Accumulation and distribution of nitrogen in tobacco from different sources and their effects on quality of flue-cured leaves

Accumulation of dry matter, absorption and distribution of nitrogen in tobacco from fertilization and soil nitrogen, and the effects of nitrogen fertilization and soil nitrogen on quality of flue-cured tobacco leaves were studied by using 15N-labelled field experiment on a paddy soil. The experiment was carried out in two fields at Zhaowei Village Group 6 (A) and the Zhaowei Experiment Base (B) located in Hongta District, Yuxi City, Yunnan Province, China, respectively. There are two treatments in each field, without nitrogen fertilization and application nitrogen fertilizer at a rate of N 90 kg/ha. The results indicated that dry matter and nitrogen content of flue-cured tobacco were significantly increased with application of nitrogen fertilizer. However, both dry matter accumulation and nitrogen absorption were excessive in the latter growth periods of tobacco. In the fertilization treatment, the main source of nitrogen for tobacco was from soil nitrogen, and the ratio of nitrogen uptake from the soil to the nitrogen from the both sources (fertilization and soil) was evidently increased with growth period extending and stalk position ascending. The ratio was up to 0.69 and 0.74 at the end of growth period in A and B fields, respectively. The results also showed that the nitrogen content and nicotine of leaves without nitrogen fertilization were lower than those with the application nitrogen fertilizer, and the ratio of nitrogen to nicotine was lopsided under the condition of without the fertilization. The content of nitrogen in leaves was appropriate in the fertilizer treatment, while the nicotine content of upper leaves were too high due to the fertilization. The study indicates that it is important to choose fields with appropriate organic matter concentration to plant tobacco and to control nitrogen application amount in latter growth periods for reducing nitrogen and nicotine concentration of upper leaves and improving the overall quality of flue-cured tobacco.