Biomass production of lettuce: Nitrogen fertiliser and harvesting period effects on phytochemical composition in growth chamber-grown

Concern over the potential health benefits of the phytochemical compounds in lettuce has grown as intake of leafy vegetables, especially lettuce, has increased. This study was to investigate the effect of periods harvesting and the different dose of nitrogen fertilisation, including low, normal and high (100, 200 and 300 mg/L) respectively, on level of phytochemical compounds such as phenolic acids, flavonoids, carotenoids and chlorophylls in lettuce. The experiment was conducted in the growth chamber at Newcastle University. The plants were randomly designed for 3 treatments with 15 replications. Plants were harvested in three different periods. The first harvest took place after 6 weeks from planting, and the second and third harvests were done after 7 and 8 weeks from planting, respectively. After each harvest, the chlorophyll content and total carotenoids and other phytochemicals were measured by high performance liquid chromatography (HPLC) before and after drying the plants. The plant biomass was higher at normal nitrogen application (200 mg/L) in all periods of harvesting. As well as, significantly increased plant phytochemicals including carotenoids and chlorophylls, while, the composition of phenolic acids and flavonols were not affected such as, higher level of nitrogen fertiliser to the soil has resulted in a higher concentration of chlorophyll a and chlorophyll b in the lettuce by 154.2~420.3%, 72.1~287.9% respectively. As well as, that lutein was increased from 209 µg/g dry weight at the first period of harvest to 287 µg/g dry weight at the second period of harvest. Furthermore, the total phenolic increased by 25%. The findings of the current study showed that plant maturity has a positive correlation with plant phytochemicals.