Effects of Different Organic Amendments on Root System, Growth, Yield and Quality of Flue-Cured Tobacco in the Ruyuan Tobacco-Growing Region

Abstract: Excessive reliance on chemical fertilizers has raised concerns regarding soil degradation and tobacco quality in subtropical growing regions. This study evaluated the effects of different organic amendments on root development, physiological performance, yield, and leaf quality of flue-cured tobacco in the Ruyuan tobacco-growing area. A field experiment with six treatments was conducted, including conventional fertilization alone (CK) and five organic amendment treatments: rice straw biochar, bagasse, rapeseed cake fertilizer, rice straw returning, and bio-organic fertilizer. Organic amendments significantly promoted root growth and plant development. Biochar application showed the most pronounced effects, markedly increasing root biomass and root activity compared with the control. Improvements in root development were accompanied by enhanced agronomic performance, particularly during the vigorous growth stage, when plant height, stem girth, and leaf expansion were substantially improved. Photosynthetic capacity was also enhanced under organic amendment treatments, as indicated by higher SPAD values, net photosynthetic rate, stomatal conductance, and transpiration rate. In addition, antioxidant enzyme activities in leaves were significantly elevated, suggesting improved physiological resilience. Organic amendments further optimized leaf chemical composition by regulating sugar accumulation and mineral nutrient balance, which contributed to increased yield and a higher proportion of medium-to-high grade tobacco leaves. Among the tested materials, rice straw biochar and bagasse showed the most consistent benefits in promoting plant growth and improving leaf quality. Overall, the results indicate that carbon-rich organic amendments are effective in enhancing soil–plant interactions and tobacco production performance, and biochar or bagasse application is recommended for improving flue-cured tobacco quality in subtropical tobacco-growing regions. Keywords: organic amendments; flue-cured tobacco; root development; photosynthesis; leaf quality; yield