Support Vector Machine and Nonlinear Regression Methods for Estimating Saturated Hydraulic Conductivity

Pedotransfer functions (PTFs) are widely used for hydrological calculations based on the known basic properties of soils and sediments. The choice of predictors and the mathematical calculus are of particular importance for the accuracy of calculations. The aim of this study is to compare PTFs with the use of the nonlinear regression (NLR) and support vector machine (SVM) methods, as well as to choose predictor properties for estimating saturated hydraulic conductivity (Ks). Ks was determined in direct laboratory experiments on monoliths of agrosoddy-podzolic soil (Umbric Albeluvisol Abruptic, WRB, 2006) and calculated using PTFs based on the NLR and SVM methods. Six classes of predictor properties were tested for the calculated prognosis: Ks-1 (predictors: the sand, silt, and clay contents); Ks-2 (sand, silt, clay, and soil density); Ks-3 (sand, silt, clay, soil organic matter); Ks-4 (sand, silt, clay, soil density, organic matter); Ks-5 (clay, soil density, organic matter); and Ks-6 (sand, clay, soil density, organic matter). The efficiency of PTFs was determined by comparison with experimental values using the root mean square error (RMSE) and determination coefficient (R2). The results showed that the RMSE for SVM is smaller than the RMSE for NLR in predicting Ks for all classes of PTFs. The SVM method has advantages over the NLR method in terms of simplicity and range of application for predicting Ks using PTFs.