Hevea brasiliensis, commonly known as the rubber tree, is a tropical species native to the Amazon Basin in Brazil and neighboring countries. In the early stages, particularly up to about 1910, most rubber was harvested from “wild trees” growing in the Amazon Basin.
Other natural sources of rubber, such as Ficus elastica, were also found in the Congo Basin of Africa. Rubber cultivation spread from the Amazon to South Asia (Sri Lanka) and Southeast Asia (Singapore and Malaysia) through the efforts of the British Colonial Office, where it was initially grown experimentally and later on plantations.
Following this, rubber cultivation expanded to regions such as Indochina (Vietnam and Cambodia), the Dutch East Indies (Indonesia), Thailand, and parts of Africa, including Liberia, Nigeria, and Côte d’Ivoire. Initially, plantations were the primary method of cultivation, but smallholders soon adopted rubber farming as a source of income.
History of Rubber Usage and Cultivation
Rubber has been cultivated for centuries in Central and South America. Ancient Mesoamerican civilizations used rubber, primarily from Castilla elastica. One notable application was in the Mesoamerican ballgame, where rubber balls were used.
Several Pre-Columbian rubber balls have been discovered, with the earliest dating back to around 1600 BC. The Spanish Conquistadors, upon witnessing the bouncing rubber balls of the Aztecs, were amazed, speculating whether the balls were enchanted.
The Maya civilization also created temporary rubber shoes by dipping their feet into a latex mixture. In addition to sports and footwear, rubber was used in various contexts, such as securing stone and metal tools to wooden handles and providing padding for these handles.
Although the Mesoamericans did not have vulcanization technology, they developed organic methods of processing rubber. They mixed raw latex with saps and juices from vines like Ipomoea alba, a species of morning glory, achieving similar results to vulcanization.
In Brazil, indigenous people were aware of rubber’s use in producing water-resistant clothing. One notable story recounts that the first European to bring samples of such water-repellent rubberized cloth to Portugal shocked people so much that the individual was accused of witchcraft.
Rubber’s Introduction to Europe and Asia
When rubber samples first arrived in England, Joseph Priestley, in 1770, observed that a piece of rubber was excellent for erasing pencil marks on paper, which led to the creation of the eraser. The Para rubber tree, originally from South America, was the primary source of latex throughout much of the 19th century.
Approximately 100 years ago, the Congo Free State in Africa became a significant source of natural rubber latex, often gathered through forced labor. This territory was ruled as a personal colony by the Belgian King Leopold II.
Following multiple efforts, rubber was successfully cultivated in Southeast Asia, where it is now extensively grown. In India, commercial rubber cultivation was introduced by British planters. The initial experimental attempts to grow rubber on a commercial scale in India began as early as 1873 at the Botanical Gardens in Kolkata. The first commercial Hevea plantations in India were established in 1902 at Thattekadu in Kerala.
Botany and Climatic Requirements of Rubber
Several plant species produce natural rubber, but considerations of quality and economics limit the primary source of natural rubber to Hevea brasiliensis. This species, native to the Amazon Basin, was introduced to tropical regions of Asia and Africa during the late 19th century. It is one of the most successful plant introductions in history, leading to the establishment of over 9.3 million hectares of rubber plantations, 95% of which are in Asia.
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Functions of Latex in Rubber Plants
Latex, the milky fluid produced by rubber plants, serves various functions. Some theories suggest it acts as stored food, while others propose that it is an excretory product in which plant waste is deposited. Latex may also help protect the plant by sealing wounds and preventing the entry of fungi and bacteria.
Latex could deter browsing animals, as it is often bitter or even poisonous in some plant species. It is likely that latex serves all of these functions to different extents in the numerous plants where it occurs.
Uses of Latex
Latex is widely used across industries, with its primary use being the production of rubber. Other latex products include chicle, which is used as a base for chewing gum. Synthetic latex is also used in latex paint, which has low flammability, minimal odor, and forms a dry film after curing. Natural latex finds applications in manufacturing latex mattresses, beauty application pads, and cushioning materials. Additionally, poppy latex serves as the source of opium and its derivatives.
Characteristics of Hevea brasiliensis
Hevea brasiliensis, commonly known as the Para rubber tree after the Brazilian port of Para, is a fast-growing, sturdy, perennial tree that reaches a height of 25 to 30 meters. It features a straight trunk and thick, somewhat soft, light brownish-gray bark. The tree exhibits alternating periods of rapid growth and consolidated development during its early stages. Its trifoliate leaves are borne on long stalks.
