06/09/2005" By Dr. N. Yogaratnam, Consultant at National Institute of Plantation Management
Research and development efforts on rubber in Sri Lanka have centred around public sector organizations since 1930. These institutions have been in the forefront, their findings and programmes providing considerable economic benefits to the rubber industry. They are now faced with the daunting task of maintaining their traditional glory and rendering the much needed assistance to overcome the industry’s current problems and to meet its long-term goals as rubber plantations still remain vital in the economy of Sri Lanka.
Although Sri Lanka’s total rubber planted area has declined from about 280,000 hectares in the late 60s to about 128,000 hectares in 2004, the yield per unit area increased considerably, it being more rapid in the last two to three decades. These increases in productivity are mainly the outcome of innovations emanating from research, complemented by contributions from the private sector, and extension and development agencies. Through breeding and selection of new clones and improvements in agronomic practices, it has been possible to increase the yield over time. Nevertheless in addition to increase in yield and productivity, research innovations should also include issues of early returns to investments, reduced labour requirement, and conservation of the environment.
In the earlier years of breeding, the emphasis was on total yield over the life of the planting. This approach continued until the development of RRIC 100 series clones. With increasing concern for quicker returns to investments, selection criteria emphasized on early high yield, in addition to total high yield and related secondary characteristics. This is now reflected in a yield of about 3500 kg/ha/yr in the first five years.
In the smallholder sector also, RRIC clones now account for a larger percentage of planted area. It is a well accepted fact that in the estate sector, clones produced by the RRI eg. RRIC and RRISL series are dominant now.Genetic potential
Due to wide variability in management practices and, to a lesser extent, soil and climatic conditions, the genetic potential of the existing commercially planted clones is not fully achieved. The average yield per hectare in most estates is 1500 kg/ha/yr. Yet these yields varied from a low of 1000 to a high of 2000 kg / ha. The data reflects that even then there is a gap between the average yield in experimental plots ( about 3500 kg / ha) and the best managed estates ( about 2000 kg / ha); such differences exist in other crops too, as, understandably, scales of operations vary.
However, the low national average yield of about 900 kg/ha for example, reflects that the industry is still short of the commercial potential by about 1000 kg/ha/year. In short, the research outputs on improved genetic material and agronomic practices have not been fully utilized. Breeding for newer clones has progressed relatively fast, despite the fact that Hevea is a tree crop. In the earlier years, breeding for newer clones generally took 30 – 40 years from the production of hand-pollinated seeds to the evolution of the release of new clones for commercial planting. Newer approaches in breeding and selection programmes have now resulted in the cycle being shortened. Molecular biological techniques now available to the breeders should be exploited fully to reduce the selection cycle even further.Propagation
For a long time since the inception of using clonal materials, budding of field planted seedlings about 15 to 20 months after planting was the norm. Subsequently, budding of plants of about two to eight months old seedlings, known as ‘green budding’, was introduced and this became the accepted practice. Later developments led to techniques for budding on seedlings of three to five months. Additionally, research findings led to field planting (field budding being changed to budding in the nursery, either in the ground nursery and transferred to polybags as budded stumps or by raising seedlings in the bags for budding) and transplanting in the field as one to two whorled plants.
The various techniques developed were implemented and effects evaluated in the commercial sector. The newer techniques of green buddings in intensively managed nurseries and transplanted as two-whorled plants not only came into tapping earlier ( in 59 months as opposed to 67 months) but also gave higher initial yield.Subsequently green budding gained dominance and green budding in bags and transplanting as one to two-whorled plants has become the norm.
The recent developments to tissue culture techniques enabling the production of transgenic plants etc. have now opened up new potentials.Agro management
The potential of a given clone is best realised with optimal agromanagement where soil management, balanced fertilizer use, plant protection and exploitation practices are some of the important components.
