Impact of Urea Supplements and Cultivars on Yield, Nitrate Accumulation and Some Phytochemical Properties in Lettuce Grown under Greenhouse Conditions

A greenhouse experiment was assayed to study the impact of urea supplements 100, 200, and 300 kg ha-1 and cultivars Nadir, Polaris, and Fajir on the yield, nitrate accumulation and some phytochemical contents in lettuce. The results indicated that all supplemental urea treatments significantly improved stem diameter, chlorophyll intensity in outer leaves, plant yield and total marketable yield. In addition, the urea doses markedly increased nitrate accumulation in leaves, while its accumulation declined at the highest level compared to the other doses. Furthermore, the TPC significantly decreased at the high dose of urea supplement. Additionally, the urea supplement, especially 100 and 300 kg ha-1, notably increased TFC. The Polaris cultivar showed the highest stem diameter, chlorophyll intensity in the inner leaves, dry matter percentage, plant yield, total marketable yield as well as accumulated minimal nitrate in their leaves. Moreover, the highest content of TPC and TFC was obtained by Nadir cultivar. In addition, the Fajir cultivar recorded the highest activity of total antioxidants. Finally, the interaction between Polaris cultivar and 200 kg ha-1 urea maintained a good balance between the yield and its quality. As a result, the findings of this study may help our growers adopt the optimum urea concentrations with lettuce cultivars in their fields under greenhouse circumstances.