May 9, 2018
High-tech controls key features of OSU greenhouse

Computerized irrigation based on vapor pressure deficit (VPD) and a shade curtain for summer that doubles as an energy curtain in the winter were two of the key features discussed during a recent tour through the new, hydroponic greenhouse at Ohio State University’s Agricultural Technical Institute (ATI) in Wooster, Ohio.

The hydroponic greenhouse for vegetable production was opened in the spring of 2017, said Nate Donley, ATI greenhouse manager.

The greenhouse tour was part of a recent hydroponic greenhouse workshop at Ohio State University’s Ohio Agricultural and Research Development Center in Wooster.

Computerized controls to irrigate by VPD are being calibrated in the hydroponic greenhouse to provide for greater accuracy, such as preventing too much irrigation during cloudy days. Unlike relative humidity which is affected by temperature, VPD is independent of temperature and estimates the difference between how much moisture is in the air and how much the air could potentially hold when saturated.

“VPD is a unit of measurement made up of light level, air temperature, possibly leaf temperature, and humidity,” Donley said. “All of this information can tell us how quickly water is leaving the plant and how much needs to be replaced.”

Changing one factor changes the rate in which VPD units are accumulated. ATI is in the process of determining how many VPD units need to be accumulated during the different crop stages before irrigation is warranted.

Horizontal air flow fans maintain a gentle air movement to keep microclimates in the greenhouse consistent, which helps with powdery mildew and botrytis. Photos: Dean Peterson

The shade curtain helps keep the greenhouse cool in the summer and is automatically programmed to close if the temperature increases to higher than 85 degrees Fahrenheit. The curtain serves as an energy curtain in the winter and closes about an hour before dark to utilize what available sunlight there is. “This helps to reduce heating costs,” Donley said.

The fertilizer solution for the bato buckets is blended with calcium nitrate before application to prevent any chemical precipitation and subsequent plugging of emitters. The computerized controls keep the expected pH at 5.8 and the electrical conductivity (EC) initially at 1.8. The EC changes as the crop grows and goes up to 2.5 as the crop matures. “All of the lines are pressurized so all of the buckets’ water is turned on at the same time,” Donley said.

Citric acid is used as the acidifier rather than sulfuric acid because many of the workers are ATI students. “We want a realistic, teaching environment, but greenhouse safety is paramount, too,” he said.

Horizontal air flow (HAF) fans maintain a gentle air movement to keep microclimates in the greenhouse consistent. “The air movement also helps with powdery mildew and botrytis,” Donley said.

The greenhouse also has nutrient film technique channels for hydroponic production of lettuce and other leafy crops. It also has a micro green system for greenhouse production in stacks and equipment to simulate deep water, hydroponic systems.

ATI has a greenhouse and nursery management program that allows students to specialize in either greenhouse, nursery or greenhouse engineering technology.

A greenhouse made with blackout material to simulate short day lengths for floriculture production, and a greenhouse for new propagations were also opened in the spring of 2017.

Dean Peterson, VGN Correspondent

Top photo: Computerized controls keep the hydroponic solution’s expected pH at 5.8 and the electrical conductivity initially at 1.8. The EC changes as the crop grows and goes up to 2.5 as the crop matures, said Nate Donley, ATI greenhouse manager. Photos: Dean Peterson





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