A New Approach for in Situ Determination of Soil Bulk Density with the Thermo-TDR Technique.

Soil bulk density (BD) of a tilled layer usually has strong spatial and temporal variability. It can be difficult to capture BD dynamics with available measurement techniques. In this study we developed a method that is capable of monitoring in-situ BD. The new approach relies on an empirical model that relates soil thermal conductivity (TC) to soil particle size, BD, and water content (WC). The thermo-TDR sensor measures TC and WC simultaneously, and knowing soil texture a priori, BD can be estimated with the model. The new method was tested by comparing estimated BD with independent gravimetric BD measurements at various depths and times after tillage operations. The results showed that the BD estimates agreed well with independent gravimetric BD measurements. The new approach extends the function of the thermo-TDR sensor for characterizing soil physical properties and processes, and the newly available dynamic bulk density measurements will be useful for future studies of heat and water transfer in tilled soils.