Tob. Sci., 1991, 35, p. 74-8., ISSN.0082-4623

Optimum nutrition of flue-cured tobacco grown on a granitic sand in North Queensland

Dept. of Primary Industries, Mareeba, Queensland, Australia

Two field experiments were conducted at Southedge Tobacco Research Station, Mareeba, Queensland, Australia, in 1986 and 1987 to determine the rate of N and optimum fertilizer mixture with respect to P, K, Ca, and Mg to produce quality flue-cured tobacco (Nicotiana tabacum L. cv. ZZ100) on a granitic sand (Typic Paleustalf). Four rates of an experimental fertilizer mixture was evaluated at 4 rates of N (72, 96, 120, and 144 kg/ha). The mixture consisted of P, K, S, Ca, and Mg set at 100, 75, 50, and 25% relative to N, respectively, with the 100% mixture being 7N:2P:14K:2.5S:4Ca:1Mg. The effect of treatments on (a) plant nutrient accumulation, (b) chemical constituents of the cured leaf, and (c) extractable nutrients in the 0-30 cm soil depth was determined. The optimum fertilizer mixture which maintained agronomic performance of tobacco was 120 kg N/ha at 25% (7:0.5:3.5:0.6:1:0.25; N:P:K:S:Ca:Mg, respectively). Varying the fertilizer mixture from 100% to 25% of the m acroelements relative to N had no significant effect on the ten agronomic parameters measured. As N rate increased, consistent significant differences occurred in both experiments for green grades, leaf price, and nutrient accumulation by the plant; for N in root, stem, leaf, and whole plant; for K, Ca, and Mg in leaf and whole plant; and for Mg in root and stem for one experiment. The cured leaf concentrations of N, K, Ca, reducing sugars, and reducing sugar:alkaloid ratio were significantly altered by increased N rate in both experiments, and only in one experiment for Mg and alkaloids. Adjustment of the macroelement ratio to 75, 50, or 25% significantly altered leaf levels of P, K, and Ca in both experiments and Mg in one. Soil analysis indicated that P and exchangeable K would decrease if the 50 and 25% fertilizer mixtures were used on a granitic sand for more than 2 years at 120 to 144 kg N/ha.