The rubber tree is deciduous, shedding its leaves during the dry season and growing new leaves afterward. This process, known as wintering, lasts for about sixteen weeks (December to February in Nigeria). During wintering, the metabolism of the tree and the composition of its latex are significantly affected, leading to reduced rubber yields.
This seasonal variation, along with other climatic factors, contributes to fluctuations in natural rubber production in producing regions. After wintering, quick refoliation and copious flowering occur. The tree’s flowers are small but bloom in large clusters, while its three-lobed fruits contain three seeds, resembling castor seeds but larger in size. The seeds are oil-bearing.
Although rubber trees can live for over a hundred years, their economic life in plantations is typically around 32 years. This period consists of a 7-year immature phase and a 25-year productive phase.
Climatic Requirements for Rubber Cultivation
Rubber cultivation thrives in humid tropical climates. The rubber-growing regions experience average annual rainfall ranging from 2000 to 4500 mm. The southern parts of these regions benefit from both the southwest and northeast monsoons, while northern areas primarily receive rainfall from the southwest monsoon.
The drought period in the rubber-growing belt varies from two to five months annually, with a more uneven rainfall distribution in the northern areas. However, temperature and humidity variations in the rubber-growing regions are less significant compared to rainfall. Warm temperatures and high humidity persist throughout the year, providing optimal conditions for rubber cultivation.
Agro-Climatic Requirements for Rubber Production
1. Climatic Factors for Rubber Cultivation
Hevea brasiliensis, the primary source of natural rubber, is a tropical tree that thrives best in regions with temperatures ranging from 20°C to 28°C and an annual rainfall of 1,800 to 2,000 mm, well-distributed throughout the year. The tree grows well at elevations of up to 600 meters above sea level but is capable of growing as high as 1,000 meters, especially near the Equator. Rubber trees require adequate drainage for optimal growth, and high winds can cause damage to the trees.
Rubber is primarily grown between 10° latitudes on either side of the equator, with its major growing areas situated within this tropical belt. However, it is also cultivated in regions further north, such as Guatemala, Mexico, and China, and further south, in the Sao Paulo region of Brazil.
2. Maturity of Rubber Trees
Mature Hevea trees typically reach heights of 20 to 30 meters, with upward-extending branches and a slender trunk. These trees flower once annually and produce large fruits containing several thimble-sized seeds with hard outer coats.
Once germinated, the seeds must be planted within 2 to 3 weeks to ensure proper growth. Under optimal conditions, the seedling plants take approximately 5 to 10 years to reach maturity. Maturity is marked when the trunk reaches a circumference of about 500 mm at 1 meter above ground level, which is the stage when tapping for latex can commence.
3. Biosynthesis in Rubber Trees
Hevea brasiliensis converts inorganic nutrients from the soil and carbon dioxide from the atmosphere into organic carbohydrates, which are subsequently converted into rubber latex. The latex is transported up the tree through millions of capillary vessels located in the soft outer bark of the rubber plant. This biosynthesis process is critical for rubber production.
4. Soil Requirements for Rubber Cultivation
Rubber trees grow best in highly weathered soils, which are generally laterite or lateritic in nature. These soils are highly porous, well-drained, moderately to highly acidic, and often deficient in available phosphorus. Potassium and magnesium levels in these soils can vary. Sedimentary soils, nonlateritic red soils, and alluvial soils are also found in some non-traditional rubber-growing areas.
Red soil, common in some regions, is characterized by its reddish-brown color and fine loamy texture. This type of soil is generally acidic and highly deficient in available phosphorus.
For successful rubber cultivation, the soil should have a minimum depth of one meter without any hardpan or impenetrable layers. The water table should also be below one meter to provide sufficient aeration for root penetration. Well-drained soil is essential for the growth and yield of rubber trees. Marshy areas with poor physical properties and waterlogged conditions hinder the growth of rubber trees, resulting in poor yields.
Rubber Growing Regions of the World
Rubber is predominantly grown within the equatorial belt, between 15°N and 15°S of the equator. Major rubber-producing countries include Malaysia, Sri Lanka, India, Indonesia, Brazil, Mexico, Liberia, Nigeria, Ecuador, and the Democratic Republic of Congo (formerly Zaire). Malaysia is the world’s leading producer, contributing over 40% of global rubber production.
Propagation of Rubber
Rubber cultivation requires several agricultural management practices to ensure successful propagation and yield. The following topics are central to managing rubber plantations:
i. Clones
ii. Nursery Establishment
iii. Land Preparation
iv. Field Planting
v. Intercropping
vi. Cover Crops
vii. Mulching, Shading, and Whitewashing
viii. Diseases and Pests Management
ix. Manuring / Fertiliser Application
x. Induction of Branches
xi. Tapping and Stimulation
xii. Processing
xiii. Uses of Rubber
Clonal Seeds in Rubber Cultivation
In Nigeria, Hevea seeds typically ripen between September and December, during which time they are collected and used to raise seedlings. Early rubber plantations were established using unselected seeds, leading to lower yield potential and poor production. Over time, efforts to improve planting materials through selection and vegetative propagation (by budding) led to the development of numerous valuable rubber clones.
