Effects of Combined Application of Organic and Inorganic Nitrogen on Soil Nitrogen Forms and Tobacco Leaf Quality in Changle

This study aims to investigate the effects of combined application of organic fertilizer and inorganic nitrogen on soil nitrogen forms and tobacco leaf quality in the tobacco-growing region of Changle, Shandong Province. A randomized complete block design (RCBD) was employed, incorporating six different ratios of organic to inorganic nitrogen, to evaluate their effects on soil nitrogen dynamics, agronomic traits of flue-cured tobacco, dry matter accumulation, nutrient uptake, photosynthetic performance, and the physical, chemical and sensory qualities of cured tobacco leaves. Results indicate that 60% organic and 40% inorganic nitrogen significantly increased soil nitrate levels at both the topping and harvest stages, whereas the 100% organic nitrogen treatment notably enhanced soil ammonium nitrogen levels. Plant height, leaf dry matter, and the accumulation of nitrogen and potassium initially increased and then decreased with rising proportions of organic nitrogen. The 60% organic + 40% inorganic nitrogen treatment outperformed the 100% inorganic nitrogen treatment across these parameters. Combined organic-inorganic nitrogen application significantly improved leaf net photosynthetic rate by 30.86% to 48.85%. Tobacco leaves under the 60% organic + 40% inorganic nitrogen regime exhibited significantly greater leaf length, width, area, and single-leaf weight compared to those receiving 100% inorganic nitrogen. Organic nitrogen application significantly increased potassium concentration in cured leaves (except under 80% organic + 20% inorganic nitrogen), with the 60% + 40% ratio enhancing potassium content by 0.35 percentage points. In sensory evaluation, this treatment yielded the highest overall score, characterized by rich aroma, a pleasant aftertaste, and minimal off-flavors. In conclusion, the rational integration of organic and inorganic nitrogen fertilizers effectively enhances soil nitrate availability, promotes nutrient assimilation, and improves both the chemical composition and sensory quality of cured tobacco leaves in Changle. The optimal fertilization strategy is determined to be 60% organic and 40% inorganic nitrogen.