Real-Time Three-Dimensional Imaging of Soil Resistivity for Assessment of Moisture Distribution for Intelligent Irrigation

An affordable standalone sensor that can provide volumetric information on soil moisture distribution in real time was developed and tested for potential application in irrigation control systems. The moisture content of soil is reconstructed tomographically from electrical resistivity measured between multiple pairs of electrodes, which are installed on two opposite sides of the soil volume. The measurement of relative moisture content reconstructed from the measured resistance values demonstrated in this paper requires a simple, in-situ, two-point calibration (for dry and wet soil conditions) after electrodes are installed in place. This calibration has to be repeated once the soil conditions, such as salinity or fertilizer content, are altered as the season progresses. Historical data collected over a 12-month period can be stored locally or transferred over a wireless network at given intervals or in real time. Although existing single-point sensors can provide more accurate measurements of soil moisture, knowledge on the three-dimensional distribution of moisture around plant roots should allow substantial savings of precious fresh water resources and more intelligent multi-channel irrigation systems. The same system can possibly be extended to estimation of fertilizer distribution.