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The impacts of soils’ heterogeneity due to temporal (ET)- and seasonal (ES) changes from minute variations in precipitation (as rain, ice, and snow) and air temperatures (P+TA) on the ground-penetrating radar (GPR) responses (RGPR) are not rigorously tested. We aimed to understand how environmental changes (ET and ES) can be accountable to alter RGPR and help relate to real-time (TR) soil environmental status. Soil moisture (volumetric water content, VWC), temperature (TS), and electrical conductivity (EC) in every 30 min were recorded by soil sensors daily in different seasons to match the diurnal and seasonal changes. Readings of GPR alerts from six soil types of various GPR-suitability classes were recorded two to three times daily. Changes in P+TA, which changed physicochemical soil properties (PCSP) temporally and impacted RGPR up to 76%. The RGPR, which was negatively corelated with clay (R = –0.89) and organic matter (OM) (R = –0.91) percentages, remained low in soils when cation exchange capacity (CEC) is also high. The RGPR which were pronounced after rain, during fall, in sandy soils, and in case of neutral to basic pH impacted by narrow-range VWC variations on sandy but broad range on clay soils. Soils of same clay percent and similar OM acted differently if they have differential CEC and pH values. Ninety-six percent of RGPR, which is impacted by electric resistances and bonding nature of water and soils, were explainable if interactions of clay, OM, and VWC at TR are considered. Future insights on influences from freeze–thaw cycles and specific silica-mineral types of soils are required. [ABSTRACT FROM AUTHOR]

Understanding the spatial variability of soil texture within field soils is important due to its influence on a large number of soil and plant related processes and for site-specific application of inputs that are crucial to crop production. It remains a problem to obtain a reliable clay content map based on a limited number of sampling locations. The objective of this study was to identify spatial variability of soil clay content and the behavior of the estimation result for different spatial resolutions of measured clay content (0–20 cm depth) in combination with a coregionalization approach using apparent electrical conductivity (ECa). In a silty loam soil, soil clay content was measured at 96 points in a 50-m by 50-m grid within an agricultural field. ECa was measured using a contact sensor Veris 3150. Data were analyzed with ordinary kriging and cokriging while using ECa at a shallow depth. We analyzed different sampling scenarios based on clay subsamples of 48, 24, and 12 data points distributed over the 27-ha field. In all scenarios investigated here, the RMSE stayed in the range of 3 to 4% by using different validations, with cokriging performing constantly better than ordinary kriging. Clay content maps estimated with cokriging maintained a satisfactory precision when the sampling density was reduced to one sample per two hectares, a result that leads to the conclusion that electrical conductivity in combination with spatial coregionalization demonstrated to be a promising tool to estimate the spatial variation of clay content even at a low clay sampling density. [ABSTRACT FROM AUTHOR]

The shrinkage geometry factor connects the changes of subsidence and the total crack volume at the shrinkage of a soil layer matrix. An available approach for estimating the factor does not account for the crack volume in samples, the stretching of a shrinking soil layer, and a possible change of the factor with water content. A recent new approach for estimation of the factor enables one to account for the factor's dependence on water content and the impact of cracks in a sample. The present work also accounts for the stretching of a shrinking soil layer. Corrected value of the factor is described in terms of the shrinkage curves of: a layer including unconnected solid cubes from the available approach, a stretched layer with cracks, a sample with cracks, and the soil matrix without cracks. This correction leads to changes in the soil subsidence and total crack volume compared with those obtained from the available approach. Two known physical conditions are used: the specific soil matrix volume without cracks is the same for the sample and the layer, and, the matrix deformations of an unlimited shrinking soil layer are longitudinal those of a thin quasi-elastic plate. Two available experimental examples are considered. The former relates to clay paste samples. The latter relates to an aggregated clay soil in situ and in samples. The geometry factor from the available approach, and that obtained after correction, differ significantly. The corrected factor also shows the appreciable change with water content. [ABSTRACT FROM AUTHOR]

Sodium affected rice (Oryza sativa L.)-cropped fields are very common. Due to their high exchangeable Na percentage, clay dispersion is one of the major risks for these soils when they are flooded. During flooding, Fe2+ may become a major cation due to reductive dissolution of Fe oxides, but the flocculation effect of Fe2+ is not known. In this paper, the effect of Fe2+ on clay flocculation is studied by establishing critical coagulation concentration (CCC) curves of clays extracted from a paddy soil of Northeast Thailand. The effect of Na-Fe2+ and Na-Ca electrolytes on the CCC values is compared for sodium adsorption ratio (SAR) values ranging from 0 to 40 and total electrolyte concentration (TEC) ranging from 0.5 to 10 mmol L-1. The extracted day is a mixture of kaolinite and smectite but only the smectite and some poorly ordered kaolinite could be dispersed. The CCC values largely reflected the behavior of smectite, in agreement with previous studies. The CCC values were equal for electrolytes with Fe2+ or Ca2+ cations, suggesting that Fe2+ strongly adsorbs on smectite exchange sites and behaves similarly to Ca2+. The Fe2+ concentration needed to flocculate the clays was at maximum 0.6 mmol L-1 for the most dispersive electrolytes, which is a common concentration in flooded rice fields. Reductive dissolution of Fe can protect sodic soils from clay dispersion upon flooded rice cropping. [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]