Characterization of particle-size distribution in soils with a fragmentation model

particle-size distributions (PSDs) of soils are often used to estimate othe r soil properties, such as soil moisture characteristics and hydraulic cond uctivities. Prediction of hydraulic properties from soil texture requires a n accurate characterization of PSDs. The objective of this study was to tes t the validity of a mass-based fragmentation model to describe PSDs in soil s, Net sieving, pipette, and light-diffraction techniques were used to obta in PSDs of 19 soils in the range of 0.05 to 2000 mu m, Light diffraction al lows determination of smaller particle sizes than the classical sedimentati on methods, and provides a high resolution of the PSD, The measured data we re analyzed with a mass-based model originating from fragmentation processe s, which fields a power-law relation between moss and size of soil particle s. It was found that a single power-law exponent could not characterize the PSD across the whole range of the measurements. Three main power-law domai ns were identified. The boundaries between the three domains were located a t particle diameters of 0.51 +/- 0.15 and 85.3 +/- 25.3 mu m. The exponent of the power law describing the domain between 0.51 and 85.3 pm was correla ted with the clay and sand contents of the soil sample, indicating some rel ationship between power-law exponent and textural class, Two simple equatio ns are derived to calculate the parameters of the fragmentation model of th e domain between 0.51 and 85.3 pm from mass fractions of clay and silt.