2017 ASHS Annual Conference

Limitations in water availability and quality are among the primary challenges to achieving sustainable horticultural crop production. There is lack of information on precision methods to schedule controlled irrigation events based on actual plant water requirements, to increase water-use efficiency. In part, this requires better understanding of how soil/substrate matric potential (SMP; ψ_m) affects readily-available water (RAW) in the root-zone, that can be related to measurements of crop water stress (i.e., stem or leaf water potential). In associated research studies, we are investigating the effect of various soil/substrate moisture regimes on strawberry (Fragaria X ananassa) growth, yield and fruit quality, and on greenhouse grown poinsettia production, using both soil volumetric water content (VWC) and SMP as set-points for irrigation treatments. The primary objective in both studies was to optimize water applications without imposing plant water stress. In both studies, a wireless sensor network using nR5 control nodes (Meter-Group; Pullman, WA) was utilized with Sensorweb^TM software (Mayim, LLC; Pittsburgh, PA) to automatically control irrigation events. Soil/substrate moisture retention curves were developed using a Hyprop apparatus (UMS; Munich Germany) to relate VWC and SMP measurements. Strawberry field experiments during 2014-15 and 2015-16 showed significant decreases in irrigation water volume between -30kPa and-50kPa, but significantly decreased yield and number of fruits per plant at SMP’s below -50kPa. This indicated the sensitivity of strawberry plants to decreased RAW within a very narrow range of SMP values. In 2016, MPS-6 sensors (Decagon Devices Inc.) and high-precision T8-field tensiometers (UMS) were used to accurately quantify and validate in situ SMP’s between irrigation treatments. Similarly, in a poinsettia (Euphorbia pulcherrima cv.) greenhouse study in a 80% peat : 20% perlite substrate, plant growth parameters were not significantly affected by decreasing substrate matric potential levels from -6.3 kPa to -26.3 kPa, corresponding to 45% and 25% VWC, respectively. Increasing our understanding of plant-available water in different soils and substrates will enable us to employ irrigation sensor threshold values which are specific and clearly defined. This will enable us to save water and reduce nutrient leaching but maintain crop yields, increasing the sustainability of specialty crop production systems.