ObjectivesNitrogen is the most important element affecting the growth, development and quality of flue cured tobacco. Nitrogen deficiency or excess can greatly affect the yield and quality of flue-cured tobacco. This paper aimed to understand the relation between nitrogen supply and nitrogen uptake of flue-cured tobacco, which can provide a theoretical basis for improving management level of nitrogen nutrition of tobacco grown in southwest China.

MethodsSeveral fertilization experiments were carried out in Yunnan and Guizhou Provinces. The in situ incubation and ¹⁵N isotope tracing method were used to study nitrogen absorption of tobacco from soils and fertilizers.

ResultsThe results showed that the N amount in flue-cured tobacco was positively correlated with the soil basic N supply. Soil basic nitrogen supply (SBNS) explained the variation of nitrogen in flue-cured tobacco and soil nitrogen for 82.6% and 84.8%, respectively, which was decisive factor for nitrogen accumulation in tobacco. SBNS was closely related to the content of soil organic matter. When the soil organic matter contents were within the range of 0–35 g/kg, the SBNS increased with the increase of organic matter content. In view of the requirement of flue cured tobacco to nitrogen, SBNS with 60 kg/hm² and SOM with 20 g/kg were more suitable for the formation of tobacco leaf quality. The sources of nitrogen in flue-cured tobacco mainly included the mineralized nitrogen, initial inorganic nitrogen in soil and nitrogen fertilizers. The amounts of soil mineralized nitrogen were 19.9–38.9 mg/kg during the growing season. There was a nonlinear correlation between soil mineralized N and N in flue-cured tobacco. The N amount in flue-cured tobacco was not increased when the content of mineralized N increased to 30 mg/kg. The relationship between mineralized N and SOM can be expressed by a logarithmic equation which can predict the supply of mineralized N. The input of soil initial inorganic nitrogen and fertilizer nitrogen was 14.1–237.7 kg/hm². There was a significant positive correlation between the nitrogen input and nitrogen accumulation in flue-cured tobacco, when the input amount was more than 150 kg/hm², the nitrogen amount of tobacco became stable. Flue-cured tobacco nitrogen accumulation was increased with the increase of inorganic nitrogen supply. The increasing trend became slow when inorganic nitrogen reached more than 300 kg/hm², and at this point, the amount of nitrogen accumulation reached 100 kg/hm². The correlation coefficient between soil organic matter and nitrogen utilization efficiency was 0.783 (P < 0.01), and the utilization rates of fertilizers were from 25.4% to 37.1%.

Conclusions Overall, for the production of flue-cured tobacco in southwest China, the soils should be considered in priority in which the basic soil nitrogen supply is about 60 kg/hm², organic matter content about 20 g/kg, the supply of the fertilizer nitrogen and soil initial inorganic nitrogen should be within 150 kg/hm², total inorganic nitrogen supply within 300 kg/hm². The current average of fertilizer nitrogen utilization efficiency in this area is relatively low at about 32.6%, which could be increased by cultivating soils and improving soil fertility.