Clonal seeds are derived from these selected clones and include various types, such as monoclonal, polyclonal, legitimate, and illegitimate seeds.
Monoclonal seeds from clone Tjir 1, which produced seedlings superior to those from ordinary unselected seeds, were once widely planted in Nigeria. However, as newer and improved planting materials became available, Tjir 1 clonal seedlings were progressively replaced.
Currently, only hybrid polyclonal seeds collected from approved polyclonal seed gardens are recommended for planting. In Kanyakumari district, gardens have been established specifically for the production of good quality polyclonal seeds. Prang Besar Isolated Garden (PBIG) seeds from Malaysia were once marketed in India but have since lost prominence due to the availability of improved local seed materials.
Handling Ungerminated Rubber Seeds
Freshly collected and healthy Hevea seeds can retain their viability for about seven days when stored under shade without much moisture loss. Storing the seeds in water at ambient temperature helps increase their water content, which, in turn, prolongs their viability.
Seeds can also be stored loosely in well-aerated containers with powdered charcoal containing 20% moisture, which helps retain up to 70% viability for as long as 30 days. Alternatively, seeds can be stored at 4°C in sealed polythene bags, which allows them to maintain viability for up to four months.
Immediately after collection, seeds are typically packed in powdered charcoal (containing 20% moisture) for transportation. Common packaging materials include wooden boxes, double gunny bags, polythene-lined bags, or polythene bags. When transporting seeds over long distances, they are often packed in layers with a damp sawdust-charcoal powder mixture (at least 2 cm thick between layers of seeds) in aerated cases to preserve their viability during transit.
Nursery Establishment for Rubber Cultivation
Rubber nurseries are essential for raising seedlings, budded stumps, and budwood to ensure the successful establishment of plantations. Open, level land with easy access to irrigation is ideal for establishing a nursery. The soil should be deep, fertile, and well-drained.
1. Land Preparation for Nursery
The land should be dug to a depth of 75 cm, with all stumps, roots, and stones removed. Nursery beds should be 60 to 120 cm wide and of convenient lengths, with pathways in between to facilitate activities such as manuring, watering, and weeding. The planting distances in the nursery depend on the type of planting materials being raised. The ideal spacing for seedlings is 30 cm x 30 cm, while for budwood nurseries, spacing of 60 x 90 cm, 60 x 120 cm, or 90 x 90 cm may be used.
Nursery management focuses on the rapid production of healthy planting materials. Intensive care can be exercised in the nursery compared to the field, and unsuitable plants can be eliminated early. Main operations include weeding, mulching, irrigation during dry months, manuring, and disease and pest control. The type of nursery depends on the type of planting materials to be raised, such as seedling nurseries, budwood nurseries, or polybag nurseries.
2. Preparation of Nursery Beds
For ground nurseries, the soil is dug to a depth of 60 to 75 cm, and stones, stumps, and roots are removed. The soil is then brought to a fine tilth. Nursery beds should be 90 to 120 cm wide with convenient lengths. On level land, raised beds are made with footpaths about 45 cm wide between the beds. On undulating lands, the beds are prepared along contours.
During bed preparation, 25 kg of compost or well-rotted cattle manure and 4 kg of powdered rock phosphate (18% P2O5) are added for every 100 m² of the nursery bed. In newly cleared forest areas rich in organic matter, compost or cattle manure may not be necessary in the first year. Rock phosphate is applied once every three years when the same area is repeatedly used as a nursery. Proper drainage and pathways should also be established.
3. Germination of Rubber Seeds
Rubber seeds lose their viability rapidly if left in the field. Therefore, seeds are collected daily during the seed fall season and transported to nurseries for germination. Raised level beds with a 5 cm thick layer of river sand, 90 cm wide and of convenient lengths, are used for germination.
Partial shading is necessary to prevent strong sunlight. The seeds are sown in a single layer, touching each other, and the germination beds are kept moist (but not wet) by evenly sprinkling water in the morning and evening. The seeds are covered with loosely woven coir matting or gunny bags.
Germination starts 6 to 7 days after sowing, and sprouted seeds should be picked and planted in nursery beds or the field. The ideal stage for nursery planting is when the germinated seeds show emerging young roots. The sproutings are tender and require careful handling, and are typically transported to nursery beds in buckets half-filled with water. About 75% germination is considered good, and pickings are done over 21 days.
