LAUSR

The accurate and precise analysis of particle-size distribution (PSD) is important in soil science, geology and sedimentology (Miller and Schaetzl, 2011). Most frequently, 0.25-2 mm particles are separated by wet sieving. The under 0.25 mm separation of different-sized particles is based on sedimentation, applying either the pipette or hydrometer method (Gee and Bauder, 1986; Allen, 1990; ISO 11277:2009(E)). Stokes’ law is applied to calculate how much time is needed for a particle with a given diameter to settle in a suspension. In settlement, it is assumed that: (a) soil particles are rigid, spherical and smooth, (b) soil particles have similar densities, (c) particle-to-particle interference and boundary effects from the walls of the sedimentation column are negligible, (d) particle sizes are small enough to ensure that the induced fluid flow is within the laminar flow regime. When particles have irregular shape then deviations from the Stokes’ equation are expected, which is characteristic of silty and clayey particles (Clifton et al., 1999). The laser diffraction method (LDM) for particle-size analysis was introduced by Allen (1990). LDM is being applied more and more often in soil science for soil PSD determination (Bieganowski et al., 2018); however, the labour-intensive pipette or hydrometer methods are the ones prescribed in internationally accepted standards for © 2019 Institute of Agrophysics, Polish Academy of Sciences