Objective This study aims to investigate the effects of organic fertilizer substituting chemical fertilizer at equal-nitrogen ratios on the agronomic traits of tobacco plants, as well as on leaf yield, quality, and combustibility, so as to provide technical support for scientific fertilization in tobacco production.

Method Using the cigar tobacco variety 'SCX4' as experimental material, a field plot experiment was conducted. With identical nitrogen, phosphorus and potassium application amounts, six treatments of organic fertilizer substituting 0%, 10%, 20%, 30%, 40%, and 50% of chemical fertilizer at equal nitrogen ratios, denoted as CK, M1, M2, M3, M4, and M5, respectively. Agronomic traits of tobacco plants, leaf quality grade proportions, yield, output value, chemical composition, and combustibility were measured, and a comprehensive evaluation was performed using the entropy-weighted TOPSIS method.

Result As the substitution ratio increased, plant height, stem girth, internode length, and maximum leaf area at topping stage all significantly decreased. CK and M1 exhibited the best agronomic traits, with no significant differences in all indicators except plant height between them, and both were significantly superior to the other treatments. M5 showed the poorest agronomic traits, with plant height, stem girth, internode length, and maximum leaf area decreasing by 23.05%, 14.11%, 17.24%, and 34.98%, respectively, compared with CK. Compared with CK, M5 significantly reduced yield by 23.75%, while M1-M4 showed no significant differences. M1 achieved the highest output value of 145 288 yuan/hm², which was 22.9% higher than that of CK. The proportion of first-grade leaves in M1-M5 was significantly higher than that of CK, with an average increase of 282.95%, and M1 had the highest proportion at 43.23%. With increasing substitution ratio, the reducing sugar content, sugar-to-nicotine ratio, and potassium-to-chlorine ratio in M1-M5 decreased compared with CK, with average reductions of 49.12%, 50.48%, and 52.58%, respectively. The chlorine content in M4 and M5 was significantly higher than that in CK. Correlation analysis revealed that gray value was significantly positively correlated with combustion speed, total sugar content, reducing sugar content, and sugar-to-nicotine ratio, and the key factors influencing gray value were sugar-to-nicotine ratio and combustion speed. The combustion speed and gray value of M1-M5 were lower than those of CK, with average reductions of 35.00% and 8.10%, respectively, indicating more complete combustion and ash color tending toward gray or grayish-white. Comprehensive evaluation of agronomic traits, yield, quality, and combustibility across all treatments ranked the comprehensive scores in descending order as M1、M4、M2、M3、M5、CK.

Conclusion Organic fertilizer substituting chemical fertilizer at equal nitrogen rates can increase tobacco output value, raise the proportion of first-grade leaves, harmonize chemical composition, and improve leaf combustibility. The optimal equal-nitrogen substitution ratio of chemical fertilizer with organic fertilizer for cigar tobacco leaves is 10%.