Point pedotransfer functions for estimating soil water retention curve

A b s t r a c t. Soil water retention curve (SWRC) is one of the most important soil hydraulic properties, whose estimation is still under consideration. In this study, we used 315 soil samples from the UNSODA database to develop three models of point pedotransfer functions (PTFs) and to verify them. We also used an independent database, GRIZZLY, with 59 samples, to verify the developed point PTFs and to compare them with the Rosetta model. Multiple linear regression and stepwise methods were used to derive pedotransfer functions. In the first model, soil texture data ie sand, silt, and clay content, geometric mean particle-size diameter and geometric standard deviation as well as bulk density were used to develop point PTFs at 10 matric potentials. In the second model, water content at field capacity, and in the third model water content at field capacity and permanent wilting point were also used for developing PTFs at 9 and 8 matric potentials, respectively. To evaluate the accuracy and reliability of the point PTFs, we used crossvalidation eg repeated random splitting of the data set into subsets for development and validation. The calculated RMSE values showed that all three developed point PTFs estimated soil water retention curve better than the Rosetta model. K e y w o r d s: field capacity, point pedotransfer functions, permanent wilting point, soil water retention curve