Modelling aggregate liberation and dispersion of three soil types exposed to ultrasonic agitation

Abstract

This paper reports on a study involving the application of ultrasonic agitation to 3 soil types to assess soil aggregate disruption and subsequent dispersion. The measurement of various particle size fractions resulting after the application of ultrasonic agitation for different time periods made it possible to describe the resulting aggregate disruption using the established aggregate liberation and dispersion curve (ALDC) model. Originally this model had been used to assess only the 2–20 µm fraction liberated from Vertosols. This work has shown that the model can be applied to a variety of size fractions between 2 and 100 µm in diameter and soil types, namely Chromosols and Ferrosols. By estimating the critical energy (Ecrit) required to initiate dispersion of liberated aggregates for each fraction, it is implied that the linkage between aggregates is weaker than the linkages between the materials composing the aggregates. Further, the ratio between the rate constants in the ALDC model can be used to establish if there is a stepwise breakdown of larger aggregates, a criterion required to establish the presence of an aggregate hierarchy. Finally, by assessing the aggregate distribution on a continuous scale, it is possible to recognise unique pathways of aggregate liberation and dispersion for each soil type rather than assuming that aggregates breakdown into predefined discrete size fractions.