Title: Thermal property values of a central Iowa soil as functions of soil water content and bulk density or of soil air content
Abstract: Abstract Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content ( θ ) and bulk density ( ρ b ). Both θ and ρ b change with time, particularly in recently tilled soil. However, few studies have addressed the full extent of soil thermal property changes with θ and ρ b . The objective of this study is to examine how changes in ρ b with time after tillage impact soil thermal properties (volumetric heat capacity, C v , thermal diffusivity, k , and thermal conductivity, λ ). The study provides thermal property values as functions of θ and ρ b and of air content ( n air ) on undisturbed soil cores obtained at selected times following tillage. Heat pulse probe measurements of thermal properties were obtained on each soil core at saturated, partially saturated ( θ at pressure head of −50 kPa) and oven‐dry conditions. Generally, k and λ increased with increasing ρ b at the three water conditions. The C v increased as ρ b increased in the oven‐dry and unsaturated conditions and decreased as ρ b increased in the saturated condition. For a given θ , a larger ρ b was associated with larger thermal property values, especially for λ . The figures of C v , k and λ versus θ and ρ b , as well as C v , k and λ versus n air , represented the range of soil conditions following tillage. Trends in the relationships of thermal property values with θ and ρ b were described by 3‐D surfaces, whereas each thermal property had a linear relationship with n air . Clearly, recently tilled soil thermal property values were quite dynamic temporally due to varying θ and ρ b . The dynamic soil thermal property values should be considered in soil heat and mass transfer models either as 3‐D functions of θ and ρ b or as linear functions of n air . Highlights Thermal property values for a range of θ and ρ b were measured on undisturbed soil cores. Freshly tilled soil thermal property values were quite dynamic temporally. The thermal property values of a tilled soil were described as 3‐D surfaces with θ and ρ b . The thermal property values of a tilled soil varied linearly with n air .