Growing Lettuce in Non-Aerated, Non-Circulated Hydroponic Systems

Abstract

Abstract Low density, plant-holding trays conveniently float on nutrient solution in hydroponic systems, but they do not provide an air space to the plant root zone. Astudy was conducted to determine if an air space between the tank cover and the nutrient solution affected lettuce using three non-aerated hydroponic methods that were also non-circulated. ‘Red Sails’ leaf lettuce (Lactuca sativa L.) was grown in 5-cm net pots supported by expanded polystyrene bead board tank covers where the board was supported by the tank frame and remained fixed, the board floated on the nutrient solution, and the board initially floated on the nutrient solution and sank to a 5-cm depth as the solution was depleted. Tanks were 8.9-cm high and contained 7.6 cm (109 L) of non-circulating nutrient solution. No additional nutrient solution was added. Lettuce was harvested when only 1.3 cm of nutrient solution remained in the tank. When the board remained fixed, head fresh weights averaged 220 g during seven crops over a period of one year. Head weights were 19% lower when the boards floated on the nutrient solution for the duration of the crop. However, head weights were only 7% lower when the boards were initially floated on the nutrient solution and then rested on a 5-cm high support during the latter stage of growth. A greater growth rate was encouraged by an air space with high relative humidity between the nutrient solution and the expanded polystyrene bead board tank cover.