Yield and Nicotine Content of Flue-Cured Tobacco as Affected by Soil Nitrogen Mineralization1

Nitrogen (N) supply is the most important factor affecting yield and quality of flue-cured tobacco (FCT). A field experiment and an in situ incubation method were used to study the effects of soil N mineralization in the later stages of growth on yield and nicotine content of FCT in Fenggang and Jinsha, Guizhou Province. The yield and market value of FCT at Fenggang were much lower than those at Jinsha. However, the nicotine content of middle and upper leaves was much higher at Fenggang than at Jinsha when the same rate of fertilizer N was applied, which might be due to a higher N supply capacity at the Fenggang site. At later stages of growth (7–16 weeks after transplanting), the soil net N mineralization at Fenggang (56 kg N ha−1) was almost double that at Jinsha (30 kg N ha−1). While soil NH4-N and NO3-N were almost exhausted by the plants or leached 5 weeks after transplanting, the N taken up at the later growth stages at Fenggang were mainly derived from soil N mineralization, which contributed to a high nicotine content in the upper leaves. The order of soil N contribution to N buildup in different leaves was: upper leaves > middle leaves > lower leaves. Thus, soil N mineralization at late growth stages was an important factor affecting N accumulation and therefore the nicotine content in the upper leaves.