Effect of mean soil radius on estimation of water-soil moisture curve based on Aria- Paris model

It is much easier to measure solid phase data or particle size distribution than soil water retention curve, some researchers use the similarity between the shape of particle size distribution and soil water characteristic curve. One of the soil water characteristic curve is the Aria and Paris model. The Aria and Paris model is a physical based model that is widely used to obtain the soil water retention curve. In this model, the particle size distribution curve was divided into n separate fractions, which the diameter of each fraction is equal to the mean of the upper and lower limit diameter. This model usually uses arithmetic average. In this study, the effect of arithmetic mean, geometric and harmonic means as the mean radius of solid particles in different soil textures and suctions were investigated. For this purpose, 19 soil samples in SiStan regoin with sandy, sandy loam, loam, silty loam and clay textures were evaluated. In coarse soils such as sandy and sandy loam, the best results were obtained when the harmonic mean was used In the loam and silt loam soils, the best results were obtained when geometric average was used as the mean diameter of the different fractions .In clay soil, the best results were related to arithmetic average. In general, it can be concluded that using the different methods of means the accuracy of Aria and Paris models increases in estimating the water content.