Comparison of four methods for liberating various aggregate fractions in Vertosols to study their morphology

Abstract

Topsoil samples from 3 Vertosols located at Narrabri, Warren, and Dalby were treated with 4 aggregate liberation methods to determine their suitability for analysis by scanning electron microscopy (SEM). In addition to the ability of each method to liberate aggregates for assessment, the potential for consequent morphological deformation was also considered. It was found that the aggregate slaking in water and modified wet sieving methods were suitable for liberating aggregates >100 μm in diameter, whereas the ultrasonic agitation method readily liberated aggregates <50 μm in diameter. End-over-end shaking is not recommended for preparing aggregates for SEM as the method appeared to cause morphological deformation of the liberated aggregates. The systematic use of the 4 aggregate liberating methods, assuming an increase in the intensity of the energy supplied, enabled the partitioning of the aggregates of these Vertosols into pragmatic aggregate size fractions defining a hierarchy, i.e. >250, 100–250, 20–100, 2–20, and <2 μm in diameter.