Automated Fertigation and Irrigation Control Based on Measurements of Substrate Water Content and Pore Water EC

Sensor-automated irrigation is used in a variety of research and commercial applications. In greenhouses, irrigation and fertilization management are closely related. Using novel sensors (GS-3, Decagon Devices), which measure both substrate volumetric water content (VWC) and pore water electrical conductivity (EC), we have developed a system that automates both irrigation and fertigation. The automated fertigation system is based on a datalogger, which measures both VWC and EC using GS-3 sensors. The datalogger compares the measured VWC and EC to specific thresholds. If both VWC and EC are below their respective threshold, then the datalogger opens a solenoid valve that applies fertilizer solution to the plants. If only the VWC, but not the EC is below the threshold, then a solenoid valve connected to a line with just water will open for irrigation. Initial testing with sweet potato (Ipomoea batatas) indicated that control of pore water EC is more complicated than controlling VWC. We observed short-term fluctuations in pore water EC that appear to be related to changes in substrate VWC and/or substrate temperature. Despite the difficulty of precisely controlling pore water EC, we were generally able to maintain different EC levels in different plots. In a second study, we grew Lenten rose (Helleborus × ericsmithii ‘Champion’) at two VWC and eight EC thresholds to determine optimum fertility levels for this popular perennial plant.