Implementing Substrate Moisture Set-point Irrigation Control in Cut-flower Greenhouse Production

We used a wireless substrate moisture sensor network, to compare the effect of time-based vs. sensor-based irrigation scheduling on the water use, yield, and quality of Antirrhinum major (snapdragon) in cut-flower production. We calibrated soil moisture capacitance sensors (EC-5; Decagon Devices, Inc., Pullman, WA) for use in the perlite substrate (Pennsylvania Perlite Co., Bethlehem, PA), used by a commercial greenhouse operation in Jarrettsville, MD. Sensor-based control was achieved using a prototype nR5 radio node (Decagon Devices, Inc.), in concert with advanced control software (Sensorweb; Carnegie-Mellon Robotics Institute, Pittsburgh, PA), to independently control irrigation events using solenoids. This was done using the average substrate moisture content data from the crop measured on a 15-minute basis at various positions on each production bench. The lower irrigation setpoint for the automated irrigation control was set at 0.28 m³·m^-3, which was based upon the experience of grower and the water needs of the crop. The automated irrigation system only irrigated when the average substrate volumetric water content (VWC) from four sensors in different locations decreased below 0.28 m³·m^-3. This sensor-based irrigation treatment was compared to the traditional, time-based irrigation schedule employed by the grower (typically 4–6 irrigation events of 3-minute duration) every day, measured independently using EM50R monitoring nodes with EC-5 sensors, as the control treatment. All the monitoring and control data was transmitted nodes to a basestation located in the greenhouse office, and then relayed to the internet via a dedicated website. During eight-week growing period, the sensor-based irrigation irrigated only 28% of the manually-irrigated events, but applied 76% of the total irrigation volume (i.e. longer but less frequent irrigations). A repeated experiment with higher substrate VWC set-points (0.30 m³·m^-3) is currently under way, to increase the precision of VWC set-point irrigation scheduling and to evaluate potential savings in water, fertilizer and labor costs for greenhouse cut-flower production.