Abstract: Taking three flue-cured tobacco (Nicotiana tabacum L.) varieties Y5, Y7, and NC89 as test objects, this paper studied the effects of nitrogen fertilization on their leaf senescence, photosynthetic characteristics, yield, and quality. Increasing nitrogen supply increased the leaf superoxide dismutase (SOD) activity, chlorophyll content, and photosynthetic performance, and decreased the leaf malondialdehyde (MDA) content significantly. Accordingly, the leaf senescence was delayed. Compared with Y5 and NC89, variety Y7 had higher leaf MDA content and lower leaf SOD activity, chlorophyll content, and photosynthetic performance, and thus, its leaves senesced faster. High quality tobacco leaves with higher average price, gross value, superior leaves percentage, and reasonable chemical constituents were harvested under the application of 45 kg N·hm^-2,compared with applying 60 and 75 kg N·hm^-2. It was suggested that different flue-cured tobacco varieties had obvious differences in their leaf senescence physiological characteristics, and nitrogen fertilization played important roles in regulating their leaf senescence, yield, and quality. Appropriate nitrogen fertilization could improve the quality of tobacco leaves, and achieve higher economic benefits.

Key words: flue-cured tobacco, nitrogen, leaf senescence, photosynthetic characteristic, yield, quality, landscape character, visual character, aesthetic assessment, landscape stewardship, field pattern.