Coupling published pedotransfer functions for the estimation of bulk density and saturated hydraulic conductivity in stony soils Behzad Nasri a,b, ⁎, Olivier Fouché a,b , Dino Torri c a LEESU-DR, Ecole des Ponts ParisTech, Université Paris-Est, 6 et 8 avenue Blaise Pascal, Cité Descartes, 77455 Marne-la-Vallée, Cedex 2, France b Laboratoire Géomatique et Foncier (GeF), Ecole supérieure des Géomètres et topographes (ESGT), Conservatoire national des arts et métiers (Le Cnam), 1 boulevard Pythagore, F-72000 Le Mans, France c CNR-IRPI, Perugia, Italy abstract article info Article history: Received 17 November 2014 Received in revised form 10 March 2015 Accepted 30 March 2015 Available online 7 April 2015 Keywords: Residual humidity Soil texture Rock fragment Guelph permeameter Wastewater Prediction performance Saturated hydraulic conductivity (Ks) is one of the key parameters in the design of engineering and environmen- tal structures built in the unsaturated zone for infiltration purpose. Unfortunately, its field determination is labo- rious and expensive and suffers non-uniqueness. Besides, pedotransfer functions (PTFs) have been established to translate some measured soil matrix properties such as bulk density, organic matter and soil texture into Ks. Es- pecially when the soil is heterogeneous, these PTFs may exhibit large differences between the matrix-predicted and in situ measured Ks. Moreover, there is no published PTF to predict Ks in stony soils. In this study, the objec- tive is to estimate Ks in heterogeneous stony soils by combining already published PTFs. A methodology has been developed to evaluate the performance of the combinations of ten published PTFs predicting Ks from bulk density in fine soil matrix (BD m0 ) with thirty two published PTFs predicting BD m0 from the soil matrix texture properties. These 320 combined functions are likely to allow finding a correct estimation of Ks in most of fine soils but not in stony soils. To test this assumption, in situ Ks measurements with a Guelph permeameter and matrix texture and organic matter determinations in laboratory were carried out in a stony soil (colluvium from limestone). The magnitudes of measured Ks are much higher than the values predicted for the given texture of the matrix by 320 combined functions. This suggests that the rock fragment fraction in the soil plays an important role in accel- erating the evacuation of water by increasing the cinematic porosity. Then, the empirical relation of Torri et al. (1994) is used to take into account this additional porosity within the real bulk density of the soil matrix. The re- tention capacity of the stony soil is controlled by the matrix content, which provides for a relation between rock fragment content and residual water content. Finally, six combined functions transformed by the Torri's relation are selected which predict Ks for a stony soil. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Saturated hydraulic conductivity denoted Ks (m/s) is an important soil physical property, especially for modeling water flow and solute transport in soil, irrigation and drainage design, groundwater modeling and other engineering or environmental processes. Due to the importance of Ks, many direct methods have been devel- oped for its measurement in the field and laboratory (Libardi et al., 1980; Klute and Dirksen, 1986). Comparative studies of the different methods have shown that their relative accuracy varies among different soil types and field conditions (Gupta et al., 1993; Paige and Hillel, 1993; Mallants et al., 1997). No single method has been developed which performs well in a wide range of circumstances and for all soil types (Zhang et al., 2007). Moreover, direct measurement techniques of Ks are costly and time consuming, and display large spatial variability which is problematic in hydrological modeling (Christiaens and Feyen, 2001; Islam et al., 2006). Consequently, indirect methods have been developed (Jabro, 1992; Schaap and Leij, 1998) allowing prediction of Ks from more easily measured soil properties, such as texture classes and organic matter content through empirical relations referred to as pedotransfer functions (PTFs). Bulk density BD (g/cm 3 ) is an essential parameter in many calcula- tions and models, and particularly BD is a predictor for estimating Ks in some Ks-PTFs. However, measuring the bulk density of the soil takes time and is difficult to achieve in some soils. As a confirmation, Drew (1973) observed that measuring BD is avoided in many studies where it should nevertheless be included. The BD of the soil is defined as the ratio between the mass of the soil sample dried in the oven and the apparent volume of the sample in situ. Values of BD are required for calculating the porosity of the soil (Blake and Hartge, 1986). The Catena 131 (2015) 99–108 ⁎ Corresponding author at: Laboratoire Géomatique et Foncier (GeF), Ecole supérieure des Géomètres et topographes (ESGT), Conservatoire national des arts et métiers (Le Cnam), 1 boulevard Pythagore, F-72000, Le Mans, France. E-mail address: behzad.nasri@cnam.fr (B. Nasri). http://dx.doi.org/10.1016/j.catena.2015.03.018 0341-8162/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena