A Low Cost, Arduino-based System for Monitoring and Controlling Substrate Water Content

Soil moisture sensors can be used to schedule irrigation. Inexpensive, programmable microcontroller boards can make sensor-based irrigation available for both agricultural and domestic applications. Such irrigation control systems can be built with only basic programing and wiring knowledge. Our objectives were to use soil moisture sensors and microcontrollers to build an automated system to monitor and control substrate volumetric water content (VWC) based on real-time soil moisture measurements. We used an open source prototype board (Arduino Uno R3) combined with a stackable secure digital (SD) shield for datalogging. The stacked boards were connected to four capacitance-type soil moisture sensors (10HS, Decagon), a relay board with 8 relays, one 9VDC latching solenoid valve, and three 24VAC solenoid valves. The microcontroller program was written to power the sensors, read the raw signal from the soil moisture sensors, and convert it into VWC. The microcontroller then compared VWC to irrigation thresholds and opened and closed irrigation valves as needed. The latching valve is powered using a 9V battery, while the 24VAC valves require a separate power supply. The data were written to an SD card. To test the system, we performed a 53-d trial using four pots with Hibiscus acetosella ‘Panama Red’. The ability of the system to maintain VWC above different thresholds, varying from 0.2 to 0.5 m³ m^-3, was tested. The Arduino board was reliable and successfully monitored substrate VWC and controlled irrigation, requiring little maintenance. This automated irrigation controller can be used by commercial growers and homeowners, allowing irrigation-decisions to be based on plant water needs instead of visual observations or a rigid schedule. The total cost of this irrigation controller, capable of controlling four irrigation zones, is approximately $350, not including the irrigation valves.