In Situ Monitoring of Soil Bulk Density with a Thermo-TDR Sensor

Monitoring spatial and temporal dynamics of soil bulk density (ρb) can be challenging, and ideally soil ρb measurements should be continuous in situ. The thermo-time domain reflectometry (TDR) technique is emerging as a useful technique for measuring soil ρb, with the advantages of being automated, rapid, and minimally destructive. The objective of this study is to evaluate the effectiveness of the thermo-TDR technique for monitoring the temporal dynamics of soil ρb under field conditions. Thermo-TDR sensors were installed at two experimental sites with different soil textures, silt loam and sandy loam, to monitor soil ρb continuously in the 0- to 10- and 10- to 20-cm soil layers. The results showed that the thermo-TDR ρb in general agreed with gravimetric ρb from the core method, and the differences between the two methods were within 8%. Compared with the core method, the thermo-TDR technique had the advantage of capturing the in situ ρb changes over time with minimal soil disturbance. We conclude that the thermo-TDR sensors can be used effectively to continuously monitor soil ρb under field conditions.