Incorporating data-driven technologies into agriculture presents a promising approach to optimizing crop production, especially in regions dependent on irrigation, where escalating heat waves and droughts driven by climate change pose increasing challenges. Recent advancements in sensor technology have introduced diverse methods for assessing irrigation needs, including meteorological sensors for calculating reference evapotranspiration, belowground sensors for measuring plant available water, and plant sensors for direct water status measurements. Among these, infrared thermometry stands out as a non-destructive remote sensing method for monitoring transpiration, with significant potential for integration into drone- or satellite-based models. This study applies infrared thermometry to develop a crop water stress index (CWSI) model for European hazelnuts (Corylus avellana), a key crop in Oregon, the leading hazelnut-producing state in the United States. Utilizing low-cost, open-source infrared thermometers and data loggers, we aim to provide hazelnut farmers with a practical tool for improving irrigation efficiency and enhancing yields. The CWSI model was validated against plant water status metrics such as stem water potential and gas exchange measurements. Our results show that when stem water potential is below −6 bar, the CWSI remains under 0.2, indicating low plant stress, with corresponding leaf conductance rates ranging between 0.1 and 0.4 mol m² s⁻¹. Additionally, un-irrigated hazelnuts were stressed (CWSI > 0.2) from mid-July through the end of the season, while irrigated plants remained unstressed. The findings suggest that farmers can adopt a leaf conductance threshold of 0.2 mol m² s⁻¹ or a water potential threshold of −6 bar for irrigation management. This research introduces a new CWSI model for hazelnuts and highlights the potential of low-cost technology to improve agricultural monitoring and decision-making.

Development of more efficient and sustainable irrigation technology is critical to maintain horticultural production in a water scarce future. Sensor controlled irrigation is an emerging technology that has the potential to increase irrigation efficiency and reduce overwatering by using real-time data on container water status to control the timing and volume of irrigation events. This project presents a novel irrigation control system using lysimetry. We develop small scale lysimeters, referred to as mini-lysimeter, which provide a direct measure of actual evapotranspiration (ET) via a change in mass of containerized crops. As such, mini-lysimeter sensors have the potential to be an effective instrument for automatic irrigation scheduling. This paper presents the mini-lysimeter controlled irrigation system design in detail, including the mini-lysimeter sensors, data logger and control system configuration, and the hardware needed to integrate the control system into existing irrigation infrastructure. A proof of concept study is presented where mini-lysimeter (ML) controlled irrigation is compared to a traditional timer-based irrigation schedule. Results show that the ML controlled irrigation system can produce plants of equal size to traditional irrigation methods while using 26% less water on average. The outcome of this study indicates that the hardware presented here is reliable and robust enough to produce quality plants in a real nursery production setting, and this technology provides a novel approach to improving water efficiency in container nurseries.

Container production systems are critical for the horticulture industry but are particularly vulnerable to temperature extremes. This study investigated the effects of pot color (black vs. white) and irrigation frequency (single vs. cyclic) on root zone temperature and the growth of Hydrangea paniculata ‘Limelight’, one of the most popular and widely grown container-grown perennial shrubs in North America. The experiment was conducted at the North Willamette Research and Extension Center in Aurora, Oregon, USA (45°16′51″ N, 122°45′04″ W). A total of 160 Hydrangea paniculata ‘Limelight’ plants were divided into two groups of 80 and potted in black or white 11.4 L nursery containers filled with a bark-based potting mix. Pots were randomly assigned to one of two irrigation treatments based on irrigation frequency: single or cyclic. In the single irrigation treatment, pots received one irrigation event at 07:00 h. In the cyclic irrigation treatment, the same total irrigation volume was divided into three equal applications delivered at 08:00, 12:00, and 16:00 h. Results showed that black pots reached significantly higher root zone temperatures than white pots. Cyclic irrigation effectively reduced the peak root zone temperatures in black pots, cooling by as much as 6 °C during hot afternoons compared with single irrigation. Plants in black pots experienced 6×–7× more hours above critical root-zone temperature thresholds (>38 °C) compared with those in white pots. Although the literature indicates that prolonged exposure above 35–38 °C can inhibit photosynthesis and slow growth, and that root growth may cease at ~38 °C, in our study, plant growth was not significantly affected by pot color, irrigation regime, or their interaction (all p > 0.05). This study emphasizes the importance of optimizing pot color and irrigation practices to address vulnerabilities to extreme temperatures in container production systems.

Increasing frequency and intensity of heat events pose significant challenges for the production and early establishment of urban trees. This study evaluated whether horticultural interventions could mitigate heat stress and improve growth of young red maple (Acer rubrum ‘FranksRed’) under full-sun conditions representative of urban planting environments. Six treatments (control, canopy misting, paclobutrazol, propiconazole, kaolin clay, and potassium phosphite) were evaluated over two growing seasons in the Willamette Valley, Oregon, which were characterized by hot, dry summers and episodic heat waves. Canopy temperature, soil volumetric water content, and growth were monitored using high-resolution sensor networks and analyzed using mixed-effects modeling to account for repeated measures and environmental covariates. Across both years, mean canopy temperature largely tracked ambient conditions, and treatment effects on absolute temperature were modest. However, canopy misting reduced daily canopy temperature amplitude (ΔT) and maintained the highest soil volumetric water content, while both misting and kaolin consistently reduced exposure to the highest canopy temperature thresholds. Although these reductions in cumulative thermal exposure were not statistically significant, they coincided with improved tree growth. The chemical treatments produced smaller, context-dependent effects. Despite modest temperature differences, stem caliper increased by 10–20% under misting relative to the control (p < 0.05). Growth responses indicate that small changes in canopy thermal exposure and soil water availability can translate into meaningful differences in early tree performance. These results demonstrate that the absence of strong treatment effects on mean canopy temperature does not preclude biologically relevant outcomes. Management strategies that modify canopy thermal dynamics or plant water relations may improve growth and establishment potential of young trees under increasingly extreme thermal conditions, even when ambient heat loads cannot be fully mitigated.