Can hydraulic-energy-indices be effectively used to describe the saturated hydraulic conductivity?

The saturated hydraulic conductivity (K_s) and water retention curve (SWRC) parameters are important properties for simulating soil hydrological processes and characterizing soil conservation around the world. Therefore, K_s and SWRC are related with the soil physical quality (SPQ) and several SPQ indices can be derived from SWRC, such as the pore size distribution, relative field capacity, plant available water, drainable porosity, and soil hydraulic-energy indices (SHEI). It is well known that the soil structure can be assessed by using SHEI, but a possible physical relationship between K_s and SHEI was not examined yet. Therefore, the objective of this study was to investigate the behavior of K_s as function of SHEI for several soil textural classes. If this relationship be proved, then SHEI might be applied to improve the K_s prediction by PTF models. In this work, a data set of 395 measured SWRC's were fitted to the vG equation to obtain the SHEI to verify whether they are statistically correlated and physically dependent on K_s. The resulting parametric and non-parametric correlation results were split up according to six textural classes. The significant influence of K_s on at least one of the absolute SHEI (A_a or WR_a) was verified on the numerical scale when all textures were grouped and on numerical and pF scales for clayey and silty textures. K_s showed significant impact on A_a and WR_a indices in four textural classes. Furthermore, K_s had influence on the sum A_a + WR_a denoted in pF scale for five of the six textural classes, with a significant linear correlation in the clayey texture when log (A_a + WR_a) was applied. The significant and high correlation of K_s on the ratios WR_a/AWC and A_a/φ_D was also observed in four of the six classes, and therefore the use of these indices is recommended for the development of PTFs for K_s prediction.