A Heat Pulse-Based Approach for Simultaneous Determination of Soil Bulk Density and Water Content.

Soil bulk density (ρ_b) and volumetric water content (θ) are the basic parameters that determine the volume fractions of soil solids, water and air, and influence mass and energy transfer in soils. It is desirable to monitor ρ_b and θ simultaneously and nondestructively. We present and evaluate a method for simultaneously determining ρ_b and θ from soil thermal properties measured with a heat pulse sensor. The method uses equations that relate ρ_b and θ to soil volumetric heat capacity (C) and thermal conductivity (λ). Knowing soil texture and specific heat of soil solids a priori, a three-step calculation procedure is used to solve for ρ_b and θ. For laboratory samples of various textures, ρ_b and θ, the three-step method provided reliable ρ_b and θ data at θ greater than 0.10 m³ m^-3, but there were relatively large errors for θ less than 0.10 m³ m^-3. In a field study the heat pulse method was able to distinguish the influences of tillage treatments on ρ_b and θ with relative errors generally within 10%. The heat pulse-based approach enables simultaneous determination of ρ_b and θ.