The rubber fertilizer use polices in Sri Lanka demand a new strategy, emphasis to be directed more only to the critical immature phase, to be then followed by a NIL fertilizer use phase after commencement of tapping for a reasonable period during maturity say five years particularly during the economically lean years ( unfavourable trading conditions for crop and / or fertilizers), and finally a phase of periodic tree monitoring, at three to five year intervals by soil and leaf nutrient survey approach, a technique perfected in the late 70’s for corrective and cost effective fertilization as and when, required, until 8 to 10 years prior to replanting.
During the critical immature phase it is expected that NPKMg fertilizers are applied regularly at the current normal rates or even may be in excess by 45 to 50% of the currently used level, to meet immature growth patterns and tree nutrient needs and appropriate methods, time and frequency of application, are adopted to ensure efficient nutrient uptake, enlarged nutrient retention within the tree system and enhanced vigorous growth. This would a adequately meet the trees requirements during the early period of the mature phase. Non discriminatory use of the discriminatory fertilizer use technique is undesirable, as it goes against the principles based on which the discriminatory site specific fertilizer technique was formulated.
Also, Soil and foliar survey date collected from a handful of estates in a single year cannot form the basis of recommendation for the entire rubber industry. The industry expects firm and accurate recommendation based on sound field experimentation. Fertilizer trials conducted over a very long period have not exhibited positive responses during the mature phase. If NPKMg fertilizers are required during the mature phase, then scarce resources should not be wasted in conducting the soil and foliar survey programme. Let us be realistic and not blindly follow what was thought fit 30 years ago.
The importance and benefits of legume covers and manuring during immaturity on initial as well as subsequent yields should be recognized by the industry and accepted as a sound agro management practice.
It also appears that the limiting factors for rubber production are not nutritional. Therefore, it is likely that the mature yield and harvest index may be increased by other methods related to exploitation rather than manuring practices.
The advent of ethephon as a yield stimulant has also enabled earlier expoloitation of trees at girths smaller than conventional girths. A minimum of 50 cm was for long considered the norm before exploitation could commence. The current thinking is that commercial areas could be exploited at smaller girths provided adequate management input are supplied. In fact, with controlled use of low concentration of ethephon, trees of girth of 43 cm or over are being exploited economically in some countries.
A number of other practices are available to reduce the unproductive phase of the trees and thus increase profitability. These include inherent properties of clones, planting materials, management practices and exploitation systems.
The newer clones are more vigorous and tappability ( at 50 cm girth) could be achived in 4.5 to 5 years compared to period of 5.5 to 6.0 years for older clones. The newer clones now being made available are more profitable than the older clones.
The factors contributing to earlier monetary returns, and thus also higher economic returns, are however dependent not only on clonal vigour but also on initial high yields.
With increasing labour wages and with lack of available labour for the plantation sector, the need for labour saving approaches should be addressed although a major drawback is that the new clones do not lend themselves to be exploited by any non-conventional systems.Low Frequency systems
Nevertheless, the introduction of ethephon stimulation has enabled the development of lower frequency of tapping, labour intensity is reduced and area covered per tapper increased.
Until recently, almost all estates followed the d/2 frequency ( once in two days) of tapping for buddings; but currently d/3 frequency ( once in three days) is a accepted system for tapping. The use of ethephon allows further reduction to d/4 ( once in four days) or maybe even to d/6 ( once in six days). However, to obtain acceptable yields, these low frequency systems should be introduced from the commencement of tapping.
The development of long flow systems, which in addition to increased yield, could lead to less labour-intensive system, e.g. through increased tapping task etc. should be considered.
