Abstract: This paper studied the carbon and nitrogen metabolism of flue-cured tobacco under effects of six treatments, i . e . , no topping (T₁), topping (T₂), topping+topdressing K₂SO₄ (T₃), topping+spraying IAA （indole-3-acetic acid）1 time (T₄), topping+topdressing K₂SO₄+ spraying IAA 1 time (T₅), and topping+topdressing K₂SO₄+ spraying IAA 2 times (T₆). The results showed that from the day of topping to the following 30 days, the amylase activity of flue-cured tobacco had a trend of decreasing first and increasing slightly then, while invertase (INV)activity decreased gradually. The activities of these two enzymes were the highest in T₆ and the lowest in T₁, with a significant difference. Except in T₁ , the starch content in all treatments increased gradually, and the total sugar content increased first but decreased then. At the 30th day after topping, the starch and total sugar contents were the highest in T₆, and the lowest in T₁. Nitrate reductase (NR) activity and protein content had a decreasing trend with the growth of tobacco, and were the highest in T₆ at the 30th day after topping. Treatment T₅ had the highest ratio of NR/INV after 30 days of topping. Spraying IAA at the top of tobacco plant on the day of topping combined with K topdressing could promote the growth and the carbon and nitrogen metabolism of flue-cured tobacco.

Key words: Soil nitrogen, Nitrogen cycle, Model, Simulation