Developing Soil Calibration Equation for Sentek’s New Drill & Drop™ Capacitance Probe.

Default calibration equations of soil moisture sensors may not be accurate for particular soil type. To convert soil moisture sensor readings of a particular site into values that represent absolute volumetric soil water content a site-specific calibration must be performed for that site. The objective of the study was to generate a calibration curve relating the volumetric water content (VWC) obtained by physical soil sampling to the Scaled Frequency of the electronic Drill & Drop probes. Six Drill & Drop probes (120cm long) were installed at the University Farm of Prairie View A&M University. The soil type of calibration site was Wockley fine sandy loam. The soil profile has fine sandy loam at top 56 cm and sandy clay loam from 56 to 203 cm depth. A range of water contents were arranged around the probes and readings were taken. The soil profile immediately adjacent to the probes were sampled for gravimetric water contents. From this, volumetric water contents were calculated. These VWC values were correlated with Scaled Frequency values from the sensors, and mathematical relationships (usually a power function) were formulated.