Testing laboratory methods to determine the anisotropy of saturated hydraulic conductivity in a sandy–loam soil V. Bagarello ⁎, S. Sferlazza, A. Sgroi Dipartimento di Ingegneria e Tecnologie Agro-Forestali, Università degli Studi, Viale delle Scienze, 90128, Palermo, Italy abstract article info Article history: Received 30 December 2008 Received in revised form 18 September 2009 Accepted 28 September 2009 Available online 25 October 2009 Keywords: Saturated soil hydraulic conductivity Anisotropy Constant-head laboratory permeameter Anisotropy, a (the log of the ratio of horizontal to vertical conductivity, log 10 (K h /K v )), of saturated soil hydraulic conductivity, K s , affects transport processes in soil but is not routinely measured, probably because practical and validated methods are lacking. The objective of this investigation was to determine the effects of different constant-head laboratory and sampling procedures on anisotropy of saturated hydraulic conductivity measurements. The sequence of K s measurements was varied (vertical conductivity, K v , first, then horizontal, K h , second and vice versa) for an experimental set-up considering five variables: 1) water ponding type (Mariotte or siphon); 2) saturation state prior to experiment start (unsaturated or saturated); 3) experiment duration (long or short); 4) sample geometry or extraction (cube or core); and 5) sample volume. The Mariotte, unsaturated/saturated, long experiment for a single soil cube resulted in unreliable mean anisotropy results, where a differed in sign. Generally, the sequence of measurements had a negligible impact on a for a siphon, saturated, short experiment for a soil cube. Furthermore, different a were obtained by varying the undisturbed soil sample collection procedure (cube vs. core). The conclusion of this investigation was that using a siphon and a short-duration run on an initially saturated cube of soil encased in foam is generally expected to yield reliable bi-directional K s results. However, a check of the independence of the estimated anisotropy on the order of measurements for the sampled soil is recommended. An alternative procedure to determine a mean anisotropy for an area of interest would be to measure K v and K h on different soil cubes. Finally, the ratio between the mean K h and K v results varied from a not statistically significant factor of 1.02 to a statistically significant factor of 1.95 during the one-year investigation period (five sampling dates). Therefore, anisotropy of this sandy–loam soil varied with time but it was always low or negligible. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The hydraulic conductivity of saturated soil, K s , is one of the most important soil properties controlling many hydrological processes. This property depends on soil texture, particle arrangement, and structure and can vary in space, time, and flow direction. In anisotropic soils, the vertical saturated hydraulic conductivity, K v , of a given volume of soil differs from the horizontal saturated conductivity, K h , of the same volume of soil (Beckwith et al., 2003). The anisotropy of K s has been measured for peat (Chason and Siegel, 1986; Schlotzhauer and Price, 1999; Beckwith et al., 2003; Surridge et al., 2005) and mineral soils (Bouma and Dekker, 1981; Dabney and Selim, 1987; Bathke and Cassel, 1991; Caris and Van Asch, 1991). However, anisotropy is not routinely determined because practical and validated methods are still lacking. Furthermore, anisotropy of K s may change with time (Petersen et al., 2008), but data on temporal variability of anisotropy is scarce. The constant-head laboratory permeameter (CHP) method (Klute and Dirksen, 1986) is widely used for measuring K s . There are two primary methods for obtaining undisturbed soil samples: 1) Two-Core Method (TCM, Dabney and Selim, 1987; Bathke and Cassel, 1991; Dörner and Horn, 2006; Petersen et al., 2008) and 2) Cube Method (CM, Bouma and Dekker, 1981) or Modified Cube Method (MCM, Beckwith et al., 2003). Anisotropy measured on soils extracted using TCM involves measuring K v and K h on two different samples where cylinders in both the vertical and the horizontal direction are pushed into exposed soil surfaces. On the other hand, CM and MCM measure K v and K h on a single soil sample where the soil sample is obtained by carving a soil cube in situ by gently removing soil along its sides. With CM, all except two opposing cube faces are encased in a slurry of gypsum. When the gypsum is cured, the soil cube encased in gypsum is removed from the pit and water flow rates through open sides are measured in the laboratory, yielding a measurement of K v . The faces are then sealed with gypsum and the cube is rotated. Two faces at right angle to the original Geoderma 154 (2009) 52–58 ⁎ Corresponding author. E-mail address: bagav@unipa.it (V. Bagarello). 0016-7061/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2009.09.012 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma