Optimizing particle size distribution measured by laser diffraction technique for estimating soil hydraulic properties

Particle size distribution (PSD) is the fundamental characteristic that gives information about soil physical properties. It is the essential predictor used in most predictive programs for predicting water flux, solute, and heat transport in soil. Predictive programs such as Rosetta, RETC, and HYDRUS-1D are usually used PSD measured by the pipette method (PM), whereas the usage of PSD measured by laser diffraction technique (LDT) yields a large estimation error in heavy soil. The aim of the work was to optimize PSD measured by LDT for approaching to PSD measured by PM by suggesting Pedotransfer functions (PTFs). Furthermore, it is to evaluate the efficiency of PSD calculated by the proposed PTFs for estimating soil hydraulic properties using Rosetta program. Particle size distribution was measured by two methods: LDT and PM using the same dispersion factor (sodium pyrophosphate solution 4%). Proposed PTFs were derived for calculation of particle size distribution using a linear regression between PSD measured by LDT as an independent variable and PSD measured by PM as a dependent variable. PSD calculated using proposed PTFs leads to optimize values of PSD measured by LDT for approaching to values of PSD measured by PM. Optimizing PSD by proposed PTFs was suitable for calculating soil hydraulic parameters using Rosetta program with a little estimation error, for agro-soddy podzolic with soil texture as silty loam and silty clay loam.