Pedotransfer functions for converting laser diffraction particle‐size data to conventional values

The objective of this study was to develop pedotransfer functions (PTFs) for converting soil particle‐size distribution (PSD) data from the laser diffraction method (LDM) to the classical sieve–pipette method (SPM) for use on a wide range of temperate soil types. Four hundred soil samples, representative of European soil types and climate zones, were selected from the LUCAS (Land Use/Land Cover Area Frame Survey) topsoil database and their PSDs were determined with LDM and SPM. The LDM measurements were made on samples with (i) their organic matter (OM) removed and (ii) their OM content present. The ranges of PSD obtained with the two pretreatment methods enabled clay–silt and silt–sand boundaries from LDM (6.6 and 60.3 µm for soil with OM, respectively, and 5.8 and 69.2 µm for soil without OM, respectively) to be optimized. Optimization of the boundaries of the fractions considerably improved the prediction performance of SPM PSD from LDM PSD. Specific PTFs with different input requirements were developed for continental scale applications in Europe to convert data from LDM to SPM. The predictions of SPM clay, silt and sand contents were the most accurate with PTFs that used PSD from LDM and soil chemical properties (R² 0.83, 0.81, 0.94; RMSE 6.14, 7.91 and 6.58%, respectively). For the most accurate results no pretreatment for OM removal was required, but data on chemical properties were necessary. If no soil chemical data are available, the most accurate PTFs need input data of LDM PSD that originate from samples on which the OM content was removed prior to the PSD analysis. HIGHLIGHTS: PTFs are developed to harmonize PSD data between laser diffraction (LDM) and sieve–pipette (SPM) methods. PTFs are derived from a representative dataset from Europe for application at the continental scale. Clay–silt and silt–sand boundaries for LDM without removing OM are at 6.6 and 60.3 µm, respectively. Clay–silt and silt–sand boundaries for LDM with OM removed are at 5.8 and 69.2 µm, respectively.