Excess Nitrogen Exceeds the European Standards in Lettuce Grown under Greenhouse Conditions

Nitrogen is one of the most important plant nutrients for lettuce (Lactuca sativa L. var. Kitare). However, excess use of N causes environmental and health problems. In this study, the response of lettuce plants to different amount of N and irrigation levels were studied. The experiment was conducted under glasshouse conditions for winter and spring growing seasons in Bati Akdeniz Agricultural Research Institute (BATEM), Antalya, Turkey. This study used a factorial design with three replications. Plant evapotranspiration varied from 14.4 to 28.8 and 16.3 to 32.6 L plant(-1) in winter and spring, respectively. Nitrogen fertilizer levels affected lettuce yield in both growing seasons, whereas irrigation levels did not impact yield. The average yield varied from 354 to 472 g plant(-1) in the winter growing season and from 333 to 611 g plant(-1) in the spring growing season. The nitrate concentration in lettuce leaves increased with N rate and irrigation level, and was lower in spring than winter. The average nitrate accumulation varied from 4000 to 6000 and 2100 to 3600 mg kg(-1), in the winter and spring growing season, respectively, exceeding the health standards of the European Union.