Disruptive methods for assessing soil structure

The description and quantification of soil structure is very important because of the many agronomic and environmental processes related to the arrangement of secondary soil units (aggregates, peds or clods) and their stability. The purpose of this review is to present and discuss methods and indices used to characterize soil structure based on the size distribution and stability of fragments produced by breaking apart the soil matrix. The size of fragments is inversely related to the mechanical stress applied. Thus, the selection of an appropriate fragmentation procedure is critical if information on soil structure is to be recovered, and often depends upon the soil process of interest. Soil fragmentation starts at sampling in the field and continues during laboratory separation of soil units by sieving. It is useful to characterize the fragment mass-size distribution with parameters from a model, such as the log-normal distribution function. Fractal theory provides a physically based link between the size distribution and stability of fragments. Structural stability is based on the ratio of fragment mass-sizes measured before and after low and high mechanical stresses, respectively. Thus, an adequate description of the applied stress conditions is essential for the parameterization of structural stability as well as the fragment mass-size distribution.