1. CHAPTER -2
LITERATURE REVIEW
2.1. Tea: A Golden Beverage
Human civilization has hitherto discovered three non-alcoholic stimulating beverages, namely coffee, cocoa and tea. Tea is regarded as the most popular temperance drink. Its use as a beverage has been in vogue long before the Christian era and is deep rooted in Chinese mythology. Today, tea is virtually regarded as a universal beverage and even as a national drink of many countries. Tea is made from the shoots of tea plant, Camellia sinensis (L) under a botanical family Theaceae. Linnaeus described tea plants in two genera, Camellia and Thea in 1737. Tea leaves contain several chemical compounds having medicinal properties, such as, caffeine, polyphenols and alkaloids. This is the caffeine that acts as mild stimulant, while polyphenols contribute to colour and strength of liquor. Other non additive drugs, such as theobromine, theophylline, useful fluorides, volatile oils and vitamin B are also present.
2.2. Tea Horizon:
Today, Tea horizon of modern world is comprised of as much as 29 countries and seen to extend from the latitude 430N (Georgia, USSR) to 270S (Corrientes, Argentina).
2.3. Genesis of Bangladesh Tea:
The genesis of Bangladesh Tea may be divided into three distinct Eras of Enterprises:
- Era of British Enterprise (1840-1947)
- Era of Pakistan Enterprise (1947-1971)
- Era of Bangladeshi Enterprise (1971-to date)
2.4. Structure and Growth of Bangladesh Tea:
Tea areas in Bangladesh are located in two divergent ecological zones, namely (i) Sylhet zone in the Surma valley, and (ii) Chittagong zone in the Halda valley. The Surma valley are traditionally sub-divided into six circle , namely, No- rth Sylhet, Juri, Lungla, Mono-doloi, Balisera and Luskerpur, which have 131 tea estates , while there are 21 estates in the Halda valley in Chittagong and 1 estate in Bramanbaria. Total grant area of all tea gardens is allotted to be 113,603ha, of which 39.8% area is used for tea plantation and about 38% of the land comprising bamboo thickets, khets, factory premises, roads and uncultivable waste, etc. which are not suitable for tea cultivation. The remaining 22% comprises forests (17%) and fallow land (5%).
2.4.1. Growth:
Tea estates are grouped into 4 classes, viz. A, B, C, U in accordance with the productive level. There are 68 estates belonging to A class which produce more than 180,000 kg of tea annually, 23 estates to B- class producing 108,000 kg to less than 180,0000 kg; 26 estates to C-class producing 27000 kg to less than 108,000 kg., while 36 estates belonging to U-class (unclassified) which produce annually less than 27000 kg. All estates belonging to C and U class are, however, less developed and faced with various constraints of productivity and finance.( Anon, 1979.).
2.5. TEA ECOSYSTEM:
Tea is an agro-ecosystem comprising tea plants, shade tree and other ancillary crops along with various abiotic elements. The life processes of biotic community are critically balance with the tea biosphere which includes climate and soil. The climatic elements vary from place to place and season to season owing to the diversity of geological locations, the phisiography, the distribution of land and water, altitude, mountain barriers, ocean currents, semi-permanent high/low pressure-belts, wind, storms, etc. in a country.
2.5.1. Tea Climate:
Bangladesh climate is considered to be tropical monsoon with three distinct seasons: Warm season (mid Feb-mid May), Monsoon season (mid May-mid Oct), and Cold season (mid Oct-mid Feb). The climate of Bangladesh is discussed under three important parameters like Rainfall regime, Temperature regime, and Humidity-Evaporation cum Sunshine regime which are responsible for a successful tea culture.
Temperature rainfall and relative humidity are the most important factors for the growth and development of tea crops and cultivated best in temperature ranges from 12.70C-280C and rainfall ranges from 2500mm.-5000mm. and humidity ranges from 56-86%.( Zaman, 1980.)
