Geoscience Reference
In-Depth Information
4
Theoretical Insight on
the Measurement of Soil
Electrical Conductivity
Dennis L. Corwin, Scott M. Lesch, and Hamid J. Farahani
ContentS
4.1 Introduction ........................................................................................................................... 59
4.1.1 Background: Definition and Brief History of Soil Electrical Conductivity .............. 60
4.1.2 Misconceptions Surrounding the Apparent Soil Electrical Conductivity (EC
a
)
Measurement..............................................................................................................64
4.2 Basic Principles and Theory of EC
a
...................................................................................... 66
4.3 Guidelines for Conducting a Field-Scale EC
a
-Directed Soil Sampling Survey for
Agriculture ............................................................................................................................ 69
4.3.1 EC
a
-Directed Soil Sample Design ............................................................................. 69
4.3.2 Calibration of EC
a
to Soil Properties......................................................................... 71
4.3.3 Determination of the Soil Properties Influencing EC
a
.............................................. 72
4.3.4 Case Studies ............................................................................................................... 74
4.3.4.1 Coachella Valley Wheat (Triticum aestvum L.) Field.................................. 74
4.3.4.2 Coachella Valley Sorghum Field .................................................................. 74
4.3.4.3 Broadview Water District (Quarter Sections 16-2 and 16-3)........................ 74
4.3.4.4 Fresno Cotton (Gossypium hirsutum L.) Field............................................. 74
4.3.4.5 Coachella Valley—Kohl Ranch Field .......................................................... 76
4.3.4.6 Broadview Water District (Quarter Section 10-2) ........................................ 76
4.4 Closing Remarks ................................................................................................................... 77
References ........................................................................................................................................ 77
4.1 IntRodUCtIon
Due in large measure to the research that has been conducted at the U.S. Department of Agricul-
ture-Agricultural Research Service (USDA-ARS) United States Salinity Laboratory over the past
50 years, the measurement of electrical conductivity (EC) has become a standard soil physicochem-
ical measurement both in the laboratory and in the field to address agricultural and environmental
concerns. In particular, the geospatial measurement of EC with geophysical techniques, including
electrical resistivity (ER), electromagnetic induction (EMI), and time domain reflectometry (TDR),
has burgeoned into one of the most useful field agricultural measurements, particularly for spatially
characterizing the variability of soil properties such as salinity, water content, and texture (Corwin,
2005).
The value of spatial measurements of soil EC to agriculture is widely acknowledged due to its
ability to characterize spatial variability, with applications in solute transport modeling at field and
landscape scales (Corwin et al., 1999), salinity mapping and assessment (Corwin et al., 2003a),
mapping soil texture (Doolittle et al., 2002) and soil type (Anderson-Cook et al., 2002; Jaynes et al.,
59
