2017 ASHS Annual Conference

High quality water is often used in a recirculating hydroponic system. However, high quality water is not always accessible to growers, especially in water scarce regions. Limited information is available on the effect of water quality on plant growth and quality. A greenhouse experiment was conducted to evaluate the feasibility of using marginal water for leaf vegetable production in a nutrient film technique (NFT) system. Seeds of Brassica rapa var. chinensis ‘Tokyo Bekana’, ‘Mei Qing Choi’, and ‘Rosie’ (pac choi) and Lactuca sativa ‘Tropicana’ (leaf lettuce) were germinated and grown in a growth chamber. Seedlings were transplanted to the NFT systems on 22 Sept. 2016. Nutrient solutions were prepared by using CNS17 grow solution diluted with three water sources (treatments): reverse osmosis (RO) water, tap water, and tap water plus NaCl with final electrical conductivity (EC) of 1.6, 2.4, and 3.2 dS/m, respectively. Nutrient solution was replenished on 5 Oct. and 10 Oct. using the one third strength of CNS17 solution diluted with RO, tap water, and tap water plus NaCl at EC of 0.7, 1.6, and 2.4 dS/m, respectively. The four vegetable varieties responded to base water quality differently. No differences between RO and tap water were found in all growth parameters and SPAD readings of ‘Tropicana’ lettuce, ‘Mei Qing Choi’, and ‘Tokyo Bekana’. For ‘Rosie’, plant growth was better in tap water than RO was as the base water source. High salinity reduced all growth parameters and SPAD readings of ‘Tropicana’ lettuce and ‘Rosie’, whereas fresh weight and height of ‘Mei Qing Choi’ and ‘Tokyo Bekana’ were reduced. The NO₃^- concentration in the nutrient tank decreased to below 500 mg/L in the third week in all treatments. K⁺ decreased to zero in the last three days with RO and tap waters as the base water, indicating additional K⁺ is necessary in replenishing solution. Other ion concentrations of the tank solution did not decrease except for P. Mineral analysis indicated that leaf mineral contents varied with type of vegetables. High salinity reduced Ca and Mg in ‘Tokyo Bekana’. For micronutrients, RO water treatment slightly reduced leaf Fe and Cu in ‘Tokyo Bekana’ and leaf Cu in ‘Rosie’. Leaf Na was increased by high Na in the nutrient solution in all vegetables. More studies are needed to determine the threshold of NaCl in marginal water that affects the growth and quality of leaf vegetables.