2.5.2. Tea Soil
Texture and Topography of Tea Soil:
Soils of Sylhet Tea zone have different characteristics depending on age, drainage, and parent material. Soils in Hills are generally very steep, yellowish- brown, well-drained with a moderate blocky structure, and having bedded sand, sandstone or shale at a depth of 0.6-1.5m (2 to 5 feet), loamy to silty or clayey. Soils in Surma-Kushiyara Flood Plain are grey gradually stratified, silty and loamy occurring on gently undulating ridges and basins. The soils of Outwash Plain are mostly silty to clayey, grey with some melting in the subsoil and have weaker structure than the Flood plains. Most of the soils of Sylhet basin overlie stratified material at 0.6-1.5m 2 -5 feet depth, seasonally flooded, grey or locally deep grey with blocky structure.( Sana, 1989.)
Texturally, the tea soils in Bangladesh are predominantly loamy. Soils of Balisera, Monodoloi and Luskmipur circles are loamy to sandy loam from surface downwards, while loamy sand in north Sylhet circle, but soils in Chittagong zone are most loamy.
Topographically, tea zone of Bangladesh may be divided into 3 units, viz.
(i) Tillah or low hills which are outliers of the Tripura hill Range in India
(ii) High flat which are the higher valleys constitute about 45% of the land. The soils are suitable for tea cultivation.
(iii) Low flat which are the valley floor and constitute about 23% of tea land.
2.6. Some Agro-types of Tea in Bangladesh:
Ø China type
Ø Assam-type
Ø Manipuri-type
Ø Burma-type
Ø Hybrid-I
Ø Hybrid-II
Ø Hybrid-III, etc.
A great deal of research has been devoted to the vegetative propagation of tea with a view to produce commercial plants having superior yield and quality attributes. To this endeavor, Russia, Japan, India and Sri Lanka have made a great contribution. Russian clone No. 257 (out of 16 released), Indian TV1 (out of 24 released) and the 2020 series of Sri Lanka and Yabukita of Japan were found to be excellent. In Bangladesh, six outstanding clones, namely BT1, BT2, BT3, BT4, BT5 and BT6 have so far been released. Of these clones, BT2 combines high yield and flavor throughout the season.
2.7. Tea Management System:
2.7.1. Management of Tea land:
Tea is grown on a variety of land with various topographical, textural and structural characteristics. Tea, being a perennial plantation crop, needs to be cultivated under suitable climatic and edifice conditions, but the Bangladesh tea is grown under marginal land and climatic conditions such as, low elevation, poor relief (topography), the presence of impervious sub-soil layer (Hardpan), and low nutrient status, etc. Under such conditions, a careful consideration is to be made through a well planned soil survey and profile study prior to selecting a new site for plantation. Following methods are adopted:
Ø Nature of vegetation
Ø Nature of relief (topography) of land.
Ø Study of soil profile.
Soil Conservation:
Main theme of soil conservation is to maintain an optimum soil moisture and soil-fertility for the normal growth of plant. Most plants are unable to thrive under either water-surplus or water stress. Tea plants do not grow well under these conditions. Soils are eroded and depleted from soil surface by excessive water flow or water logging. As a result, soil conservation of prime importance against soil erosion which is caused either by a heavy runoff (water erosion) or deforestation (wind erosion). (Sana, 1989)
2.7.2. Shade Tree Management:
The use of leguminous trees as shade for tea is common in India, Sri Lanka, Indonesia, Bangladesh and Africa. In Sri Lanka and Indonesia some non-leguminous species, viz. Grevillea robusta, and deciduous trees are also used at high elevation where the leguminous shade species do not grow well. Shade management on India and Bangladesh, most common shade species are Albizzia odoratissima occupying about 75% of tea area, A. moluccana, about 7%; Derris robusta. 8%, A. procera, 4%; A. lebbeck and Cassia siamea about 3%. In some old sections, A. stipulata; A. lucida and Dalbergia assamica are also found.( Hasan, 1963.)
2.7.3. Green Manuring and Cover Crops Management:
The use of green manuring crops in tea culture has long been in vogue to safeguard the young tea in nursery from the duress of drought and nutrition- supply. Green manuring crops which are predominately leguminous plants, help enriching the soil –fertility and soil moisture through its lopped materials. These also act as miniature shade trees and protect young plants in the nursery.
