Fragmentation fractal dimensions of Vertisol samples: influence of sieving time and soil pretreatment

Compaction is a major problem in Vertisols. Physical parameters to quantify the degree of compaction are required. The objectives of this work were to (i) compare the fractal dimensions estimated for soil pre-treated by two different methods and (ii) study relationships between the fragmentation fractal dimension, Df, and the sieving time. Soil samples were collected from the top layer (0–10 cm) of a Vertisol (heavy clay, montmorillonitic). Two methods of soil drying were employed: air-drying, and air-drying, saturation in ethanol, and air-drying again. Fragmentation fractal dimensions were estimated by sieving in a nest of sieves with mesh sizes ranging from 0.25 to 10 mm. The number-based method was used for the estimation. In addition, soil samples were sieved using the following times: 1, 5, 10, 20, 30, 40, 50, 60, 70, and 80 min. The saturation of soil samples in ethanol prior to sieving reduced the resistance of soil to fragmentation. The fragmentation fractal dimension increased as a function of the time of sieving following an exponential model. Df is a valuable parameter to characterize the resistance of Vertisols to fragmentation.