Differences in particle density between field-moist and oven-dry samples from Allophanic Soils

Abstract

Particle density is used to calculate total soil porosity and related measurements such as macroporosity and water storage capacity. Methods for measuring particle density often advise using dry samples. This study measured particle density by displacement of water using both field-moist and oven-dry samples from 4 New Zealand Allophanic Soils. There were significant differences in particle density between the 2 methods. Oven-dry samples under-estimated particle density by up to 0.33 Mg/m ³ and as a result, calculations of porosity were under-estimated by up to 0.05 m ³/m ³ . Under-estimation of porosity can result in incorrect interpretation of a soil's aeration and water holding status. Allophanic Soils are known to undergo irreversible physical changes on drying and it is likely that these changes caused the difference in measurements. Only field-moist samples should be used to determine particle density of Allophanic Soils to ensure accurate calculation of soil porosity.