The natural rubber tree (Hevea brasiliensis) is a native of South America introduced to Southeast Asia during the 19th century. Rubber trees can grow to a height of 18 to 39 meters and they grow best in warm and moist climate ranging from 70-95 Fahrenheit or 21-35 Centigrade with an annual rainfall of 80-120 inches (2,000-3,000 mm).
The young rubber plants are raised in nurseries for 6 to 8 months and budded with bud scion from identified source before transplanting in using population of 400 to 555 trees per hectare. In five to seven years, the trees have stems of 18-20 inches (45-50cm) circumference and are ready for tapping or harvesting. Tapping can continue up to 40 years or beyond depending on the techniques of management.
Rubber is one of the top 5 priority commodities of the Department of Agriculture. Aside from generating employment in the rural areas and planting rubber in idle hillylands and uplands will enhance environmental rehabilitation, being a good plant species in sequestration of carbon dioxide.
Rubber has been commercially grown in Mindanao with great success and in most Southeast Asian countries, particularly Malaysia, Indonesia, Thailand, Cambodia, Vietnam and Southern China. The Department of Agriculture is now looking into the potential of Luzon and the Visayas for rubber production.
Climatic and Soil Requirement
Since rubber cultivation is confined to the humid tropical zones, particularly South-East Asia, rubber is not grown on such a diverse range of soils as many other tropical crops. It is frequently grown on leached acidic inland soils of the humid tropics (latosols) which are often well structured and deep profiled but low in nutrients, or on coastal clay soils which are usually richer in nutrients (particularly those formed under a marine environment) but on which drainage problems are encountered. Wycherley (1963) reports that in Malaya the best-yielding areas are on inland soils because coastal areas,though fertile, experience higher disease incidence and heavy rains interfere with tapping. Rubber is also grown extensively on basaltic latosols which are deep, well-structured soils, higher in cationic nutrients than the latosols derived from other parent materials and with a higher reaction, but nevertheless still on the acidic side. Obviously nutrient requirements and fertilizer practice are given further on.
The optimal pH for rubber lies in the range pH 4 to pH 6.5 (Planters Bull. 50 (1960) but the crop tolerates pH in the range 3.8-8.0 (e.g. Kortleve, 1928; Vollema, 1949). Young seedlings tend to be more sensitive to low pH than mature trees. Soil pH above 8.0 definitely causes growth retardation, but most humid tropical soils are acidic in reaction.
Soils of the humid tropics which are less suitable for rubber, but are nevertheless often planted with the crop, are peat soils (in which tree support is a problem and various nutrient deficiencies occur), acid sulphate soils (which develop very acid reactions on drainage), impoverished inland alluvia, and soils with a truncated profile due to a hard-pan clay layer or concretions of laterite.
Most coastal soils will require field drainage to at least 18″ (e.g. Planters Bull. 28 (1957) and main drains with a depth of two meters. In low-lying coastal areas tidal gates are required. Most tropical soils require phosphate which is generally supplied in the form of rock-phosphate during the immature years. Phosphate nutrition in mature rubber is done sparingly. Liming is not usually carried out unless soils are excessively acid as calcium has a yield-depressing effect on rubber due to the enhancement of plugging in the latex vessels. Hence, phosphate fertilizers containing calcium are also used sparingly after the initiation of tapping. Likewise, magnesium is also supplied sparingly to mature rubber.
Land and climatic requirement (Alcala 2007)
1. flat/plain land well-drained with deep water table
2. gently sloping/undulating to rolling terrains
3. soil pH of 4.0-6.5
4. good soil aeration
5. topsoil containing abundant organic matter
6. temperature range 20-34 Centigrade, average 25-28 C
7. 80% atmospheric humidity with moderate wind speed
8. average rainfall of 2000mm evenly distributed throughout the year
9. bright sunshine amounting to about 2000 hrs, with at least 6hrs/day
10. no distinct dry and wet seasons
Adequate clearing of the planting site is recommended to avoid competition for nutrients with weeds and second growth forest trees. In flat cultivated areas, plow he area twice before laying out. In hilly lands, terracing is encouraged following the contour lines. Terracing must be done to prevent soil erosion (Alcala 2007).
Plant spacing largely depend on the topography of the area and the possibility of planting intercrops. Dr. Acala (2007) has a list of recommended plant spacing for rubber in hilly areas, flat or undulating areas, and in avenue system of planting.
Plant propagation practices
Select seeds that are fresh, big, heavy and shiny. Before sowing the seeds, they must be soaked in water overnight. 10 kg of seeds can be germinated in every one-square meter of seedbed, 10cm thick, with fine river sand or sawdust as seedbed medium, and with partial shade. In sowing the seeds, they should be pressed firmly into the seedbed until the top of the seed is level with the surface, then cover the seeds thinly with the medium to prevent exposure to direct sunlight. Water the seeds twice a day and in 10-14 days, the seedlings can be pulled and planted into polybags or in ground nursery.
Preparation of nursery beds
Land preparation should be done prior to seed germination. The area should be cleared and clean. The size of poly could either be:
a. 6 x 12 in #.003 – for young green seedlings with 1-2 leaf storey
b. 7 x 14 n #.003 – for brown seedlings with 2 leaf-storey
The perforated polybags are filled with loam soil and placed in a shallow canal arranged in east-west orientation with 2 polybags per row spaced 36 inches between rows.
In the absence of soil analysis, apply 10-15 grams of 14-14-14 fertilizer per bag every 3-4 weeks.
Budded seedlings ready for planting have matured top leaf whorls with healthy and vigorous appearance with dark green color. The size and shape of the planting hole would depend largely on the soil condition and planting materials. In fertile and light soils, holes should measure 25-30 cm in diameter and 40-45 cm deep. In poor and heavy soils, bigger holes are required – 40-45 cm diameter and 50-60 cm deep. Further, if the land is currently being cultivated, smaller holes will do, but in uncultivated land, bigger holes are needed (Alcala; 2007).
Tree management (Pruning)
Pruning must be done regularly to develop a smooth trunk without branches or large scars on the stem/trunk along the optimum height of 2.5-3.0 meters from the ground. This should result to the bigger tapping panel. Pruning/cutting the top portion of the tree is not a recommended practice.
The first three years of plantation establishment is the most critical period where complete nutrition should be provided to the plant. Ideally, fertilizer application should be based on the results of soil and plant tissue analysis, to ensure that the optimum amount is applied. Hole, broadcast and ring methods of fertilizer application can be used and application is made at the start and before the end of the rainy season. Organic fertilizers can be used – with the rate of application based on the kind of organic fertilizer and recommendations.
Weeds in rubber farms can be controlled by line weeding, slashing, round/ring weeding, and the use of herbicides. Weeds in rubber areas must be controlled or minimized to prevent stunted growth of the rubber trees and to prevent fires during the dry season.
There are about sic foliar fungal diseases of rubber: 1) bird’s eyespot; 2) powdery mildew; 3) leafspot; 4) leaf blight; 5) anthracnose; 6) algal spot.
Nursery diseases consist of seedling blight and tip blight (see Alcala; 2007 for further info).
Harvest Management (Exploitation system)
Rubber trees are ready for tapping when the trunk circumference at 75 cm from the stock-scion union reaches 40-50 cm in circumference. It requires around five (5) year growing period under good management. Tapping should start on the 6th or 7th year after planting (Alcala; 2007)
References: Alcala, E. A. 2007. Rubber: Manual for Rubber Smallholders in the Philippines. Kabacan, North Cotabato. USM and PRBI. 72 pp.