Bangladesh Tea Research Institute Research Articles

Present Status and Future Prospects of Tea production and Research on Varietal Improvement in Bangladesh

Tea is one of the most important non-alcoholic beverage in the world and has been gaining further popularity as an important ‘health drink’ in view of its inferable medicinal value. In Bangladesh, commercially tea was cultivated since 1854 by establishing first tea garden Malnicherra Tea Estate in Sylhet. From 1947 to 2020, tea growing area, production and per hectare yield were increased 127.71%, 370.53% and 137.96% respectively. The major reasons behind the increasing tea productivity are extension of tea growing areas as well as cultivation of the tea clones (BT clones) released by Bangladesh Tea Research Institute (BTRI). Till now BTRI released 23 clones and 5 biclones, having average per hectare yield of 3461.67 kg. In the world, tea production, consumption and exportation have increased significantly. Unlike world condition, there is a negative relation between tea production and export in Bangladesh. From 1980 to 2020 the quantity of tea exports was decreased by 92.99%. This situation emphasizes the need for exploring alternative means by the tea industries of increasing profits from tea cultivation and tea export. As a result, researches on tea varietal improvement is needed for rapid economic growth and development of tea industry as well as to encourage tea plantation business to go ahead with more production to meet our own demand along with quality tea to flourish tea business in Bangladesh.

Effect of Different Types of Pruning Operations on Yield and Quality of Tea

Aims: Pruning is the cutting of branches of a tea bush at predetermined height and at a specified interval in order to reinvigorate and bring tea bushes within reach of the pluckers, which directly related to the productivity and quality of tea. In Bangladesh, Three and four year pruning cycles were the conventional recommendations for the tea plantation. In this experiment, along with BTRI recommended four types of pruning operations (LP, DSK, MSK and LSK), two more types of pruning operations such as: UP (Unprune) and LoS (Level of Skiff) were considered as treatments. This experiment was conducted with two main objectives: to evaluate the yield and yield related parameters of tea due to different types of pruning operations as well as to find out the effect of pruning operations on organoleptic quality of black tea.
 Study Design, Place and Duration of Study: This experiment was conducted ‘D2 Thall’ area at the main research farm of Bangladesh Tea Research Institute (BTRI) from December 2017 to November 2019. The experimental design was Randomized Completely Block Design (RCBD) with six treatments and three replications.
 Methodology:
 The treatments are denoted as T1 (UP: Unpruned) control, T2 (LP: Light Pruning), T3 (DSK: Deep Skiffing), T4 (MSK: Medium Skiffing), T5 (LSK: Light Skiffing) and T6 (LoS: Level of Skiffing) respectively. Data were collected under the following parameters:
 
 Number of plucking point or pluckable shoot/bush in each plucking
 Fresh weight (g) of 100 shoots (three leaves and a bud)
 Oven Dry weight (g) of 100 shoots (three leaves and a bud) to calculate Dry Matter Content
 Green leaf weight (kg) to calculate Yield of each treatment
 Number of plucking round to calculate Yield gap of each treatment
 Black Tea Quality of each treatment by Organoleptic Tasting Method.
 
 Results: It was found that, number of plucking points/pluckable shoot and yield were found significantly high in T6 (Level of Skiffing), T5 (Light Skiffing) and T1 (Unpruned) than the other treatments. But in terms of tea quality, lowest quality tea was found in T1 (Unpruned), T6 (Level of Skiffing) and T5 (Light Skiffing) treatment. So, it can be concluded that, ‘Skiff Pruning’ or ‘Unprune’ technique had positive effect on yield but the quality of these technique were poor in comparison with other treatments. T2 (Light Pruning) treatment gave more tender and fresh shoot than the other treatment. For this reason, dry matter was low in T2 (Light Pruning) treatment but tea quality was much better than the other pruning technique.
 Conclusion: Pruning has positive or negative effect on yield and quality of tea. ‘Skiff Pruning’ or
 ‘Unprune’ has positive effect on yield but the quality of is poor than the other treatments. Best Quality tea can be produced from Light Pruning tea section because of having more tender and fresh shoot than other treatments.