4. Planting in Nursery Beds
Germinated seeds are planted in small holes, about 5 cm deep, made in the nursery beds. The seeds are placed horizontally with the radicle pointing downwards and covered with soil. Germinated seeds should be planted when the young root is less than 2 cm long to prevent damage to the radicle.
Spacing in the nursery depends on the type of planting material being raised. For seedling stumps, a 30 x 30 cm spacing is commonly adopted. Green-budded stumps are spaced at 23 x 23 cm, while brown-budded stumps are spaced at 30 x 30 cm or in staggered pairs of rows, with 60 cm between rows and 23 cm between plants.
For stumped buddings, spacing ranges from 60 x 60 cm, 90 x 30 cm, 90 x 60 cm, to 90 x 90 cm. Soil core plants may be spaced at 35 x 35 cm, 38 x 30 cm, or 60 x 60 cm. In budwood nurseries, the spacing is typically 90 x 60 cm or 120 x 60 cm, with wider spacing between rows.
The rows are marked using row markers, and a long cord with planting distances marked is stretched along the length of the bed. Germinated seeds are planted at each marked spot along the line. In budwood nurseries, budded stumps are planted at the required spacing. Alternatively, seeds can be directly sown in beds and budded in situ. Once the bud has taken, the plants are cut back, and the scion is allowed to develop.
Types of Nursery
1. Polybag Nursery: Polybag nurseries are widely used for growing planting materials. This method involves planting in polybags, which can be done using two approaches:
i. Budded Stumps: Budded stumps are planted in polybags, allowing the scion to grow until they are ready for field planting.
ii. Germinated Seeds: Germinated seeds are planted in polybags and bud-grafted when they are five to six months old. The first method allows better selection of vigorous plants and reduces wastage from poor seedlings or budding failures.
To promote root growth, the roots of budded stumps can be treated with indolebutyric acid (IBA) or dipped in cow dung slurry before planting.
2. Polybag Materials:
i. Bags can be black or transparent polyethylene, with black being preferred as it prevents issues with root development.
ii. Bag sizes differ based on the plant size being grown: for two to three whorls, 55 to 60 cm long and 25 to 30 cm wide bags are used, and for six to seven whorls, 65 x 35 cm bags holding 23 kg of soil are used.
iii. Low-density polyethylene (LDPE) sheets of 400 to 500 gauge thickness are used for bag production, with high-density polyethylene (HDPE) also an option, although HDPE is prone to sun damage.
3. Soil Requirements: The soil used in polybags should have good moisture and nutrient retention and promote root development. Clay-loam textured soils with good structure and friability are ideal. Fertile topsoil collected after clearing vegetation is recommended. Soil should be clean, free from large clods, stones, or stubbles, and gently tapped into the bags to avoid air spaces.
4. Nursery Setup: Filled bags can be placed in trenches or supported on the ground with wooden poles. Trenches are better for protecting bags and promoting plant growth. For small bags, trenches are dug about 20 cm deep, while for larger bags, they are 30 cm deep. Spacing between bags and trenches allows for optimal growth and maintenance.
5. Cultural Practices:
i. Regular tasks include manuring, watering, weeding, shading, and pest protection.
ii. A fertilizer mixture of NPK Mg (10-10-4-1.5) is applied monthly, starting with 10 g per bag and gradually increasing to 30 g.
iii. Watering is done after fertilizing, and excessive watering is avoided to prevent waterlogging.
iv. During dry seasons, irrigation may be needed, with sprinklers or drip systems preferred for large nurseries.
Polybag nurseries allow for advanced planting materials, reducing the immaturity period, ensuring uniform stands, and aiding in vacancy filling.
6. Transplanting Polybag Plants:When polybag plants are ready for transplanting, their top whorl of leaves should be fully mature. The bags are removed from the trenches, and root dressing is done if necessary.
A planting hole slightly larger than the bag is prepared. The bottom of the bag is cut, and the plant with the soil core is placed into the hole. The plastic sleeve is carefully removed as the hole is filled to avoid damaging the roots. The soil is packed firmly around the plant to ensure stability.
During planting, the scion of the polybag plant should be directed towards the northeast to protect the bud patch from direct sunlight.
7. Transporting Polybag Plants: When transporting polybag plants, care is taken to avoid damaging the soil core or tearing the bags. For short distances, the bags are carried on the head or shoulder. For long-distance transport, vehicles such as lorries or trucks are used. Bags should always be kept vertical during transport to prevent soil core breakage. Shade is also provided to protect the plants from the sun.
