Objective In order to explore the effects of different proportions of biochar on the quality of tobacco leaves, optimize the production measures of tobacco leaves and improve the quality of tobacco leaves, to provide theoretical basis and technical support for the green and high-quality production of flue-cured tobacco.

Method This study carried out field experiments in Luliang, Yunnan Province. Using 'Honghuadajinyuan' as the test material, six treatments were established: the control (CK) with conventional fertilization (pure nitrogen 97.5 kg/hm²); 20% nitrogen reduction (T1); conventional fertilization + 1 125 kg/hm² biochar (T2); conventional fertilization + 2 250 kg/hm² biochar (T3); 20% nitrogen reduction + 1 125 kg/hm² biochar (T4); 20% nitrogen reduction + 2 250 kg/hm² biochar (T5). The effects of these treatments on soil physical and chemical properties, agronomic traits, chemical composition and sensory quality of tobacco leaves were systematically analyzed.

Result Biochar application significantly improved soil structure, increased nutrient content, and had a positive effect on the quality of tobacco leaves. Among them, T3 treatment was the most prominent in soil fertilization. The soil available potassium content was 887.00 mg/kg, and the organic matter content was 54.33 g/kg, which was 75.0% and 38.5% higher than CK, respectively. In terms of agronomic traits of tobacco leaves, T5 treatment was significantly better than other treatments in plant height and maximum leaf area, and T3 treatment had the best number of leaves per plant. The chemical composition analysis showed that the nicotine content of T5 treatment was the lowest, which was 47.5% lower than that of CK, and the coordination of sugar and alkali was better. The content of reducing sugar and total sugar in T4 treatment was the highest, showing good chemical coordination. The results of sensory evaluation showed that the total score of CK was the highest (84.50 points), while the total score of T3 treatment was the second (82.75 points), but it was better in the improvement of aroma quality (12.25 points) and the decrease of irritation (11.8 points), and the comprehensive quality was outstanding. The total sensory score of tobacco leaves treated with T5 was 80.20 points, which was lower than that of CK, but it maintained good performance in key dimensions such as aroma quality (11.30 points) and irritation (11.8 points).

Conclusion This study confirmed that the application of 2 250 kg/hm² biochar in Luliang tobacco area could synergistically improve soil and regulate tobacco leaf quality; among them, the conventional fertilization combined application (T3) is the comprehensive optimal solution, and the 20% nitrogen reduction combined application (T5) is an ideal alternative to achieve green production.