2018 ASHS Annual Conference

In response to increasing interest in greenhouse production and difficulties imposed by adverse environmental conditions in the southeastern United States, a study was conducted with green and red-leaf lettuce cultivars grown in a deep-water culture production system. Plants were seeded in Rockwool and germinated under greenhouse conditions (Verona, MS; 34° N Lat.) at 25/20 °C (day/night) for 21 days before transplanting. The experimental design was a randomized complete block with a 2 x 3 factorial arrangement of cultivar and nutrient treatments that consisted of six replications, with individual tubs representing an experimental unit. Treatments consisted of two lettuce genotypes 1) green (Winter Density) and 2) red (Rhazes) and three nutrient treatments containing electroconductivity (EC) levels of 1) 1.0, 2) 2.0, and 3) 4.0 mS·cm^-1. After 50 days, plants were harvested, processed, and analyzed to determine marketable yield, biomass, plant height, and stem width. Additionally, nutritional quality was assessed by determining flavonoid and phenolic content and leaf elemental nutrient concentrations. Project results demonstrated that the interaction between growing season and lettuce cultivar was the predominant factor influencing yield, biomass, and plant quality. Nutrient solution EC treatment significantly affected shoot dry mass, biomass, and water content. EC treatment also significantly impacted the concentration of 3-O-glucoside and uptake of phosphorous, potassium, iron, boron, zinc, and molybdenum. Results from this study indicate that the effects growing season and cultivar on leafy lettuce performance (yield and quality) was more pronounced than the effect of nutrient solution EC treatment. However, despite statistical insignificance, all elemental nutrients increased with increasing solution EC. Thus, greenhouse production of green and red-leaf lettuce cultivars in the southeastern, United States should be conducted in the spring and fall growing seasons with elevated nutrient solution EC of ≈4.0 mS·cm^-1 to maximize yield and quality. The current study may spur research into the performance outcomes of increasing individual solution nutrients in conjunction with production season and green and red-leaf lettuce cultivars.