Abstract
Information on spatial and temporal variations of soil hydraulic conductivity (k) is essential to improve soil and water management. However several techniques have been proposed for measuring of soil hydraulic conductivity above water surface table, but reliability and easy use of these methods in various conditions were always concern for engineers. The purposes of this study are measuring of the soli hydraulic conductivity by Guelph permeameter as a reliable method and determination of the best single-depth analysis method equivalent to two- depth method. To achieve this goal, 40 boreholes with depth of 60 cm were drilled in a grid of m in the research farm of agricultural faculty, Razi University, Kermanshah. Soil texture of the study area is silty-loam. After identification tests such as soil gradation, determination of the soil liquid and plasticity limits and determination of the specific gravity, soil saturated hydraulic conductivity and matric potential were measured by Guelph permeameter for three fixed ponding depths 5, 15 and 25 cm. Because of heterogeneous of equations in three-depth method only 17 success well obtained while in two-depth method for two ponding depths 5 and 15 cm, 26 successful well obtained. Data of these 26 boreholes were used for statistical analysis. The results of statistical analysis showed that: 1) Mean of soil hydraulic conductivity in the study area is , 2) Among the single depth methods, Richards regression basic analysis with values of 0.205 and 0.994 for and respectively is the nearest method to tow-depth method, 3) There is a significant difference at 5% level between the results from two-depths analysis of Guelph permeameter with Richards and Laplace single-depth methods, 4) Average values of and in the study area were calculated and respectively, and 5) Values of have less variation coefficients and standard deviation than values of sorptive number ( ).

Keywords: Hydraulic conductivity, Guelph permeameter