How does pretreatment of dry steppe soils affect particle size analysis by laser diffraction?

After extensive research on different methods to measure particle size distribution (PSD), soil scientists are proposing the laser diffraction method (LDM) as a standard method for soil texture analysis. However, the effects of different pretreatments on particle size analysis of dry steppe soils with LDM has not been tested so far. This study aims to evaluate different pretreatment methods with the purpose to disperse aggregates and remove binding agents in Chernozem and Kastanozem soils. To cover a wide range of different land-use types and farming methods, 112 surface soil samples were taken from 13 fields on four different test sites in Kazakhstan. Before LDM analysis, all samples were pretreated with either H₂O₂ to remove organic carbon or HCl to remove carbonates. The results showed that removing organic matter with H₂O₂ led to complete sample dispersion while HCl pretreatment caused incomplete dispersion, likely due to aggregation by calcium ions released by the dissolution of carbonates.