2019 ASHS Annual Conference

Ebb-and-flow subirrigation is a closed system that applies water to the bottom of the containers, reducing water and nutrient losses due to recirculation of fertilizer solution (FS). The technology can accelerate plant growth and eliminate the improper disposal of salts into the environment. Sensor-based ebb-and-flow benches can be used by the citrus nursery industry to automate subirrigation operation and apply water on demand instead of on a rigid schedule. There is a need for establishing irrigation guidelines to produce different citrus rootstocks. The objectives of this study were: 1) automate ebb-and-flow subirrigation operation using soil moisture sensors, 2) evaluate the system performance on plant growth and water use, and 3) evaluate if subirrigation shorten crop cycle and accelerate citrus liners propagation time compared to overhead irrigation. The treatments tested were five irrigation methods [three ebb-and-flow subirrigation benches with different volumetric water content (VWC) to trigger subirrigation [Ѳ 0.24, 0.36 and 0.48 m³/m³], capillary mat and overhead irrigation] and six citrus rootstocks (Kuharske, UFR-2, UFR-16, US-802, US-812, and X-639), arranged in a 5×6 factorial split-plot design (irrigation method as main plot), with four replications. The system was automated by 20 capacitance sensors connected to a data logger, multiplexer and relay drivers, which controlled independent submersible pumps and solenoid valves. Subirrigation was turned on when VWC dropped below the set thresholds, while capillary mat and overhead ran on a rigid schedule. Sensors effectively monitored substrate VWC and controlled subirrigation. Treatments with highest VWC had higher substrate moisture and number of irrigations over time. Subirrigation at Ѳ 0.48 m³/m³ increased plant growth in 29% and reduced water use in 98% compared to capillary mat and overhead irrigation. Subirrigation shortened crop cycle and accelerated citrus liners propagation time compared to overhead irrigation, anticipating the liners transplanting for grafting. The volume of water applied was higher on capillary mat and overhead irrigation. VWC Ѳ 0.48 m³/m³ is indicated for liner production in cone-shaped containers. US-802, US-812, and X-639 rootstocks resulted in the tallest seedlings, while Kuharske showed the widest stem diameter.