Need to increase productivity of yielding rubber plantations

It is well known in the rubber industry that the yield productivity in the early years of tapping on the first renewed panel, on completion of 10 years tapping of basal virgin panels, is poor and generally much lower than the average yield productivity recorded on basal virgin panel tapping.

This in most cases can be attributed to a number of factors, namely that the renewed bark is not of adequate bark thickness due to the limited period for bark regeneration, the poor quality or uneven bark renewal due to poor standards of tapping resulting in serious wounding to the cambium and the restriction in drainage areas due to variation in heights of opening for tapping of basal virgin panels.

Additionally, with the introduction in recent times of precocious high-yielding clones, which tend to give high-yield productivity on basal virgin panels but which then register a decline in yield productivity when tapped on basal renewed panels.

Limited duration for bark renewal

It is t he standard practice i n several plantations to commence tapping of panel B1-1 immediately after completing tapping of panel B0-2. The period for regeneration of bark on basal renewed panel B1-1 is limited to five years, which is the normal period for tapping of second virgin basal panel (B0-2). In some situations, this period is less than five years because of high rate of bark consumption particularly by less experienced tappers or due to use of ineffective tapping knives.

Hence, it is not uncommon for both basal virgin panels to be consumed in nine years or less. The limited period of bark regeneration results in inadequate bark thickness of less than 10 mm, which due to reduced number of latex vessel rings results in low yield productivity. Hence, there is a need for a longer duration for the bark renewal on tapped basal panels such that the bark thickness achieved is 10 mm in thickness or more.

Poor quality bark renewal

It is now well known the problem faced by rubber plantations is employing skilled tappers due to the rapidly declining availability and the inability to attract labour to work as tappers in rubber plantations. This has consequently resulted in plantations employing less skilled or unskilled tappers who besides consuming excessive bark consumption also induce extensive wounding with deep tapping to the wood. This results in poor or uneven bark regeneration and renewed bark with burrs, protuberances and bulges. This problem is quite acute in rubber plantations in Sri Lanka.

It is apparent from the condition of the renewed bark that tapping of these panels will be difficult and the yield productivity is expected to be very poor. The economic life span of rubber trees using conventional exploitation systems, involves 10 years of tapping on basal virgin panels, eight years tapping on basal renewed panels and six to eight years tapping on high virgin panels.

However, the economic lifespan will be markedly reduced if the basal renewed panels cannot be exploited for the projected duration of tapping on these panels unless the economic life span of the high virgin panels can be extended or prolonged by use of very short cuts (1/8s) on reduced frequency of tapping (d/3 or d/4) in combination with potent methods of stimulation e.g. RRIMFLOW gaseous stimulation.

Basal virgin panels

It is a common practice in some plantations to open the first virgin panel (BO-1) at height of 120 cm and the second virgin panel (BO-2) at height of 150 cm thus creating a bark island effect when the virgin bark above the renewed bark (Panel B1-1) is tapped down from height of 150 cm.

The yield productivity from tapping of this bark island is generally low or poor due to progressive restriction in drainage area as the tapping cut approaches the junction between the virgin bark and the renewed bark. The drainage area for latex is confined to the area of virgin bark below the tapping cut with no contribution in yield from the renewed bark below due to different ages of the bark and because the latex vessel rings are not contiguous between the virgin and renewed bark.

Similarly the adjacent renewed bark on panel B1-2 will also not contribute any yield to the tapped virgin bark island because of the different ages of bark and the latex vessel rings are not contiguous.

Malaysian experience

It has been reported that precocious highyielding clones tend to give good yield productivity during the early years of tapping on basal virgin panels and then register a decline in yield productivity when tapped on renewed panels. This is supported by published data summarized in the table.

It is likely that the partition of assimilates is skewed more towards latex production rather than biomass and this could be a contributory factor for poorer bark regeneration in precocious high-yielding clones. This in turn could result in lower-yield productivity when the renewed panels are tapped. It may therefore be necessary for these clones to allow for longer duration of more than five years to facilitate better bark regeneration and hence better yield productivity.

