Influence of nitrogen rate, harvest frequency, lower leaf management, and chemical topping on mammoth cultivars of flue-cured tobacco
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Mammoth cultivars of tobacco do not flower under normal production conditions. A field management system must be devised for these cultivars to optimize agronomic traits and chemical constituents of the cured leaf. Field experiments were conducted at the Southern Piedmont Agricultural Experiment Station near Blackstone, Virginia in 1987 and 1988 to determine the influence of nitrogen rate, harvest frequency, and time and number of basal leaf removal on several agronomic and chemical properties of a mammoth cultivar of flue-cured tobacco. The feasibility of chemically topping two mammoth cultivars was also investigated. Increasing nitrogen rates increased values per hectere by $176 and total alkaloids by 0.5% in 1987. Increasing the number of harvest increased percentage lugs (X) and reducing sugars for stalk position B in 1988 but decreased reducing sugars for stalk positions A and C in 1988. Delaying leaf removal increased yield and values per hectare by 141 kg ha-1 and $84, respectively, and decreased lug production in 1987 and 1988. Total alkaloids decreased by 0.7% with delayed leaf removal in 1987. Delayed leaf removal increased reducing sugars at stalk position A by 2% in 1988. Removing fewer basal leaves increased yields by 115 kg ha-1, values per hectare, and percentage smoking leaf (H) for both years. Alkaloids for stalk position B increased with fewer basal leaves removed in 1988. Decreased basal leaf removal decreased plant height by 9 cm, percentage leaf (B), and reducing sugars in stalk positions A, B, and D in 1988. Delaying basal leaf removal and decreasing harvest frequency increased the percentage of cutters (C). Percentage smoking leaf increased with nitrogen rate and removal of fewer basal leaves. Chemical topping created taller plants with more leaves, narrower tip leaves, lower total alkaloids, and equal or higher reducing sugars relative to hand topping. Tip leaves from chemically topped plants were 6 to 8 cm shorter than hand-topped plants in 1987. Maleic hydrazide treatments resulted in 429 to 700 kg ha-1 lower yields and lower values than hand topping and 6 more suckers than all other treatments. The fatty alcohol / maleic hydrazide treatment produced 380 kg ha-1 higher yields and grade indices lower than the hand-topped control in 1987. Above normal nitrogen rate, 3 or 5 time harvest, removal of 4 to 6 leaves at topping or via senescence, and chemical topping with Prime+ or fatty alcohol / maleic hydrazide tank mix provided the best field management system for mammoth cultivars under the conditions of this study.
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