Soil moisture sensing in saltwater: a review

The ability to accurately obtain soil moisture contents is important in many different fields, including agriculture and branches of civil engineering including hydraulics, transportation, and geotechnical engineering. The moisture content of pavement subgrade affects pavement performance. Long-term monitoring the moisture content of subgrade can allow for better pavement design and maintenance practices. Collecting soil samples for gravimetric testing is time consuming and destructive, which is not practical for long-term monitoring. Soil moisture sensors employing a variety of technologies have been developed for recording soil moisture contents non-destructively and remotely. Soils that are exposed to irrigation or sea waters can have varying amounts of salinity. Salinity in the soil can adversely affect the performance of various sensor technologies. This review paper summarizes the difficulties associated with the use of commonly used, commercially available soil moisture sensors using time domain reflectometry (TDR), capacitance, impedance, time domain transmission (TDT), and transmission line oscillator technology.