IMPACT OF AIR TEMPERATURE AND ROOT-ZONE COOLING ON HEAT-TOLERANT LETTUCE PRODUCTION IN INDOOR FARMING UNDER LOW-SPEED AIR FLOW CONDITIONS

Abstract

Indoor farms are increasingly being used for lettuce production worldwide, but the high operating costs associated with temperature control via air cooling limit their profitability. In this study, we investigated the effect of adapting higher air temperature setpoints, heat-tolerant crops, and root-zone cooling (RZC) for improving the resource use efficiency of indoor farming systems in terms of biomass production, energy, and water use efficiency. Three lettuce cultivars with known heat tolerance were selected for this study: Skyphos, Muir, and Rex (control). Trials were conducted where all lettuce was grown under warm air temperature settings of 24°C, 26°C, 28°C, and 30°C with root zones either cooled to 22°C or left without cooling. Results indicate that cultivar significantly influences lettuce quality regardless of air temperatures. RZC lowered biomass production and light and energy use efficiencies but improved the water use efficiency at all air temperatures. Heat-tolerant lettuce had better fresh biomass production, with Muir yielding the highest shoot fresh weight in the higher temperatures, including the 28°C and 30°C control groups compared to both root-zone conditions for 24°C and 26°C and the 30°C RZC group. There was no significant difference in fresh biomass yields between the Rex and Skyphos control groups at different air temperatures. However, Skyphos in the 28°C control group yielded significantly higher fresh biomass than the RZC groups of Rex and Muir at 24°C and 26°C and both root-zone conditions for Muir at 28°C. Findings suggest that while RZC to 22°C did not enhance biomass production or tipburn prevalence, selecting heat-tolerant cultivars may optimize yield under higher temperature conditions.