| The nitrate, nitrite and alkaloids are precursor to form tobacco-specific nitrosamines (TSNA) in tobacco leaves. Factors that influence the precursor of TSNA could affect the accumulation of TSNA. Therefore, it is great important to decrease the TSNA content through controlling the accumulation of nitrate and nitrite by nutrition balance in production of high quality and low harm tobacco leaves. This experiment was conducted on the farm of Tobacco Corporation of Jinsha County, Guizhou Province in 2001. Through 6 single-factor experiments, including nitrogen form and rate, phosphate fertilizer, organic fertilizer, leaf surface nutrition, the proportion of base fertilizer to dressing fertilizer and methods of fertilization, effects of above nutrition conditions on nitrate and nitrite contents in both fresh leaves and cured leaves of flue-cured tobacco were studied. The results were as follows:1. There existed extensive variation for nitrate contents of both fresh leaf and flue-cured leaf and also for nitrite content of flue-cured tobacco among different leaf positions with large coefficients of variation. The variation of nitrate nitrogen content of flue-cured tobacco was highly significant at 1% level among different environments and leaf positions. It is possible to reduce nitrate nitrogen content of flue-cured tobacco by controlling the balance of fertilization and improving the technique of flue-curing.2. The nitrite content was found zero or trace in fresh leaves. The nitrate content of fresh leaf was lower than that of flue-cured leaf, and had highly significant positive correlation with the nitrate and nitrite contents of flue-cured leaf, which indicated the nitrate nitrogen content of flue-cured leaf being controlled by the nitrate content of freshleaf in the fields. The change of nitrate content showed the same trend as that of nitrite content among the different leaf positions, but the contents of nitrate and nitrite of cutters were bigger than those of upper leaves. In addition, the correlation coefficients of nitrate content were highly significant at 1 % level with the nitrite content in flue-cured leaf.3. As to the experiment of different nitrogen forms, the nitrate contents of both fresh leaf and flue-cured leaf, and also for nitrite content of flue-cured leaf, had significant positive correlation with the ratio of NH5/NO3. But the correlation coefficients of nicotine content and total nitrogen content in flue-cured leaf were nonsignificant at 5% level with the NH4/NO3 ratio. In the experiment of nitrogen rate, with the amount of nitrogen fertilizer increasing, the nitrate nitrogen contents of both fresh leaf and flue- cured leaf were increased, and had highly significant positive correlation at 1% level with the amount of nitrogen fertilizer. The correlation coefficients of nicotine content and total nitrogen content in flue-cured leaf were highly significant at 1% level with the amount of nitrogen fertilizer.4. With the amount of phosphate fertilizer increasing in this experiment, the contents of nitrate and nitrite decreased. The nitrate contents of both fresh leaf and cured leaf had significant or highly significant negative correlation with the amount of phosphate fertilizer. The change of nitrite content of flue-cured leaf showed the same trend as that of nitrate content. But the correlation coefficients of the amount of phosphate fertilizer with nicotine content, total nitrogen content and protein content were not significant at 5% level.5. Nitrate and nitrite contents could be decreased for cutters but increased for uppers in flue-cured tobacco leaves by applying different organic manures. Comparison among different treatments indicated that it was the lowest for the nitrate nitrogen content by applying fully- fermented plant manure, ranked second by applying oil cake,and highest by applying chicken droppings with oil cake together.6. The effect of the proportion of base fertilizer to dressing fertilizer (PBD) on nitrate and nitrit...
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