Recommendations for soil sample preparation, pretreatment, and data conversion for texture classification in laser diffraction particle size analysis

With regard to the differences between soil particle size distribution (PSD) obtained by sieve-sedimentation methods (SSMs), e.g., the sieve-pipette method (SPM) and the laser diffraction method (LDM), usually, the clay fraction content in LDM measurements is lower than in SSM. Two groups of reasons can be identified for this. Firstly, differences resulting from the features of the methods themselves. Secondly, differences resulting from the soil sample preparation (after sampling) and pretreatment (disaggregation). These differences not only cause difficulties in the PSDs comparability but also make it difficult, and sometimes even impossible, to apply the LDM results to soil texture classification. The solution to this difficulty may be to use pedotransfer functions and standardization of measurement procedures. The aim of this work was to validate the pedotransfer function proposed by Makó et al. (2017) on a Polish soil physics database for recalculating the results from LDM to compare them with SPM results and assess how the soil preparation and pretreatment influenced the obtained PSD and resulting soil texture classification. Using the pedotransfer function, 74 % accuracy was achieved, which is comparable with the results of other pedotransfer functions reported in the literature. Comparing the PSD results for the methods of sample preparation found in the literature after sampling (analysis of fresh, air dry and oven-dried – in 105 °C – soil) and pretreatment before the measurement (breaking soil aggregates chemically and physically) allows recommending the conducting of LDM PSD measurements using air dry soils and soil ultrasound disaggregation.