8. Seed Germination Beds: Rubber seeds are germinated in well-drained, shaded germination beds raised 10 to 15 cm above the soil surface to avoid waterlogging. The seeds are laid out in a single layer, covered with a material like coir matting to prevent moisture loss, and watered regularly. Germinated seeds are collected within six to seven days for planting in nursery beds or the main field.
9. Budwood Nursery: Manuring is essential in budwood nurseries to promote the growth of budwood for propagation. A basal dressing of powdered rock phosphate is applied, and an NPKMg fertilizer is given in two split doses for the first crop of budwood and once for subsequent crops. The fertilizers are applied during specific months, ensuring that the plants grow healthy and productive budwood for further propagation.
10. Seedling Stumps: Healthy one-year-old seedlings with a minimum girth of 7.5 cm at the base are pruned and prepared as seedling stumps. The roots and lateral branches are trimmed to specific lengths, and the cut end of the stem is sealed with paraffin wax to avoid water loss. The stumps can be stored for short periods or packed carefully for transport over long distances.
11. Stumped Buddings: Stumped buddings are prepared either as mini stumps or maxi stumps. The scion is cut back to specific heights, and the cut end is treated with wound dressing and whitewashed with lime to prevent dehydration and sun-scorching. After allowing time for the buds to activate, the plants are pulled out, pruned, and packed for transport.
12. Seed at Stake Planting: In this method, germinated seeds are planted directly in the field. Field budding is done on the most vigorous plant after thinning out weaker plants. This technique is preferred when field budding is planned.
13. Tissue Culture Propagation: Rubber can be propagated through tissue culture, using small pieces of plant tissue like embryo, shoot tip, or anther. The Rubber Research Institute of India has developed successful tissue culture techniques for rubber plants, although it is a laborious and time-consuming process with low multiplication rates. However, tissue-cultured plants have been established in the field, and clones are being evaluated.
Nursery Management
Efficient management of nurseries is essential for the economic and rapid production of high-quality planting materials. The goal should be to produce the maximum number of healthy and transplantable seedlings by the end of a 10-month period, with any unhealthy and weak plants removed early. Vigorous and stunted seedlings become distinguishable three to four weeks after the first fertilizer application, making this an ideal time for culling.
1. Weed Control in Nursery Beds
Maintaining weed-free nursery beds is crucial, with three rounds of weeding typically required. In India, hand weeding is common, with the first round occurring just before the first fertilizer application and the second before the second dose.
The third round is conducted before budding, usually in May or June. The first manual weeding can be replaced with pre-emergence herbicides like diuron (2.5 kg/ha in 700 L water). By using this method, weed-free beds can be maintained for 6 to 8 weeks, eliminating the need for disturbance during planting.
2. Mulching in Seedling Nurseries
Mulching plays an important role, especially before the summer season and after the second round of fertilizer application. Common natural materials like dry leaves, grass cuttings, or cut cover crops are used for mulching. A single round of mulching in December is often sufficient. Black polythene sheets can also be used as a mulch material, secured by anchoring them to the soil and covered with a thin soil layer to prevent displacement.
3. Manuring in Nurseries
Soil analysis helps determine the specific fertilizer requirements of individual nurseries, but if that is not possible, general fertilizer recommendations can be followed (discussed under “Manuring/Fertilizer Application”). Adequate fertilization ensures optimal growth of seedlings, contributing to better transplanting success rates.
4. Irrigation Management
Irrigation is necessary during the dry season, which usually spans from December to April. Overhead sprinkler systems are recommended for large nurseries, while manual watering is more suitable for smaller nurseries. It is essential to mulch the nursery beds before irrigation begins. Watering should occur daily during the first few weeks of plant growth, and later, the frequency can be reduced to once every two or three days. Once seedlings are grown, they can be used for budding or as seedling stumps.
Seedling Nursery
1. Basal Dressing: For every hectare, 2.5 tonnes of compost or well-rotted cattle manure and 400 kg of powdered rock phosphate (18% P₂O₅) should be applied. This equates to 25 kg of compost and 4 kg of rock phosphate per 100 m² of nursery bed. In newly cleared forest areas, compost or manure may not be required in the first year; rock phosphate alone suffices. If the same bed is reused, rock phosphate should be applied every three years.
2. Top Dressing: Apply 2500 kg of NPKMg mixture (10-10-4-1.5) per hectare six to eight weeks after planting. This amounts to 25 kg per 100 m² of nursery bed. A second top dressing of 550 kg urea per hectare (5.5 kg per 100 m²) is applied six to eight weeks after the first top dressing. It is important to avoid direct contact between the fertilizer and the plant stem and ensure adequate soil moisture during application.
