2017 ASHS Annual Conference

Integrating precise irrigation application systems with need-based irrigation scheduling can increase water use efficiency by applying the appropriate amount of water only when needed to support plant growth and avoiding over or under-watering. Using amendments such as biochar manipulates substrate particle size and reduces the proportion of large components, which increases the amount of available water and improves irrigation efficiency and plant growth. The objective of this research was to evaluate the impact of biochar and need-based irrigation scheduling on gas exchange, plant water relations, and biomass gain of container-grown ‘Silver Dollar’ hydrangea with the goal of reducing water use and maintaining or shortening production cycles. Containers were filled with either 100% pine bark or amended with (v/v) 10% or 25% hardwood biochar. Plants were automatically irrigated by one of three irrigation systems. The conventional irrigation system delivered 0.7 inch of water every day and was compared with one of two on-demand irrigation schedules: 1) a system that maintained a volumetric water content (VWC) to support photosynthesis at 90% of the maximum predicted photosynthetic rate, or 2) a system based on substrate physical properties where irrigation was applied when the substrate water content decreased to the driest point at which there was plant available water, -0.1 bar. Both on-demand treatments used less water than the conventional irrigation system with equal or higher water use efficiency. The amount of water used over the 8-week experiment was reduced from 35 liters in conventional irrigation to 19 and 30 liters in 10% and 25% biochar treatment in substrate-based irrigation schedule and 18 and 20 liters in 10% and 25% biochar treatment in plant physiology-based irrigation schedule. Photosynthesis, stomatal conductance and plant water potential were not different with respect to irrigation treatment, although both on-demand irrigation systems decreased water use. Biomass metrics were generally unaffected by treatments or were lower for intermediate biochar treatments in on-demand irrigation systems. This research demonstrated that on-demand irrigation scheduling with a physiological basis or substrate physical properties basis in combination with biochar substrate amendment could be an effective approach to reduce water requirements for container-grown nursery crops without negatively affecting plant growth.