In Bangladesh, green manuring crops with leguminous species, like Crotalaria anagyroides, Tephrosia candida (Bogamedeloa) Priotropies cytisodes, Desmodium gyroides, Cajanus cajan (Arhar) etc. are used in newly planted area for soil-rehabilitation.( Sana, 1989.) A few grasses like Tripsacum laxum (Guatemala), Pennisetum purpureum (Napier), Cymbopogon citratus (Citronella), Cymbopogon winteranus (Lemon grass) are found to be useful for soil rehabilitation. As cover crops Mimosa invisa, Calopogonium mucunoides, Strylosenthes gracilis are effectively used in tea for conservation. They are twining or prostrating creepers and can smoother any weed including Mikania scandens and Cuscuta within a few months.
2.8. Tea agro techniques:
Tea production technology involves various agro techniques, which may be put two management components.
I. nursery management
II. crop management
2.8.1 Nursery management
It can be divided in to two types
A. seed nursery
B. vegetative propagation nursery
2.8.1.a.1. Seed nursery:
Tea seeds are collected from either general seedbarie or bi /poly clonal seedbarie. To obtained viable seeds, the collection of seeds that lay on the ground beneath the seed bearers is made daily or alternate day. After collection, seeds are preliminary sorted out according to the sizes, viz. small, medium or large, which may vary from jat to jat. Thereafter the seeds are passed through the sieve having 9-11 mesh to categorize the seeds for germination test.
2.8.1.a.2. Germination test:
All seeds that passed over the shifter are placed in a large receptacle full of water, about 15cm deep above the level of seeds that sink for about 24-72 hours. The true sinkers and floaters are separated. The true floaters are then spread on a large tarpaulin. The cracked or split seeds are picked by hand and put immediately in the nursery bed. Seeds which are cheesy, starred or damaged are discarded.
2.8.1.a.3. Seed Nursery bed:
The nursery site is selected near the plantation. The nursery beds are designed with proper drains, paths and roads. Beds may be of any length but the width of them should not exceed 1.5m. Generally abed 1.5mx30m in size, may accommodate about 37.32kg of seeds which is sufficient to plant as much as 0.08 ha area.
The seeds are put in triangular pattern, about 3cm beneath the soil and covered with loose soil light mulch. If the plants are to be lifted at 12th month, the spacing, 20cm is suitable, while 25cm is suitable if the plants are to be lifted after 18-24 months.
Proper shading and watering is necessary for the development and growth of seedlings. Beds may be constructed with or without shade. Green crops like Bogamedeloa, Tephorosia candida or Priotropis cytisoides or Crotalaria anagyroides are suitable. Green crops are sawn in lines by dibbling. These are regularly hedged or lopped and used as mulch. The loppings are thinly spread over the bed so that the young seedlings can easily push through.
2.8.1.b.1. V.P. Nursery:
The purpose of vegetative propagation is to strike the nodal leaf-cuttings from the desired tea plant and put in a suitable rooting medium for raising individual plants having similar genetic constitution of the parents. For a successful nursery management through vegetative propagation, it is essential to maintain ready stock of mother tea bushes from which the nodal cuttings are supplied to the V.P. nursery. The mother tea bushes are selected either from the existing tea plantation or a separate Nucleus Clone Plot (NCP).
2.8.1.b.2. Management of Mother Tea Bush:
2.8.1.b.2.1. Selection of Mother Tea Bush:
Mother Tea Bushes are preliminary selected from an existing tea plantation on the basis of some selection-criteria of morpho-physiological characteristics of the plant, viz. bush-frame, vigour and growth, leaf-pubescence, the density of plucking-points on plucking table, etc. The final selection is made by several laboratory tests and field trials, viz. rooting trial, yield trial and quality tasting, etc.
2.8.1.b.2.2. Nucleus Clone Plot (NCP)
The selection of mother tea bushes from the existing tea plantation is time consuming and laborious. For continuous supply of tea cuttings of highly productive quality clones, a separate area is planted with recognized clones that are known as Nucleus Clone Plot. The NCP is built for each type of clones to be propagated in three ways, viz. (i) by using the existing clonal plantation, if any, in an estate, (ii) by converting a proportion of mature seedling tea plantation through grafting of desired clone, or (iii) by planting a separate area with desired clones.
Generally the NCP is design to plant 400 plants in a block, 100 plants in each of 4 sub-blocks.
