In order to study the effect of different levels of irrigation and nitrogen on some physiological traits of signet marigold (Tagetes tenuifolia), a study was carried out in greenhouse of Ferdowsi University of Mashhad, Iran in 2012 on the basis of a Randomized Complete Block Design with three replications. The main plot was irrigation interval at three levels of 2, 4 and 6 days and the sub-plot was N fertilization at three levels of 0, 15 and 30 g. Analysis of variance showed that the effect of irrigation interval was not significant on chlorophyll index, stomatal conductance and leaf area. N fertilization level significantly influenced total leaf area, but its effect was not significant on chlorophyll index and stomatal conductance, so that the increase in N fertilization level significantly increased total leaf area by 3.8%. So, it is recommended to use irrigation interval of 2 days and 30 g N fertilization to achieve the highest level of the studied physiological traits.

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