Evaluation of laser diffraction analysis of particle size distribution of typical soils in China and comparison with the sieve-pipette method

Laser diffraction method (LDM) provides a rapid solution for obtaining soil particle size distribution (PSD) especially in the analysis of a larger number of soil samples. However, there are disadvantages associated with the use of LDM for PSD measurements over the traditional sieve-pipette method (SPM). The present study is aimed to assess the suitability of LDM as a routine method for determining soil PSD, evaluate the precision or its repeatability of PSD parameters, and establish a simplified protocol for transforming the LDM results into SPM ones. The soil samples (n = 43) from 13 Chinese provinces were analyzed, and the results indicated that the relative errors for clay, silt, and sand fractions by the LDM were 35.34, 27.38, and 19.41%, respectively, compared with those by the SPM in the condition of limited sample numbers and large between-sample variation; samples could best be run at least twice during the LDM analysis to reduce the error caused by a limited sample volume; and a soil particle refractive index of 1.50 and a soil particle absorption index of 0.01 were found to be optimal for the Mie theory model. With relatively limited sample numbers and apparent textural difference between the samples, the distinct incompatibilities were observed in the present work between the PSD obtained by the LDM and SPM. However, depending on the specific research purpose, the deviations between the LDM and SPM may be considerably reduced with an increase in the sample capacity or a decrease in the spatial scale.