Current practices

It has been recommended by some research centres that the high virgin panels (H0) be tapped for two to three years on conventional 1/4s ^ (20 cm length cutz) d/3 or d/4 system in combination with Ethephon stimulation after completion of tapping on panel B0-2, to allow for a longer duration for the regeneration of bark on panel B1-1.

However, this system is not very practical because of the possible high bark consumption on the high panel due to the long cut and the likely consequence of valuable bark being sacrificed without the compensatory increase in yield productivity. This is further aggravated in countries such as Sri Lanka where the tappers are not adequately skilled to even tap basal panels and hence are likely to consume more bark coupled with deep tapping to the wood on upward tapped long cuts.

It will be difficult for less skilled tappers to control the slope and length of cut for upward tapping on long cuts. Managements of plantations in Sri Lanka fearful of this situation occurring are wary of adopting this approach to overcoming the problem highlighted.

RRIMFLOW system

This system of exploitation, which is well proven and established in the industry, involves tapping of very short cuts (1/8s or 10 cm length of cut) on reduced frequency of tapping on d/3 or d/4 in combination with gaseous stimulation once in 10 days or three applications per month. This system was engineered in compliance with key physiological principles that govern processes of latex flow in rubber trees.

This system has been proven to be a safe system to use on rubber trees because the stimulant used is a natural plant growth regulator, intermittent gassing with a pulse of gas allows the tree to respond and recover physiologically before the next dose or pulse of gas is applied, use of short cuts (10 cm) means that only 2.1 square centimetres of bark is removed at each tapping as opposed to 6.35 sq.cm of bark with conventional tapping with less energy expended by the tree to replace removed bark tissues.

Reduced frequency of tapping means that there is enough time for the latex vessels to be replenished before the next tapping and the yields extracted from rubber trees with RRIMFLOW system of exploitation are moderate when related to the physiological potential yield that can be extracted from the rubber trees.

RRIMFLOW system, a viable solution

It is recommended that the RRIMFLOW short-cut system of exploitation be implemented on high panels (HO) on completion of tapping on basal virgin panel B0-2. This will involve opening a 1/8s cut on virgin bark (HO-1) above basal renewed bark on panel B1-1 and tapping upwards on d/3 or d/4 frequency in combination with RRIMFLOW gaseous stimulation into an applicator fixed on adjacent panel to the right of the tapped panel with gassing once in 10 days or three times a month. On completion of one-year tapping on panel H0-1, a new 1/8s cut will be opened on adjacent panel H0-2 to the left of the first panel in a clockwise direction and tapped upward. The new applicator will be fixed either 30 cm above the new cut or on adjacent panel to the left of the new panel to be tapped. On completion of the second year of tapping, a new 1/8s cut will be opened on panel H0-3 to the right of the panel tapped in the first year. The applicator can be fixed either above the cut on the new panel or on adjacent panel to the right of the new panel to be tapped. On completion of three years upward tapping using the RRIMFLOW system, tapping will be reverted to the basal renewed bark on panel B1-1 using conventional tapping system (1/2s d/3) in combination with Ethephon stimulation. The bark thickness of renewed bark on panel B1-1 is expected to be about 10 mm with the additional three years allowed for the process of renewal and this will also contribute to better yield productivity on this panel. The use of very short cut of 1/8s or 10 cm in length will ensure that bark consumption will be well managed without excessive bark consumption as would be the case if conventional long cuts are used. It will be easier to carry out upward tapping with very short cuts with minimal skill required for this mode of tapping. This is further facilitated with use of a specially modified controlled upward tapping knife designed exclusively for use to tap very short cuts. It is obvious that the inherent fear of plantation managements that the trees will be slaughter tapped with indiscriminate bark consumption and damage to the trees when early upward tapping is adopted is hence not well founded. The use of the correct upward tapping knife and pre-marking on the tapping panel the allowed bark consumption per month will ensure that the trees are well tapped and the economic lifespan particularly of the high-yielding upward panels are not compromised. Early controlled upward tapping with the RRIMFLOW system of exploitation for a limited period of three years will enable plantations to sustain the high-yield productivity realized on basal panel B0-2 and which will not be possible if basal renewed panel B1-1 is tapped immediately upon completion of tapping on basal panel B0-2. (Source: Sivakumaran S, 2015, unpublished, Malaysia)