Combining pedotransfer functions with physical measurements to improve the estimation of soil hydraulic properties

Simulation modelling is an important tool in evaluating the economical and environmental effects of different farm management practices. Availability and quality of input data are crucial factors that determine the accuracy of modelling results. With respect to soil water regimes, much depends on the accuracy of soil hydraulic properties. These are conventionally derived through expensive laboratory measurements. Pedotransfer functions have been developed to increase cost effectiveness: hydraulic properties are estimated using basic soil properties that can be measured with relative ease. This study compares four methods to derive hydraulic properties by analysing their effect on simulated soil moisture contents. Applied methods include: (A) laboratory measurements, (B) class pedotransfer functions, (C) continuous pedotransfer functions and (D) continuous pedotransfer functions combined with simple laboratory measurements. Modelling performance was evaluated by comparing simulated and measured soil moisture contents for three sites and two depths. Modelling uncertainty was evaluated through Monte Carlo simulations. The combination of continuous pedotransfer functions and simple laboratory measurements (method D) clearly produced best results. Modelling performance was highest overall and results were consistent for individual profiles and depths. Modelling uncertainty was lowest, far lower than the uncertainty resulting from the measured data set (method A). Based on these results, a general procedure was defined to combine continuous pedotransfer functions with simple soil physical measurements.