Multiobjective Optimization of Chlorine Fertilization Enhances Yield and Quality in Cigar Tobacco

<title>Abstract</title> <p> Chlorine (Cl) is a critical but understudied micronutrient of cigar tobacco ( <italic>Nicotiana tabacum</italic> L.), influencing both yield and leaf quality. This study evaluated the effects of exogenous Cl application on yield, physical traits, and chemical quality of two cigar tobacco varieties, CX-26 and CX-14, under field conditions in China. A six-level Cl gradient was applied, and phenotypic and chemical analyses were conducted over two consecutive years. Principal component analysis was used to synthesize multiple chemical quality indicators into a single comprehensive score, and regression modeling and multiobjective optimization were used to determine optimal Cl application rates that balance yield and quality. Results showed different varietal responses. CX-26 benefited from moderate Cl input, achieving peak growth and yield at intermediate rates, whereas CX-14 was more sensitive to Cl, with growth and yield reduced at higher rates. For both varieties, the Cl content increased with Cl application, concurrently reducing the potassium-to-chlorine (K/Cl) ratio. Glycoalkaloid content and reducing sugar were also affected by Cl addition but their responses varied with varieties. The comprehensive chemical quality score peaked at intermediate Cl levels but decreased sharply at high Cl rates, underscoring the detrimental impact of excessive Cl on the overall chemical quality of cigar tobacco. Based on the combined evaluation of yield and quality, the recommended Cl application rates were 47.43 kg/hm² for CX-26 and 44.50 kg/hm² for CX-14. This study pioneers the multiobjective optimization of cigar tobacco yield and chemical quality, offering practical Cl fertilization guidance and new insights into Cl nutrition. </p>