Reduced N supply limits the nitrate content of flue-cured tobacco

Among tobacco components, nitrate is one of the most harmful for human health because during tobacco burning nitrate reacts with alkaloids to form tobacco-specific nitrosamines. Nitrosamines are carcinogenic compounds identified in tobacco products and smoke. Despite a general consensus on the relevance of nitrate on human health, nitrate is currently not considered in the routine analysis of flue-cured tobacco, unlike total alkaloids, reducing sugars, total nitrogen, pesticides and chemicals for sucker control residues. In implementing strategies for tobacco cultivation, it is critical to minimize the nitrate content of the harvested product. On the other hand, the agronomic practices devised to reduce nitrate content should not adversely impact either the yield or commercial characteristics of the product. We carried out a field experiment over three years at one site of the Veneto plane, Northern Italy. We studied the influence of nitrogen supply on productivity and relevant chemical characteristics of flue-cured tobacco. Treatments consisted of four rates of nitrogen supply and one unfertilized control. The rates of nitrogen applied were 0, 15, 30, 45 and 60 kg N ha−1 in 1997, and 0, 20, 40, 60 and 80 kg N ha−1 in both 1998 and 1999. Our results show that annual fertilization rates within 40 kg N ha−1 fulfilled the crops’ requirements for productivity, with no adverse effects on product quality. Higher rates of nitrogen supply resulted in undesired increment in nitrate concentration and reduced sugar content in the cured product, without any gain in productivity. Moreover, we found no correlation between total nitrogen and nitrate concentrations of tobacco cured leaves. Since our data provide evidence that nitrogen content is not a reliable estimator of the harmful nitrate content, we suggest that nitrate should be taken under control in the routine analysis for assessing flue-cured tobacco quality.