Errors in water retention curves determined with pressure plates: Effects on the soil water balance R. Solone a , M. Bittelli a,⇑ , F. Tomei b , F. Morari c a Department of AgroEnvironmental Science and Technology, University of Bologna, Viale Fanin 44, 40127, Bologna, Italy b Regional Agency for Environmental Protection, Hydro-Meteo-Climate Service, Emilia-Romagna, Italy c Department of Agronomy, Food, Natural Resources, Animal and Environment, University of Padova, Italy article info Article history: Received 19 April 2012 Received in revised form 3 August 2012 Accepted 11 August 2012 Available online 21 August 2012 This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of J. Simunek, Associate Editor Keywords: Soil water retention curve Pressure plate apparatus Dew point potential meter Hydraulic properties Water budget abstract Pressure plates apparatus are very common experimental devices utilized to measure the soil water retention curve. Many studies have demonstrated the lack of reliability of pressure plates apparatus when they are used to measure the soil water retention curve in the dry range, due to low plate and soil conductance, lack of hydrostatic equilibrium, lack of soil–plate contact and soil dispersion. In this research, we investigated measurements of soil water retention curves obtained with a combination of Stackman’s tables, pressure plates apparatus and the chilled-mirror dew point technique. Specifically, the aim of this research was: (a) to investigate the differences in the measured soil water retention curves by the different experimental methods, (b) evaluate relationships between the experimental differences and soil texture, (c) analyze the effect of experimental differences on hydraulic properties parameteriza- tion and (d) investigate the effects of the different parameters set on water transport computation. The results showed differences in measurements made by the combination of Stackman’s tables and Richards’ pressure plates apparatus as compared to the dew point method, for fine textured soils, while no signif- icant differences were detected for coarse textured soils. Computed cumulative drainage and evaporation displayed lower values if soil water retention curves were obtained from data obtained with the Stack- man’s tables and Richards’ pressure plates apparatus instead of the dew point method. In soils, where the soil water retention curve was measured with traditional methods (Stackman’s tables and Richards’ pressure plates apparatus) average cumulative drainage was 173 mm, with respect to a combination of methods including the dew point methods, where the average cumulative drainage was 184 mm. Aver- age cumulative evaporation was 77 mm for the traditional methods, while it was 91 mm, for the combi- nation of methods. Overall, when simulation models are used for studies related to solute transport, polluted soil remediation, irrigation management and others, erroneous measurement of the SWRC for fine textured soils, may lead to erroneous computation of the soil water balance. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The soil water retention curve (SWRC) is the relationship be- tween water content and matric potential. Knowledge of the SWRC is important to solve Richards’ equation (Campbell, 1985) and quantifying soil water flow. Many applications in agriculture and hydrology require the quantification of water flow, such as compu- tation of irrigation volumes, fertilization, remediation of polluted sites and many others. Specifically, the numerical solution of Rich- ards’ equation requires knowledge of the soil hydraulic properties as input parameters, namely the SWRC and the hydraulic conduc- tivity curve (HCC). Several mathematical formulations for describ- ing the SWRC are available (Brooks and Corey, 1966; Durner, 1994; van Genuchten, 1980; Vogel and Cislerova, 1988). Parameterization of the SWRC can be obtained by: (a) fitting a mathematical model to experimental data using least-squares non-linear fitting algorithms or neural networks (Schaap et al., 2001), (b) employing inverse methods, which are methods where model parameters are iteratively changed so that a given selected hydrological model approximates the observed response (Vrugt et al., 2008) and (c) using pedotransfer functions (PTFs), which are regression equations based on the dependence of the SWRC on basic soil properties such as particle size distribution (PSD), bulk density and organic matter (Guber et al., 2009; Morari et al., 2004; Schaap et al., 2001). In recent decades, PTFs have been widely used because the use of Geographic Information Systems (GIS) coupled with crop and hydrological models, have increased the demand for soil databases at larger scales, such as catchment and regional-scale, requiring 0022-1694/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhydrol.2012.08.017 ⇑ Corresponding author. Tel.: +39 051 2096779; fax: +39 051 2096641. E-mail addresses: r.solone@unibo.it (R. Solone), marco.bittelli@unibo.it (M. Bittelli), ftomei@arpa.emr.it (F. Tomei), francesco.morari@unipd.it (F. Morari). Journal of Hydrology 470–471 (2012) 65–74 Contents lists available at SciVerse ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol