This study was conducted to investigate the effect of different irrigation and nitrogen levels on lettuce yield characteristics in greenhouse condition from December 2006 to March 2007. Irrigation levels of 100% of total class A pan (S1), 80% of total class A pan (S2), 60% of total class A pan (S3) and nitrogen levels of 0 kg ha^-1 (N1), 100 kg ha^-1 (N2), 200 kg ha^-1 (N3), and 300 kg ha^-1 (N4) were applied by drip system. Irrigation levels did not show any significant effect on head weight, marketable head weight, number of leaves, height of plants, head circle, root length, and root extent except core length and total soluble solid, TSS. The highest head and marketable head weight were found as 355.17 and 334.78 g in S1 application, respectively. Nitrogen levels had no significant effect on measured parameters. These values were the highest as 365.06 and 342.93 g in N3 application.

Key words: Lettuce, drip irrigation, nitrogen applications, greenhouse, head weight.