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Rhuanito Soranz Ferrarezi, Sue K. Dove, and Marc W. van Iersel

Substrate volumetric water content (VWC) is a useful measurement for automated irrigation systems. We have previously developed automated irrigation controllers that use capacitance sensors and dataloggers to supply plants with on-demand irrigation. However, the dataloggers and accompanying software used to build and program those controllers make these systems expensive. Relatively new, low-cost open-source microcontrollers provide an alternative way to build sensor-based irrigation controllers for both agricultural and domestic applications. We designed and built an automated irrigation system using a microcontroller, capacitance soil moisture sensors, and solenoid valves. This system effectively monitored and controlled VWC over a range of irrigation thresholds (0.2, 0.3, 0.4, and 0.5 m3.m−3) with ‘Panama Red’ hibiscus (Hibiscus acetosella) in a peat:perlite substrate. The microcontroller can be used with both regular 24-V alternating current (AC) solenoid valves and with latching 6- to 18-V direct current (DC) solenoid valves. The technology is relatively inexpensive (microcontroller and accessories cost $107, four capacitance soil moisture sensors cost $440, and four solenoid valves cost $120, totaling $667) and accessible. The irrigation controller required little maintenance over the course of a 41-day trial. The low cost of this irrigation controller makes it useful in many horticultural settings, including both research and production.

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Jong-Goo Kang, Rhuanito Soranz Ferrarezi, Sue K. Dove, Geoffrey M. Weaver, and Marc W. van Iersel

Abscisic acid (ABA) is a plant hormone involved in regulating stomatal responses to environmental stress. By inducing stomatal closure, applications of exogenous ABA can reduce plant water use and delay the onset of drought stress when plants are not watered. However, ABA can also cause unwanted side effects, including chlorosis. Pansy (Viola ×wittrockiana) has been shown to be particularly susceptible to ABA-induced chlorosis. The objective of this study was to determine if fertilization rate affects the severity of ABA-induced chlorosis in this species. ‘Delta Premium Pure Yellow’ pansy seedlings were fertilized with controlled-release fertilizer incorporated at rates from 0 to 8 g·L−1 of substrate. When plants had reached a salable size, half the plants were sprayed with a solution containing 1 g·L−1 ABA, whereas the other plants were sprayed with water. Leaf chlorophyll content was monitored for 2 weeks following ABA application. Leaf chlorophyll content increased greatly as fertilizer rate increased from 0 to 2 g·L−1, with little increase in leaf chlorophyll at even higher fertilizer rates. ABA induced chlorosis, irrespective of the fertilizer rate. Plant dry weight was lowest when no controlled-release fertilizer was incorporated, but similar in all fertilized treatments. ABA treatment reduced shoot dry weight by ≈24%, regardless of fertilization rate. This may be due to ABA-induced stomatal closure, which limits carbon dioxide (CO2) diffusion into the leaves. We conclude that ABA sprays induce chlorosis, regardless of which fertilizer rate is used. However, because leaf chlorophyll concentration increases with increasing fertilizer rates, higher fertilizer rates can mask ABA-induced chlorosis.

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Matthew Chappell, Sue K. Dove, Marc W. van Iersel, Paul A. Thomas, and John Ruter

Water quality and quantity are increasingly important concerns for agricultural producers and have been recognized by governmental and nongovernmental agencies as focus areas for future regulatory efforts. In horticultural systems, and especially container production of ornamentals, irrigation management is challenging. This is primarily due to the limited volume of water available to container-grown plants after an irrigation event and the resultant need to frequently irrigate to maintain adequate soil moisture levels without causing excessive leaching. To prevent moisture stress, irrigation of container plants is often excessive, resulting in leaching and runoff of water and nutrients applied to the container substrate. For this reason, improving the application efficiency of irrigation is necessary and critical to the long-term sustainability of the commercial nursery industry. The use of soil moisture sensing technology is one method of increasing irrigation efficiency, with the on-farm studies described in this article focusing on the use of capacitance-based soil moisture sensors to both monitor and control irrigation events. Since on-farm testing of these wireless sensor networks (WSNs) to monitor and control irrigation scheduling began in 2010, WSNs have been deployed in a diverse assortment of commercial horticulture operations. In deploying these WSNs, a variety of challenges and successes have been observed. Overcoming specific challenges has fostered improved software and hardware development as well as improved grower confidence in WSNs. Additionally, growers are using WSNs in a variety of ways to fit specific needs, resulting in multiple commercial applications. Some growers use WSNs as fully functional irrigation controllers. Other growers use components of WSNs, specifically the web-based graphical user interface (GUI), to monitor grower-controlled irrigation schedules.