. Single degree of freedom o
rthogonal contrast tests determined from analysis of variance showed s
ignificant differences between the fractal dimension for (1) forest an
d cultivated cores versus uniformly packed cores, (2) two groups of un
iformly packed cores made of different aggregate sizes, and (3) forest
versus cultivated cores.