Nurseries are established and maintained for raising various propagation materials for planting. These include seedling stumps, budded stumps and advanced planting materials like polybag plants, stumped buddings and soil core plants. Mother plants or source bushes for the multiplication of budwood are also grown in nurseries. Raising of plants is easier and cheaper in nurseries than in the main field. Moreover, nurseries offer an opportunity for selection of vigorous and uniform plants.
In India, rubber plantations are established in forest clearings, rubber replantings or by crop replacement. Most of the areas available for rubber cultivation are highly undulating and the extent of flat lands suitable for planting rubber is limited. These situations necessitate clearing of the land and adoption of proper soil conservation measures before planting rubber. Since June-July is the ideal period for planting rubber in South India, all the pre-planting operations should be completed before the onset of monsoon.
3 Land Clearing
The land to be brought under rubber cultivation should be cleared of all vegetation. Large trees of economic value should be removed first followed by felling and removing of smaller trees and slashing of the under growth. A light burn after felling and drying facilitates planting operations and slows down the regeneration of weeds. Nevertheless, excessive cleaning and burning may cause the destruction of soil and expose the soil to erosion. Replanting the old areas has to be thought of when the yield falls and the cultivation becomes uneconomic. The old trees may be slaughter tapped with yield stimulant application before felling. Lining and digging of pits can be started before felling of trees to save time. But there are chances of damaging the terraces at the time of felling.
4Roads, Fences and Buildings
A well-planned network of roads and footpath is necessary for the easy transportation of inputs to the various fields, latex to the factory and for the efficient supervision of field operations. The roads should be preferably traced before the commencement of lining so that sufficient strip of land could be reserved. Sufficient provision should be made for estate office, stores, processing factories and residential accommodations. The plantation should be protected all around by erecting fences or walls to keep away grazing cattle and to prevent pilferage.
Lining should be based on plant spacing and planting density to be adopted. Rubber can be planted by adopting square or rectangular planting system. Square planting is suitable for level and near level lands. Rectangular system can be adopted in flat lands and slopes. In rectangular planting the lines should be oriented in the East West direction to intercept maximum sunlight. Contour lining is done in undulating and hilly areas where the slope exceeds 8 per cent. Here the planting points are marked as lines passing through points of the same elevation. The planting density recommended is 420 to 500 plants per ha in the case of buddings or plants proposed to be field budded and 445 to 520 plants per ha in the case of seedlings. Higher initial stand is recommended for allowing proper thinning out.
On hilly and undulating terrain, cutting of terraces along the contour is a recommended practice to conserve moisture and prevent erosion. The soil on the hill side is cut from a distance of 60-75 cm in front of the planting row and thrown back in such a way that the terraces so formed will have a width of 1.25 to 1.5 metre and an inward drop of 20-30 cm. Steps of uncut earth are left out at intervals along the terraces to check lateral flow of water. For economy, planting on hillside may be done on square platform of size 1.25 x 1.25 metre (honey comb terrace) during the year of planting and later on joined together to form a complete terrace.
Proper drainage enhances aeration, microbial activity, ground cover establishment and helps in the development of an extensive root system. Natural waterways available in the area may be cleared, dressed or deepened to form a good drainage system. If not, drains are dug at an interval of 100-200 metres depending on the slope and drainage problem.
8Construction of Silt Pits and Contour Bunds
Silt pits are trenches of about 120 cm length, 45 cm width and 60 cm depth taken along the contour at suitable intervals to check erosion and to conserve water. Pits can be taken at the rate of 150-250 per ha depending on the degree of slope. They are aligned in such a way that the pits in the adjacent inter-rows are in a staggered manner. Construction of stone pitched contour bunds is another method to check erosion in steep slopes.
