Combined effects of root cutting,auxin application,and potassium fertilizer on growth,sugar: nicotine ratio,and organic potassium index of flue-cured tobacco

The total sugars and nicotine content in tobacco leaves affects the acid-base balance,while the ratio of total sugars to nicotine reflects the balance between tobacco taste and stimulation. The Project of International Quality Tobacco Development specified that the suitable ratio of total sugars to nicotine in Chinese tobacco was 8—12. Tobacco with high potassium content burns well with little tar release and has a satisfactory flavor. However,higher Cl-and SO2-4contents in tobacco are associated with lower potassium contents and reduced leaf flammability. The combination of potassium and organic acids contributes to the combustibility of tobacco leaf. The organic potassium index is the total potassium content minus the combined contents of Cl-and SO2-4. As a composite index,the organic potassium index reflects all the ions that affect the quality of flue-cured tobacco. The combustibility of tobacco with a low organic potassium index will be low,even if its total potassium content is relatively high. Varieties of flue-cured tobacco with a high total sugar: nicotine ratio and a low organic potassium index have been grown in tobacco-growing areas of Jiyuan,Henan Province,for a long time. Cutting roots can promote the growth of new roots and improve root activity. Applying auxin and potassium fertilizer can increase the potassium content in tobacco leaves,and strengthen the carbon and nitrogen metabolism of flue-cured tobacco after topping.However,the combined effects of root cutting,auxin application,and potassium fertilizer on tobacco quality had not been evaluated. In this study,we applied the following five treatments to tobacco: root cutting while topping( C); root cutting and auxin( indole-3-acetic acid; IAA) application while topping( C + I); root cutting and potassium topdressing while topping( C+K); root cutting,IAA application,and potassium topdressing while topping( C + K + I); and topping only( CK). We determined the effects of these treatments on tobacco biomass,the sugar: nicotine ratio,and the organic potassium index of tobacco in field experiments. All of these measures increased the biomass of roots and leaves at the advanced stage of maturity,compared with those of CK. Compared with the C treatment,the C +K +I treatment increased biomass of roots and leaves. All of these measures also decreased nicotine accumulation and total sugar content in upper leaves. Spraying tobacco plants with IAA reduced the sugar: nicotine ratio in various parts of tobacco plants; the largest decrease in the leaf sugar: nicotine ratio was in the C + K + I treatment. In that treatment,the sugar: nicotine ratio in the lower,middle,and upper tobacco leaves decreased by 19. 12%,15. 33%,and 8. 15%,respectively,compared with those in CK. In all of the treatments,the potassium content increased and the Cl-and SO2-4contents decreased,compared with their respective contents in CK. The C+K+I treatment increased the organic potassium index in lower,middle,and upper leaves. The largest increase was in the middle and upper leaves,which showed a 125% and 209% increase in organic potassium index,respectively,compared with that of the respective tissues in CK. From these results,we can conclude that the combination of root cutting,IAA application,and topdressing with potassium fertilizer contributes to the accumulation of dry matter,decreases the sugar: nicotine ratio,and increases the organic potassium index of flue-cured tobacco. Because most tobacco grown in China has a high nicotine content and a low ratio of total sugars to nicotine,this treatment could be used in different areas according to each local situation. Further research is required to clarify the mechanisms by which cutting,plant hormones,and potassium fertilizer treatments cause these physiological changes.