Effects of Numbers of Leaves Remained and Topping Stage on Flue-cured Tobacco under Low Nitrogen Level

The effects of topping stage and numbers of leaves remained on the yield and quality of flue-cured tobacco under low nitrogen level were studied.The results showed that the topping stage influenced the upper leaves size significantly,while it had little influence on the middle and lower leaves size.Few leaves remained or later topping had adverse influence on the yield and quality of leaves.Topping at initial flowering stage and remaining 22 pieces of leaves,the yield,output value and price of leaves were the highest.Topping at initial flowering stage and remaining 18 pieces of leaves,the percentage of high class leaf was the highest.Remaining 14 or 18 pieces of leaves,the nicotine content increased,the reducing sugar content and the ratio of sugar to nicotine decreased,and the difference between total sugar and reducing sugar increased at early period,then decreased,and increased at later period with the delay of topping.