The 2012 ASHS Annual Conference

Hydroponic greenhouse production is currently practiced in many US regions, which enables growers to meet increasing consumer demand for local, year-round, fresh vegetables. However, a key limiting factor for hydroponic greenhouse growers in northern climates is the need for supplemental light in winter production. Currently, supplemental lighting in greenhouses is often provided with high pressure sodium (HPS) lamps. However, recent research has focused on light emitting diode (LED) and hydro induction (HI) lighting alternatives with the potential to reduce energy consumption and tailor growing environments to crop needs through provision of specific wavelengths. Therefore, LED and HI lighting could provide growers an opportunity to increase efficiency and/or crop quality in greenhouse hydroponic crops. This work evaluates LED and HI lighting in leafy crops in Ohio winter production. All crops were produced in a polyethylene greenhouse in Wooster, OH. Three commercial lettuce (Lactuca sativa) cultivars (‘Fidel’, ‘Multy’, ‘Ferrari’) and ‘Genovese’ basil (Ocimum basilicum) were grown using nutrient film systems with solutions maintained at 1.8 mS·cm^-1 electrical conductivity and 5.8 pH. Greenhouse aerial temperature, relative humidity, and solar radiation in addition to nutrient solution pH, EC, and temperature were continuously monitored. Seeds were germinated in rockwool cubes (2.5 x 2.5 x 3.8 cm), transplanted to the growing channels after 2 weeks, and harvested after an additional 4 weeks. Fresh shoot weight was measured on all harvested plants along with fresh root weight, dry shoot weight, and dry root weight on a subset of plants. Experiment one (Jan.–Feb. 2010) compared biomass and quality across two solution temperatures (21 °C and 27 °C) and three lighting methods (LED1, LED2, HPS). Results showed no difference between the two solution temperatures, while higher biomass was produced with HPS lighting. However, laboratory and panel evaluations indicated that red-leaved lettuce tended to be more darkly pigmented in some LED treatments.  Experiment two (Jan.–Feb. 2012) compared biomass production and energy consumption in HI and HPS lighting systems each programmed to reach a lighting target of 14 mol·m^-2 per day.  Results showed no biomass difference between the two lighting systems, while demonstrating a potential energy savings of 2.3% to 16% for HI versus HPS lighting. These two experiments indicate opportunities for alternative lighting systems to impact crop yield, quality and energy use during winter leafy crop production in greenhouse hydroponic systems in northern US climates.