The best mathematical models describing particle size distribution of soils

Since particle size distribution (PSD) is a fundamental soil physical property, so determination of its accurate and continuous curve is important. Many models have been introduced to describe PSD curve, but their fitting capability in different textural groups have been rarely investigated. The aim of this study was to evaluate the fitting ability of 15 models on 2653 soil samples from 13 province of Iran, and to determine the best model among them for the PSD of all soil samples as well as for each soil textural group based on evaluation criteria. Results showed that the Weibull model was the most accurate model for all soil samples as well as for the clayey and loamy groups. After the Weibull, Fredlund, Rosin–Rammler and van Genuchten were the most accurate models. However, their differences were not significant (p ≤ 0.05). Also, for the coarse texture group the S-shape model showed the better fit than the others. These results showed the performance of a particular model varies with the soil textural characteristics.