Budding Process
Budding involves replacing a plant’s shoot system with that of a more desirable variety. A patch of bark from the stock (seedling plant) is replaced with a bud patch from a selected clone. Once attached, the stock is cut above the budded area, and the bud develops into a new shoot (scion), forming a tree with the stock’s root system and the scion’s shoot system.
Types of Budding
A. Brown Budding
This method uses brown buds from budwood of about one year’s growth and stock plants with 10 months of growth and 7.5 cm girth at the collar region. Budding occurs when the bark peels off easily, usually when the top whorl of leaves is fully developed.
B. Green and Young Budding
These methods use green, tender buds.
Steps for Brown Budding
- Clean the stock plant’s base (15 cm) and make two parallel vertical cuts 5 cm long and 1.5 cm apart.
- Connect the cuts with a horizontal cut, allowing latex to ooze out before lifting the bark flap.
- Prepare a bud patch by making two vertical cuts around the bud and two horizontal cuts.
- After allowing latex to drain, remove the bud patch and ensure the core is intact.
- Insert the bud patch into the stock’s cut panel, ensuring proper contact with the cambium, and bandage the area using polythene strips.
Preparation and Packing of Propagation Materials
The propagation materials managed by rubber growers include ungerminated seeds, germinated seeds, seedling stumps, brown budwood, green bud shoots, brown budded stumps, green budded stumps, polybag plants, and stumped buddings.
Proper preparation techniques are essential to maintain the quality of these materials, as poor preparation can reduce their effectiveness in the field, leading to poor establishment post-planting.
After preparation, the materials may need to be stored or transported, which increases the risk of damage due to moisture loss, physical damage (e.g., breaking, rubbing, bruising, crushing). To prevent this, specific packing and transportation methods are adopted to protect these materials.
1. Land Preparation
Rubber plantations in Nigeria are typically established in rain forest areas. The land, which varies from gently undulating slopes to flat terrain, must be prepared before planting can begin. All pre-planting activities should be completed before the onset of the rainy season. The key activities include:
i. Clearing Roads, Constructing Fences, and Buildings
ii. Lining
iii. Terracing
iv. Drainage
v. Construction of Silt Pits and Contour Bunds
vi. Pitting and Refilling
2. Lining
Lining for rubber planting should be based on the plant spacing and planting density being adopted. Rubber can be planted using a square or rectangular planting system. Square planting is suitable for level or near-level land, while rectangular planting can be used for flat lands and slopes.
In rectangular planting, the lines should be oriented east-west to capture maximum sunlight. For areas with slopes greater than 8%, contour lining is done, where planting points are marked along lines of equal elevation.
The recommended planting density ranges from 420 to 500 plants per hectare for buddings or plants that will be field-budded, and 445 to 520 plants per hectare for seedlings. Higher initial plant densities allow for appropriate thinning as the plants grow.
3. Terracing
In hilly or undulating areas, terracing along the contour is recommended to conserve moisture and prevent soil erosion. Terraces are formed by cutting the hillside soil 60-75 cm in front of the planting row and throwing it back to create a terrace width of 1.25 to 1.5 meters, with an inward drop of 20-30 cm.
Uncut earth steps are left at intervals to prevent lateral water flow. For economic reasons, square platforms (honeycomb terraces) measuring 1.25 x 1.25 meters may be used during planting, and later joined together to form complete terraces.
Digging (Pitting) and Refilling of Field Holes
Pitting is crucial for creating an ideal environment for the young rubber plant’s root system. The standard pit size is 75 cm x 75 cm x 75 cm, although it varies based on the planting material. Stumped buddings require deeper and larger pits, while smaller pits are sufficient for small and medium-sized polybag plants.
In loose, friable soils, pits may be wider at the top and tapering at the bottom, or they may have a central hole for the taproot. In compact or stony soils, wider pits are necessary.
Pitting should begin early, with filling completed in advance of planting to allow the soil to settle. The topsoil and subsoil should be kept separate during digging, and filling should be done using the topsoil.
Organic manure and phosphatic fertilizers should be mixed with the top 20 cm of soil in the pit, which should be filled to about 5 cm above ground level. A peg is placed in the center of the pit to mark the planting point.
Increasingly, tractor-mounted hole-digging machines are used for pitting, with machines available that can dig pits with a 60 cm diameter and up to 90 cm depth.
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Diseases and Pests of Rubber Plantations
Crop losses in rubber plantations are significant due to various diseases and pests. Effective plant protection measures ensure healthy growth and optimal production. Below are some major diseases and pests affecting rubber.
