Novel Mobile Soil Water Content Sensing Techniques

Abstract

Soil constituency plays a significant role in the dielectric permittivity-water content relationship which informs electromagnetic sensor-based readings. Sensor output generally provides a bulk determination of permittivity that must be converted to soil volumetric water content. The objective of this work was to evaluate the potential for a Time Domain Reflectometer (TDR) and open-ended dielectric probe (OEDP) to provide electromagnetic-based (EM) mobile soil water content determination. Open-ended dielectric probes were made from a variety of coaxial fixtures and tested using an Anritsu portable network analyzer (PNA). After TDR and analyzer calibrations using an open, short and load, measurements were compared for accuracy using reference dielectric liquids. Bilinear analysis was used to derive frequency dependent permittivity. Both blade and surface OEDP’s were tested for permittivity measurement capability (PNA) and waveform consistency (TDR). Additional work is needed to understand the impact of soil compaction on readings. Dynamic effects on soil structural properties need to be studied to determine the effect on sensing volume at the soil probe interface. Reliable and rapid mobile measurement of soil water content at the field-scale could greatly enhance many agronomic activities such as development of reclamation strategies, reducing fertilizer application and optimizing fresh and saline water use. This capability will require improvements in sensor design, signal analysis and novel application of the technology before real-time field-scale measurements for precision agriculture are readily available.