2.8.1.b.2.3 Tea Seedbarie:
Tea is a self-sterile cross-fertilized plant. The self-incompatibility nature of tea thus puts a great hindrance to the development of improved planting materials. During last decades, BTRI has endeavored to produce improved seeds that can supersede the existing seeding tea and be at par with the clonal tea in respect of yield and quality potential. To the present, two types of improved seeds, viz Bi-clonal and poly clonal seed have been evolved, which are seemingly better than the general seeds.
Plantation Management:
Land Preparation:
After selection of plantation site, the land is cleaned off of jungles, stubbles, stones, gravels, grasses and unwanted vegetation. Trees are ring barked uprooted, and remove away from the site. Old stumps, tree roots, trashes should not be burnt in-situ as that may spoil the soil structure and micro-flora or fauna. The land is then opened up for cultivation.
After clearing, the land is laid out in accordance to the topo-sequence by making roads, paths and drains. High tillah land with 30% slope is subjected to soil erosion. Moreover, the exposed tillah may cause wind erosion. Erosion can also occur even when the land is only sloping gently. Teas grown on these sites are subjected to too much evaporation of dry winds. After 5 years of planting, erosion is less serious as a thick mat of leaf and pruned branches under tea absorb the run-off. Proper soil conservation measures are taken by making drains, contour paths and contour boxes.
The cut-off drains are dug across the top tillah plantation to prevent rain water running down the hill ceusing soil erosion. The entire area of proposed plantation site is surveyed using Dumpy level /Ceylon Tracer/ Spirit level. The contour map is drawn. Accordingly, the contour paths, 50-60m.wide, are made in a gradient of 1:500 and the inter-contour distance is about 9-15m.
Plantation techniques:
There are various types of planting system, viz. Triangular, Square and Hedge. In Bangladesh tea, the single hedge planting is in vogue. The spacing distance is 120 cm.x 60 cm. (4 X 2).( Kibria, etl. 1988.). This type of planting system is found to be superior to others in respect of quick coverage, highest plant density per unit area and convenience for inter-cultural operations. The population load per unit area may be calculated by using the following formula:
it is thus estimated that about 13450 plants/ha are required for tillah plantation using spacing 120 cm. x 60 cm., while 10760 plants for flat plantation using 120 cm. x 70 cm.
In field practice, the staking and lining is done simultaneously prior to planting green crops or shade. After staking, the digging of planting pits is done along the line. The size of the planting pits varies for the clonal tea seedling tea. For clonal tea the pit size is 25-30 cm. wide x 30-35 cm. deep, while for seedling tea, 25-30cm. wide x 40-45cm. deep. The excavation of soil from the pit is done in sequence. The top soil is cut 20cm. deep x 30cm. wide (across) and kept separately. Then the lower sub soil is dug 15cm. deep x 30cm. wide for clonal plant of 35cm. for seedling tea ( Mandi, 1971)
2.8.2 Crop management:
It consists with two types.
A. Young tea management.
B. Mature tea management.
2.8.2.a. Young Tea Management:
A tea plantation is, according to age, grouped as either young tea (0-5 years old), Mature tea (5-40 years old) or old tea (more than 40 years old). At present, the tea plantation of Bangladesh constitutes about 4% young tea, 51% mature tea and 45% old tea. Under this perspective, the importance of young tea management to boost up the tea productivity can not be overlooked. Following operational sequences for young tea management are maintained from the very beginning of land preparation to the bringing up and maintenance of planted tea in the field
2.8.2.a.1. Bringing up Young Tea:
The methods that are employed to train young tea after planting until it is ready for first plucking, is termed as Bringing up into bearing. Three methods are generally used such as
(i) Decentering
(ii) Pruning and Pegging or
(iii) Ring-pegging.
(i)Decentering:
The initial pruning is first done when the plants are 12 months old after planting out in the field. The aim is to stop upward growth and encourage side-ways spread so that a good plucking surface is developed in due course. The pruning cut may be given at 15-23 cm. and when the developed branches have red striated bark, the stem at the pruning-height is about 6 mm. thick; a regular tipping is done according to the merit of the plant.
(ii)Pegging Method:
Pegging may be made either by hooked pegs or by combination of ring and peg method. In this system, the shoots which develop from a stump or after the first prune of a sleeved plant, are bent down and pegged so that they radiate outwards and upwards from the main stem.
