The dual‐probe heat‐pulse (DPHP) method provides a means of estimating volumetric soil water content (θ) and change in volumetric water content (Δθ) from measurements of volumetric heat capacity. The purpose of this investigation was to characterize the accuracy and precision that can be achieved in measuring θ and Δθ with the DPHP method. Tempe pressure cells fitted with DPHP sensors were used to conduct desorption experiments in which DPHP‐based estimates of θ and Δθ were compared with values estimated by the gravimetric method. For water contents corresponding to soil water pressure potentials below −100 kPa, comparisons were made by packing the pressure cells with soil wetted to known water contents. The investigation was conducted with seven soil materials representing a wide range of physical properties for mineral soils. The DPHP sensors slightly overestimated θ at low water contents, but it was shown that the bias could be removed by using an empirical calibration equation, θ = 1.09 θDPHP − 0.045. This relationship appears to be general inasmuch as it was shown to be applicable for all seven soil materials and for water contents ranging from 0.02 to 0.59 m3 m−3 The general calibration equation was also shown to be effective in removing bias in Δθ estimates. Pooled regression analysis (all soil materials) showed that θ can be measured with a root mean square error (RMSE) of 0.022 m3 m−3 Greater precision can be achieved with Δθ measurements (RMSE = 0.012 m3 m−3); however, the results indicated a decrease in precision with increasing magnitude of Δθ.

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Soil erosion from agricultural fields is a fundamental water quality and quantity concern throughout the U.S. Watershed models can help target general areas where soil conservation measures are needed, but they have been less effective at making field-level recommendations. The objectives of this study were to demonstrate a method of field-scale targeting using ArcSWAT and to assess the impact of topography, soil, land use, and land management source data on field-scale targeting results. The study was implemented in Black Kettle Creek watershed (7,818 ha) in south-central Kansas. An ArcGIS toolbar was developed to post-process SWAT hydrologic response unit (HRU) output to generate sediment yields for individual fields. The relative impact of each input data source on field-level targeting was assessed by comparing ranked lists of fields on the basis of modeled sediment-yield density (Mg ha-1) from each data-source scenario. Baseline data of field-reconnaissance land use and management were compared to NASS and NLCD data, 10 m DEM topography were compared to 30 m, and SSURGO soil data were compared to STATSGO. Misclassification of cropland as pasture by NASS and aggregation of all cropland types to a single category by NLCD led to as much as 75% and 82% disagreement, respectively, in fields identified as having the greatest sediment-yield densities. Neither NASS nor NLCD data include land management data (such as terraces, contour farming, or no-till), but such inclusion changed targeted fields by as much as 71%. Impacts of 10 m versus 30 m DEM topographic data and STATSGO versus SSURGO soil data altered the fields targeted as having the highest sediment-yield densities to a lesser extent (about 10% to 25%). SWAT results post-processed to field boundaries were demonstrated to be useful for field-scale targeting. However, use of incorrect source data directly translated into incorrect field-level sediment-yield ranking, and thus incorrect field targeting. Sensitivity was greatest for land use data source, followed closely by inclusion of land management practices, with less sensitivity to topographic and soil data sources.