Effects of different potassium and magnesium fertilizer treatments on physiology， yield， and quality of tobacco leaves of Hainan cigar tobacco

【Objective】 This study aimed to investigate effects of different potassium and magnesium fertilizer treatments on physiology， yield， and quality of Hainan cigar tobacco， elucidating how combined application of potassium and magnesium fertilizers balanced tobacco plant nutrition and improved tobacco leaf quality， thereby providing references for high-quality cigar tobacco production in Hainan.【Method】 Using the cigar tobacco cultivar Haiyan 103 as the tested materials， a rando-mized block design was used to set six treatments of different ratios of potassium and magnesium fertilizers： T0 （conventional fertilization）， T1 （with increased potassium）， T2 （1-stable potassium and increased magnesium）， T3 （2-stable magnesium and increased potassium）， T4 （1-increased magnesium and potassium）， and T5 （2-increased magnesium and potassium）. Indexes of agronomic traits， relative chlorophyll content （SPAD）， key enzyme activities in carbon and nitrogen metabolism， physical traits， chemical components， yield， and quality of tobacco plants at mature stage were measured.【Result】 Compared with T0， all treatments with increased magnesium and potassium fertilizers significantly increased plant height， underground part dry weight， and SPAD values （P<0.05， the same below）. Different treatments markedly affected key enzyme activities in carbon and nitrogen metabolism. The nitrate reductase （NR） activity in T3 was significantly higher than in other treatments， showing a 42.11% increase compared to T0， while amylase （AL） activity increased by 8.65% compared to T0. Tobacco leaf tension was the highest in T1， followed by T3， and the tension in both T1 and T3 was significantly higher than in the other treatments. Leaf thickness in T3 decreased by 1.71% compared to T0. Except for T5， the stem rates in all other treatments were significantly lower than in T0. Total sugar content in tobacco leaves was the highest in T3， with an 8.20% increase compared to T0. Reducing sugar content was the highest in T4 （0.39%）， followed by T3 （0.38%）. The sugar-nicotine ratio was the highest in T3 and T5， both showing increases of 19.23% compared to T0. Total tobacco leaf yield was the highest in T3， with a significant increase of 21.62% compared to T0. The wrapper yield and wrapper yield rate were the highest in T3， reaching 199.99 kg/ha and 22.48%， respectively. Economic benefits ranked as T3>T1>T4>T2>T0>T5， with T3 showing a significant increase of 46.19% compared to T0.【Conclusion】 Based on conventional fertilization， applying 300 kg/ha MgSO₄ improves physical traits and chemical composition of Hainan cigar tobacco leaves， promotes plant growth and development， substance accumulation， and carbon and nitrogen metabolism， and enhances tobacco leaf yield and economic benefits， thus providing a theoretical basis and technical reference for producing high-quality cigar in Hainan.