Journal of the Rubber Research Institute of Sri Lanka
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Item Role of potassium on growth and water relations of rubber plants(Rubber Research Institute. Agalawatta, 1993) Samarappuli, L.; Yogaratnam, N.; Karunadasa, P.; Mitrasena, U.; Hettiarachchi, R.Item Effect of soil moisture on establishment success of different planting techniques in rubber(Rubber Research Institute. Agalawatta, 1993) Samarappuli, L.; Yogaratnam, N.; Hettiarachchi, R.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 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 Comparison of the effectiveness of liquid and granule fertilizer mixtures on rubber plants raised by young budding technique(Rubber Research Institute. Agalawatta, 1997) Dharmakeerthi, R.S.; Yogaratnam, N.Y.; Samarappuli, L.; Silva, S.N.; Yakandawala, A.Effectiveness of granule fertilizer mixtures was compared with currently used liquid formulations on plants raised by young budding technique.Granule formulations are agronomicaly effective provided that they are applied in small quantities.Urea based mixtures was found to be comparatively mire detrimental than sulfate of ammonia based mixtures when used at concentrations higher than the recomended levels.Currently recommended fertilizer schedule with liquid formulations was the most effective programme for young budding among the treatments tested.Reduced frequency of application increased the deiback percentage significantly.However,it could be applied at two-week intervals instead of weekly intervals equally effectively,thereby reducing the application cost almost by half.Item Urea hydrolysing potential of the rubber growing soils of Sri Lanka(Rubber Research Institute. Agalawatta, 1997) Dharmakeerthi, R.S.; Samarappuli, L.; Silva, S.N.; Yakandawala, A.The ability of the rubber growing soils to hydrolyse urea under natural conditions was evaluated by measuring the urease activity using a non buffer method.The temporal variability of urease activity was also investigated during the period February 1994 to February 1995.The urease activity has been ranged from 14.5 to 292.4 ug NH4+-N released/g/h with a mean of 83.84 in all soils.The Matale series soils had a significantly high level of urease activity (120.22) compared to that of the Parambe series(47.88).The level of urease activity in these soils was found to be much higher than the values reported earlier for the same soils.During the first several months after wintering,i.e. from April to September,urease activity was high where as during the period of November,December and January the activity was low in all the series studied.In Parambe and Homagama series soils the urease activity was as low as zero in the months of November and December.The significance of high and low levels of urease activity with regard to urea fertilization in the rubber growing areas was discussed.Item Litter accumulation from Mucuna bracteata cover crop and its effects on some soil chemical properties in rubber plantations(Rubber Research Institute. Agalawatta, 2010) Chathurika, S.; Samarappuli, L.; Mapa, R.B.Item Distribution of Mn and Zn in rubber growing soils and its status in relation to selected management practices(Rubber Research Institute. Agalawatta, 2000) Samarappuli, L.; Perera, A.M.A.; Lalantha, H.K.; Rajapakse, W.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 Tolerance of rubber plantations to drought and atmospheric warming-a review(Rubber Research Institute. Agalawatta, 1998) Samarappuli, L.; Yogaratnam, N.Cultivations of deep rooting perennial crop like rubber is considered as a very desirable from of land use. They not only provide a canopy which reduces the adverse effects of excessive atmospheric warming but also many beneficial effects such as non removal of significant amount of soil water per unit area of land. Rubber plantations simulate to a natural forest condition but with an economical benefit.