Last Updated : 30 June 2008 at 12:25 IST
Indian Natural Rubber: From plant to tree
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Many plant species produce natural rubber. Considerations of quality and economics, however, limit the source of natural rubber to one species, namely Hevea brasiliensis.
It is a native of the Amazon basin and introduced from there to countries in the tropical belts of Asia and Africa during late 19th century. It can be termed as the most far reaching and successful of introductions in plant history resulting in plantations over 9.3 million hectares, 95 per cent of it across the globe in Asia.
Hevea brasiliensis, also known as the Para rubber tree after the Brazilian port of Para, is a quick growing, fairly sturdy, perennial tree of a height of 25 to 30 metres. It has a straight trunk and thick, somewhat soft, light brownish gray bark. The young plant shows characteristic growth pattern of alternating period of rapid elongation and consolidated development.
The leaves are trifoliate with long stalks. The tree is deciduous in habit and winters from December to February in India. Refoliation is quick and copious flowering follows. Flowers are small but appearing in large clusters. Fruits are three lobed, each holding three seeds, quite like castor seeds in appearance but much larger in size. The seeds are oil bearing.
The rubber tree may live for a hundred years or even more. But its economic life period in plantations, on general considerations is, only around 32 years – 7 years of immature phase and 25 years of productive phase.
Propagation of Rubber
In India, Hevea seeds normally ripen during July-September when the seeds are collected and seedlings raised. All earlier plantations were raised from unselected seeds. The yield potential of these having been low, the production of those plantations was poor.
Selection work on Hevea with a view to improving the planting materials and the introduction of vegetative propagation by budding led, in course of time, to the establishment of numerous valuable clones.
Rubber Growing Regions
The rubber growing regions in India can be classified under two major zones, traditional and non-traditional on the basis of agro-climatic conditions.
Rubber cultivation in India has been traditionally confined to the hinterlands of the southwest coast, mainly in Kanyakumari District of Tamil Nadu and Kerala
These are hinterlands of coastal Karnataka, Goa, Konkan Region of Maharashtra, hinterlands of coastal Andhra Pradesh and Orissa, the northeastern states, Andaman and Nicobar Islands etc, where rubber is now being grown.
Humid tropical climate prevails in the rubber-growing tract. Average annual rainfall in the tract varies from about 2000-4500 mm. The southern parts of the traditional tract enjoy southwest and northeast monsoons almost equally while the northern areas receive mostly the southwest monsoon. From south to north the drought period extends from two to five months in a year and the distribution of rainfall becomes more uneven. However, variation in temperature and humidity in the rubber tract is not so marked as that of the rainfall. The temperature remains very warm and humidity very high throughout the year.
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.
Tapping and Stimulation
Latex is obtained from the bark of the rubber tree by tapping. Tapping is a process of controlled wounding during which thin shavings of bark are removed. The aim of tapping is to cut open the latex vessels in the case of trees tapped for the first time or to remove the coagulum which blocks the cut ends of the latex vessels in the case of trees under regular tapping.
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