Determination of Green Tea Recovery Percentage and Its Relation to Different Weather Parameters

Aims: Green tea is one of the most popular drinks and millions of cups are consumed every day in entire world. In Bangladesh, people mainly prefer CTC (Crush-Tear-Curl) black tea but now-a-days health conscious people are being habituated to green tea due to its beneficial effect to health. Since our green tea production is very little compared to black tea production, our concept and knowledge about green tea is also very low. This experiment was conducted with two main objectives: to determine the green tea recovery percentage and to find its relation to different weather parameters.
 Study Design: This experiment was conducted by following Factorial Completely Randomized Design (CRD) with four replications.
 Place and Duration of Study: This experiment was conducted at Miniature Factory of Bangladesh Tea Research Institute (BTRI) Sreemangal, Moulvibazar-3210 from March 2017 to November 2017.
 Methodology: BTRI recommended green tea manufacturing process (Green Leaves→ Steaming→ Cooling→ Rolling→ Drying) was followed in this experiment to calculate the recovery percentage. Weight of green leaves after each stage and recovery percentage were calculated. Monthly weather data of four parameters: temperature (°C), rainfall (mm), relative humidity (%) and sunshine hour were also collected. Correlation Coefficient (r) was calculated by Pearson’s mathematical formulation to quantify the degree of relationship. Linear regression equation was also generated to predict recovery percentages against different weather parameters only when the relationship was significant.
 Results: In case of BTRI recommended green tea manufacturing process the average recovery percentage was 19.19% with an average moisture content of 3.72%. Among four weather parameters, temperature (°C) has negative insignificant (correlation coefficient, r=-0.43 and P=0.2523) relation on recovery percentage. But there was a strong significant (P=0.000146) negative effect (r=-0.942) of rainfall on recovery percentage. While a moderate non-significant (P=0.322807) negative relation (r=-0.37) of relative humidity and a considerable high positive non-significant (P=0.073687) relation (r=0.62) of sunshine hour on recovery percentage was found in this study.
 Conclusion: Green tea recovery percentage was 19.19% with an average moisture content of 3.72% which can be different with different weather conditions in every month. Among four weather parameters, mainly rainfall was responsible for the variation of recovery percentages in different months.

Effect of different pruning operations on the incidence and severity of various diseases of tea plant

To analyze the effect of different pruning operation on the incidence and severity of different diseases of tea (Camellia sinensis) plant. An experiment was carried out at the Bilashchara Experimental Farm of Bangladesh Tea Research Institute (BTRI), Srimangal. Three places of the sections were selected randomly that received LP (Light Prune), DSK (deep skiff), MSK (medium skiff) and LSK (light skiff) operations. Every bush was critically observed before and after pruning operations and all infected diseases were recorded. Disease severity was expressed as percent disease index (PDI). MSTAT program was used for statistical snalysis. After pruning operation, maximum incidence 33.33% and severity 8.20% of Grey brown blight was found in LSK. Horse hair blight maximum incidence (18%) and maximum severity (6.27%) both were found in LSK. In thread blight maximum incidence was in MSK 22.67% and maximum severity was 7% in LSK. The highest % reduction of branch canker both in incidence and severity was observed in LP section followed by DSK, MSK and LSK. In case of Gall disease maximum incidence and severity both was LSK 24.67% and 7.60%. The highest incidence of black rot was in LSK 41.33% and severity 12.87% was in MSK. From the study, it was recommending that without using any chemicals, only by different pruning operations and proper cleaning can reduce the in incidence and severity of those diseases.J. bio-sci. 24: 01-09, 2016

