Resistivity characteristics of organic soils under different water content and temperature conditions
Description
This dataset provides raw AC impedance measurements and derived electrical resistivity of an organic-matter-amended clay-rich soil under controlled temperature (including frozen states), water content, and organic-matter (OM) content. We hypothesize that soil resistivity is governed by the coupled effects of temperature/freezing, moisture level, and OM amendment, while compaction-induced porosity variability and exogenous water chemistry are minimized so that observed electrical differences primarily reflect the designed factors. A composite bulk soil sample was collected from 10 random points (20–50 cm depth) within a relatively uniform field site in Lintong District, Xi’an, China, homogenized in the laboratory, and characterized by basic physical properties, particle-size distribution, and qualitative XRD mineralogy (illite/kaolinite with quartz). Sycamore residues were dried, ground (<2 mm), and mixed into the soil at OM contents of 1%, 3%, 4%, and 5%, with target gravimetric water contents of 12%, 14%, 16%, and 18%. Specimens were compacted in a fixed-volume ring cutter (D = 61.8 mm, L = 20 mm), and representative mass checks confirm a narrow dry-density range (≈1.669–1.688 g/cm³), indicating consistent compaction among groups. A full-factorial design of 7 temperatures (10, 0, −3, −5, −10, −15, −20 °C) × 4 water contents × 4 OM contents was implemented (112 conditions), with two parallel compacted specimens tested per condition (n = 2; 224 specimens total). After isothermal equilibration (12 h at each target temperature), complex impedance was measured using a Tonghui TH2816A LCR meter at 1 kHz and 1.0 V with a two-plate electrode configuration (polished copper), OPEN/SHORT compensation, and controlled normal load. The raw outputs include the real and imaginary impedance components (R = Re(Z), X = Im(Z), in Ω) and the phase angle (φ, in degrees). Resistivity is calculated using the fixed specimen geometry as ρ = (S/L)·R = 0.15·R (Ω·m). The phase angles are consistently small and negative under the 1 kHz protocol, indicating that the response is predominantly resistive with limited reactive contribution, and contact/polarization effects are treated as part of measurement uncertainty. To aid interpretation of ionic-strength effects, electrical conductivity (EC) of 1:5 soil–water extracts was measured at 15 °C for representative OM levels (1% and 5%) with short-term repeatability checks (48 h), providing a comparable indicator of relative pore-water salinity among mixtures. The dataset can be used to quantify resistivity–temperature relationships across unfrozen and frozen conditions, evaluate the effects of moisture and OM amendment (and their interactions), and support empirical modeling or calibration/validation studies.
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Steps to reproduce
This dataset was generated by controlled preparation and AC impedance testing to quantify resistivity of organic-matter-amended clay soil under different temperatures (including frozen states), water contents, and OM contents. A composite bulk soil sample was collected from 10 random points (20–50 cm depth) in Lintong District, Xi’an, Shaanxi, China (June 2024), homogenized in the laboratory, and characterized (basic properties, particle size, qualitative XRD; reported in the manuscript). Sycamore residues were used as organic matter (OM). Soil was dried at 105 °C and OM at 50 °C for 12 h, then crushed and ground to <2 mm. Mixtures were prepared with OM contents of 1%, 3%, 4%, and 5% (by dry mass) and gravimetric water contents of 12%, 14%, 16%, and 18% using the same batch of distilled water. Each mixture was blended for 15 min, sealed, and equilibrated for 12 h. Specimens were compacted into ring-cutter cylinders (inner diameter 61.8 mm; height 20 mm; volume ≈59.99 cm³) using incremental placement and a hydraulic jack; ends were trimmed flush. Representative oven-dry mass checks at 105 °C (to constant mass) confirmed consistent dry density (Table 4). Samples were sealed and conditioned in a programmable freeze–thaw chamber at seven target temperatures (10, 0, −3, −5, −10, −15, −20 °C). At each temperature, specimens were held isothermally for 12 h before measurement; measurements were performed inside the chamber and completed within ~60 s. Complex impedance was measured using a Tonghui TH2816A LCR meter in R–X mode at 1 kHz and 1.0 V with polished copper plate electrodes (two-electrode contact). Electrodes were cleaned with anhydrous ethanol and OPEN/SHORT compensation was enabled; a constant normal load was applied, with representative load checks used to assess contact sensitivity (Table 6). Resistivity was derived from the resistive component using the fixed geometry: ρ = (S/L)·R = 0.15·R (Ω·m). The experimental design comprised 7 temperatures × 4 water contents × 4 OM contents (112 conditions), with two parallel specimens per condition (n=2), yielding 224 specimens total.