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

Particle density is used to calculate total soil porosity and related measu rements such as macroporosity and water storage capacity. Methods for measu ring particle density often advise using dry samples. This study measured p article density by displacement of water using both field-moist and oven-dr y samples from 4 New Zealand Allophanic Soils. There were significant diffe rences in particle density between the 2 methods. Oven-dry samples under-es timated particle density by up to 0.33 Mg/m(3) and as a result, calculation s of porosity were under-estimated by up to 0.05 m(3)/m(3). Under-estimatio n of porosity can result in incorrect interpretation of a soil's aeration a nd 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 dete rmine particle density of Allophanic Soils to ensure accurate calculation o f soil porosity.