Geophysical methods continue to show great promise for use in agriculture. The term "agricultural geophysics" denotes a subdiscipline of geophysics that is focused only on agricultural applications. As this geophysics subdiscipline becomes better established, there may come a time when a contracted name becomes appropriate, such as "agrigeophysics;" however, for this book, the more recognized term, "agricultural geophysics" will be used predominantly. Potential agricultural applications for geophysical methods are widespread and include precision agriculture, site infrastructure assessment, hydrologic monitoring, and environmental investigations. For example, changes in soil electrical conductivity measured across a farm field using geophysical methods may reflect spatial variability in soil properties, and this information can in turn be used along with precision agriculture techniques to ensure that the right quantity of fertilizer is applied to different parts of the field. In cases where placement records have been lost, ground-penetrating radar can be employed to locate and map buried agricultural drainage pipes. Geophysical measurements can be affected by the amount of water within soil, thereby allowing assessment of shallow hydrologic conditions. Geophysical methods could also be used in an environmental investigation to determine if there are leaks present in animal waste storage ponds or treatment lagoons.

The Handbook of Agricultural Geophysics was compiled to include a concise overview of the geophysical methods that can be utilized in agriculture and provides detailed descriptions of situations in which these techniques have been employed. The book is divided into four sections, with the first section devoted to both a general introduction of agricultural geophysics (Chapter 1) and a summary of past applications of geophysical methods to agriculture (Chapters 2 and 3). The second section systematically describes the three geophysical methods now most commonly employed: resistivity (Chapter 5), electromagnetic induction (Chapter 6), and ground-penetrating radar (Chapter 7). The second section also presents some theoretical insight on soil electrical conductivity measurement (Chapter 4) and describes, although in limited detail, three geophysical methods not typically used for agriculture but possibly having more widespread future application: magnetom-etry, self-potential, and seismic (Chapter 8). The Global Positioning System (GPS) and geographic information systems (GISs) are revolutionizing the way geophysical data are acquired and analyzed, and therefore warrant separate discussion in the third section of the book (Chapters 9 and 10). Agricultural geophysics case histories comprise roughly half the book. The resistivity and electromagnetic induction method case histories are included in Section IV (Chapters 11-22). The ground-penetrating radar method case histories are found in Section V (Chapters 23-30). The value of these case histories is that they document a wide range of scenarios in which geophysical methods have been successfully employed, thereby giving the reader an indication as to the potential effectiveness of using agricultural geophysics for their particular purpose.

Geophysicists will undoubtedly be very knowledgeable regarding most of the material presented within the first two, and probably, the third sections of this book. Although not the intended audience, geophysicists who are unfamiliar with geophysical applications to agriculture may have an interest in the case histories presented within the last two sections of the book. The primary audience for the Handbook of Agricultural Geophysics is expected to be quite diverse and include government agency personnel, university agricultural researchers, and agricultural and environmental consultants. To meet the growing demands of the intended audience, the book has been written specifically for those working in agriculture who need to use geophysical tools for gathering valuable information to solve problems. The reader of this book is therefore not expected to have a strong background in geophysics, and as such, when theoretical aspects are introduced, they are described, as much as possible, in an easy to understand manner. Furthermore, throughout the book, emphasis is placed on practical considerations regarding the application of geophysical methods to agriculture.*

Barry J. Allred M. Reza Ehsani Jeffrey J. Daniels

* Note: The use of product names throughout the book is for informational purposes only and does not imply endorsement by the editors or the organizations they represent.

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