The thermal conductivity and water content relationship is required for quantitative study of heat and water transfer processes in saturated and unsaturated soils. In this study, we developed an improved model that describes the relationship between thermal conductivity and volumetric water content of soils. With our new model, soil thermal conductivity can be estimated using soil bulk density, sand (or quartz) fraction, and water content. The new model was first calibrated using measured thermal conductivity from eight soils. As a first step in validation, predicted thermal conductivity with the calibrated model was compared with measured thermal conductivity on four additional soils. Except for the sand, the root mean square error (RMSE) of the new model ranged from 0.040 to 0.079 W m−1 K−1, considerably less than that of the Johansen model (0.073–0.203 W m−1 K−1) or the Côté and Konrad model (0.100–0.174 W m−1 K−1). A second validation test was performed by comparing the three models with literature data that were mostly used by Johansen and Côté and Konrad to establish their models. The RMSEs of the new model, the Johansen model, and the Côté and Konrad model were 0.176, 0.176, and 0.177 W m−1 K−1, respectively. The results show that the new model provided accurate approximations of soil thermal conductivity for a wide range of soils. All of the models tested demonstrated sensitivity to the quartz fraction of coarse‐textured soils.

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Soil organic carbon (SOC) and its labile fractions are strong determinants of chemical, physical, and biological properties, and soil quality. Thus, a 15-year experiment was established to assess how diverse soil fertility management treatments for winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) cropping system affect SOC and total N (TN) concentrations in the North China Plain. The field experiment included three treatments: (1) unfertilized control (CK); (2) inorganic fertilizers (INF); and (3) farmyard manure (FYM). Concentrations of SOC, TN, and different labile SOC fractions were evaluated to 1-m depth. In comparison with INF and CK, FYM significantly increased SOC and TN concentrations in the 0-30 cm depth, and also those of dissolved organic C (DOC), microbial biomass C (MBC), hot-water extractable C (HWC), permanganate oxidizable C (KMnO 4 -C), and particulate organic C (POC) in the 0-20 cm depth. Despite the higher crop yields over CK, application of INF neither increased the SOC nor the labile C fractions, suggesting that by itself INF is not a significant factor affecting SOC sequestration. Yet, POC (18.0-45.8% of SOC) and HWC (2.0-2.8%) were the most sensitive fractions affected by applications of FYM. Significantly positive correlations were observed between SOC and labile organic C fractions in the 0-20 cm depth. The data support the conclusion that, wherever feasible and practical, application of FYM is important to soil C sequestration and improving soil quality under a wheat/maize system in the North China Plain.

Time-domain reflectometry (TDR) is increasingly used for field soil water estimation because the measurement is nondestructive and less affected by soil texture, bulk density and temperature. However, with the increase in instrument resolution, the influences of soil bulk density and temperature on TDR soil moisture measurements have been reported. The influence is primarily caused by changes in soil and water dielectric permittivity when soil compaction and temperature varies. The objective of this study is to quantify the influence of soil bulk density and temperature, and to provide the corresponding correction methods. Data collected from sand, sandy loam, loam and clay loam show a linear relationship between the square root of dielectric constant of dry soil and bulk density, and a bulk density correction formula has been developed. The dielectric permittivity of soil solids estimated using this formula is close to that of oxides of aluminium, silicon, magnesium and calcium. Data collection from sandy loam show a noticeable decrease in measured soil moisture with increase in temperature when the volumetric soil water content is above 0Ð30 m 3 m 3 . A temperature-correction equation has been developed, which could provide the corrected soil moisture based on soil temperature and TDR-measured moisture. The effect of clay content has been detected, but it is not statistically significant. High clay contents cause the underestimation of soil water content in the low moisture range and overestimation of soil water content in the high moisture range.