Diversity of insect, mite and nematode species in tea ecosystem of Bangladesh

The study was undertaken on insect, mite and nematode species diversity in Bangladesh Tea Research Institute (BTRI) main farm, Baraoora and Phulcherra tea estates in Sreemangal, Bangladesh from the period of 2014 to 2015. The study was done through direct field observations, sweeping net, food trap, sticky trap, light trap and Baermann Funnel method. A total of 71 insect, mite and nematode species was recorded belonging to 45 families under 14 orders. Among these, 25.35% species were foliar insects and mites, 26.76% soil insects and nematodes, 21.13% beneficial insects and 26.76% butterflies. All the foliar and soil insects, mites and nematodes were found as recognized pests of tea. The highest number of individuals among foliar pest was the red spider mite (Oligonychus coffeae) and the lowest number was the coffee red borer (Zeuzera coffeae). Of the soil pests, 77.47% species were termites, 14.33% nematodes, 4.86% field cricket, 2.63% mole cricket and 0.72% cockchafer grub. Regarding the soil pests, live wood termite (Microtermes obesi) was the highest and dagger nematode (Xiphinema sp.) was the lowest in number. One species of foliar insect, looper caterpillar (Hyposidra infixaria) and three species of nematodes, viz. reniform nematode (Rotylenchulus sp.), ring nematode (Criconemoides sp.) and dagger nematode (Xiphinema sp.) were recorded for the first time as tea pest in Bangladesh. In case of beneficial insects, 81.49% species were predators, 16.73% parasitoids and 1.78% parasites. Lady bird beetle (Micraspis discolor) was the highest in number and anthocorids (Anthocoris sp.) were the lowest. Nineteen species of butterflies were found. Of the observed butterflies, lemon emigrant (Catopsilia pomona) was the highest and large oakblue (Arhopala amantes) was the lowest in number. According to pest status, tea mosquito bug, red spider mite, thrips, looper caterpillar, live wood termites, root knot nematode and root lesion nematode were major, and the rest of those were occasionally regarded as minor pest. The population of most of the pest species was higher in peak cropping season (April-November), whereas the lowest population was recorded in off season (December-February). According to diversity indices, the diversity of foliar pest was higher than the other groups and the foliar pest was more evenly distributed in comparison to soil, beneficial insects and butterflies.J. Biodivers. Conserv. Bioresour. Manag. 2017, 3(1): 31-44

English

A survey was carried out in 2015 at Bangladesh Tea Research Institute (BTRI) to ascertain the impact of varieties, topography, age of plants and shade condition on the incidence and severity of Black rot disease in tea. Data were collected monthly from 300 tea bushes selected randomly for each attribute with three replications. Data were recorded on the incidence and severity of the diseases by observing the typical symptom by using 0-5 scoring scale. Disease incidence and disease index was computed by following a referenced formula. In all the cases of attributes, the maximum level of incidence with Black rot disease was found in September but severity with the same was found in July. The incidence and severity of Black rot disease were significantly higher in hellock (23.52 and 16.64%) areas as compared to flat and tillah areas. Age of tea plants had no variation with severity of the disease but a significant variation was found with the incidence. Highest incidence (22.64%) was found in immature tea bushes. More amount of disease was observed in shaded areas as compared to unshaded areas. Seed tea bush (22.64 and 17.07%) was found to be more predisposed to Black rot disease than clones (20.59 and 16.38%). The findings of this study will help to understand the pattern of distribution of the disease in the commercial tea fields so that the planters can escape the diseases easily.   Key words: Incidence, severity, black rot, tea.

Biocontrol Potentiality of Isolated Trichoderma spp. against Pestalozzia theae Saw. in Tea

Isolates of Pestalozzia theae Saw. and Trichoderma spp. were collected from Bangladesh Tea Research Institute (BTRI) farm area, Bangladesh. The cultural morphology and antagonistic potentiality of Trichoderma spp. against grey blight pathogen Pestalozzia theae was studied for tea cultivation. The antagonistic potentiality of Trichoderma spp., against Pestalozzia theae showed maximum (inhibition 84.45±0.77%) after 72 hrs of inoculation under in vitro condition followed by 76.02±3.50% after 24 hrs of inoculation. This study revealed that Trichoderma strain was highly effective to control Pestalozzia theae, the causal agent of grey blight disease of tea.

