APPLICATION OF GPS AND NEAR-SURFACE GEOPHYSICAL METHODSTO EVALUATE DIFFERENCES BETWEEN AGRICULTURAL TEST PLOTS

摘要

A field research facility with two pairs of replicated agricultural test plots (four total) wasestablished at a location in northwest Ohio during 2005 for the purpose of studying water tablemanagement strategies. Initial efforts at this field research facility were devoted to evaluatingdifferences between replicated test plots in regard to topography, subsurface drainage systemcharacteristics, and soil properties. Real-time kinematic (RTK) global positioning system (GPS)receivers along with ground penetrating radar and resistivity geophysical methods were employed toaccomplish this task. Real-time kinematic GPS was used to map topography, while also determiningcoordinates for soil sampling locations and some geophysics measurement locations. Groundpenetrating radar geophysical methods were employed to assess differences in subsurface drainagesystem characteristics. Spatial variations in soil properties were gauged by mapping apparent soilelectrical conductivity with resistivity methods. The RTK-GPS topographic survey found an elevationdifference of 1 m to exist across the four test plots. The ground penetrating radar survey found a 0.25 mdissimilarity in drainage pipe placement depth between two of the replicated test plots. Resistivitymethods clearly showed differences between replicated test plots with respect to average apparent soilelectrical conductivity values and the spatial patterns of apparent soil electrical conductivity. However,soil sample physical/chemical property data indicate that the apparent soil electrical conductivityresponse is itself governed by complex interactions of several soil properties. Overall, the GPS andnear-surface geophysical information obtained at this site provided valuable insight on test plotdissimilarities that may affect differences in the hydrologic response between replicated test plots.