| The effects of drought stress on accumulation and distribution of nutrients in flue-cured tobacco (Nicotiana tabacum L.) plant and yield and quality of the leaves were studied in pot experiment. At the same time, the regulating effects of different cultivation practices on the content of nutrients in the plant and yield and quality were also studied in field experiments. The results were as follows: 1.Under drought stress, the content of N in tobacco plant increased and the content of P, K, Ca, Mg, Fe, Mn decreased significantly, while the change of Cu, Zn, B content was not significant. It was also found that the accumulation of dry matter and nutrients in the plant decreased obviously, and their distribution ratio in root and stalk was higher than that in leaves. 2. There was close relationship between dry matter accumulation and the content of nutrients in the plant and the leaf tissue under drought stress. The content of N, P, K in the plant and N, P, K, Ca, Mn in the leaf tissue was positively correlated with dry matter accumulation of the plant respectively when drought occurred at the root spreading stage. The positive relationship was found between dry matter accumulation and the content of N, P, K, Mg, Mn, Zn, B in the plant and the content of N, K, Ca, Mg, Fe in the leaf tissue under drought stress at vigorous growing stage. Dry matter accumulation was also positively related to N, P, K, Mg, Mn content in the plant and N, K, Mn content in the leaf tissue at maturing stage. Under drought stress, the effect of N content in tobacco plant on dry matter accumulation was most significant, followed by the content of P and K. The content of other nutrients was not found significantly to affect the dry matter accumulation. 3. Drought stress resulted in decrease of the yield and the content of reducing sugar of flue-cured tobacco, and increase of the content of total nitrogen and nicotine. The severer the drought, the more significant the effect was. The most noticeable influence of drought stress on yield was observed when drought occurred at vigorous growing stage. The content of nutrients in tobacco plant and the leaf tissue closely correlated with yield and quality of tobacco under drought stress. The content of N in tobacco plant was positively related to yield, content of total nitrogen and nicotine in cured leaves when drought occurred in all growing stages. However, the content of reducing sugar in cured leaves was negatively correlated with N content in the plant. The effect of nutrients content in the plant on yield and quality of the cured leaves was the same as observed in dry matter accumulation under drought stress. 4. Under drought stress, the content of N, P, K, Mn in tobacco plant increased significantly with the increasing of nitrogen, and the content of Ca, Mg, Fe decreased obviously, but the accumulation of all kinds of nutrients in the plant increased markedly. And it was also found that the distribution ratio of most of the nutrients in root and stalk was higher than that in leaf when drought occurred at root spreading stage, the opposite result was observed at vigorous growing and maturing stage. With the increase of nitrogen rate, the yield and the content of total nitrogen and nicotine in cured leaves were increased, but the content of reducing sugar was decreased under drought stress. 5. The results of field experiments showed that: ①Increasing nitrogen rate could increase the content of N, P, K, Mn in root, stalk and leaf, but decrease the content of Ca, Mg, Fe. Within the range of 0—67.5kg/hm2, the yield, high quality leaf ratio, content of total nitrogen and nicotine in cured leaves increased significantly, but the content of reducing sugar decreased obviously with the increasing of nitrogen. The suggested application rate of nitrogen was 45—67.5 kg/hm2 in which both the yield and quality of tobacco leaves would be favorable. ②With the increasing proportion of nitrate and ammonium, the content of N, K, Ca, Mg in tobacco plant, high quality leaf ratio and content of total nitrogen in cured leaves increased, the content of nicotine and reducing sugar decreased, but no significant variation was found in yield. The favorable proportion of nitrate and ammonium was 1∶1 at which both yield and quality of tobacco could be improved. ③Increasing organic fertilizer (sesame cake) supply, the content of Mg, Mn, Cu, Zn in tobacco plant increased, but the content of N, Fe and B decreased. There was not significant difference in yield when tobacco fertilized with organic nitrogen compared with mineral nitrogen, but the high quality leaf ratio and the content of total nitrogen and nicotine in cured leaves decreased significantly, while the content of reducing sugar increased obviously. Higher yield and quality of tobacco was produced when the proportion of organic nitrogen and mineral nitrogen was 1∶1. ④Application of humic acid could increase the content of N, P, K, Fe in tobacco plant. With the increasing of humic acid, the yield, high quality leaf ratio and the content of nicotine in cured leaves increased, the content of reducing sugar decreased, but the difference in the content of total nitrogen was not significant. ⑤Mulching tobacco with plastic film could significantly increase the content of N, P, K, Cu, Zn in the plant at root spreading stage, however, the content of N, P, K, Mg, Fe, Mn, Zn decreased obviously at vigorous growing and maturing stage. It was also found that both yield and high quality leaf ratio was improved significantly by plastic film mulch under drought condition, but decreased markedly under irrigation condition. ⑥Excessive potassium supply did not influence the yield and quality of tobacco. ⑦The results from all the field experiments showed that yield and high quality leaf ratio of tobacco increased significantly with irrigation, and the content of mineral nutrients in the plant and the chemical composition of the cured leaf were improved in different degrees, but the interaction of irrigation with nitrogen rates, nitrogen sources, potassium rates, organic nitrogen rates, humic acid rates on the content of nutrients and chemical components of tobacco was not significant.
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