(iii)Ring-Peg Method:
This method involves a ring of about 30 cm. diameter made of bamboo split or a panel size tree branch. A ring is placed over the shoots which are then gently spread to their side of the stem (without over-crossing them), and when the correct pegging-slope has been reached, three pegs are used to hold the ring down firmly. This method is very much used in bushes having lot of shoots.
2.8.2.b. Mature Tea Management:
Pruning, Tipping & Plucking and Fertilizing are three vital operations for mature tea management. These operations of tea husbandry should be meticulously put into practice to achieve the desired productivity from a tea section.
2.8.2.b.1. Pruning:
Pruning of tea bush has two fold objectives, such as,
(i) To limit the top growth and
(ii) To stimulate the growth of tea bush.
If unchecked, a tea bush may attain a considerable height making tea plucking impossible.( Rashid, 1986) Moreover owing to continuous plucking the growing apices gradually lose vigor and finally the growing of healthy pluck able shoots is minimized. The bushes become unproductive. When the bush is pruned, the dormant buds on the
stubs are stimulated into new growths induce the renewal of a productive systems from these hidden buds that would not have normally grown. The pruning is however a drastic operation. If the time and type of pruning, food reserve in roots and stem, general hygiene and environment are not correctly judged, the pruning of a bush might bring hazard to bush rather than making it productive. Depending on the severity of pruning operations that are in vogue in Bangladesh tea, it may be defined and described as follows:
Types of Pruning
Light Prune (LP):
Initial light pruning operation is given at 60-75 cm. and regulated in such a way that the maximum plucking level is restricted to 96-100 cm. for 15-20 years before medium pruning cycle. This will ensure the development of strong new shoots with minimum die-back.
Deep Skiff (DSK): Deep skiff is to cut the bush half-away between the last pruning mark and tipping height, usually between 75-85 cm. so as to leave a fork on the stem to increase the number of new plucking shoots.
Medium Skiff (MSK): Medium skiff is to cut the bush mid-way between the deep skiff and tipping height, usually between 85-95 cm. Its objective is to cut below the majority of the crow’s feet to remove most of the congested growth above the junction of red and green wood.
Light Skiff (LSK): Light skiff means to cut the bush at the current years’ tipping level to remove the creep foliage.
2.8.2.b.2Tipping:
The object of tipping is to establish a plucking table at a suitable height while ensuring the sufficient maintenance foliage.
On Light Pruned Tea: A tipping measure of 20 cm. above the prune is recommended. This normally means that there will be five layers of maintenance leaves between prune and plucking table.
On Deep Skiff Tea: If this operation has taken placed after a light prune at half-way between the medium prune and the tipping height, a tipping measure of 10 cm. from the skiff can be used. On the other hand, if the deep skiff has been higher or carried out following any operation other than a light prune, a 20 cm. measure from the last light prune should be used provided that at least 2 layers of new maintenance leaves remain.
On Medium Skiff Tea: A janam and full leaf taken at the centre of the bush and leveled there from will leave sufficient maintenance leaf.
On Light Skiff Tea: As the bushes will still be carrying most of their maintenance foliage from the previous year, they should be tipped to the janam.
On Over Skiff / Unpruned Tea: These areas should be plucked level on the over skiff or last plucking mark.
2.8.2.b.3. Plucking:
The objective of plucking is to produce the maximum sustainable yield of a standard sufficient to maximizing the profitability/ha of plantation. Standard plucking may be defined as taking all growths on the plucking table, leaving the janam, buds and small one leaf and a bud shoots. Standard plucking should be practiced on 7-day round. This will result making maximum sale-able crop with the best potential quality. As growth slows down towards the end of the season, the round may be gradually extended to around 10 days by the end of the October. All banji shoots must be removed at the time of plucking all throughout the season.
When standard plucking is practiced, the plucking table will gradually rise during the season. However, this rise, known as ‘creep’, should be kept to a maximum of 5 cm. This may necessitate breaking back if the round has fallen behind. Light skiffed and unpruned areas should be plucked hard to restrict creep; to not more than 3 cm. Removal of bush-side growth by pluckers must be strictly forbidden. Where there is a considerable space between bushes, this is even more important so that bushes are encouraged to spread and fill up the unit area allocated to them.
2.9. Fertilizer application
A considerable quantity of nitrogen, phosphorus and potash is lost every year from the soil in the form of plucked shoots, prunings, leaching and evaporation, to ensure good growth of tea and maintain soil fertility, these are to be replenished to the soil in the form of inorganic fertilizers organic manures.
