Quantifying clay content is a fundamental step in predicting and managing soil behaviors such as nutrient and
water retention. However, clay measurements are underestimated when using standard methods of dispersion
in soils rich in oxides and volcanic ash-derived non-crystalline minerals. Increasing levels of the chemical dispersant
and ultrasonic energy are two simple techniques found to increase dispersion and clay measurements in
temperate soils, but their effects are less known for oxidic and volcanic ash soils. In this study we investigated
the effects of increasing dispersion concentration and ultrasonic energy on clay measurements for a range of oxidic
and volcanic ash soils from Hawaii. While doubling and tripling the standard sodium hexametaphosphate
concentration of 0.441 g L−1 did not increase estimates of clay content, increasing levels of ultrasonic energy
up to 1600 JmL−1 significantly increasedmeasured clay content for all oxide and volcanic ash soils. The response
to ultrasonication was dependent on soil carbon, oxide content, and surface charge,with more energy needed to
disperse soils higher in carbon, oxides, and positive charge. Scanning electronmicroscopy revealed damage to the
sand fraction in some soils when ultrasonicated, but the extent of this damage was viewed as negligible. Porous
sand-sized particles resembling pumice grains were also observed in some soils, suggesting that conventional
particle size analysis and clay interpretations may not adequately describe surface related behaviors.