Evaluation of Saturated Hydraulic Conductivity Changes in Surface and Subsurface Layers of Loess Soils of East of Golestan Province

Soil hydraulic conductivity is one of the important parameters to estimate soil erodibility, soil water flow, estimate runoff, and design drainage systems. This study was carried out to determine the hydraulic saturation (Ks) of surface and subsurface loess soils of Aghemam watershed (2) that located in the northeast of Golestan province. For this purpose, three types of soils in this area including hill, loess plateau and alluvial terrace in two surface and subsurface layers were sampled. In this study, in addition to determining Ks using the falling head method, some physicochemical properties of soil samples such as salinity, neutral lime, organic matter and soil texture were measured in the laboratory and their relationship with Ks was investigated. Then, the spatial variations of surface and subsurface saturation hydraulic conductivity in the study area were plotted using GIS software and IDW method. The spatial variations of Ks in both layers indicated its direct relationship between the two layers. However, the value of this parameter in the surface layer is more than for the subsurface layer. Also, the amount of Ks is relatively high in the two types of loess plateau and hill (3.9 cm/h), except in the alluvial terrace type, which is generally low (0.9 cm/h). The statistical results of linear multiple regression and stepwise methods showed that among the variables studied, the organic matter and neutral lime parameters, respectively, have the most impact on determining the amount of surface Ks (R2 = 0.9556) and subsurface (R2=0.8607) in the study area.