Thermal properties of soil in the Murrumbidgee River Catchment (Australia)

This paper presents analyses of topsoil thermal conductivity, heat capacity, thermal diffusivity, water content, and bulk density obtained during the Australian Airborne Cal/Val Experiment for SMOS. The aim of the study presented here is to identify the structure and variability of the spatial distribution of soil properties and their mutual dependencies. Knowledge of the spatial distribution of soil bulk density and water content is essential to develop precise agronomic practices to manage the thermal properties of the soil and the quality and efficiency of cultivated plants. Thermal properties of soils were obtained from in situ measurements and modelled using the Usowicz statistical-physical model which is based on simple physical soil properties. Two soil water content measurement methods (gravimetric and dielectric) and two soil granulometry classification systems (USDA and Australian) were used to find the most effective approach. It is shown that: (i) quartz and water content and the bulk density of soil are the main factors affecting the thermal properties of the soil; (ii) the spatial distribution of conductivity and heat capacity is governed by the soil water content distribution, while the thermal diffusivity near its maximum is mainly driven by the spatial distribution of the bulk density; and (iii) soil thermal properties were estimated more accurately from the Australian soil granulometry than the USDA classification. The results not only improved the scarce information about thermal properties of Australian soils, but allow to estimate the soil thermal properties across large scales from the physical properties of the soil (based on existing databases) and the current soil water content (from satellite and/or in situ measurements).