Effects of Different Topping Modes on Agronomic Characters and Usability of Upper Leaves of Flue-Cured Tobacco

To explore a suitable mode of topping and the influence of upper leaves usability of flue-cured tobacco in Shixing, the northern Guangdong tobacco area, the effect of different topping modes (topping at buttoning stage, topping at budding stage, topping at early blooming stage)on the agronomic characters, major chemical composition changes of upper leaves, yield, quality and the quality of cured leaves of flue-cured tobacco was investigated. The results showed that the height of the plant, the effective leaf number and the length of inter-nodes increased significantly with a postponed topping stage, while the biggest upper leaf area and the girth growth decreased. Different topping modes made a big influence on starch, soluble sugar, nicotine for upper leaves stage, but not so obvious on total nitrogen. The output value of topping at early blooming stage and proportion of middle and superior tobacco leaves increased by 6.48% and 7.73%, respectively, compared with the common mode of topping (topping at budding stage), potassium content being 13.02%; starch and nicotine decreased by 15.68% and 5.99%, respectively, and sugar-nicotine ratio and soluble sugar-protein ratio increased slightly, and the inner elements being harmonious. In a word, topping at early blooming stage could improve tobacco upper leaves’ usability and was worth being promoted in production.