Accuracy and Calibration of Water Content Sensors

When measuring the volumetric water content (VWC) of natural and artificial plant growth substrates with dielectric moisture sensors, three distinct factors can lead to loss of accuracy in the VWC measurement: 1) inaccuracy in the sensor’s measurement of dielectric constant (sensor error); 2) error in the conversion of dielectric constant to VWC (calibration error); and 3) air voids or overly compacted substrate due to poor sensor installation. We will discuss the magnitude of possible error induced by each factor and present strategies to minimize errors and generate best possible accuracy in VWC measurements in the greenhouse and nursery settings. The associated practicum session will demonstrate methods for generating substrate specific calibrations, which are critical for accurate measurements in widely varied artificial and natural growth substrates.