Improvement of Tea (<i>Camellia sinensis</i> L.) Soil Properties by Growing Different Green Crops

Long-term tea cultivation has led to degradation of the soil. Old tea soils require rehabilitation for restoring soil health. Soil rehabilitation by growing different green crops can break the chain of monoculture of tea. An experiment was conducted at The Bangladesh Tea Research Institute (BTRI) Farm during 2008-2011 to find out the efficiency of different green crops on the improvement of soil properties. Four green crops such as Guatemala, Citronella, Mimosa and Calopogonium were grown to develop the nutritional value of the degraded tea soil. Soil samples were collected and analyzed before and at the end of experiment. Soil pH was increased in all four green crops treated plots with the highest increase in Citronella treated plots (from 4.1 to 4.5). Highest content of organic carbon (1.19%) and total nitrogen (0.119%) were found in Mimosa and Calopogonium treated plots, respectively. Concentration of available phosphorus, calcium and magnesium in all green crops treated plots were above the critical values, while available potassium content was above the critical value in Guatemala, Citronella and Mimosa treated plots. Changes in soil pH and available potassium were significant, while changes in organic carbon content, total nitrogen and available calcium were insignificant. Changes in available phosphorus and magnesium were significant. The Agriculturists 2014; 12(2) 34-38

Evaluation of Some Plant Origin Commercial Biopesticides against Red Spider Mite, <i>Oligonychus coffeae</i> Nietner (Acarina: Tetranychydae) in Tea

An experiment was conducted to evaluate some plant origin commercial biopesticides against red spider mite in tea under both in the Entomology Laboratory and main farm of Bangladesh Tea Research Institute (BTRI), Srimangal, Moulvibazar during the period from March 2013 to December 2014. Bio-Cawach ( Pongamia pinnata ), Karanza ( Azadirachta indica + Pongamia pinnata ), Miticon (Various herbs, alkaloids and salt of fatty acids), Neemakar (Neem, Karanja & Tulsi), Rescue ( Vitex negundu + Clerodendron infortunatum ) and Torpedo ( Sophora alopecuroides + Stemona sessilifolia ) were considered as treatments and dosages were @ 0.8 ml, 1.0 ml, 1.0 ml, 1.0 ml, 0.5 ml and 0.5 ml, respectively. Data were collected at 24 HAT, 48HAT, 72HAT (Hours after Treatment) in the laboratory and at weekly interval in field condition. Results indicated that all the biopesticides showed the toxic effect on red spider mite in tea and significantly reduced mite population both in laboratory and field conditions. In laboratory condition, Miticon showed the highest (93.28%) toxic effect at 72HAT followed by Karanza (92.55%) against red spider mite where as Bio-Cawach, Neemakar, Rescue and Torpedo exhibited pronounced acaricidal action (89.78%~91.67%) at 72HAT. Similar trend of toxicity was found at 24HAT & 48HAT. The mortality was in a linear trend i.e. increasing with increasing of time. From the field evaluation, it was found that the highest (81.34%) reduction in mite population was observed in Miticon treated plot followed by Rescue treated plot (81.01%). The lowest (74.07%) reduction in mite population was observed in Bio-Cawach treated plot. The order of toxicity of the six plant origin commercial biopesticides on adult red spider mite in both laboratory and field condition was: Miticon>Rescue>Neemakar>Karanza>Torpedo>Bio-Cawach. Application of the tested biopesticides did not affect the natural predators such as Stethorus gilvifrons and Oxyopes sp. Tea samples made from biopesticide-treated shoots were found taint free when subjected to organoleptic evaluation. These eco-friendly low cost plant products can therefore be incorporated in the strategy of integrated pest management (IPM) to reduce the load of chemical pesticides in tea.

