Sentek provides default calibration equations for Soil Moisture sensors that convert raw counts into estimates of soil volumetric water content. These default calibration equations have been calculated based on a range of different soil types and which can be used to show relative soil water changes in all soil types. Significant numbers of data sets collected from various soil types and crops around the world have shown that relative changes in volumetric soil water content based on the default calibration equation can be used to show the most important soil water trends in relation to optimum plant production. Almost all of the economic gains recorded with Sentek probes in commercial agriculture to date have been made using the concept of relative change in soil water dynamics.
Obtaining absolute volumetric soil water content data is useful however, for scientific studies of the soil-water-plant-atmosphere continuum, and for other purposes where it is necessary to determine absolute values of soil water content. For these applications calibration of the Soil Moisture Sensors is essential.
Calibration of Sentek's soil moisture sensors is made by comparing Scaled Frequency readings from an access tube installed in the field or in a container in the laboratory with values of the volumetric water content. Volumetric water content is determined by gravimetric sampling and bulk density determination from immediately adjacent to the tube. When these values are plotted on a graph they form a relationship that is described by a mathematical equation. In this way the readings from the sensor are directly related to real values determined in the soil.
Click here to download the EnviroSCAN and Diviner 2000 Installation Manual.
Site and soil specific calibration equations can be applied to individual sensors at every depth level measured.
For more information, click here to download the Sentek Calibration Manual.
Example comparison of soil water data determined using default Sentek equation and site specific calibration equation, showing relative trends over time.