Objective The aims of this study were to reveal the suitable water and phosphorus dosage for the growth and development of flue-cured tobacco in Qiandongnan region, Guizhou Province.

Method A field plot experiment was conducted to study the effects of coupling treatment of different irrigation rate and different phosphorus application rate and control treatment on the growth, yield and quality of flue-cured tobacco. Four irrigation levels W₀-W₃ (0.00、0.50、1.00、2.00 L/plant), and three phosphorus application levels P₁-P₃ (32、64、96 kg/hm²) were set in this field plot experiment.

Result At the mature stage, the main agronomic traits of flue-cured tobacco had a good tendency with the increase of irrigation rate and phosphorus application rate. The plant height, maximum leaf area, leaf number, stem girth, internode length and root volume of W₃P₃ treatment were 17.77%, 16.08%, 4.88%, 12.22%, 11.67% and 10.90% higher than those of W₀P₃ treatment, and 14.11%, 16.80%, 2.38%, 17.44%, 9.84% and 9.50% higher than those of W₃P₁ treatment, respectively. With the increase of irrigation rate and phosphorus application level, the major chemical composition of tobacco leaves in each part gradually became coordinated. The contents of total sugar, reduced sugar, alkaloid, total nitrogen and total potassium in C3F of W₃P₃ treatment were 19.27%, 18.15%, 12.99%, 18.95% and 28.29% higher than those of W₀P₃ treatment, and 18.82%, 19.38%, 1.16%, 18.32% and 19.00 % higher than those of W₃P₁ treatment, respectively. The chloride ion content in C3F of W₃P₃ treatment was 1.79% lower than that of W₃P₁ treatment, and 1.85% higher than that of W₀P₃ treatment.The smoking quality and appearance in different parts of tobacco leaves also increased gradually with the increase of irrigation and phosphorus application rate. The smoking quality scores of B2F, C3F and X2F of W₃P₃ treatment were 1.19, 1.08 and 1.04 times that of W₃P₁ treatment, which were 1.10, 1.11 and 1.21 times that of W₀P₃ treatment. The appearance quality scores of B2F, C3F and X2F of W₃P₃ treatment were 1.12, 1.05 and 1.05 times that of W₃P₁ treatment, which were 1.16, 1.09 and 1.05 times that of W₀P₃ treatment. Phosphorus application and irrigation rate significantly affected the yield and economic benefits of flue-cured tobacco. The yield and output value of W₃P₃ treatment were 9.26% and 13.11% higher than those of W₃P₁ treatment, and 15.32% and 24.32% higher than those of W₀P₃ treatment, respectively. The correlation analysis showed that the yield of tobacco leaves had a significant positive correlation with the plant height and root volume of flue-cured tobacco within a certain range. In summary, when irrigation rate was 1.00 L per plant or 2.00 L per plant, phosphorus application rate was 64 kg/hm² or 96 kg/hm², W₂P₂, W₃P₂, W₂P₃ and W₃P₃ had a better effect in promoting growth, and improving yield and quality of flue-cured tobacco.

Conclusion When irrigation rate was 1.00 L per plant or 2.00 L per plant, phosphorus application rate was 64 kg/hm² or 96 kg/hm², it had a better effect in promoting growth, and improving yield and quality of the flue-cured tobacco in Qiandongnan tobacco region of Guizhou Province. From the point of view of saving water and fertilizer and obtaining high yield and quality, W₂P₂ can be used as an appropriate combination under the present experimental conditions.