9Pitting and Refilling
Pitting is necessary to provide an ideal medium for the proper growth of the young rubber root system. The standard size of the pit is 75cm x 75cm x 75cm. The size of the pits varies depending upon the planting material to be used. Stumped buddings need comparatively deeper and larger pits. Smaller pits are sufficient for small and medium sized polybag plants. On economic consideration in deep, loose and friable soils, pits are sometimes dug wider at the top and tapering towards the bottom or the depth is reduced to 60 cm with a central crow bar (alavango) hole of 15 cm or more depth for taproot. But in hard, stony and compact soils, the pits should be widened. Pitting should be started sufficiently early and filling should be completed well in advance of planting so that the filled soil will get sufficient time to settle. While digging, the topsoil is kept on one side and the subsoil on another side. Filling should be done with the top fertile soil as far as possible. The organic manure and phosphatic fertilisers applied to the pits should be mixed with the top 20 cm soil in the pit. The pits should be filled to about 5 cm above ground level. A peg is placed in the centre of the pit to locate the planting point. Tractor - mounted hole digging machines are increasingly utilised for pitting. Machines which dig pits of 60 cm diameter and upto 90 cm depth are now available.
10Induction of Branches
It has been observed that to achieve a high rate of girth increase the rubber plant should produce branches at a height of about 2.5 to 3.0 m from the ground. In high branching trees girth increment has been found to be poor compared to low branching trees. Some plants show a tendency for high branching, particularly clones like RRIM 600 and GT 1. In such cases branching has to be induced by encouraging a few lateral buds to develop. The branches thus induced should develop in different directions in an equally spaced manner to ensure a well-balanced canopy. Techniques like the double blade ring cut device and the leaf cap method can be utilized for this. The double-blade ring-cut device has two V-shaped blades fixed 20 cm apart on a rod. By pressing the V-shaped blades and rotating them around the trunk complete ringing of the bark is done down to the surface of the wood. The cuts are made above a cluster of leaf scars so that a number of trunk shoots is produced around this region. This method can be applied only on greenish brown or brown tissues and is not suitable for young green tissues. In young green tissues, the leaf folding or leaf cap method can be used. In the leaf folding method, the leaves of the top whorl are folded down at the point of contact of the petiole with the lamina using only the upper few leaves to enclose the apical bud. The leaves are then tied with a rubber band. After three to four weeks they are released. In plants where the terminal whorl of leaves is in the leaflet or bud break stage, the leaf cap method is recommended. Here, three mature leaflets are taken to form a cap to enclose the terminal bud and tied with a rubber band. The cap is then removed three to four weeks later.
11Mulching, Shading and Whitewashing
Mulching or covering the plant basin with dry leaves, cover crop cuttings, grass cuttings, paddy straw etc is a recommended practice in rubber plantations to protect soil in the immediate vicinity of the plants from direct impact of heavy rains and sunlight causing soil degradation. Dried African Payal (Salvinia sp.) also can be effectively used as mulch at the rate of 5 kg per square metre (sun dried material). Benefits Of Mulching
- Improvement of water and plant nutrient holding capacity of the soil
- Maintenance of the soil around young rubber plants in a cool and moist condition during summer months
- Multiplication of microbial population of the soil, ensuring better nutrient availability
- Protection of the soil from beating effect of heavy rainfall resulting in soil erosion
- Control of weeds around the plant bases Mulching should be undertaken in nurseries and young plantations after fertiliser application and before the onset of regular summer. Usually, November is the ideal time for mulching to protect the plant from adverse effect of drought. During the year of planting young plants may be protected by shading before the beginning of summer. Plaited coconut leaves or used gunny bags can be used for this purpose. The brown bark of the young plants can be protected from the scorching action of the sun by whitewashing the main stem of the plant from the second year of planting. This may be continued till canopy of the plants develops and partially shades the plantation. However, plants on the roadsides may need whitewashing for a longer period as they are more exposed to sunlight. Whitewashing can be done using lime or china clay.
Weeds can be controlled by either manual methods or with the use of chemicals known as herbicides. However, an integrated method involving a combination of these two methods is more economical and Eco friendly.