Investigations of close-grown tobacco (Nicotiana tabacum L.) with plant populations below 136,400ha have shown that yield is increased with increased plant number. Marked differences in the appearance of stalk grown over a range of plant populations suggest that there may be physical or chemical advantages for growing close-grown tobacco at even higher populations. With the development of direct field seeding or completely mechanized transplanting techniques, production at such levels may be economically feasible.
The present study was conducted to determine the yield, alkaloid, and sugar concentrations of close-grown tobacco produced at populations ranging from 98,840 to 296,520ha.
‘Speight G-28’ was grown in a close-grown system in 1976 and 1977 at the Oxford Tobacco Research Station on a Helena loamy sand (clayey mixed, thermic, Aquic Hapludult). Treatments included factorial combinations of plant population (98,840, 148,260, 197,680, 296,52Oha), topping height (12, 16, and 20 Ieavedplant), and N-rate (168, 252, 336 kgiha). Plants were harvested once-over and yield, total alkaloids, and reducing sugars were determined for lamina, midrib, and stalk.
Whole-plant yields increased with increased plant population, Nrate, and/or topping height but yields of individual plant parts responded differently. Midrib yield did not change with any of the treatments but lamina increased with increased population and topping height through 16 leaves. Stalk followed the same yield pattern as whole-plant material and increased at a greater rate than lamina. Total alkaloids increased with higher N-rate and lower topping height but decreased with increased population. Reducing sugars did not change with increased population or topping height but decreased with increased N.
Effects of plant population and topping height are more predictable than that of N-rate which is greatly influenced by seasonal growing conditions. A maximum leaf canopy apparently exists for a given planting design and density. Increased plant number above this level results mostly in increased stalk yield. Production at high populations will therefore depend on the acceptability of significant amounts of stalk in the smoking material.