Optimization of model plant lettuce production techniques in indoor vertical farming

A study was conducted on the cultivation of Lactuca sativa L. lettuce plants in a plant factory using two hydroponic techniques (aeroponic and ebb and flow) under three different LED lighting conditions, four different photoperiods, and three different temperature regimes. In line with the aim of the study, Batavia-type "Capira" lettuce was cultivated. Twelve days after sowing, lettuce seedlings were transferred to aeroponic and ebb and flow systems. The environmental conditions in the plant factory were regulated as follows: three temperature regimes day/night (S1 = 15/10°C, S2 = 20/15°C, S3 = 25/20°C), four LED light regimes light/dark durations of 12/12 (F1), 16/8 (F2), 18/6 (F3), and 20/4 (F4) hours, with the CO₂ level maintained at approximately 400 ppm and relative humidity stabilized in the range of 60-70%. Lettuce plants were grown under three different LED lighting conditions. LED1 = 70% red (610-720 nm) + 30% blue (450-495 nm), LED2 = Full PAR spectrum (400-700 nm), LED3 = 65% red (610-720 nm) + 25% blue (450-495 nm) + 5% white (400-475 nm) + 5% far red (700-760). 72 different combinations were set up by combining two hydroponic systems, three temperature levels, four photoperiods, and three different LED lighting factors. Under these specified conditions, lettuce plants were cultivated for 30 days and then harvested. At harvest, in terms of plant weight, the S2 temperature condition showed values 246.8% higher than S1, while S3 was 193.3% higher than S1. The highest dry matter measurements were recorded under the F3 (6.51%) and F4 (5.68%) photoperiods. Regarding total phenolic content, the highest values were obtained in the ebb and flow system, particularly in the LED2 × S2 × F1 = 94.61 mg GA/100 g TA and LED2 × S2 × F2 = 94.61 mg GA/100 g TA combinationsTotal flavonoid content was found to be higher in the ebb and flow system, particularly in the LED × S2 × F2 combination, where it was determined as 78.84 mg RU/100 g TA., nitrate levels in the ebb and flow system, particularly under the S1 temperature condition, were found to be the lowest [LED1 × S1 × F3 (101.33 mg/100 g TA), LED2 × S1 × F3 (109.66 mg/100 g TA), LED3 × S1 × F3 (113.33 mg/100 g TA)]. Among macronutrients, nitrogen, potassium, and phosphorus reached their highest values under the F4 photoperiod, while calcium and magnesium reached their highest levels under the F3 photoperiod. All micronutrients recorded their highest values under the S1 temperature condition. In general, the aeroponic system can be recommended to producers for achieving higher yields in lettuce cultivation. A photoperiod of 12 hours of light and 12 hours of darkness, temperatures of 15°C at night and 20°C during the day, and the LED3 spectrum are suggested. Key words: Aeroponic, Ebb and Flow, LED, Lighting, Photoperiod, Lactuca sativa var. crispa L