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Enlightening Research

Introduction

Soil surveys require quick and, when possible, non-disturbing estimations of numerous soil properties, such as salinity, texture, stone content, groundwater depth, and horizon sequence in soil profiles; however, conducting soil measurements with a high sampling density is costly and time-consuming. Conventional methods of soil analysis mostly require disturbing soil, removing soil samples, and analyzing them in a laboratory.

Electrical geophysical methods, on the contrary, allow rapid measurement of soil electrical properties, such as electrical conductivity, resistivity, and potential, directly from soil surface to any depth without soil disturbance. The in situ methods of electrical conductivity (e.g. four-electrode probe and electromagnetic induction) are routinely used to evaluate soil salinity (Halvorson and Rhoades, 1976; Chang et al., 1983; Rhoades et al., 1989b). Some electrical geophysical methods were used to map groundwater tables (Arcone et al., 1998), preferential water flow paths (Freeland, 1997a), and perched water locations (Freeland, 1997b); to outline locations of landfills (Barker, 1990); and to evaluate water content, temperature, texture, and structure of soils. However, the relationships between electrical properties and other soil chemical and physical properties are very complex because many soil properties may simultaneously influence in situ measured electrical parameters (Rhoades et al., 1976b).

Despite the advantages of electrical geophysical methods, their applications to soil science problems are not straightforward and require thorough study. First, the theory about the nature of development and distribution of soil electrical fields, whose parameters are measured with the electrical geophysical methods, is still being developed (Pozdnyakov et al., 1996a; Pozdnyakova, 1999). Second, the equipment for geophysical methods of vertical electrical sounding, four-electrode profiling, ground-penetrating radar, etc. manufactured and readily available is not suited for measuring electrical properties in shallow (0-5 m) soil profiles. Finally, the in situ measurements of electrical parameters need a specific calibration in every study to be reliable to monitor and map different soil properties. To address the discussed problems, the objectives of this study were: (i) to study the basic law of electrophysics governing the electromagnetic fields in soils; (ii) to modify conventional electrical geophysical methods for measuring various electrical properties in soil studies; (iii) to establish relationships between measured electrical properties and other soil physical and chemical properties; (iv) to evaluate the influence of soil-forming processes on distributions of electrical properties in soil profiles; (v) to apply the modified electrical geophysical methods and the developed relationships for estimating spatial distribution of soil properties essential in soil surveys, precision agriculture practices, and environmental engineering.