The 2011 ASHS Annual Conference

Subirrigation has the potential to reduce water and nutrient runoff from greenhouses and allows for recycling and reuse of the nutrient solution. However, subirrigation systems are usually controlled by timers, irrespective of plant water requirements. Our objectives were to automate a subirrigation system using soil moisture sensors to monitor and control substrate water content and to quantify the effect of substrate water content on hibiscus (Hibiscus acetosella ‘Panama Red’) growth. Automation was accomplished by connecting three capacitance soil moisture sensors per bench to a datalogger.  When the substrate water content dropped below a threshold (10, 18, 26, 34, or 42% (v/v)), irrigation was turned on for 3 minutes, followed by complete drainage. Results indicated that sensors were effective in monitoring and controlling subirrigation, and that substrate water content thresholds can be used to regulate plant growth. The treatments with low substrate water content resulted in fewer irrigations, less nutrient solution use, and reduced plant dry weight and height.