Use of fractal scaling to discriminate between and macro- and meso-pore sizes in forest soils

Abstract

Two-dimensional image analysis of soil porosity has been used to study four forest plots. The analysis yields the number n(a) of soil pores having greater area than a, and the number n(p) of pores having larger perimeters than p. Both distributions follow power-laws of the form n(a)∼a−Da and n(p)∼p−Dp, with different exponents in two scaling regimes. The two regimes are between 10–32 mm2 (Da1) and 32–100 mm2 (Da2) for pore areas, and from 11 to 21 mm (Dp1) and 21 to 40 mm (Dp2) for pore perimeter. In all cases, the regression used to obtain the Korcak exponent was statistically significant. The higher Korcak exponents (Da2 and Dp2) correspond to larger pore areas and perimeters, and the lower ones (Da1 and Dp1), to the smaller areas and perimeters. The inflection point between the two scaling laws is at 6.4±1.0 mm diameter for pore areas and 6.8±1.4 mm for pore perimeters and it lies close to the medium/coarse soil-pore limit of 5 mm equivalent diameter [US Soil Survey Division Staff, 1993. US Soil Survey Division Staff, 1993. Soil Survey Manual. Soil Conservation Service. US Department of Agriculture Handbook 18]. This coincidence could be used for soil macro-pore classification.