1. Abnormal Leaf Fall
i. Causative Agent: Phytophthora palmivora, P. meadii, P. nicotianae var parasitica, and P. botryosa
ii. Occurrence: Annual recurrence during the southwest monsoon, especially along the southwestern coast.
iii. Symptoms: Premature leaf fall, either green or red, with lesions on petioles, midrib, and leaf blades.
iv. Clonal Susceptibility: Clones like PB 86, PB 235, PB 260, RRIM 600 are susceptible. RRII 105, PB 217 show tolerance.
v. Control Measures: Prophylactic spraying with Bordeaux mixture or copper oxychloride before the monsoon.
2. Shoot Rot
i. Causative Agent: Phytophthora palmivora, P. meadii
ii. Occurrence: Common during heavy rains in the southwest monsoon.
iii. Symptoms: Rotting of tender shoots, particularly affecting nursery seedlings and young plants.
iv. Clonal Susceptibility: Clones susceptible to abnormal leaf fall are also affected.
v. Control Measures: Spraying with copper fungicides and phosphorus acid (Akomin, Phosjet) to protect young plants. Stickers may be added to enhance adhesion.
3. Mealy Bug
i. Causative Agent: Ferrisiana virgata
ii. Occurrence: Common in nurseries.
iii. Symptoms: Soft-bodied insects with a white mealy outer covering. Damages similar to scale insects.
iv. Clonal Susceptibility: RRII 105 and RRIM 600.
v. Control Measures: Spraying with malathion 0.1% or quinalphos 0.075%.
4. Bark Feeding Caterpillar
–i. Causative Agent: Aetherastis circulata, Ptochoryctis rosaria
ii. Occurrence: Found in Nagercoil, Nedumangad, Punalur, and Thrissur.
iii. Symptoms: Caterpillars feed on dead bark, creating deep scars on the trunk, and cause latex exudation.
iv. Clonal Susceptibility: PB 86, PB 235, and PB 311 are highly susceptible.
v. Control Measures: Application of Sevin 5% or spraying with fenvalerate 0.02% on the trunk.
5. Termite (White Ant)
i. Causative Agent: Odontotermes obesus
ii. Occurrence: Found in dry regions of Central Kerala and non-traditional areas like Orissa.
iii. Symptoms: Feeds on dead bark, causing damage to young plants and building soil passageways on the trunk.
iv. Clonal Susceptibility: PB 86, Tjir 1, and RRII 105.
v. Control Measures: Soil drenching with Chlorpyriphos 0.1% solution.
6. Scale Insect
i. Causative Agent: Saissetia nigra
ii. Occurrence: Common in young plantations and nurseries.
iii. Symptoms: Black, dome-shaped insects suck sap from the leaves, leading to drying and death of plant parts.
iv. Clonal Susceptibility: RRII 105 and RRIM 600.
v. Control Measures: Natural enemies like insect parasites and fungi control the pest. Severe infestations can be treated with malathion 0.05%.
7. Mites
i. Causative Agent: Hemitarsonemus dorsalis
ii. Occurrence: Sporadic in young rubber plants.
iii. Symptoms: Minute organisms sucking sap, causing crinkling and shedding of leaves.
iv. Clonal Susceptibility: PB 217, RRII 105, and RRIM 600.
v. Control Measures: Dust or spray with sulphur 0.2% or dicofol 0.05%.
Tapping and Simulation
1. Latex Extraction by Tapping
Latex is extracted from the bark of the rubber tree through a process called tapping. Tapping involves making controlled cuts to remove thin layers of bark, which opens the latex vessels or removes any coagulated material blocking the latex flow. The goal is to maintain a steady latex flow while minimizing harm to the tree.
2. Bark Composition
The rubber tree bark is made up of several layers: an inner soft bast, an intermediate hard bast, and an outer cork layer. Latex vessels are concentrated within the soft bast, arranged in concentric rings. The distribution and density of these vessels vary significantly among seedling populations, but are more consistent in budded clones.
3. Latex Composition
Latex from tapped rubber trees contains 30-40% rubber, suspended in a hydrosol protected by a complex film. Besides rubber particles, latex also contains other particles such as lutoids, which are associated with vessel plugging, leading to the eventual cessation of latex flow after tapping.
4. Latex Flow Process
Upon tapping, the latex vessels release viscous latex due to pressure changes. This latex displacement is followed by water entry from surrounding tissues, which dilutes the latex and decreases its viscosity. Eventually, the osmotic imbalance within the latex vessels causes lutoid particles to break down, releasing a protein called hevein.
This protein cross-links rubber particles, resulting in coagulation at the cut ends of the vessels, leading to the cessation of latex flow. This process is most efficient in acidic conditions.