Drying tea in a kilburn vibro fluid bed dryer

The fluidized bed drying principles for drying of tea in Bangladesh is thoroughly studied. The experiments were conducted to determine the drying curve, drying time, drying constant and dynamic equilibrium moisture contents of tea at the Bangladesh Tea Research Institute. Drying of tea in a fluidized bed dryer (Kilburn Vibro Fluid Bed Dryer) takes only 20 min for drying from an initial moisture content of 69.1% to a final moisture content of 2.8%. Temperatures of drying air were recorded to be 130°C at the inlet and 90°C at the outlet. The drying constant was found to be 31.05 h-1 and the dynamic equilibrium moisture contents were in the range of 18.3 to 2.0%. Finally the principle of fluidized bed drying was compared with the principle of conventional endless chain pressure type drying. DOI: http://dx.doi.org/10.3329/jbau.v11i1.18227 J. Bangladesh Agril. Univ. 11(1): 153-158, 2013

Comparative Studies on the Performances of Some Plant Cakes and Synthetic Chemicals Against Nematodes in Tea in Bangladesh

A comparative study was undertaken to evaluate the performances of plant cakes and synthetic chemicals against nematodes infesting tea at Bangladesh Tea Research Institute (BTRI) during March 2012 to June 2012. The indigenous plants i.e. Bishkatali (Polygonum hydropiper), Mahogani (Swietenia mahagoni) and Neem (Azadirachta indica) and synthetic chemicals i.e. Carbofuran (Furadan 5G), Fipronil (Goolee 3GR) and Rynaxypyr (Ferterra 0.4G) were considered as treatments. The dose of tested plant cakes @ 50g/pot and synthetic chemicals i.e. Furadan 5G @ 35g/pot, Fipronil 3GR @ 35g/pot and Rynaxapyr 0.4G 15g/pot were used in this experiment. Soil samples are regularly collected at weekly interval and samples were analyzed for nematode count at Entomology Laboratory through Baermann funnel method. Result revealed that all the treatments had showed the toxic effect on nematodes and significantly reduced nematode population from the soil. The nematode population in the soil treated with Rynaxypyr 0.4G was the lowest due to the highest mortality of nematodes (85.80%) followed by Fipronil 3G (82.00%), and Carbofuran 5G (81.71%) which was satisfactory. Among the plant cakes, Mahogani cake showed the highest (79.89%) mortality of nematodes in the treated soil. The cakes of Bishkatali (74.82%) and Neem (71.57%) also reduced the nematode population significantly. Rynaxapyr and Mahagani Cake can be used as soil treatments for the management of nematodes to get nematode free soil or safe soil with less nematode for establishing tea nursery. Crude plant cakes of P. hydropeper, S. mahagoni and A. indica can effectively be utilized beside the use of chemical nematicides as safer nematicidal products in integrated pest management of nematodes in tea in Bangladesh.

In Vitro Biological Control of Branch Canker (Macrophoma theiocola) Disease of Tea

Antagonist microorganisms, such as Trichoderma spp. have long been recognized as biological agents, for the control of plant disease and for their ability to increase root growth and development, crop productivity, resistance to abiotic stresses, and uptake and use of nutrients. An attempt was made to evaluate the in vitro biocontrol of branch canker (Macrophoma theicola) of tea plants by Trichoderma spp. Isolation of Trichoderma spp. and M. theiocola was done carefully. Pure culture of Trichoderma spp. and M. theiocola and their morphological characteristics were studied at different intervals. Five M. theiocola and five Trichoderma isolates were collected from mature tea plants and tea soils respectively of Bangladesh Tea Research Institute (BTRI) main farm area. The cultural morphology and antagonistic potentiality of Trichoderma spp. against branch canker pathogen (M. theiocola) were taken into consideration. Trichoderma spp. controls the growth of M. theiocola at different intervals. After 24 hour growth rate of Trichoderma was 9.3% and M. theiocola was 0.88%. The antagonistic potentialities of isolated Trichoderma against pathogens (M. theiocola) were observed at different intervals (24-120 hrs) and the percentage of inhibition was 82% which were observed after five days (120 hours) of inoculation. The Trichoderma spp. antagonizes the pathogens by several mechanisms such as antibiosis, competition, mycoparasitism or other form of direct exploitation. From this study it was revealed that, the Trichoderma spp. was highly effective to control the isolates of M. theiocola that is responsible for branch canker in tea cultivation.

