Yili Lu

Extrapolative capability of two models that estimating soil water retention curve between saturation and oven dryness.

Accurate estimation of soil water retention curve (SWRC) at the dry region is required to describe the relation between soil water content and matric suction from saturation to oven dryness. In this study, the extrapolative capability of two models for predicting the complete SWRC from limited ranges of soil water retention data was evaluated. When the model parameters were obtained from SWRC data in the 0–1500 kPa range, the FX model (Fredlund and Xing, 1994) estimations agreed well with measurements from saturation to oven dryness with RMSEs less than 0.01. The GG model (Groenevelt and Grant, 2004) produced larger errors at the dry region, with significantly larger RMSEs and MEs than the FX model. Further evaluations indicated that when SWRC measurements in the 0–100 kPa suction range was applied for model establishment, the FX model was capable of producing acceptable SWRCs across the entire water content range. For a higher accuracy, the FX model requires soil water retention data at least in the 0- to 300-kPa range to extend the SWRC to oven dryness. Comparing with the Khlosi et al. (2006) model, which requires measurements in the 0–500 kPa range to reproduce the complete SWRCs, the FX model has the advantage of requiring less SWRC measurements. Thus the FX modeling approach has the potential to eliminate the processes for measuring soil water retention in the dry range.

Simultaneous determination of soil bulk density and water content: a heat pulse-based method: Determining soil bulk density and water content

Soil bulk density (ρb) and volumetric water content (θ) determine the volume fractions of soil solids, water and air, and influence mass and energy transfer in soil. It is desirable to monitor ρb and θ concurrently and non‐destructively. We present a heat pulse‐based method for simultaneous determination of ρb and θ from soil thermal properties. The method uses equations that relate ρb and θ to soil volumetric heat capacity (C) and to soil thermal conductivity (λ). We developed a three‐step procedure to calculate ρb and θ from C and λ measured by a heat pulse sensor, with soil texture and specific heat of soil solids known a priori. Laboratory evaluation of soil samples with various textures showed that the three‐step method provided reliable estimates of ρb and θ at θ values greater than the critical water content (θc) when λ started to respond notably to increases in θ. This method provides a new way to determine ρb and θ simultaneously with heat pulse sensors. HIGHLIGHTS: We developed an approach to determine soil bulk density (ρb) and water content (θ) simultaneously with a heat pulse sensor. We estimated ρb and θ from soil thermal properties based on heat capacity and thermal conductivity models. The new approach provided reliable ρb and θ values at water contents >θc, the critical value. At θ < θc, the approach gave unstable results because soil thermal conductivity was insensitive to ρb.

An Empirical Model for Estimating Soil Thermal Diffusivity from Texture, Bulk Density, and Degree of Saturation

AbstractSoil thermal diffusivity κ is an essential parameter for studying surface and subsurface heat transfer and temperature changes. It is well understood that κ mainly varies with soil texture,...