Section IV

Resistivity and Electromagnetic Induction Case Histories

There has been a long history in agriculture regarding the use of geophysical methods to measure soil electrical conductivity, or its inverse, soil electrical resistivity. Two different geophysical methods, resistivity and electromagnetic induction, are employed for measuring in situ bulk soil electrical conductivity, which is commonly referred to as "apparent soil electrical conductivity" (ECa). An historical perspective on the agricultural use of geophysical methods to measure soil electrical conductivity can be found in Chapter 1, and to a far greater extent, in Chapter 2. Some theoretical considerations with respect to soil electrical conductivity are discussed in Chapter 4. Detailed descriptions of the resistivity and electromagnetic induction methods can be found in Chapters 5 and 6, respectively.

Initial geophysical ECa measurement efforts in agriculture were focused largely on soil moisture monitoring and salinity assessment. However, within the last fifteen years, there has been a dramatic increase in the number of different agricultural uses found for geophysical soil electrical conductivity measurement. Many of these more recent agricultural applications for resistivity and electromagnetic induction methods are documented within Section IV of this book. Chapters 11, 12, and 13 detail the spatial correlation between electromagnetic induction ECa and various soil properties. Capabilities for mapping pesticide partition coefficients with resistivity and electromagnetic induction methods are addressed by the Chapter 14 and Chapter 15 case histories. The employment of resistivity method ECa mapping to delineate management units, soil drainage classes, and productivity zones within agricultural fields are topics in Chapters 16, 17, and 18. Geophysical ECa measurement methods have additionally been utilized to monitor nutrient levels (Chapter 19), gauge uniformity and variability between research field plots (Chapter 20), and provide insight on subsurface features and conditions beneath golf course greens and tees (Chapter 21). The Chapter 22 case history compares results between resistivity and electromagnetic induction methods. These Section IV case histories list but a few of the potential geophysical ECa measurement applications in agriculture, and there are many more new uses likely to be discovered in the near future.

Apparent Electrical Conductivity for Delineating Spatial Variability in Soil Properties

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