In addressing the issue of shortage of skilled tapping labour, Malaysia has considered the use of mechanized tapping knives, auto-tap( using mechanized tapping knife attached to trees) , collection of latex by pipe systems and many others. So far, their research has not provided a practical application system but such approaches may provide a solution by the turn of the century.Crop Protection
Crop protection is an aspect that includes control of both weeds and diseases. In disease control, e.g. for oidium, sulphur-dusting was replaced by some oil-based formuations. However, this is more an emergency measure, as disease avoidance is the majorapproach, which should be continued. In this approach, climatic factors and disease out breaks are considered. Additionally, all clones are screened for the major diseases. The final selection of clones for commercial planting should therefore be based on avoiding susceptible clones in areas where the disease outbreak is likely. The nutrition of trees as a means of overcoming severity of infestation, e.g. due to odium etc. should also be looked into.
In addition to diseases, weed competition adversely affects growth and productivity of rubber. At the same time, control of weeds accounts for over 30 percent of upkeep costs of young rubber. Research should fully address the issue of choice of chemicals and applicators to increase the effectiveness of weed control while at the same time reducing costs.Environment
The use of terracing for soil conservation on sloping lands, an accepted practice both in the estate and smallholders sectors should be continued. In addition, the use of legume covers enhances soil’s physical properties, reduces erosion losses to almost nil on full establishment and reduces leaching of nutrients to lower depths.
Intensive efforts to find economically and environmentally acceptable herbicides combinations that should dominate the chemicals used in the rubber industry should be made. Large quantities of effluents (process waste) emanate in the processing of rubber. In the earlier years, these effluents used to be discharged indiscriminately into water ways. Biological treatment of effluent (through anaerobic and aerobic digestion) has been developed. The treatment of effluents before discharge should be an accepted practice and should be governed by clear guidelines from the authorities concerned. Effluent can also be recycled and used as source of nutrients for crops.
The early treatment of the felled rubber trees to convert the trunks into valuable medium hardwood timber opened up a huge potential. In addition to contributing to reduction in Co2 buildup, rubber plantings also reduce pressure on natural forests.Challenges
Continued and enhanced progress in all facets of production is crucial to a viable rubber industry. Of crucial importance is less labour-intensive systems, particularly in tapping. A system amenable to, say, exploitation once a week on a simple puncture(s) system, appears a possibility. Such a system should work on existing clones for it to be of immediate benefit to the rubber industry.
Will a clone produced from the existing germplasm collection bridge the yield gap that exists between the experimental yields of 3500 kg / ha/ yr and the maximum yield potential ( theoretical) of 10,000 kg/ha./yr?
Mechanization appears to be also an important proposition. This holds promise in areas of land preparation and, more importantly, in transplanting of more and more advanced materials. In addition, mechanization including robotics has a key role in tapping and collection and this is being pursued with vigour in some countries.
The approach to rubber as a monocrop, solely for latex, is slowly phasing out. In such in event, it appears that rubber trees may be planted for the timber as a primary product and latex will only be an important byproduct which will pay for the up keep of the trees until they are harvested for timber.
In the smallholder sector, integration of other tree crops with rubber, possibly in avenue planting should be of common occurrence. The area under mixed cropping in Sri Lanka is still rather small. Constrained by available resources and knowledge, researches into mixed cropping in plantations are also very limited and superficial. Some traditional intercrops can be continued with but some new intercrops with high market potentials must be introduced into the cropping scheme. Environmental concern must be a further factor for consideration in the mixed crop decision making process. Another aspect for concern is that of rural social development.Privatization
The industry always looks for new options for improving the viability of the plantations. The pubic sector research should therefore be made compatible with a private sector industry. With privatized management of plantations and limited privatization oftraining of plantation personnel, the question that arises is whether such a measure is required for research as well. At least a limited privatization of research may not be counter productive and will be in line with the Governments policy frame work that encourages greater private sector participation as it has been recognized that the state has too great an involvement in the provision of goods and series that would be more efficiently under taken by the private sector.
Another question that comes in mind is, has the role of research and extension been clearly defined eg. Soil and foliar survey for fertilizer application should be an Extension and not a Research programme. Such programmes can be done more efficientky by the private sector than the public sector as is being done in other rubber producing countries.