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Item Preliminary studies on the use of neutron probe in some rubber growing soils(Rubber Research Institute:Agalawatta, 1992) Samarappuli, L.; Yogaratnam, N.; Karunadasa, P.; Mitrasena, U.Studies carried out on the use of Neutron Probe in soil/water relations indicate that this can be used as an effective technique in immature Hevea plantations. It had been possible to establish a fairly reliable calibration curve for the subsurface soil 10 - 160 cm the calibration curve obtained is moisture content, Qv = 0.52 CR - 0.39, where CR stands for Count Ratio. It appears that during dry period, distances varying from 0 - 1.2m from the trunk of the tree are suitable for assessing the water content of the soil profile. The available soil water storage capacity of 104.2 mm with the upper lower limits of 235.5 131.3mm, respectively, is likely to be the amount of water that is available to the plants, both rubber covers over a period of 12 months.Item Effect of potassium and magnesium on growth of young Hevea brasiliensis(Rubber Research Institute:Agalawatta, 1988) Weerasuriya, S.M.; Yogaratnam, N.The effect of potassium and magnisium fertilisers on growth of young Hevea brasiliensis were studied using clones PB 86, RRIC 100, RRIC 103, and RRIC 121 with the objective of determining the requirement of these elements during the early phase of establishment of these clones. Three commercial fertilisers were evaluated as of magnesium. Potassium requirement of clone PB 86 during the first year was found to be approsimately 33g K/plant/year. It was found that clones. RRIC 100 and RRIC 121 needed higher amount of K than PB 86 for normal growth. Potassium application caused an overall reduction in growth of clone RRIC 103 where the soil K level was 0.07 me./100g suggesting that this level is adequate for this clone during its first year of growth. Total dry weight was significantly increased when Mg application was increased from 11 to 22g/plant/year in clone RRIC 103 but such effects were not seen in clones PB 86, RRIC 100 and RRIC 121Item 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 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 Rubber land suitability evaluation(Rubber Research Institute of Sri Lanka:Agalawatta, 2000) Yogaratnam, N.Item Processing of NR and some developments in rubber chemistry and technology in Sri Lanka(Rubber Research Institute of Sri Lanka:Agalawatta, 1998) Yogaratnam, N.; Tillekeratne, L.M.K.; De Silva, K.G.K.; Siriwardena, S.; Samarappuli, I.N.Item Weed control in rubber plantations(Rubber Research Institute of Sri Lanka:Agalawatta, 1991) Yogaratnam, N.; Samarappuli, L.; Dissanayake, D.M.A.P.Item Soil management practices in rubber plantations and their effects on the environment(Rubber Research Institute of Sri Lanka:Agalawatte, 1997) Samarappuli, L.; Yogaratnam, N.Item Multicropping of Rubber lands with Tea(1995) Yogaratnam, N.; Iqbal, S.M.Item Outlook for development and trends in production and consumption of Sri Lankan rubber industry(1998) Tillekeratne, L.M.K.; Samarappuli, I.N.; Yogaratnam, N.; Wickramaratne, C.S.