Rubber (Hevea brasiliensis) has a high export potential in the Philippines and is rated one of the most profitable agro-industrial ventures in this country.
Rubber has varied industrial, technological, and domestic uses today. It is used in rubber tires, flexible pipes, shoes, gloves, mattresses, bags, upholstery, raincoats, insulated floorings, tennis and golf balls, and pillows.
Proper cultural management should be strictly followed during the immature stage (1–6 years after planting) to hasten the formative stage of the rubber trees and, thus, provide the farmer with a bigger income earlier.
What are the cultural management practices in establishing a rubber plantation?
Various types of lands are utilized for rubber production (i.e., flat lands, hilly and mountainous lands, forest areas, and cultivated lands). Land preparation does not differ much except between flat and hilly lands.
In areas with big trees, in virgin forests, or in second-growth forests, clear the undergrowth first to facilitate the cutting of bigger trees. Cut the large trees of economic value into logs and remove these from the site. Cut and heap the smaller trees or trees with lesser economic value along the expected rows of rubber.
Minimize burning to avoid the loss of the organic matter and humus in the soil.
Remove the cogon grass (Imperata cylindrical) entirely since it can stunt the growth of rubber. Remove the cogon along the rubber rows in hilly areas where cultivation is difficult.
Plow the area twice in flat but cultivated areas before laying it out.
In hilly lands, prepare the ground following contour lining and land terracing.
Laying out in flat lands
Set the rows of rubber at an east-west row orientation to get maximum sunlight. Make the longest boundary line along the east-west direction as a convenient baseline.
Use the following for lining: two pieces of rope of at least 100 m long compass, measuring tape, and bamboo sticks (at least 1 m long). Use one of the ropes as a baseline and the other as a guideline.
Use contour lining in hilly lands of more than 20 degrees gradient. Mark the planting points in level lines across the slope. Select a line of average slope and divide the slope according to the distance between the rows of rubber.
To locate the contour lines along the slope, use an A-frame. Mark the distance between rows with a stick and place the A-frame level at the base of the guide stick. Adjust the legs of the A-frame until the bubble in the carpenter’s level floats to the center.
Center a stake between the legs of the A-frame to mark the planting holes.
After laying out the contour lines along the slope, cutting the planting terraces are necessary to prevent soil erosion and make tapping convenient. Cut the soil back to the hill 1.0–1.5 m from the planting guide stick with a 25–50 cm drop to the back of the terrace.
Distance of planting largely depends on soil fertility, type of clones to be planted, typed of planting materials, and plant population density.
Hole size and shape depend largely on soil conditions and planting materials. Compact hard soils need bigger holes than loamy soils. Likewise, large planting materials need bigger holes than smaller ones. Generally, however, the planting hole should be 24 cm x 30 cm.
Plant preferably when rainy weather is expected.
Correct planting methods to prevent the development of elephant foot.
Transplant the budded seedling when the leaves from the second top storey are fully expanded, dark green, and mature.
Cut the bottom of the bag with a sharp knife and make a vertical cut from the bottom of the plastic sleeve, taking care not to damage the lateral roots. Lower the seedling into the planting hole, then pull the plastic sleeve upward and fill the hole with topsoil or any fertile soil.
Fertilize the young plants to give them a head start over the weeds. During the first three years of the plantation, complete nutrition must be given to the trees.
Cover cropping is the establishment of leguminous plants before, during, or after planting rubber. Cover crops suppress weeds and augment soil fertility, thus reducing the cost of weeding and fertilizers. They also converse soil moisture, thus creating favorable growing conditions for the rubber trees. In hilly areas, they minimize soil erosion.
Weed control is indispensable in the cultural management of immature rubber trees. When trees are green, weeds usually grow luxuriantly because the canopy of rubber is still limited.
Inadequate weed control at this stage, mainly when cogon is present, may delay the maturity of rubber and expose the plantation to fire hazard,s especially during summer. Cogon grass not only competes for nutrients and light but also secretes allelopathic substances which restrict the growth of rubber (Mercado, 1986 as cited by CEMARRDEC, 1990).
