Cooling the high temperature nutrition solution to improve growth, yield and water productivity of hydroponic red lettuce (Lactuca sativa L Var Red rapids) in a tropical location

Red lettuce is preferred because of its high nutritional, vitamin, and antioxidant contents. Hydroponic cultivation has been known to successfully improve the quality and productivity of red lettuce. But the efforts to increase the productivity of hydroponic red lettuce face constraints of high temperatures in the tropics. The aim of this study was to compare the growth, yield, and water productivity of red lettuce in three hydroponic systems namely wick, floating raft, and dry systems by controlling the temperature of the nutrient solutions using protected nutrient containers. The experimental design of  randomized complete block split plots with the main plots of the nutrient containers which consisted of three levels: Refrigerated container, styrofoam-insulated container, and bare bucket container in which the nutrient solution was delivered to plants in three separated gutters as the cultivation beds, then recirculated back to the corresponding nutrient container. The secondary plot is hydroponic systems including three systems namely wick, floating raft, and dry systems. The blocks were the arrangement of plants according to the flow direction of the nutrient solution, namely upstream, middle and downstream in each gutter. Each experimental unit was represented by 3 plants. Data sets were analyzed by using analysis of variance and followed by LSD multiple comparisons at the 5% level. The results showed that the temperature of the nutrient solution controlled by the three containers had a significant effect on all observed plant parameters. Meanwhile, the hydroponic systems and the blocks had no significant effect. The use of Refrigerated container showed the best performance in improving the growth, yield, and water productivity of the red lettuce.