Influencing Factors and Prediction of Hydraulic Conductivity in Fine-Textured Alkaline Soils

Hydraulic conductivity is an essential parameter in hydrological cycle studies. Determination of saturated hydraulic conductivity (Ks) in fine-textured, especially alkaline, soils is a difficult process and takes time. In this study, the effects of some soil properties on Ks in fine-textured alkaline soils were determined, and Ks values were predicted using pedotransfer (PTF) models. Ks, which varied between 0.011 and 0.625 cm h(-1) in 64 different soil samples, significantly decreased with increasing exchangeable Na percentage (ESP), sodium absorption ratio(SAR), exchangeable Na (exch. Na), and clay content of soils. The correlation coefficients were divided into a series of direct and indirect effects of the soil properties on Ks by path coefficients. The direct effects of selected properties on Ks were in the following order; exch. Na (42.6%) > ESP (37.0%) > clay (21.3%) > CEC (16.8%) > SAR (9.7%) > pH (8.4%) > silt (6.4%) > electrical conductivity (EC) (0.8%). The highest indirect effect on Ks was obtained with EC (43.0%) mediated by exch. Na. Accuracy and reliability of PTFs were assessed with the average of root mean square error (RMSE) and R-2 values in the training and testing data sets, respectively. Using clay and silt fractions together with EC, exch. Na, ESP, or SAR in the second order equations significantly increased the accuracy and reliability of PTFs. Exchangeable Na was one of the most important soil properties that affected Ks directly in these soils. Using soil chemical properties in PTFs with soil physical properties showed that saturated Ks values can be predicted more accurately in fine-textured alkaline soils.