2.10. Tea Pest, Diseases and Weed:
Tea pest and tea productivity are two antagonistic factors. Literally, the word, pest is a collective term for a wide range of organisms like virus, bacteria, algae, fungi, insects mites birds, rodents, etc. which are noxious, troublesome and destructive to crops, food-
supply and human property. In Bangladesh Tea, the annual crop loss due to various pests, diseases and weeds is estimated to be about 10-15%, of which 9% is caused by weed infestation alone. Besides, the yield-loss caused directly by major pest and diseases, many obscure and minor pest such as Termite, Taggotworm, Branch canker and root diseases permanently inhibitat the tea plantation. These contribute significantly to the debility of tea bushes. Moreover, crop losses to the extent of 50% or more may be inflicted by the advent of an epidemic or outbreak of specific pest or diseases in particular season or tea estate. The weed flora in Bangladesh tea is virtually diversified in nature and as many as 36 weed species have so far been recoded. ( Sana, 1978.) Today, the concept of pest management has, considering the pest problem as a part of whole ecosystem, become a multi-dimensional system, called Integrated Pest Management.(IPM). These concepts are economically viable and environmentally acceptable system of tea crop protection
2.11. Multiple land use by multi crops in the tea estates:
Essential components of agro crops in the tea estate included such as Rubber, Oil Palm, Citrus and Tea. Not only tree species, the group also includes crops such as banana, pineapple and sugar cane. There is a second and much larger group of tree crops which are sometimes grown in pure stand, but more frequently are found in mixed cultivation and grown by smallholders. Essentially these are grown in agro-forestry and homestead systems, though are occasionally found in pure stand cultivation. They include coconut, cocoa, coffee, many tropical fruits and nuts (such as mango, avocado, cashew, tamarind, breadfruit, jackfruit mangoes, and durian) and several spices such as clove, cinnamon and nutmeg. (Roger W. Smith, 2001)
2.12. Tea and Rubber combination in the tea estate:
Planting times and planting conditions for rubber and tea generally are the same. Tea leaves are first collected when the plant reaches the age of three, its production peaks at 6 -7 years, but production commonly can last for twenty-five years to as much as 50 years; rubber trees in monoculture plantations are tapped at age seven (Zheng et al., 1991). However, where rubber is intercropped with tea, rubber can be tapped safely at age six (Feng, 1989; Hao, 1986, and Zheng et al., 1991).
Research on rubber & tea agro forestry systems (referred to in the text as the rubber /tea system) started in Hainan in the early 1960s (Feng, 1986; Xu, 1993). Considerable attention was given to protecting the rubber trees from low temperature. Tea plants to the rubber plantations, the added plants might help protect the rubber trees from cold. In addition, the researchers felt that because the shallow rubber -tree roots are largely concentrated in the top 20 cm of the soil, the tea plants would help lessen the soil heat loss and would also act as a wind break. The rootlets of the tea plants, on the other hand, tend to grow mostly 20 to 50 cm below the soil surface. Therefore, the root systems of the rubber trees and the tea plants should be in minimal competition with one another for nutrients and water. (Zheng et al., 1991).
Consequently, various rubber /tea planting designs were tested to see how various rubber and tea arrangements might moderate the air temperature near the base of the rubber trees and protect the trees from excessive cold (Feng, 1986). Experimental spacing in intercrops of rubber trees and tea bushes vary. Regardless of the spacing, the goal is to achieve about 30 percent shade for the tea to produce the best product (Feng, 1986).
2.13. Physical and biological data of tea and rubber:
After planting densely spaced tea within stands of rubber trees, temperatures and wind velocities near the base of the rubber trees in the rubber /tea system showed moderation in winter with respect to those of monoculture rubber plantings. Further, the relative humidity within the rubber/tea systems overall was higher because of the complicated vegetation structure than in monoculture rubber plantings (Feng, 1989). The benefits of the rubber/tea system showed that the:
· daily average and maximum air temperature between 20 and 50 cm rose 0.3 - 0.4o C;
· night time rubber-tree trunk temperatures at 50 and 150 cm above the soil surface rose 0.6 -2.1o C and 0.3 - 0.5o C respectively,
· Relative humidity between 20 and 50 cm above the soil surface decreased 1 - 2% (Ma, 1989).
