Success with Geophysics FastTIMES welcomes short articles on applications of geophysics to the near surface in many disciplines, including engineering and environmental problems, geology, soil science, hydrology, archaeology, and astronomy. In the articles that follow, the authors present the latest application of geophysical techniques to improve agricultural processes.
Application of GPS and Near-Surface Geophysical Methods to Evaluate Agricultural Test Plot Differences by Barry Allred, USDA/ARS, Soil Drainage Research Unit, Columbus, OH (barry.allred@ars.usda.gov), Bruce Clevenger, Ohio State University, OSU Agricultural Extension, Defiance, OH, and Dharmendra Saraswat, University of Arkansas, Department of Biological and Agricultural Engineering, Little Rock, AR.
Introduction Surface elevation measurements obtained using real-time kinematic (RTK) global positioning system (GPS) receivers and near-surface geophysical surveys can provide important information on topography, buried infrastructure, and soil properties within agricultural settings. This article describes the use of RTK-GPS and near-surface geophysical methods to determine differences between test plots at a agricultural field research facility. The study conducted at this site provides a good example of how RTK-GPS and near-surface geophysics can be employed to characterize farm fields. The field research facility itself is located in northwest Ohio near the Defiance town airport, and it is being used to evaluate the impacts on crop yield and water quality due to different shallow water table management strategies. Shallow water tables are controlled at the site with subsurface drainage pipe networks that have integrated hydraulic control structures. The decision to construct this research facility was due largely to an airport expansion that encroached on northern portions of pre-existing test plots. Much of the subsurface drainage pipe infrastructure was already in place, and with limited modifications a research facility was built having two pairs of replicated test plots (four total). All four test plots have an area of 1 hectare. The drainage pipe infrastructure, based on construction reports, was expected to be the same for both test plots within a replicated pair of test plots. The drainage pipe infrastructure characteristics described in both the older and also more recent construction reports are listed as follows: Test Plot 2 – drainage pipe diameter = 5 cm; drain line spacing distance = 3 and 6 m; drainage pipe depth = 0.51 to 0.61 m. Test Plot 3 – drainage pipe diameter = 10 cm; drain line spacing distance = 6 and 12 m; drainage pipe depth = 0.76 to 0.91 m. Test Plot 4 – drainage pipe diameter = 5 cm; drain line spacing distance = 3 and 6 m; drainage pipe depth = 0.51 to 0.61 m. (Same as Test Plot 2.) Test Plot 5 – drainage pipe diameter = 10 cm; drain line spacing distance = 6 and 12 m; drainage pipe depth = 0.76 to 0.91 m. (Same as Test Plot 3.) Test Plots 2 and 4 are a replicated pair, and likewise, Test Plots 3 and 5 are a replicated pair. Every test plot is divided into two water table management zones, with each water table management zone having its own hydraulic control structure and drainage pipe system. Figure 1 is a schematic of the facility showing drainage pipe, main conveyance pipe, and hydraulic control structure locations.
FastTIMES v. 14, no. 3, September 2009
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