Journal of the Rubber Research Institute of Sri Lanka
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Item Effectiveness of low frequency harvesting systems in rubber smallholder sector of Eastern province (IL2) of Sri Lanka(Rubber Research Institute:Agalawatta, 2016) Lakshman, R.G.N.; Kudaligama, K.V.V.S.; Rodrigo, V.H.L.; Nugawela, A.; Attanayake, A.P.; Perera, M.K.P.; Madushani, P.D.T.L.Item Field performance of young coffee seedlings and cuttings intercropped with rubber(Rubber Research Institute. Agalawatta, 1988) Rodrigo, V.H.L.; Nugawela, A.; Kariyawasam, L.S.; Aluthhewage, R.K.Coffee may be planted either using seedlings or cuttings. Anyhow, a comparative study of their field establishment and performance has not been made. Iin this study seedlings and cuttings of Coffea canephora intercropped with rubber were compared for their field stablishment and growth. It is evident that there is no difference in the success of their field establishment. The dry matter yield determinants of plants, i. e. light intercept ion, conversion efficiency and rate of loss of dry matter, estimated by total leaf area, CO2 assimilation rate and dark respiratory rate respectively, are also similar in both seedlings and cuttings. This is confirmed by the similar mean total dry weight of a seedlings and a cuttings. The partitioning of assimilates is more towards root development in the cuttings and is evident by the significantly high root dry weight and the root/shoot ratio. The percentage of assimilates partitioning towards the growth of aerial parts is less in the cuttings, i. e. 52 and 67perc. for cuttings and seedlings respectively. Despite of similar light levels, the CO2 assimilation rates are lower in the afternoon in both seedlings and cuttings. The perc. deeline is 23.5 and 18.6perc. for seedlings and cuttings respectively.Item Clonal differences in growth parameters of young Hevea buddings and their relation to field performance(Rubber Research Institute. Agalawatta, 1986) Nugawela, A.; Aluthhewage, R.K.Hevea trees when tapped exhibited a depression of girth increment and canopy growth. Hence a high growth rate is required to maintain the growth whilst giving a high yield. Growth parameters of 5 Hevea clonal buddings were determined after different growth intervals viz., 3, 6 , 9, and 12 months to study the correlation they show with the field performance of the same clones. Clonal differences were significant, but did not necessarily correlate with the field performance. Growth rates gradually increased with age during the peeriod of investigatiion. Thepossibility of using growth parameters together with gas exchange capacities determinedin earlier studies in predicting later field performance are discussed.Item Effect of different levels of supplemental nitrogen on CO2 assimilation rates and productivity of Pueraria phaseoloides (Roxb) Benth and Desmodium ovalipolium (prain) wall. ex ridely grown in agalawatta series soil(Rubber Research Institute. Agalawatte, 1985) Nugawela, A.; Jayasinghe, C.K.; Aluthhewage, R.; Wettasinghe, S.Plant dry matter production is linked to CO2 assimilation rates, respiratory losses and total leaf area. Experiments were undertaken to determine the effect of different levels of supplimental nitrogen given to legume cover crops, on their CO2 assimilation rates and productivity. They were found to be highest for Pueraria phaseoloides and Desmodium ovaliforlium when given around 140 and 35 ppm of supplimental nitrogen. Reciprocal of specific leaf area and laef nitrogen content were also determined and they showed a positive linear relationship with supplemental nitrogen levels. How nitrogen could a influence the CO2 assimilation rates of cover crops studies are discussed.Item Gas exchange parameters for early selection of Hevea brasiliensis Muell. Arg(Rubber Research Institute. Agalawatte, 1985) Nugawela, A.; Aluthhewage, R.K.Selecting high yielding progeny from Hevea breeding programmes is a money and time consuming approach and limits the progress of breeding, Girth, bark thickness, numberof lates vessel rings, latex vessel density and first few years yield of 7-8 year old Hevea budding are reported to be correlated to the yield potential. These parameters are used by some breeeders for a primary selection using smalle scale clone trials. Latex is biosythesised from sucrose in latex vessels and the potential of sucrose supply to latex vessels depends on CO2 assimilatory capacity of the canopy and the partitioning of assimilates. Attempts were made to estimate the mean CO2 assimilatory capacity of a healthy and a matur eleaf whole in year old Hevea clonal buddings. Preliminary studies show the mean CO2 assimilatory capacity of a whole and its ratio with water use efficiency value to be correlated qith yield potential. These observation suggest that effective selection of clones for further testing in large scale clone trials could be done on this basis, when buddings are around a year old.Item Variations involved in field measurements of transpiration rates and stomatal diffusive resistance of Hevea brasiliensis Muell. Arg. clones and the relationship of the latter with net photosynthetic rates(Rubber research Institute. Agalawatte, 1984) Nugawela, A.; Wickremasinghe, W.N.; Aluthhewage, R.K.Variance