Evaluating soil aggregate stability using classical methods and fractal models

Soil structure is an important indicator for optimal management of soil and water resources. Because it directly influencing several physical characteristics of soils such as soil water status، hydraulic conductivity، heat and air contents، soil porosity and bulk density. However، due to complexity of soil structure، its quantitative description is rather difficult. One of the relatively new methods proposed to explain soil structure in a quantitative manner is the so-called fractal geometry concept. In this concept، by determining the fractal dimension of bulk soil، the stability of aggregates can be quantitatively analyzed at different scales. The objective of this study was to quantify soil structure stability using some classic indicators and fractal approach in a large scale. Consequently، 41 intact soil samples were taken from an agricultural area and their particle size distribution، soil bulk density and aggregate bulk density، were measured. The weighted mean diameter and geometric mean diameter of both dry and wet aggregates were measured using dry and wet sieving method. The fractal dimensions of all dry and wet aggregates were obtained using fractal models of Mandelbrot، Tyler-Wheatcraft and Rieu-Sposito. The results indicated that fractal dimensions of the number-size model of Mandelbrot for dry sieve series and the number-size model of Rieu-Sposito in the wet sieve series perform quite well. These two models could also provide reasonable agreement with classical geometric mean and weighted mean diameters of aggregates.