2017 ASHS Annual Conference

Making irrigation decisions in a commercial nursery can be difficult given the range of species and growth stages and changing environmental conditions across a season. To simplify, growers often make the same irrigation application throughout the nursery. A one-size-fits-all approach can cause some plants to be over-watered and some to be under-watered. Substrate moisture sensors connected to a data logger that is programmed to control solenoid valves provide an opportunity to actuate irrigation in real-time in response to plant and environmental demand. The objective of this experiment was to develop and evaluate an on-demand irrigation system and compare it to a conventional 2hr daily irrigation system using ‘Kwansan’ cherry (Prunus serrulata) trees potted in 14.3L containers. The treatments were (1) Conventional Irrigation – Irrigate from 8:00 am to 10:00 am and again for 75-90 minutes in the afternoon if the temperatures equaled or exceeded 85F and (2) On-demand, substrate moisture sensor-based – Irrigate anytime two conditions were met: the substrate dried to the set point and it was between 8:00 am to 5:00 pm daily. The set point that triggered irrigation was 25% volumetric water content (VWC). Plants were irrigated the amount of time calculated to return VWC to container capacity based on a known irrigation flow rate and established container capacity (29% VWC). Cumulative and daily water use was measured using water meters on the lateral line to each zone. To monitor zone plant growth, 10 plants/zone were selected and tagged and height and caliper were measured periodically during the experiment. From August 31 to September 23, 2015, the on-demand system used 1,628 gallons per day, 30% less than the 2,321 gallons per day used in the conventional treatment and had 51% less leachate volume than the conventional treatment. During the experiment, increase in plant height was 4.2 cm and 1.4 cm for on-demand and conventional, respectively, and increase in caliper was 1.7 mm and 2.8 mm for on-demand and conventional, respectively. Throughout the experiment, the on-demand system maintained a higher and more consistent substrate moisture level than the nursery’s conventional irrigation system.