The purpose of this research is to determine how increasing levels of nitrogen (N) fertilizers, locations, and cultivars affected yields, biomass accumulation, and polyphenol concentrations in lettuce. This study is carried out at the North Mississippi Research and Extension Center (NMREC) and Northwest Washington Research and Extension Center (NWREC). The experiment is a randomized complete block design arranged in a 2 × 2 × 4 factorial with 4 replications. Treatments include two cos (romaine) lettuce cultivars, ‘Salvius’ and ‘Thurinus’. N treatments include 42, 63, 105 and 189 kg·ha−1
. ‘Salvius’ has greater fresh mass (FM) and dry mass (DM), and a smaller DM:FM ratio when compared to ‘Thurinus’. The NWREC location has higher lettuce FM and DM. Quercetin-3-glucoside (Q-3-G) increases with increasing N concentrations. There are interactions between locations and lettuce cultivars for chlorogenic acid, Q-3-G, and quercetin/luteolin glucuronide (QL-G). There is increased chlorogenic acid content in ‘Salvius’ at the NMREC and increased concentrations of Q-3-G and QL-G in ‘Thurinus’ compared to the NWREC location. ‘Thurinus’ has significantly more chicoric acid and quercetin-malonyl-glucoside (QM-G) than ‘Salvius’. Lettuce at the NWREC has significantly more chicoric acid and cyanidin-3-glucoside (C-3-G). Lettuce at the NWREC has greater yields and biomass accumulation. Lettuce at the NWREC also has greater amounts of flavonoids and anthocyanins. ‘Salvius’ has greater amounts of phenolic acids and ‘Thurinus’ has greater amounts of flavonoids and anthocyanins.
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