Weeds can be controlled chemically, mechanically, or manually. Chemical weed is more practical and less expensive, especially in rolling or hilly areas. Use glyphosate (Round-up) herbicides to control cogon and other grasses. Glufosinate can be used for mixed weeds.
Manual weeding can be done by slashing, line, or ring weeding. In slashing, the weeds of the entire plantation are cut, while in line weeding; only weeds along the rows of rubber are cut. In ring weeding, weeds around the base of the plants are cut.
Replant only until the second year of plantation establishment so the replants can develop fully before the canopy closes. Use polybag buddings of the same age as that of the initial plants in the field.
Prune trees to a height of 2.0–2.5 m to ensure the development of a smooth trunk without branches or large scars.
For polybag buddings, allow the plant to grow without branches until 2.0–2.5 m from the union, then prune.
Pruning also allows the development of a balanced canopy. Maintain 4–5 well-spaced branches to prevent wind damage.
Some clones grow branches late and become spindly without branches. Such slender-stemmed trees are susceptible to wind damage.
Induce these trees to branch artistically by making two-ring incisions immediately above a whorl of bud eyes about 2.5 cm from the union of an 18-month-old rubber tree. Allow only 4–5 vigorous and well-spaced branches to develop. This technique widens the girth of the tree, which helps the tree to resist wind damage.
Intercropping in rubber plantations
Intercropping various crops during the immature rubber stage provides alternative income sources to small farmers. It also reduces to less than 50% the cost to establish and maintain rubber during its immature stage. In addition, intensified cropping controls weeds and improves soil properties, especially when the intercrops are fertilized.
The most common intercrops with immature rubber trees are peanut, upland rice, corn, sorghum, mungbean, soybean, sweet potato, pineapple, and squash.
Rubber can also be intercropped with perennial crops like durian, rambutan, lanzones, coffee, calamansi, and banana. These intercrops can be grown up to or even beyond the productive years of rubber.
You can adopt the most profitable crop combinations to increase farm income without sacrificing the growth and yield of rubber.
What are the factors to consider in selecting your intercrops?
The selection of intercrops for immature rubber trees depends on several factors. These include:
- The terrain of the plantation. In flat and slightly-sloping areas, use intercrops such as legumes, cereals, and sweet potatoes, which generally require land preparation and interrow cultivation. In hilly regions, use intercrops such as pineapples which do not require intensive cultivation.
- Age of rubber. For three-to-five-year-old rubber trees, use intercrops such as mungbean’s and pineapples, which are slightly tolerant to shading. Pineapples can be grown until the fourth year after planting rubber.
- Distance of planting. Close planting distances like 4 m x 5 m, 3 m x 6 m, or 4.5 m x 5.0 m are unsuitable for intercropping. Instead, use the avenue planting distances (2 m x 24 m double row). They expose the intercrops to sunlight, particularly in east-west row orientation. Under these conditions, intercrops can be grown favorably even up to five years after planting of rubber.
- Planting season. Plant upland rice during the wet season and corn and peanut during both wet and dry seasons. Use sorghum, soybean, and mungbean during the dry season.
- Optional scheme of intercropping. Annuals and biennials are commonly selected as intercrops. Alternatively, perennials may be chosen. The selection of perennial crops is dependent on soil and climatic conditions, and prevalence of pests and diseases, among others.
Rubber can likewise be planted to marginal areas as a high-yielding value crop to replace poor-yielding, short-term crops such as monoculture corn gradually. This practice can improve land productivity and profitability in the long term.
Livestock and poultry such as goats and chicken can also be integrated in the production system to supplement a farmer’s income during the unproductive stages of rubber.
The schemes offer the advantage of not disturbing the rubber while cultivating the intercrops and improving soil fertility. Furthermore, these encourage rubber trees to grow faster and be trapped earlier than those trees in mono-cropped plantations.