Yield Performances and Cup Quality of Some BTRI Test Clones of Tea

A long term experiment was conducted to investigate the yield and quality performances of four vegetative propagated test clones of tea coded as A/8/01, A/17/22, A/22/27 and A/22/40 at Bangladesh Tea Research Institute (BTRI) farm during 1996-2010. A standard clone BT1 was considered as control. Cuttings of the test clones were collected from the selected bushes of Amo tea estates and were raised at BTRI nursery. Then saplings were put to long term yield and quality trial following Latin Square Design (LSD) with 3 replications. The green leaf was harvested at weekly interval during the plucking season starting from mid March to mid December throughout the experimental period. Yield data were recorded and analyzed statistically using MSTAT programme. Results of the experiment revealed that among the test clones A/22/40 gave the highest significant yield of 3509.1 kg ha-1 of made tea followed by BT1 (3203.69 kg ha-1), A/8/01 (2912.24 kg ha-1), A/17/22 (2817.76 kg ha-1) and A/22/27 (2278.78 kg ha-1) from the average of 9 years (2002-2010) at mature stage. At immature stage i.e. 1st year to 5th year after plantation yield difference was insignificant. The overall cup quality of the test clones was assessed by conventional organoleptic test. The cup quality of A/8/01, A/17/22, A/22/40 as well as the standard clone BT1 was found to be above average (AA) while the cup quality of A/22/27 was average (A). Considering the yield and quality potentials, the test clone A/22/40 has appeared quite promising to be released as a standard clone. DOI: http://dx.doi.org/10.3329/ijarit.v1i1-2.13925 Int. J. Agril. Res. Innov. & Tech. 1 (1&2): 24-28, December, 2011

Yield and quality performances of four tea test clones

An experiment was carried out during 1994–2007 to investigate the yield and quality performances of four vegetatively propagated test clones of tea viz. SH/D/11/13, SH/D/11/333, B/HB/2/3 and B/HB/6/4. Two clones, BT1 and TV23, were used as check for quality and yield, respectively. Cuttings of the test clones were collected from the selected bushes of Shumshernugger Tea Estate and hybrid lines of Bangladesh Tea Research Institute (BTRI) and were raised at BTRI nursery. Then the saplings were managed for long term yield and quality trial following randomized complete block design with 5 replications. The green leaf was harvested at weekly interval during the plucking season starting from mid March to mid December throughout the experimental period. The overall cup quality of the test clones was assessed by conventional organoleptic test. At the immature stage (2nd–5th year after plantation), all test clones showed similar yield trend as that of check BT1. At the mature stage (6th–13th year), the test clones SH/D/11/333 and B/HB/6/4 gave the significantly higher average yield (3095 and 3342 kg ha–1 made tea, respectively) compared to the check BT1 (3042 kg ha–1 made tea). The cup quality of all the test clones and BT1 was found to be “Above Average” while the cup quality of TV23 was “Average”. Considering the overall performances, the test clones SH/D/11/333 and B/HB/6/4 have been released as BT13 and BT14, respectively for commercial plantation in the tea estates. DOI: http://dx.doi.org/10.3329/jbau.v10i1.12036 J. Bangladesh Agril. Univ. 10(1): 33–38, 2012

