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This study developed a comprehensive database of soil physical properties to expand the potential applications of soil moisture observations across the Kansas Mesonet environmental monitoring network. The database comprises 14 site‐ and depth‐specific soil hydraulic properties for 40 stations monitoring soil water content. The measured soil hydraulic properties include sand, clay, and silt contents; bulk density; particle density; total porosity; effective saturation; saturated hydraulic conductivity; and water retention at six matric potentials. The soil database spans eight soil textural classes, with silty clay loam, silt loam, and silty clay soils dominating the fine‐textured soils, and sandy loam and sandy clay loam soils comprising the only coarse‐textured soils. All the measured soil hydraulic properties showed low coefficient of variation (CV ≤10%) within soil textural classes, except for the saturated hydraulic conductivity, which varied from a median of 0.520 ± 308 cm d–1 in the clay soils to 47.1 ± 119 cm d–1 in the sandy loam soils. The uncertainty of the Kansas Mesonet soil water content observations was reduced by at least 29% using laboratory sensor calibration equations instead of the factory default sensor equation. Our soil physical property database offers new prospects to use historical and near real‐time in situ soil water content observations across the Kansas Mesonet for diverse agricultural and hydrological applications, including drought monitoring, wildfire preparedness, and estimating potential drainage and groundwater recharge rates. Core Ideas: This study developed a comprehensive soil physical property database for the Kansas Mesonet.The database comprises 14 site‐ and depth‐specific soil hydraulic properties for 40 stations.The soil database is dominated by fine‐textured soils with 92% of the soils having >20% clay content.Laboratory sensor calibration equations reduced the uncertainty of the water content measurements by at least 29%. [ABSTRACT FROM AUTHOR]

There is a need for improved knowledge of the limits to the available water range for root growth in the subsoil. The objective of this study was to recalculate the upper and lower limits of the least limiting water range (LLWR) concept by using respectively the air-filled porosity (εa) at which 0.005 of the relative gas diffusivity (Ds/Do) is reached and readily available water (RAW). The refined upper limit estimates the variation in εa related to pore connectivity and the refined lower limit expresses the boundary at which plants suffer physiological water stress. This study was based on soil sampled in compaction trials on two sandy loam soils. Soil samples were taken from plots with no compaction (Control), and compaction with 78 kN (M8) and 58 kN (M6) wheel loads with multiple wheel passes. The soil cores were analyzed for εa, Ds/Do, bulk density (rb) and penetration resistance (PR). Heavy farm machinery impact of M8 and M6 led to subsoil compaction up to depth of 0.5 to 0.7 m for the soils under study. The subsoil structure was affected by compaction across depths with the decrease in εa (~33-46%) and Ds/Do (~37-61%) and increase in rb (~4-8%) and PR (~40-50%, at -100 hPa at 30-cm depth). The refined LLWR showed a wider water range compared to the original approach. We anticipate that the refined LLWR well reflects the limiting soil physical conditions for root growth for the studied soils, but validation by combined soil physical and plant growth measurements is needed.

The increased use of soil moisture retrieval from satellites has heightened the need for improved accuracy of point measurements that are used to validate remotely sensed soil moisture products. A wide range of devices can be installed for operational monitoring of soil moisture; however, many of these devices have not been tested in situ in soils with a very high reactive clay content. The objective of this study was to evaluate the accuracy in field performance of five soil moisture sensors: the enviroSCAN probe, the Diviner 2000 (both from Sentek Technologies), the Hydra Probe soil sensor (Stevens Water Monitoring Systems), the Thetaprobe ML2x (Delta-T Devices), and the ECH2O EC-5 (decagon devices) in soils that had about 71% clay content. The instruments' default calibrations were tested against observed soil moisture from core samples using the thermogravimetric method. New calibration equations were developed for each device, which were evaluated using an independent data set. The ThetaProbe had the lowest root mean square error (RMSE) of 0.025 m³ m-3 and mean bias error (MBE) of 0.002 m³ m-3 in the precalibration analysis. Although the Hydra Probe showed the highest precalibration errors, the instrument made the greatest improvement in post-calibration analysis, with an RMSE of 0.129 m³ m-3 using the default equation reduced to 0.014 m³ m-3 using in situ calibration, and the 0.110 m³ m-3 MBE was reduced to 0 after applying in situ calibration. [ABSTRACT FROM AUTHOR]

