Effects of different hydroponic nutrient solutions on biomass production and nutritional quality of aeroponically grown lettuce

The effects of five hydroponic nutrient solutions, Hoagland formula, Japanese Yamazaki formula (JY), Japanese Garden formula (JG), South China Agricultural University (SCAU) formula B for leafy vegetables and England Hewitt formula (EH) on the biomass production and nutritional quality of aeroponically grown lettuce (Lactuca sativa L.) were compared. The results showed that the pH levels of five solutions were increased to some extent during the treatment. The highest increase in pH was observed in EH, while the lowest was in SCAU formula B. Plants grown in SCAU formula B solution showed high fresh and dry mass of roots and shoots, compared to the plants grown in other four nutrient solutions. Furthermore, The plants treated with SCAU formula B showed the highest ascorbic acid content, FRAP (ferric reducing/antioxidant power) value, DPPH (1, 1-diphenyl-2-picrydrazyl) radical scavenging rate, as well as soluble sugar content in the leaves among all nutrient solution-treated plants. However, the soluble protein content was comparable to that of JG-treated plants, while the glutathione contents was lower than that of JG-treated plants. Furthermore, the nitrate contents of stems and leaves of SCAU formula B-treated plants were significantly lower than those of EH and Hoagland-treated plants, but a little higher than those of JG and JY-treated plants. These results indicate that aeroponically grown lettuce in SCAU formula B solution produce high biomass yield, high antioxidant content and antioxidant activity, and low nitrate content, suggesting that SCAU formula B is the most ideal nutrient solution for aeroponically grown lettuce, whereas EH and JY formulas are unsuitable for aeroponically grown lettuce.