A hardpan, which is a dense soil layer near the ground surface, is an undesirable feature of many soils in the Southeast U.S., especially sandy Coastal Plain soils. Shallow hardpans restrict root growth and water penetration through the soil profile, in turn reducing the effective crop root zone and thereby limiting crop production. Knowledge of hardpan existence, depth, and spatial extent is valuable, and can be used by farmers to improve soil, water, and crop management. This hardpan problem is similar to challenges faced with claypan soils in the Midwest U.S. (i.e., Missouri), where electromagnetic induction (EMI) geophysical methods have been successfully tested by investigators for determining claypan depth and spatial extent. Consequently, near-surface geophysical methods may also supply useful information on hardpan depth and spatial extent. Three near-surface geophysical methods were therefore tested on a hardpan present in an agricultural field near Blackville, South Carolina. The three near-surface geophysical methods evaluated were; 1) apparent soil electrical conductivity (ECa) mapping of the top 0.3 m and 0.9 m of the soil profile using an on-the-go resistivity measurement system, 2) ECa mapping of the top 0.75 m and 1.5 m of the soil profile using EMI, and 3) subsurface imaging using ground-penetrating radar at three different antenna frequencies. Near-surface geophysical results were then compared to cone penetrometer measurements and analysis of soil samples to determine the strengths and weaknesses of each near-surface geophysical method for providing insight on hardpans within agricultural settings.


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