Tapping Standards and Height of Opening
For budded plants, tapping can begin when the tree reaches a girth of 50 cm at a height of 125 cm from the bud union. Seedling trees are tappable when they attain a girth of 55 cm at a height of 50 cm, although tapping can be initiated at 90 cm for trees with a girth of 50 cm. Subsequent panels for budded trees are opened at the same height (125 cm), whereas seedling trees follow a height standard of 100 cm.
It is generally economical to begin tapping when about 70% of the trees in an area meet the required girth. On average, rubber trees take seven years to become tappable, though planting advanced materials like polybag plants can reduce this time. In India, March-April is the preferred period to start tapping, with a second chance for trees that don’t meet the girth requirements in September.
1. Tapping Systems
Different tapping systems suit different rubber tree clones. Budded trees are usually tapped using the half-spiral alternate daily (1/2S d/2) system, while seedlings are tapped on a half-spiral third daily (1/2S d/3) system. Medium-yielding clones, such as RRIM 600 and GT 1, benefit from alternate daily tapping, while high-yielding clones, like RRII 105 and PB 260, often use low-frequency tapping systems combined with stimulation to enhance latex yield.
2. Tapping Notations
Tapping notations represent the method, panel position, and type of stimulation used in tapping operations. These notations help describe the type of cut, its length, direction, and tapping frequency. The international notation system is used to maintain consistency across different regions.
Latex Processing
Latex collected from multiple rubber trees is mixed with formic acid, which acts as a coagulant. After coagulation, the rubber sheets are pressed to remove excess water and then sent for further processing at factories, where vulcanization and additional treatments occur.
For technically specified rubber, the latex is coagulated with acid, passed through cutting machines and creping rollers, and converted into rubber crumbs using hammer mills or granulators. The crumbs are then screened, washed, dried, and packed.
In the production of ribbed smoked sheets, coagulated latex is passed through rollers to form thin sheets with a ribbed pattern. The ribbed texture increases the surface area, aiding in drying. The sheets are then placed in a smokehouse at 60°C for one week, graded, sorted, and packed in bales.
Natural rubber is compounded similarly to unsaturated synthetic rubbers, using accelerators, activators, antioxidants, fillers, and other agents to achieve specific properties.
Safety Precautions in Processing
Mechanized production methods such as rollers and centrifuges pose hazards, requiring strict safety measures during their installation, operation, and maintenance.
Workers should be trained in safe practices, including chemical handling, and appropriate measures should be taken to prevent slips, trips, and falls. Supervision is essential to avoid accidents associated with heat used during curing processes.
Uses of Rubber
Rubber has an extensive range of uses across various sectors, from household items to large industrial products. It enters the production process either at intermediate stages or as finished goods.
A significant portion of rubber consumption is attributed to tires and tubes, which accounted for around 56% of the total global rubber consumption in 2005. The remaining 44% is used in the production of general rubber goods (GRG), which encompass all rubber-based products except tires and tubes.
Key Uses of Rubber:
1. Automotive Industry:
i. Tires and Tubes: The automotive industry remains the largest consumer of rubber, especially in the production of tires and tubes.
ii. Under the Bonnet Products: These include hoses, belts, and dampeners used in automobiles for various engine and mechanical components.
2. Gloves:
i. Medical, Household, and Industrial Gloves: Rubber, especially concentrated latex, is extensively used for making gloves in medical, household, and industrial applications.
3. Adhesives: Rubber is used as an adhesive in numerous industries, with significant applications in the paper and carpet sectors.
4. Vulcanization:
Natural rubber is often vulcanized, a process that involves heating the rubber and adding sulfur, peroxide, or bisphenol to enhance resilience, elasticity, and prevent degradation. Vulcanization greatly improved rubber’s durability and usefulness, with Charles Goodyear being closely associated with the successful development of this process.
5. Additives:
i. Carbon Black: This is a common additive used in rubber to improve its strength, particularly in vehicle tires.
Natural rubber is an essential agricultural product used in the manufacture of various products that are integral to modern life. Its production from the Hevea brasiliensis tree plays a crucial role in the socio-economic well-being of many developing countries, where over 20 million families rely on rubber cultivation for their primary income.
Despite its significance, low market prices for natural rubber have contributed to rural poverty, particularly affecting smallholders in Southeast Asia, where currency fluctuations have reduced their purchasing power for essential goods. Large estates have become less prominent, with many small growers, some managing two hectares or less, bearing the brunt of economic challenges.
Products made from natural rubber, such as tires, engineering components, and latex goods, continue to be indispensable in industries worldwide, contributing to transportation, medical advancements, and various engineering applications.
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