Impact of sample pretreatment on the results of texture analysis in different soils

Soil texture, derived from the particle size distribution, is an essential soil parameter as it influences numerous soil properties. Most determination methods include a pretreatment that removes bonding agents like organic matter, chalk and/or iron oxides in order to guarantee full dispersion of the soil particles. Particle size analysis with no pretreatment of the samples causes shifts in the particle size distribution that lead to a coarser soil texture. Particle size analysis (sieve and sedimentation method) with pretreatment and with no pretreatment was performed on 93 top- and subsoil samples, subdivided into four sample groups from Germany (glacial and marine sediments) and one sample group from the Ukraine (loess). Particle size analysis with no pretreatment significantly reduced the clay content (by 54–89% of the content after particle size analysis with pretreatment) and increased the silt content (by 13–36 % of the content after particle size analysis with pretreatment) and sand content (by 3–483 % of the content after particle size analysis with pretreatment) in all sample groups. The shifts in the particle size distribution were attributed to the preservation of water stable aggregates and correlated with soil organic carbon content, pH, and exchangeable cation composition. The specific surface area of the soil samples decreased significantly (by 38–65%) after particle size analysis with no pretreatment in all sample groups. The derivation of soil parameters from no pretreatment texture reduced the estimates of effective cation exchange capacity by 29–62% and the estimates of not plant available water capacity by 18–54% compared to the estimates from pretreatment texture. For soils with a high aggregation potential at the microscale, new pedotransfer functions for the derivation of soil parameters based on no pretreatment texture data should be developed.