2018 ASHS Annual Conference

Controlling irrigation using timers, or manually operated systems are the most common irrigation scheduling methods in container production systems. Improving irrigation efficiency can be achieved by scheduling irrigation based on plant water needs and the appropriate use of sensors rather than relying on periodically adjusting irrigation volume based on perceived water needs. Substrate amendments such as biochar, a carbon-rich by-product of pyrolysis or gasification, can increase the amount of available water and improve irrigation efficiency and plant growth. Previous work examined two on-demand irrigation schedules in controlled environments. The objective of this research was to evaluate the impact of these on-demand irrigation schedules and hardwood biochar on water use and biomass gain of container-grown Hydrangea paniculata ‘Silver Dollar’ in a typical outdoor nursery production environment. Eighteen independently controlled irrigation zones were designed to test three irrigation schedules on ‘Silver Dollar’ hydrangea grown outdoors in pine bark amended with 0% or 25% hardwood biochar. The three irrigation schedules were conventional irrigation and two on-demand schedules, based on substrate physical properties and plant physiology. The conventional irrigation delivered 18 mm (0.7 inches) of water in one event each day. The substrate physical properties irrigation scheduling was based on the soilless substrate moisture characteristic curve. Irrigation was applied when the substrate water content decreased to the driest point at which there was plant available water, -10 kPa. The plant physiology irrigation schedule was based on a specific substrate moisture content derived from the relationship between substrate moisture content and photosynthetic rate. This system maintained volumetric water content (VWC) to support photosynthesis at 90% of the maximum predicted photosynthetic rate. Total water use was unaffected or lower in the on-demand irrigation systems. However, plant dry weight was 22% and 15% greater, water use efficiency was 36% and 40% greater, and total leachate volume was 25% and 30% lower in the substrate physical properties-based and plant physiology-based irrigation scheduling systems, respectively, compared to the conventional irrigation. This research demonstrated that on-demand irrigation scheduling with a physiological-basis or substrate physical properties-basis could be an effective approach to increase water use efficiency for container-grown nursery crops without negatively affecting plant growth.