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

Abstract

SummarySoil 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.