Mass-size fractal dimension of primary and aggregated particles and soil profile development

Fractal dimension can be used to characterize fragmented systems such as soil particle size distribution (PSD) and aggregate size distribution (ASD). However, less than 2-mm size distributions in soils include both primary particles and aggregates, depending on the energy input during the determination. In this work, we evaluated the fractal behavior of PSD-ASD in 85 soil horizons from 31 soil profiles characterized by different development stages and processes (Entisols, Inceptisols, Mollisols, Alfisols). Sample texture was determined using the pipette method and comparing three treatments: water dispersion (W), chemical dispersion with Na-hexametaphosphate (NP), chemical dispersion plus removal of organic and inorganic binding agents (P). The coarse sand-sized fraction decreased from W to NP to P. The clay was characterized by a greater prevalence of fine particles, whereas the clay-sized followed the opposite trend, and they showed a negative correlation (r = -0.47 for W, r = -0.65 for NP, r = -0.66 for P, always P < 0.001). The fragmentation fractal dimension (Df) enhanced differences in mass-size distributions for soil orders/horizons and determination methods. It provided evidence for different driving processes in soil development and aggregation types by summarizing textural information through a unique numeric value. In the study area, Df ranged from 2.582 (W) to 2.727 (NP) to 2.837 (P). Lower values after chemical dispersion (NP) were observed for Mollisols (P < 0.001), showing more pronounced aggregation. Among soil horizons, B showed a higher amount of fine material, thus greater Df. An index evaluating the increase in Df when cement removal is applied ([DfP-DfNP]/DfNP) helped us discriminate among soil types, therefore among aggregation properties.