Overall, the rubber/tea system moderates fluctuations in its microclimate (Xu, 1993). The rubber/tea system keeps the system warmer in winter and cooler in summer than in a monoculture rubber planting. A shade range of 30-40 percent is beneficial to dry matter accumulation of the system (Feng, 1986; Huang et al.1991) and also to the quality of tea (Huang et al., 1991). The rubber/tea system produces a higher soil organic matter content than a rubber monoculture because incoming sunlight is used more effectively (Feng, 1989).
With the increased vegetative cover of the rubber/tea system runoff and soil erosion decreased and soil moisture increased (Feng, 1989). The increased vegetation and its close spacing in the rubber/tea system reduced the direct impact of the rain drops with the soil. In the rubber monoculture, only 12 percent of the raindrops were intercepted whereas in the rubber/tea system 28.7 percent were intercepted (Xu, 1993). An eleven year comparison of runoff and soil erosion (Xu Z, 1993) shows the benefit of the rubber/tea system over monoculture rubber in slowing erosion and runoff (Table 1).
Because runoff slowed, the annual rate of water loss in the rubber/tea system was 42 percent less than that of a monoculture rubber planting (Feng, 1989).
Subsequent analyses showed that the soil humus content of the rubber/tea system was 15 percent higher than that of a monoculture rubber planting, and 2 percent higher than that of a tea planting (Feng, 1986). The rubber/tea system also fostered a higher number of soil microorganisms, increased mineral nutrient availability, and improvement in the soil fertility (Feng, 1989).
2.14. Different economic crops in the tea estate along with rubber:
The general method for establishing the rubber /tea system was derived partly from farming practices of Yunnan minority communities (Xu Z, 1990). The general planting procedure follows: plant and fertilize rubber -tree seedlings on prepared terraces; plant upland rice (Oryza sativa), maize, and peanuts and other leafy crops between the rubber trees; harvest the rice, maize, etc. at the end of year one; plant pineapples in spaces previously occupied by harvested crops; harvest peanuts in year two and pineapples in year two through year four; replant spaces previously occupied by pineapples with tea in year four; rubber trees at this point are tall enough to provide enough shade for tea plants; tap the rubber trees in year six; start tea harvesting three years after planting. The rubber /tea system can operate effectively for thirty years at which time the entire system is started again (Zhou S, pers. comm., 1990). The rubber /tea system is intended to keep the underlying soil covered with vegetation throughout the system’s life thereby minimizing soil erosion (Gong, 1989).
A government Tea estate is being developed in Kewzing in the western part of Sikkim in India. There is one more Tea estate at Temi. Both these estates extend over an area of 400 acres. Under horticulture, large quantities of oranges and apple are raised. Vegetables, pineapple and banana are other cash crops of Sikkim. (Sana,1989)
2.15. The role of tree crops in sustainable agricultural systems
Tree crops have three important roles:
(i) As producers of items of food or other products needed by humankind, and the generation of income.
(ii) As a means of extracting nutrients and minerals from deep within soil profiles, as a sink in which nutrients and minerals are stored and as a mechanism for recycling those materials and producing soil organic matter.
(iii) For their ability (along with other perennial plants) to maintain a cover over the soil thus providing protection against oxidation of soil organic matter and reducing the impact of heavy rain on soil structure thereby reducing run-off, soil erosion and leaching of nutrients; to intercept solar radiation to maximize production of carbohydrates by photosynthesis, and, uniquely, to provide wind breaks and shelter.
( W. Smith,2001)
2.16. Economics of Sustainable, Tree-based Systems:
Earlier in this paper I said that I would return to the matter of economics in relation to the sustainability of tree-based production systems. High productivity, as I frequently argue, depends upon the provision of inputs, particularly of fertilizers, to compliment the naturally available fertility of the soil and the contribution which trees can make to the recycling of nutrients. Fertilizers are expensive, and certainly beyond the reach of subsistence farmers. However, as farmers, even small farmers, become more commercially orientated they will generate cash incomes from the sale of both surplus food and the products of the trees in their systems. This generation of cash is essential if the farmers are to sustain ably produce high the yields of food needed to feed the population of the tropics over the next 25 years.
