Simultaneous water content, air-filled porosity, and bulk density measurements with thermo-time domain reflectometry

The partitioning of the soil volume between water, solids, and air strongly influences many soil processes. In this paper we demonstrate a new approach to nondestructively measure this partitioning. A thermo-time domain reflectometry (thermo-TDR) probe was inserted into sandy loam soil and used to apply thermal and electromagnetic pulses an to monitor the transport of these pulses through the soil. We used the resulting data to determine the soil water content, air-filled porosity, and volume fraction of solids, as well as degree of saturation and bulk density. When calibrated for this soil, the standard errors between thermo-TDR measurements and gravimetric measurements were 0.02, 0.07, and 0.05 m(3) m(-3) for water content, volume fraction of solids, and air-filled porosity, respectively. The standard error for degree of saturation was 0.08 m(3) m(-3), and for bulk density was 0.18 Mg m(-3). This technique has great potential for soil research and management, particularly if the accuracy of the bulk density measurement can be improved.