If the land has a slope of more than 8o, an A-frame can be used to lay out planting rows along the contour lines ( Fig. 1(77)).
- Rubber should always be planted along the contour lines on sloping ground.
- Digging the planting hole and giving a basal application of manure and phosphorous fertilizer should be done 10 - 15 days before the planting date. The hole should be 60 x 60 cm, and 60 cm deep ( Fig. 2(82)).
Popular planting densities in Vietnam are 555 trees/hectare, and 512 trees/hectare ( Fig. 3(78)).
Different Planting Materials
Several different kinds of planting material can be used. They can be grafted budwood, or plantlets grown from seed. The most commonly used materials are:
- Ten-month-old grafted budwood;
- Grafted budwood in plastic bags, with pruned trunk and dormant buds;
- Rubber plantlets in plastic bags with a single leaf; and
- Rubber plantlet in bags with 2 -3 leaves.
The trees are planted at a spacing of 6 x 3 meters.
Hold the plantlet erect, and place the bottom of the trunk into the middle of the planting hole. Make sure that the grafted bud is turned in the direction of the prevailing wind. The hole is then filled with fine soil. Soil around the trunk should be pressed down firmly.
Planting Seedings in Plastic Bags
The bottom of the bag should be cut off and thrown away. Trim off any rootlets which are coiling around the bottom of the bag. Place the plantlet in the middle of the hole, with the grafted bud turned in the direction of the prevailing wind. Cut away, the rest of the bag, from the bottom upward. Fill the hole with soil, and firmly but gently press the soil down around the plantlet. Make sure that the surface of the soil is about 1 cm below the grafted bud.
Put a small piece of bamboo into the ground beside the tree, so as to protect the bud. Put a bamboo stake beside a plantlet with leaves, and fasten it to the plant, to prevent any damage from strong winds.
Management of Immature Rubber Plantations
The growth of the rubber trees is defined by the perimeter of the trunk, measured at 1 m above the soil surface. When the trunk measures 46 cm around, it is time to start harvesting the rubber. In better soils this is generally the seventh year after planting. In poorer soils, the trees may not be ready for harvesting until the eighth year.
Weeding between the trees
This should be done 4 - 6 times a year, especially when the trees are small. Weeds should be cleared in a diameter 1.5 meters around the tree.
Weeding between the plantation sections
This can be done by hand, by machines or by applying herbicide. Within the plantation, weeding can also be done by machine when the trees are 2 - 3 years old. Make sure that the machines are only allowed to operate at least 1.5 m away from the foot of each tree.
Mineral fertilizers should be applied every year. Two applications should be made during the rainy season each year. The application rates are shown in Table 1(98). The fertilizers should be broadcast beneath the canopy of the rubber trees. Fertilizer can also be applied by digging holes in the spaces between the trees, and manure placed in the holes. This practice helps to maintain the humus content in the topsoil.
Mulching and Pruning
Mulching should be done at the end of the rainy season, using rice straw or dried weeds. The mulch layer should cover the soil under the tree canopy and should begin 10 cm from the tree foot. A thin layer of soil should be used to cover the mulching material. To help aerate the roots, turn over the soil surrounding the foot of the tree.
Prune the shoots regularly and selectively, making sure to maintain 1 - 2 leaf layers under the main shoot to create favorable conditions for photosynthesis and nutrition of the trees.
At the beginning of the dry season, it is necessary to clear the vegetation and debris from a broad band six meters wide all around the plantation. This ring of bare earth will act as a firebreak, and protect the plantation from fire.
While the rubber trees are immature, it is recommended to grow selected legume cover crops over the whole rubber plantation.
Intercropping can be carried out with coconut trees and banana plants within the rubber plantation. Sometimes banana alone is used as an intercrop. Intercropping can also be carried out with coffee trees and hot pepper.
Intercropping while the rubber trees are immature can generate extra income, and make farming on the rubber plantation more intensive.
Index of Images
Figure 1 Layout of New Rubber Plantation, Following the Contours
Figure 2 Checking the Hole Size (60 CM X 60 XM X 60 CM)
Figure 3 Mature Rubber Plantation<BR>
Table 1 Fertilizer Application Rates for Rubber (Note: Fertilizer Should Be Applied Twice Per Year. the Rates Shown below Are Per Application, Not Per Year
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