Self-similar organization of Vertisol microstructure: A pore–solid fractal interpretation

Soil microstructure is an important component of soil architecture. For interpreting soil evolution it is necessary to search for physical links between components of the soil structure. The objectives of this work were to (i) estimate relevant scaling parameters from particle-size distributions (PSD) and microaggregate-size distributions (MSD) and (ii) correlate those scaling parameters to some empirical or semiempirical indexes of a swelling soil (e.g. dispersion index, instability index and soil swelling parameter). The study was conducted on a Vertisol profile. Soil samples were collected from six different depths ranging from 0–0.03 m (mulch layer) to 1.30–1.40 m. We used a Pore–Solid Fractal approximation for deriving and interpreting the scaling parameters in terms of soil microstructure. A linear relationship between D (PSD) and Df (MSD) was found (R = 0.94, p < 0.05), indicating a connection between both organizations. In addition, soil swelling and instability index increased both D (PSD) and Df (MSD) while dispersion index increased the probability of failure. All of this could be associated to the behaviour of solid–solid and pore–solid interfaces as related to physico-chemical processes.