Two standard tests for soil stability in water involve assessment of the readily dispersible clay (RDC) content of predried soil samples. It is shown that this predrying limits the applicability of the tests to very dry soils. Ways to avoid this limitation are developed. Undisturbed soil samples were collected from the 10-to 15-cm depth of arabic topsoils at Villamblain and Faux Perche and from the 0- to 5-cm depth from plowed and direct-drilled plots at Boigneville. These soils in north-central France were collected from the field when moist (near field capacity). A range of water contents and corresponding pore water potentials (or stictions h) was produced by slow drying in air. For moist soils at field capacity (h = 100 hPa) the amount of RDC was large. Readily dispersible clay decreased progressively with increasing antecedent suction, h. For soil samples dried to beyond h > 10 MPa, the RDC was reduced to small values. With such intensely dried soils, rewetting for up to 2 wk did not reverse the effect on RDC. At h = 4500 hPa, re-equilibration to h = 100 hPa reversed the effect of this moderate drying on RDC. Two standard conditions (moist and dry) are proposed for measurement of clay dispersion from soil into water. The moist condition is relevant to soil at the end of along, wet period (e.g., at the end of the winter in temperate climates), whereas the dry condition is relevant to dry surface crusts and dry topsoils. We conjecture that the soil "resets" during long, wet periods to values of stability and RDC at equilibrium with field capacity. Experimental procedures used to determine the content of RDC in moist and dry soils are described. [ABSTRACT FROM AUTHOR]

To understand the hydraulic properties of soils, accurate prediction of the unsaturated hydraulic conductivity is needed, which is commonly derived from the soil water release characteristic. In fine-textured soils, the modified Mualem-van Genuchten (MMVG) function has been used extensively to predict the change in relative conductivity with changes in matric potential, but this assumes that the soil is rigid with a constant porosity (CP), which is unrealistic for shrinking soils. We used a triaxial cell apparatus to accurately monitor soil volume changes during water release in a clay soil. From this we derived relative hydraulic conductivity functions based on either MMVG (CP), or based on geometrically similar shrinkage (GSS) of all pore sizes by a constant factor as calculated from the measured shrinking porosity (SP). The MMVG (CP) function predicted a decline in relative conductivity of up to three orders of magnitude from 0 to -400 kPa matric potential. This was similar to published data on the response of conductivity in the same soil to consolidation of larger pores. Based on SP, however, the soil remained effectively tension saturated (>0.97) down to a matric potential of-85 kPa due to normal shrinkage. The corresponding GSS (SP) function predicted only a modest decrease in relative conductivity from I to 0.85 across this range. In this case the larger pores, although reduced in size, are assumed to be still water filled and conducting. The GSS function was probably the most realistic portrayal of hydraulic functioning in a tensionsaturated shrinking clay soil. [ABSTRACT FROM AUTHOR]

Increasing precipitation storage as plant-available soil water increases dryland crop yields on the semiarid southern Great Plains. The dominant soil in this region is a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll), which features dense subsoil layers that limit infiltration and root proliferation. Deep (∼0.7 m) plowing may eliminate these layers, but the duration of treatment efficacy must be sufficient to recoup costs. Our objective was to quantify the long-term effects of deep plowing on soil bulk density (BD), penetration resistance (PR), ponded infiltration, and crop yield. In fall 1971, paired 24- by 460-m level conservation bench terrace plots at the USDA-ARS Conservation and Production Research Laboratory, Bushland, TX (35°11′ N, 102°5′ W) were moldboard plowed to 0.7 m or untreated and, subsequently, maintained with conventional sweep tillage. Grain sorghum [Sorghum bicolor (L.) Moench] was grown intermittently during the next 34 yr for 15 paired yield comparisons. Compared with the control, deep plowing significantly decreased BD and PR and increased water infiltration. Long-term mean grain yield of 2.86 Mg ha-1 with deep plowing was greater (P < 0.05) than the 2.61 Mg ha-1 yield in control plots. Approximately 89% of the 15-yr 3.75 Mg ha-1 cumulative yield increase with deep plowing occurred during 4 yr with large early growing season rains. We attributed this yield increase with deep plowing to greater internal drainage that reduced crop injury during infrequent floods and not greater root growth through the dense subsoil. Thirty years after deep plowing, high water intake suggests that flow-limiting subsoil layers had not yet redeveloped. The sustained deep-plowing benefit extends the period to recoup the 1971 plowing costs of US$160 ha-1. [ABSTRACT FROM AUTHOR]

Capacitance probe sensors are a popular electromagnetic method of measuring soil water content. However, there is concern about the influence of soil salinity on the sensor readings. In this study capacitance sensors are calibrated for a saline silty clay soil. An electric circuit model is used to relate the sensor's resonant frequency F to the permittivity (ε) of the soil. The circuit model is able to account for the effect of dielectric losses on the resonant frequency. Dielectric mixing models and empirical models are used to relate the permittivity to the soil water content (θ). The results show that the electric circuit model does not fit the F-ε(θ) data if the calibrated bulk electrical conductivity (EC) model is used. The dielectric losses are overestimated. Increasing the exponent c in the tortuosity factor of the bulk EC model and thereby lowering the bulk EC and the dielectric losses improves the performance of the model. Measured and calculated volumetric water contents compare reasonably well (R² = 0.884). However, only 73 out of 88 data points can be described. The rejected points are invariably at high water contents where the high dielectric losses result in the sensor frequency being insensitive to ε(θ). [ABSTRACT FROM AUTHOR]