Soil water content variability impacts crop productivity, irrigation management strategies, and natural resource management. To address the need for rapid, high-resolution mapping of field-scale soil water distributions, a time domain reflectometry (TDR) sled was developed and tested at a farm site in southwest GA. A surface probe was constructed by fitting three steel rods of square cross section into machined slots in a 2.5 cm slab of Delrin plastic. The probe was mounted on a steel frame and pulled across the soil surface immediately following plowing and cultivating to a depth of 20-25 cm. The soils were classified as Greenville sandy clay loam (fine, kaolinitic, thermic Rhodic Kandiudults). Proximate stationary and moving sled data were compared to conventional TDR probes that integrated depths of 0-2.5 cm, 0-20 cm, and 0-30 cm at 33 locations. The moving sled was used to obtain volumetric water content data at around 6 m intervals along parallel transects separated by about 30 m. These volumetric water content data were mapped using ordinary kriging and compared with 0.5 m elevation contours. The moving vs. stationary sled were in agreement and correlated linearly (R2 = 0.27). Correlations between sled and conventional measurements decreased with integration depth. The semi-variogram fit an exponential model with a range length of 119 m. Despite the narrow range of soil water content observed (0.043 to 0.097 m3m-3 at 0-2.5 cm), soil water appeared to be concentrated along low lying areas and drainage pathways. The system is capable of collecting soil water and global position data every four seconds. This initial evaluation suggests that the TDR sled shows promise as a tool to provide high-resolution estimates of soil water content variability at field scales.
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