Measuring a soil water retention curve (SWRC) with the pressure plate device is generally limited to matric suctions ≤1500 kPa. A few models have been proposed to describe the SWRC from saturation to oven dryness using measurements in the pressure plate matric suction range. The development and validation of these models were mostly based on a limited set of published measurements, and in general, the models have not been validated by independent data from additional soils. In this study, we tested the hypothesis that these models were able to predict the complete SWRC from a limited range of water retention data or by using water retention parameters available from the literature. Soil water retention measurements from saturation to oven dryness were conducted on disturbed, repacked soil samples of various textures using the pressure plate method and the dew point potential technique. When the model parameters were obtained from water retention data in the 0 to 1500 kPa range, the RMSE of water content was approximately 0.01. The RMSE of the Fayer–Simmons model was slightly larger than that of the Webb model and Khlosi model. In addition, the Fayer–Simmons model was sensitive to the data point near the matric suction of 1500 kPa. The Khlosi model produced acceptable results if data sets from 0 to 500 kPa were used for model establishment; larger errors were observed on some soils if the measured data were limited to the 0‐ to 100‐kPa range. All three models could provide reliable results across the entire range of soil water content if measurements in the 0‐ to 1500‐kPa range were available.

The main distresses of asphalt pavements in seasonal frozen regions are due to the effects of water action, freeze-thaw cycles, traffic, and so on. Fibers are usually used to reinforce asphalt mixtures, in order to improve its mechanical properties. Basalt fiber is an eco-friendly mineral fiber with high mechanical performance, low water absorption, and an appropriate temperature range. This paper aims to address the freeze-thaw damage characteristics of asphalt mixtures (AC-13) reinforced with eco-friendly basalt fiber, with a length of 6 mm. Based on the Marshall design method and ordinary pavement performances, including rutting resistance, anti-cracking, and moisture stability, the optimum asphalt and basalt fiber contents were determined. Test results indicated that the pavement performances of asphalt mixture exhibited a trend of first increasing and then deceasing, with the basalt fiber content. Subsequently, asphalt mixtures with a basalt fiber content of 0.4% were prepared for further freeze-thaw tests. Through the comparative analysis of air voids, splitting strength, and indirect tensile stiffness modulus, it could be found that the performances of asphalt mixtures gradually declined with freeze-thaw cycles and basalt fiber had positive effects on the freeze-thaw resistance. This paper can be used as a reference for further investigation on the freeze-thaw damage model of asphalt mixtures with basalt fiber.

Due to the negative effects that derive from large impervious surfaces in urban areas, pervious concrete has been developed, and has become an environmentally friendly pavement material. As a porous and permeable material, pervious concrete presents an overwhelming advantage in solving urban problems, such as flooding, groundwater decline, urban heat island phenomena, etc. Waste crumb rubber has been verified as a feasible modifier for pavement material. The objective of this paper is to explore the effects of rubber particle size and incorporation level on the permeability, mechanical properties, and freeze–thaw resistance of pervious concrete. Two kinds of rubbers (fine and coarse) with four incorporation levels (2%, 4%, 6%, and 8%) are used in the experiment. Permeability, compressive strength, flexural strength, flexural strain, and freeze–thaw resistance are tested. The results indicate that the addition of rubber slightly decreases strength and permeability, but significantly enhances ductility and freeze-thaw resistance. Fine crumb rubber with a suitable incorporation level could remarkably improve the ductility and freeze–thaw resistance of pervious concrete without sacrificing excessively strength and permeability.

multiplexed TDR systems (Baker and Allmaras, 1990; Heimovaara and Bouten, 1990;Herkelrath et al., 1991). The thermo-time domain reflectometry (thermo-TDR) techniqueThe heat-pulse technique is also emerging as a valuprovides a valuable tool for monitoring coupled heat, water, and chemical transport in the vadose zone. This study evaluated the heat-able method for estimating . Laboratory and field studies pulse and the TDR methods for soil water content determination indicate that the method offers the benefits of determining using the thermo-TDR probe. Laboratory measurements were con-