Soils play a critical role in the cycling of water, energy, and carbon in the Earth system. Until recently, due primarily to a lack of soil property maps of a sufficiently high‐quality and spatial detail, a minor emphasis has been placed on providing high‐resolution measured soil parameter estimates for land surface models and hydrologic models. This study introduces Probabilistic Remapping of SSURGO (POLARIS) soil properties—a database of 30‐m probabilistic soil property maps over the contiguous United States (CONUS). The mapped variables over CONUS include soil texture, organic matter, pH, saturated hydraulic conductivity, Brooks‐Corey and Van Genuchten water retention curve parameters, bulk density, and saturated water content. POLARIS soil properties was assembled by (1) depth harmonizing and aggregating the pedons in the National Cooperative Soil Survey Soil Characterization Database and the components in Soil Survey Geographic Database into a database of 21,481 different soil series, each soil series having its own vertical profiles of different soil properties, (2) pruning the original POLARIS soil series maps using conventional soil maps to improve soil series prediction accuracy, and (3) merging the assembled soil series databases with the pruned POLARIS soil series maps to construct the soil property maps over CONUS. POLARIS soil properties includes 100‐bin histograms for each layer and variable per grid cell and a series of summary statistics at 30‐, 300‐, and 3,000‐m spatial resolution. Evaluation of POLARIS soil properties using in situ measurements shows an average R2 of 0.41, normalized root‐mean‐square error of 12%, and a normalized mean absolute error of 8.8%.

Soil hydraulic parameters used in estimating soil water and energy fluxes are included in a lookup table in the Noah Land Surface Model (LSM). The purpose of the study was to examine the Noah default soil hydraulic parameters and compare them to soil measurements across Texas, USA. These default soil parameters were compared to measured soil properties from a soil database including 6,749 soil samples located within and around Texas. Mean differences between measured and default soil parameters were tested using a t-test (α = 0.05). To assess the proposed changes to default soil parameters, water retention curves were created using updated parameters and compared to measured soil moisture content at field capacity (θ fc) and permanent wilting point (θ wp). Spatial trends across major land resource areas in Texas were also demonstrated for water retention parameters. Our findings indicate that 95% of the default soil parameters were significantly different from the region-specific measured values. Measured soil water content at air-dry, θ wp , and θ fc are better replacements than default values. Consequent changes in θ wp and θ fc yielded a 35 to 76% decrease in plant available water compared to default. Updated water retention curves showed improved agreement between estimated soil water and measured values in 95% of cases. For three texture classes, the standard deviations of parameters for water retention parameters ranged 30% for the slope of the water retention curve and 65% for saturated hydraulic conductivity. These results indicate the importance of accounting for spatial variability of soil parameters rather than combining these parameters into texture classes alone. The revised parameter table improves modeling of soil hydraulic properties. Ultimately spatially distributed databases of hydraulic soil parameters will better capture variability and spatial structure of soil processes modeled by Noah LSM.

Switchgrass (Panicum virgatum L.) and biomass sorghum (Sorghum bicolor L. Moench) are two candidate bioenergy crops for the US Southern Great Plains region. In this water-limited region, there is a need to partition evapotranspiration (ET) and to determine the water use efficiency (WUE) of these potential feedstocks. Both crops were grown in a field plot experiment at Stillwater, OK. Soil water content measurements were made by neutron probe every two weeks to a depth of 2.0 m in 0.2-m intervals over the course of three growing seasons. Growing season ET was estimated as the difference between growing season precipitation and change in root zone soil water storage. Evapotranspiration was partitioned by measuring canopy interception using interception trays and estimating soil evaporation using the FAO-56 dual crop coefficient method. Transpiration was calculated as ET minus soil evaporation and canopy interception. Transpiration was the largest component of ET; however, soil evaporation and canopy interception accounted for 28% of growing season ET for switchgrass and 42% for biomass sorghum. Although the non-productive losses were greater from biomass sorghum, WUE values of 9-49 kg ha-1 mm-1 based on ET and 22-83 kg ha-1 mm-1 based on transpiration were observed for biomass sorghum, which were greater than the WUE values of switchgrass, 8-21 kg ha-1 mm-1 based on ET and 12-28 kg ha-1 mm-1 based on transpiration. These results demonstrate that biomass sorghum is a candidate feedstock with potential to achieve greater WUE than switchgrass at this location; however, other factors such as economics and ecosystem services should also be considered.

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Understanding soil water dynamics and evapotranspiration (ET) is imperative to predict the interactions between bioenergy cropping systems and water resources; yet measurements of these variables under bioenergy crops in the U.S. Southern Great Plains (SGP) are limited. The objectives of this study were to quantify and compare soil water dynamics and ET under switchgrass (Panicum virgatum L.), biomass sorghum [Sorghum bicolor (L.) Moench], and mixed perennial grasses managed for biofuel production. Soil water content was measured from 2011 through 2013 at Stillwater, OK, and from 2012 through 2013 at Chickasha, OK, and ET was estimated using the soil water balance approach. For these crops, soil water depletion occurred mainly above the 2.0‐m depth, suggesting negligible root water uptake below 2.0 m. Growing season soil water depletion ranged from 4 to 287 mm and was greater (α = 0.10) for sorghum than switchgrass in 2 out of 5 site‐yr, while mixed grasses exhibited the greatest soil water depletion in 1 out of 3 yr. Growing season soil water depletion was positively related to initial soil water content. Crop year ET ranged from 493 to 846 mm and was greater for switchgrass than sorghum in 2 out of 3 site‐yr. At Stillwater, average crop year ET measured for 2 yr was 676 mm for switchgrass, 630 mm for sorghum, and 717 mm for mixed grasses. In the SGP, rainfed bioenergy production systems based on biomass sorghum may consume less water per unit land area than systems based on perennial grasses.