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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 Virgin bark tapping of some RRIC 100 series clones(Rubber Research Institute. Agalawatta, 1987) Samaranayake, C.; Waidyanatha, U.P. De S.; Pathiratne, L.S.S.; De Soysa, A.G.A.All RRIC 100 series clones reached tappability much earlier than the two control clones viz. RRIM 600 and PB 86. Significantly higher yield per tree per tapping was obtained in the first year on a 1/2 S d/3 system compared to 1/2S d/2 tappings in many of the clones tested. However, during the second year there was no significant differences in yields obtained on both frequencies indicating that the tree was able to replenish the latex removed in a tapping, much faster than in the first year of tapping. The data presented indicate the possibility of tapping all recommended clones on 1/2S d/32 system of tapping from the second year, without any adverse effects.Item Accumulation of free proline in bark and latex of Hevea brasiliensis affected by brown bast(Rubber Research Institute. Agalawatta, 1986) Wickramasinghe, S.I.; Yapa, P.A.J.; De Soysa, T.V.W.Free proline accumulation in clone RRIC 101 of Hevea brasiliensis was investigated. The bark and the latex samples collected from both healthy and brown bast effected trees were analysed for free prline content. The average bark proline concentration/unit present in the brown bast trees was found to be considerable higher (P = 0.10) than that of healthy trees. The accumulation of free proline in latex was found to be significant in brown bast trees.Item Ferilizer responses in mature Hevea under Sri Lankan conditions(Rubber Research Institute. Agalawatte, 1984) Yogaratnam, N.; Weerasuriya, S.M.The results of three out of a series of eight experiments that have been in progress (most of them) since 1976, are discussed. Yield increases in the existing plantations could be obtained with increased applications of nitrogen fertilizers in the form of urea. The level of application could be increased to double that of the currenly recommended rate. Some yield increases were also obtained with applications of potassium. It has also been shown that application of rock phosphate to mature rubber trees is not always benificial. Similary, applications of magnesium containing fertilizers to mature rubber should not also be made indiscriminately. Although the leaf K concentration showed K deficiency in one experiments, application of potassium has increased the K may have to be clone specific and at least for the clone RRIC 45, the leaf K levels may have to be reviced. In general, fertilizer application to mature rubber with complete NPKMg mixtures, may not be economically justified, particular ly in the present context of fertilizers and rubber price. The results reported have covered only parts of the planting cycles following fertilizers application. The experiments are still in progress and will be continued at least until the responses have stabilized. A detailed economic analysis at the end of this period would then give a more realistic picture on the economics of fertilizer application for mature rubber under Sri Lankan agro-climatic conditionsItem 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 Towards shorter immaturity and improved yields by mulching with rice straw(Rubber Research Institute. Agalawatta, 1992) Samarappuli, L.; Yogaratnam, N.; Samarappuli, P.; Mitrasena, U.In this study with immature Hevea brasiliensis, multing with paady straw around the base of the tree was found to be a better agronomic practice than growing leguminous cover crops such as Pueraria phaseoloides and Desmodium ovalifolium or allowing natural vegetation to grow in the inter-row area. Girthing had been much higher with mulching which resulted into reduction of the immature, unproductive period by approximately 18 and 12 month in comparison with naturals and creeping legumes respectively. In addition to early tapping, yield of latex was also higher during the early stages, increases in the region of 33perc. and 40perc. in comparison with creeping legumes and naturals respectively. The present value of the benefit achieved from mulching amount to Rs. 31,088/= per hectare of which Rs. 19,740/= is due to extra yield and the balance of Rs. 11,348/= is saving on inputs as a result of early maturity. Consequently, a net present value (NPV) of Rs. 7.8 million at national level can be achieved with the above practice at 50perc. level of adoptionItem Performance of some RRIC 100 series clones under different soil moisture regimes(Rubber Research Institute. Agalawatta, 1992) Samarappuli, L.; Yogaratnam, N.; Hettiarachchi, R.Results obtained on the performance of recently developed RRIC 100 series clones when sujected to water deficit situations are presented in this paper. The plant diameter of RRIC 121 and RRIC 102 was found to be superior to other clones tested such as RRIC 100, RRIC 110 and PB 86 even at the very low soil moisture level of 10% available water. Similar results were recorded in relation to plan height, number of whorls and relative growth rates of clones RRIC 121 and 102 even under low soil moisture conditions. Data obtained also showed that clones RRIC 102 and 121 had the highest plant nitrogen and potassium contents. Moreover, even under very low soil moisture levels plant P content was greater in clones RRIC 121 and 102. Most of the data on growth are also consistat with the physiological parameters such as leaf water protential (LWP) relative water content (RWC), transpiration rate (TR) and leaf diffusive resistance (LDR). It was further noted that the LWP and RWC were highest while TR was lowest in clone RRIC 102. Moreover, the clone RRIC 102 had the highest LDR compared to other clones, confirming the ability of this clone in maintaining a higher water holding capacity under low soil moisture conditions.Item Effect of potassium on growth, yield and mineral composition of young Hevea brasiliensis(Rubber Research Institute of Sri Lanka. Agalawatte, 1995) Iqbal, S.M.M.; Yogaratnam, N.Item Effect of planting density on growth, yield related factors and profitability of rubber (Hevea brasiliensis Muell.Arg.)(Rubber Research Institute of Sri Lanka. Agalawatte, 1995) Rodrigo, V.H.L.;Data available on an experiment on planting density of rubber in Kalutara region of Sri Lanka were analyzed in view of investigating how planting density affects yield, yield related factors and financial return. Experimenet comprised six planting densities from 400 to 920 trees per hectare and three clones PB 86, RRIC 101 and RRIC 103. Planting density has affected plant girth of all clones from fourth year onwards. Density effect on girth of RRIC 101 was higher than that of other clones. With increasing planting density bark thickness and number of latex vessel rings declined in all clones and relatively more marked in clone RRIC 101. Similarly, yield per tree per tapping decreased, but yield per hectare per tapping and net present value increased with the increase in density. Nevertheless, with only two years of yield data and also without knowing number of tapping days for each density tested, it is not possible to arrive at definite conclusions. Less variation in girth increment among different densities towards later stage of plant growth indicates that apparent effect of density in this stage could be a cumulative effect over the period but not the effect of this stage. No density effect on canopy light interception was evident. Available data justifies further investigations and it is suggested that more adoptability trials located in different agro-climatic regions are to be conducted using new clones before arriving at definite conclusions. In these srudies due consideration should be given to tappable stand, incidence of tapping panel dryness and tapping days.Item Fertilizer use among perennial crops(Rubber Research Institute of Sri Lanka. Agalawaththa, 1982) Peries, O.S.; Yogarathnam, N.