Physics of the soil medium organization part 2: pedostructure characterization through measurement and modeling of the soil moisture characteristic curves

Amjad T Assi,Joshua Accola,Gaghik Hovhannissian,Rabi H Mohtar,Erik Braudeau

doi:10.3389/fenvs.2014.00005

Abstract

Accurate measurement of the two soil moisture characteristic curves, namely, water retention curve (WRC) and soil shrinkage curve (SSC) is fundamental for the physical modeling of hydrostructural processes in vadose zone. This paper is the application part following the theory presented in part I about physics of soil medium organization. Two native Aridisols in the state of Qatar named locally Rodah raod´ə soil and Sabkha sab′kə soil were studied. The paper concluded two main results: the first one is about the importance of having continuous and simultaneous measurement of soil water content, water potential and volume change. Such measurement is imperative for accurate and consistent characterization of each of the two moisture characteristic curves, and consequently the hydrostructural properties of the soil medium. The second is about the simplicity, reliability, strength and uniqueness of identifying the characteristic parameters of the two curves. The results also confirmed the validity of the thermodynamic-based equations of the two characteristic curves presented in part I.

Highlights

The hydrostructural properties of a structured soil medium have been characterized by two fundamental curves: water retention curve (WRC) and the soil shrinkage curve (SSC)
Compared with the existing studies, this study presents three new issues regarding to: the type of the studied soil; the apparatus used for measuring the WRC and SSC, and the models used for both WRC and SSC
THE MEASURED WATER RETENTION AND SOIL SHRINKAGE CURVES The continuous and simultaneous measurements of the WRCs and SSCs for reconstituted and undisturbed Rodah soil samples are shown in Figure 6, while Figure 7 shows the measurements for the reconstituted and undisturbed Sabkha soil samples

Summary

Introduction

The hydrostructural properties of a structured soil medium have been characterized by two fundamental curves: water retention curve (WRC) and the soil shrinkage curve (SSC). In the rubber balloon method, reconstituted soil cores were used in most studies (Tariq and Durnford, 1993a; Cornelis et al, 2006) In this approach, the soil samples were submerged into water and the change in the sample volume was determined from the volume of displaced fluid; (ii) physical measurement-based approach: where the soil cores “disturbed or undisturbed” dimensions were measured directly using a vernier caliper (Berndt and Coughlan, 1977; Huang et al, 2011), a linear displacement transducer (Boivin et al, 2004; Braudeau and Mohtar, 2004) or a thin metal stick (Kim et al, 1992); (iii) laser sensors-based approach: where the soil core diameter and height were determined through laser beams such as the retractometer apparatus (Braudeau et al, 1999), (iv) imagebased approach: where the volume of the soil sample (either clod or core) was either scanned with a 3-D optical scanner (Sander and Gerke, 2007) or by a simple standard digital camera (Stewart et al, 2012). Several studies have discussed and compared these methods, Cornelis et al (2006) showed that there www.frontiersin.org

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Conclusion