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

Monitoring spatial and temporal dynamics of soil bulk density (rho(b)) can be challenging, and ideally soil rho(b) measurements should be continuous in situ. The thermo-time domain reflectometry (TDR) technique is emerging as a useful technique for measuring soil rho(b), 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 rho(b) under field conditions. Thermo-TDR sensors were installed at two experimental sites with different soil textures, silt loam and sandy loam, to monitor soil rho(b) continuously in the 0- to 10- and 10- to 20-cm soil layers. The results showed that the thermo-TDR rho(b) in general agreed with gravimetric rho(b) 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 rho(b) changes over time with minimal soil disturbance. We conclude that the thermo-TDR sensors can be used effectively to continuously monitor soil rho(b) under field conditions.