Influence of age and girth at opening on rubber yield, biochemical and tapping panel dryness parameters of Hevea brasiliensis in determining tapping norms

The incidence of several girths or tapping start period on the parameters of rubber yield, the physiological profile and the sensitivity to tapping panel dryness of Hevea brasiliensis have been studied for a decade in southeastern rubber growing area of Côte d'Ivoire. The study was conducted from so called early (tapping start at 40, 45 cm girth) and/or late (opening at 55, 60 and 65 cm girth) tapping applied to clones GT 1, PB 217 and PB 235. This study shows that starting tapping clone GT 1 at 40 cm girth and clones PB 217 and PB 235 at 50 cm are the best treatments in terms of rubber yield, physiological parameters and tapping panel dryness. These girths at the opening were reached at approximately 6 years after planting, regardless of the clone. The satisfactory results recorded demonstrate the preponderance of the notion of "opening age" over that of circumference of tapping start. Thus, the age of 6 years after planting seems to be the best period to start tapping rubber trees, because it is a good benchmark of physiological maturity in Hevea brasiliensis. Despite this precedence of the age over the girth, the different results indicate the need to use both criteria to take into account a delay in the growth and especially a difference in the vegetative growth of the clones planted.