components and their percentage contribution to total variation during field measurements of stomatal diffusive resistance (DR) and transpiration rates (TR) were studied for Hevea clones. Variance from the plant component was much higher than other components viz., leaves of the same plant and determinations of the same leaf. DR, TRand coefficient of varian for DR and TR varied significantly with leaf age and time of the day. The three leaflets in a leaf were similar in respects to DR and TR. Within a whorl, the comparatively smalle leaves at the top of differed significantly withrespect to DR and TR from the rest. DR and Tr of clones RRIC 100, RRIC 103, RRIC 45, PB 86 and IAN 710 were significantly different at 0.1perc. level. Initial studies show stomatal diffusive resistance to have a tendancy to be correlated with net photosynthetic rates (NPR). Other possible factors that might bring about clonal differences in NPR are discussed.Item The effect of tapping on the assimilation rates of Hevea brasiliensis Muell. Arg. leaves(Rubber Research Institute. Agalawatta, 1990) Nugawela, A.; Aluthhewage, R.K.The CO2 assimilation rates at leaf level were compared in tapped and untaped trees of two Hevea brasiliensis genotypes. In both genotypes, the CO2 assimilation rates of the leaves in the upper stratum were lower in tapped trees. Simmilary, in young microtapped plants the CO2 assimilation rates were lower than in the untapped plants. The decrease in CO2 assimilation rates due to tapping cannot be attributed to an increase in either stomatal or mesophyll limitations. Tapping increases the sink demand for photo assimilates, but it also results in the loss of water, inorganic nutrients and proteins from the plant. Loss of water, inorganic nutrients may results in lower CO2 assimilation rates of the tapped trees. In the long-term this could result in lower sucrose content in the latex. This may be a probable cause for the physiological disorder, tapping panel dryness in rubber.Item An economic evaluation of the use of rainguards(Rubber Research Institute. Agalawatta, 1993) Rodrigo, V.H.L.; Herath, P.H.M.U.; Nugawela, A.Use of rainguards can minimize the loss of tappping days and hence the loss in rubber crop. A simple model was developed to study different components determinig the profitability of using rainguard is discussed. Price of rubber, yield potential of a plant and tapping wage rate were identified as most important factors which determine the worthiness of the use of rainguards. Sealent price is also a major factor in deciding profitability. If the price of scalent is less than Rs. 20/= per kg, the profilability from both the apron and the gutter types is sameItem Seed production of clones PB 86, RRIC 100 and RRIC 121 in three rubber growing areas of Sri Lanka(Rubber Research Institute. Agalawatta, 1997) Seneviratne, P.; Nugawela, A.; Amaratunge, K.A.G.B.; Karunasena, R.P.; Wilbert, S.The rubber seed production in wet rubber growing areas in Sri Lanka has gone to very low levels in the recent past affecting the culling process that should be adopted in establishing rootstock nurseries.From the three rubber growing areas studied satisfacton seed production irrespective of the clone was observed only in Kegalle region.Regional differences may be due to direct or influences of the climate and weather during flowering and pod set. Clonal differences seems to be existing in regions where climate or the weather is favourable for spread of diseases.Further RRIC 100 being a resistant clone for oidum and phytopthora.produced a higher percemage of good quality seeds compared with the other two clones.PB 86 and RRIC 121 which have below average tolerance to these two diseases.However currently country as a whole produces enough seeds to fulfill country's annual seed requirement for the production of rootstocks provided the seeds are collected and transported without delayItem Factors affecting the budgrafting success and the scion growth of young budding of Hevea(Rubber Research Institute. Agalawatta, 1994) Seneviratne, P.; Nugawela, A.; Samarakoon, S.M.A.The size of the bag in which the stock plant is grown seems to have an effect on the growth of the seedling; from the three bag sizes tested, ie 15 x33 cm, 18 x 38 cm, 23 x 45 cm, it was found that the diameter the number of leaf whorls of the seedling increased with the increase of the bag size.Though the differences are not statistically significant, the budding success too increased in the same pattern. There was no effect of the bag size on the growth of the scion. The two types of buds, axillary scale, showed no difference either on bud grafting success or on the growth of the scion. The growth stage of the top most leaf whorl of the stock plant, either mature or immature, had no effect on the peeling qualities budgrafting success though a little higher budgrafting success was seen when the top flush was immature. There was an effect of the snag, on the scion growth; when the snag was shorter the sprouting took place earlier but, the scion growth was slightly poor as was evident by the diameter the length of the scion. Long snags delayed the sprouting , but the scion growth was better. The best growth of the scion was obtained when the snag was long with a few leaves attached to it.