Effect of Gamma Rays on the Growth Performance of Bangladesh Clone Tea

The experiment was carried out to investigate the effects of gamma radiation on the early growth performance and physiological traits of BT2 clone tea, the most promising cultivar released by Bangladesh Tea Research Institute. The fresh shoot cuttings were irradiated with seven different levels of gamma radiation such as 0, 10, 20, 30, 40, 50 and 60 Gy from Cobalt 60Co source (Dept. of PlantBreeding, Bangladesh Institute of Nuclear Agriculture). Thereafter, the irradiated shoot cuttings were planted in polythene bags and kept under natural conditions. It was observed that callusing was initiated from 8th weeks after placement of tea shoot cuttings in the polythene bags and completed by 12th weeks. The morphological growth of tea shoot cuttings were recorded under varying levels of gamma radiation and growth stages. It was observed that the number of leaves, number of primary branches, base diameter, root length and total leaf area per plant significantly increased with the progress of time and increasing levels of gamma radiation, however, the plant height showed decreasing trend with the increasing levels of gamma radiation, which could be due to the change in chromosomal structure and genetic makeup. After 56 weeks of planting, the plant height, the number of leaves and primary branches per plant, base diameter, root length and total leaf area per plant recorded were 65.70 cm, 30.67, 7.33, 1.48 cm, 23.50 cm, and 1250.67 cm2 per plant respectively under the radiation level 60 Gy, whereas the corresponding figures of the above parameters at the control treatment were 76.21 cm, 18.33, 3.67, 0.92 cm, 17.75 cm and 778.33 cm2 per plant, respectively. A significant relationship was observed among the physiological growth parameters with the increasing levels of gamma radiation. The total dry matter gain, leaf area index, absolute growth rate and relative growth rate were significantly influenced with the rising levels of gamma radiation (up to 60 Gy), whereas the net assimilation rate of individual tea plant non-significantly responded as compared to those of control treatment. Finally after 56 weeks of planting, the maximum total dry weight gain, leaf area index, absolute growth rate, relative growth rate and net assimilation rate recorded under 60 Gay radiation level were 40.25 g/plant/week, 4.25, 1.18 g/week, 0.0621g/g/week and 17.07 g/m2/week respectively.

Field Performance And Economic Analysis Of Some Commonly Used Insecticides Against Tea Mosquito Bug, <i>Helopeltis Theivora</i> W.

A study was undertaken to evaluate the field performance and economic analysis of some commonly used insecticides against Tea mosquito bug, Helopeltis theivora Waterhouse at Bangladesh Tea Research Institute (BTRI), Srimangal, Moulvibazar. Six different insecticides–Thiodan 35EC (Endosulfan), Ripcord 10EC (Cypermethrin), Decis 2.5EC (Deltamethrin), Dimethion 40EC (Dimethoate), Metasystox 25EC (Oxydemeton), and Malathion 57EC (Malathion) were applied in the plots as recommended dose of BTRI. The shoot infestation reduction as well as yield response of all the insecticides treated plots were superior over the control but there was no significant difference among the insecticidal treatments. Better field performance against Helopeltis was found in Malathion 57 EC treated plots in respect to shoot infestation reduction over control (87.09%). Per hectare yield (1910.33 kg) as well as per hectare net return (Tk. 300927.80) were also higher in Malathion 57EC treated plots. The highest marginal rate of return (2580.57%) was obtained by spraying Metasystox 25EC over control followed by Ripcord IOEC (1710.87%) and other insecticides. The most economically acceptable insecticide against tea mosquito bug was Metasystox. Keywords: Field performance; economic analysis; insecticides; tea; Helopeltis theivora. DOI: http://dx.doi.org/10.3329/bjar.v36i3.9273 BJAR 2011; 36(3): 449-454

Assessment of Microbial Biomass Carbon and Nitrogen in Some Tea Soils of Bangladesh

Microbial biomass carbon (C) and nitrogen (N) and their contribution to soil organic carbon and total N contents were assessed in soils collected from Bilashchara Tea Estate under Bangladesh Tea Research Institute (BTRI), Srimangal of Moulavibazar district, and Sripur Tea Garden under Jaintapur of Sylhet district. Microbial biomass C and N in Bila shchara Tea Estate soils varied from 90.4-144.0 and 20.5-29.0 mg/kg soil, and that of Sripur Tea Garden soils varied from 120.7-362.0 and 26.6-59.5 mg/kg soil, respectively. Within the two tea growing areas biomass C/N ratios ranged from 3.35-6.12. Relationships between biomass C and organic carbon and biomass N and total N were positively correlated. The contribution of biomass C to soil organic C was 1.23%, ranging from 0.9-1.55% and the contribution of biomass N to total N content of the soils ranged from 1.19-2.89%. Keywords: Biomass carbon (C); Biomass nitrogen (N); Organic C; Total N; Tea soilDOI: http://dx.doi.org/10.3329/bjm.v25i1.4850 Bangladesh J Microbiol, Volume 25, Number 1, June 2008, pp 21-25