Objective  Optimal number of canopy leaves on exit-nursery Hevea brasiliensis buddings cultivated using large polytubes was investigated.

  Method   Rubber plant buddings raised in large polytubes with 6 to 8 leaves on the canopy were grown by hanging root control method in separate batches denoted as Y6, Y7, and Y8, respectively. In addition, plants with retained one canopy leaf, P1, two leaves, P2, 3 leaves, P3, and 4 leaves, P4 were also included. The growth vigor, exit-nursery performance, and size of stem girth after 0.5 years of large polytube cultivation of the plants were evaluated by a fuzzy membership function method.

  Result   With significant differences between treatments, the plant height, canopy leaf count, and total leaf number of the buddings ranked Y6＜Y7＜Y8. In contrast, the average distance between two canopy leaves was Y6＞Y7＞Y8. The sprouting rates of the buddings with varied exit-nursery canopy leaf counts ranging from 93.34% to 94.25% were not significantly different among treatments. The rates of successful exiting nursery of the buddings were Y6＞Y7＞Y8, while the planting survival rates Y7＞Y6＞Y8. Upon leaving the nursery, the leaf retention proportions, which ranked P3＞P4＞P2＞P1, and the planting survival rates, which ranked P4＞P3＞P1＞P2, were both statistically significant. The significantly different stem girths of the exited plants were Y6＜Y7＜Y8 with Y6 being significantly smaller than the others after cultivating for half a years, but not significantly different between Y7 and Y8. The stem diameters of P1 and P2 were significantly smaller than those of P3 and P4 at time of exiting the nursery, whereas that of P2 significantly smaller than those of others after the 0.5-year cultivation.

  Conclusion  Considering the rates of successful nursery exiting, leaf retention, and survival after planting as well as the stem diameter and exit-nursery canopy leaf count, the large polytube-raised H. brasiliensis buddings with 7 canopy leaves (Y7) had a higher survival rate and stronger field growth than the others. After exiting the nursery, the 3-canopy-leaf P3 buddings appeared to be most successful among all regarding the exit-nursery proportion and large after 0.5-year-cultivation stem girth. These parameters could be used as an indicator for determining numbers of kept canopy leaves to be retained on the large polytube-raised H. brasiliensis buddings.