Agronomic Practices to Reduce Alkaloid Levels in Dark Fire-Cured Tobacco

Field experiments were conducted at two locations over two years to evaluate the effects of agronomic practices on physical and chemical properties of dark fire-cured tobacco. Locations were at the Highland Rim Research and Education Center in Springfield, TN, and at the University of Kentucky Research and Education Center in Princeton, KY. One experiment was conducted in Springfield, TN, in 2016 and experiments were conducted at both locations in 2017. These experiments evaluated two dark tobacco varieties (KT D14 LC and KT D18 LI), two nitrogen rates (84 kg N/ha applied preplant and 196 kg N/ha - 84 kg applied preplant followed by 112 kg at layby), three topping stages (early button, late bloom, and immediately prior to harvest), and two sucker control methods (dropline application with fatty alcohol solution and hand-suckered). The 2017 experiments did not evaluate the sucker control treatments. Soil amendments, pest control, and all other production practices were carried out according to university recommendations. The effects of variety and nitrogen rate on yield were inconsistent. However, similar yield and quality was observed for both varieties when averaged across all years and locations. Leaf chemistry was inconsistent between both varieties. Reduction of nitrogen reduced alkaloids, nicotine, TSNA, and NNN, while earlier topping increased alkaloids, nicotine, TSNA, and NNN. However, results could have been influenced by the amount of days after topping until harvest. While topping immediately prior to harvest significantly reduced alkaloids, nicotine, TSNA, and NNN, this practice also severely decreased yield and quality. Leaf from higher stalk positions produced higher levels of all chemical constituents, except nicotine to nornicotine conversion and NNK. Conversely, lower stalk positions resulted in higher levels of nicotine to nornicotine conversion and NNK. Based on the results of this study, reduced nitrogen and later toppings decreased the amount of certain chemical constituents in the cured leaf.