Effect of Planting Density on Light Transmittance and Canopy Photosynthesis of Flue-cured Tobacco Plants

Canopy photosynthetic capacity determines the yield and quality, while planting density affects the growth and canopy development of a flue-cured tobacco plant. Varied planting densities (i.e., D₁at 16 529 plants per hm², D₂ at 18 182 plants per hm², and D₃ at 20 202 plants per hm²) were applied to study their effect on the leaf area index (LAI), light transmittance (LT), photosynthesis, and economy of the canopies on Yunyan 85tobacco plants. The results showed that, during the entire course of canopy development, LAI was at its highest level and the distance between leaf tips of adjacent lines (DLT) and LT at their lowest in the dome stage. As the leaves matured and upon harvest, LAI declined, while DLT and LT increased. Consequently, the canopy photosynthetic rate (RCP) peaked during the dome stage. In comparison, in the same period, an increased planting density would induce a heightened LAI but lowered DLT and LT. On the other hand, the changes of planting density or leaf-harvesting did not significantly affect RCP on the plants. LAI was found inversely correlated to DLT and LT.The correlation between RCP and planting density varied at the dome stage. RCP raised as the density increased from D₁ to D₂, but decreased from D₂ to D₃. And, RCP correlated to leaf-removal, but insignificant. RCP could not be continually risen with increasing planting density. In fact, it declined when the density exceeded a certain level. Yield and output on tobacco leaves increased significantly as the planting density increased from D₁ to D₂, but decreased from D₂ to D₃. The percentage of high-grade tobacco was maximized with D₂ among the 3 treatments. Taking the canopy development, field management and production cost together into consideration, a planting density approximating 18 182 plants per hm²seemed optimal for Yunyan 85 cultivation.