Nutrient Solution Temperature Affects Growth and °Brix Parameters of Seventeen Lettuce Cultivars Grown in an NFT Hydroponic System

Nutrient solution temperature in a hydroponic system affects degrees Brix and yield of lettuce; thus, it is important to maintain the water temperature within an appropriate range. Nutrient-film technique (NFT) trials were conducted to investigate the effects of different water temperatures (18.3 degrees C, 21.1 degrees C, and ambient) on growth and degrees Brix of 17 cultivars from five different types (Loose leaf, Romaine, Butterhead, Salanova, and Batavian) of lettuce. The average daily water temperature for ambient treatment was recorded to be 20 to 26.5 degrees C. The study was conducted in a split-plot design with three replications over time. Results indicated that water temperature affected root and shoot fresh and dry weight, plant width, and degrees Brix for lettuce. Lettuce grown at 21.1 degrees C were 15% greater for shoot fresh weight than plants grown at ambient conditions. All the growth and quality parameters of lettuce were found to be affected by cultivars, with "Coastal Star" showing the best results in both growth and degrees Brix parameters. All the cultivars of the Romaine type showed greater growth and degrees Brix, while Salanova lettuce did not perform well in all treatments compared to other lettuce types. For CO2 assimilation, the interaction between water temperature and cultivars was significant, with "Parris Island" having the greatest rate at ambient water temperature. These results suggested that maintaining water temperature at 21.1 degrees C produced lettuce with greater growth and biomass but had 26% lower degrees Brix than lettuce grown at 18.3 degrees C.