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Journal of the National Science Foundation of Sri Lanka
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  This is an Open Access Journal Open Access journal
     ISSN (Print) 1391-4588
     Published by Sri Lanka Journals Online Homepage  [41 journals]   [SJR: 0.144]   [H-I: 4]
  • Changes in soil carbon stocks under different agricultural management
           practices in North Sri Lanka

    • Authors: RR Ratnayake, T Kugendren, N Gnanavelrajah
      Abstract: There is great potential of storing and improving carbon in tropical agricultural soils by applying ecologically sound management practices. In this study, soil carbon fractions and stocks under different agricultural management practices were studied in North Sri Lanka. Five land use types, namely, annual crop organic fertilizer only (A-OF), annual crop inorganic fertilizer only (A-IF), annual crop organic + inorganic fertilizer (A-O/IF), perennial crops (PC) and a home garden (HG), which use different tillage practices and fertilizer applications were selected. A home garden abandoned for 20 years (AHG) was included to study no tilled conditions. From the five land use types A-OF showed the highest soil organic carbon (SOC) fractions probably as a result of continuous supply of organic fertilizer for years. Conversely a lower SOC and other labile fractions were observed in A-IF probably due to greater decomposition of native soil organic matter under mineral fertilizer. Microbial biomass carbon (MBC) was significantly different among the treatments with the highest (631 mg/kg) in A-OF. AHG having the highest litter fall with zero tillage maintained the highest SOC content (68 %). Comparatively high water soluble C content (0.055/ 0.57 mg/kg) in both home gardens (HG/ AHG) and PC (0.055 mg/kg) could be possibly due to fresh residues returning to the soil whereas no residues return in annual crop sites. The potential stable carbon stock was the highest in AHG (15.40 t/ha) followed by A-OF (11.17 t/ha) compared to the other agricultural land uses. Active C was the highest in AHG (4.34 t/ha) followed by 3.98 t/ha in HG. A-IF recorded the lowest amount of active C (1.73 t/ha). Soil C stocks of annual crops can be improved compared to all other perennial land uses by using organic fertilizer application. Inorganic fertilizers in annual crops improve soil carbon storage only when combined with organic fertilizers.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 37-44
      PubDate: 2014-03-11
      Issue No: Vol. 42 (2014)
  • Remediation of soil past erosion effects through amendments and agronomic

    • Authors: W Ahmad, Farmanullah Khan
      Abstract: In Pakistan there has been a trend to shift agriculture towards steep lands, where soil erosion is one of the most significant ecological restrictions to sustainable agricultural production. This study was focused to find ways to ameliorate the soil fertility degraded by past soil erosion. Different cropping patterns viz maize-wheat-maize rotation (C1), maize-lentil-maize rotation (C2) and maize-wheat+lentil intercrop-maize rotation (C3) and different soil treatments, namely, the control (T1), 50 % NP (also called the farmer’s practice) (T2), 100 % NPK or the recommended dose of NPK (T3) and 20 t ha-1 farmyard manure integrated with 50 % N and 100 % PK (T4) were tested in a randomized complete block (RCB) design with split plot arrangements. Integrated use of organic manure (farmyard manure) and inorganic NPK fertilizers (T4) produced the highest wheat grain yield (4730 kg ha-1), which was 9 % higher than the 100 % inorganic NPK (T3, 4349 kg ha-1) and more than twice the control (T1, 2072 kg ha-1). The increase in lentil grain yield in T4 (1112 kg ha-1) was 7.4 % higher than in the recommended NPK levels for lentils (T3, 1035 kg ha-1) and 79 % higher than the control. A significant nutrient enrichment and an improvement in soil fertility parameters was recorded by T4 over T3. This was further augmented by the application of cereal-legume rotation (C2) in the traditional cereal-cereal rotation (C1) and their combination showed a significantly improved residual effect on soil fertility in the subsequent year. In conclusion the degraded soil fertility of Missa gullied soil cannot be ameliorated to its full potential with only the recommended dose of mineral fertilizers. 50 % N from organic fertilizer sources and the inclusion of legumes in the crop rotation is necessary to ensure agricultural sustainability on such soils.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 46-62
      PubDate: 2014-03-11
      Issue No: Vol. 42 (2014)
  • Comparative analysis of trypsin inhibitor levels in sweet potato cultivars
           in Sri Lanka

    • Authors: S Senanayake, KKDS Ranaweera, Arthur Bamunuarachchi, Anil Gunaratne
      Abstract: Sweet potato [Ipomea batatas (L) Lam.] is a commonly consumed root crop in Sri Lanka. A study was undertaken to estimate the nutritional aspects in terms of trypsin inhibitory activity (TIA) of five different cultivars of sweet potato (SWP1 - Wariyapola red, SWP3 - Wariyapola white, SWP4 - Pallepola, SWP5 - Malaysian variety and SWP7 - CARI 273) commonly consumed in Sri Lanka. The moisture level ranged between 65.0 ± 3.4 and 74.6 % ± 1.9 and the crude protein content varied between 1.2 ± 0.1 and 3.3 % ± 0.1. The TIA in unheated and heated sweet potato root samples varied between 1.9 ± 0.01 to 15.4 ± 0.4 and 0.156 ± 0.01 to 13.0 ± 0.01, respectively. In all the cultivars studied the TIA was significantly different at p < 0.05 and there was a significant reduction in TIA levels in all the heated samples compared to the raw samples. The highest TIA level was observed in SWP4 and the lowest in SWP1 in both heated and unheated samples. In terms of nutritive quality, SWP 7 cultivar was comparatively superior to the other cultivars studied with regard to the dry matter content, crude protein level and the TIA level per gram of protein. It may be possible to improve the nutritive quality of other cultivars through crop enhancing with high protein levels while lowering the TIA.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 63-69
      PubDate: 2014-03-11
      Issue No: Vol. 42 (2014)
  • Host tree specificity and seed germination of Dendrobium aphyllum (Roxb.)
           C.E.C. Fisch. in Sri Lanka

    • Authors: HB Chathurika Harshani, SP Senanayake, H Sandamali
      Abstract: Tree species can be considered as hosts for many epiphytes and the orchids, as epiphytes, display a biased distribution among hosts. It is possible that the barks of these hosts have some chemical and physical characteristics that influence the seed germination of orchids. The dependence on symbiotic fungi for seed germination is also a crucial factor for orchid distribution. Dendrobium aphyllum is an orchid species with restricted distribution in the sub - montane region of Sri Lanka. The aims of this study were (1) to determine the host tree specificity of the epiphytic D. aphyllum using physical and chemical bark characteristics of the host, (2) to isolate and identify the symbiotic fungi in D. aphyllum roots and (3) to determine the effect of tree bark extracts on symbiotic seed germination of D. aphyllum. Methanol, dichloromethane, hexane and water were used to extract the chemical compounds in tree barks. Aqueous and organic bark extracts of non host species (Erythrina sp., Erythrina berteroana, Eurya accuminata, Semecarpus marginata, Symplocaceae cochinchinensis) inhibited the seed germination of D. aphyllum. However, the effect of host tree species (Eurya ceylanica, Actinodaphne stenophylla, Eurya sp., Antidesma zeylanicum, Citrus maxima, Semecarpus nigra-viridis and two Syzygium spp.) on seed germination fluctuated with the concentration of host bark extracts. The physical characteristics of bark such as texture, peeling behaviour and thickness showed a positive correlation with the host tree specificity of D. aphyllum. Symbiotic fungus Rhizoctonia sp. was isolated as the associate in D. aphyllum roots.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 71-86
      PubDate: 2014-03-11
      Issue No: Vol. 42 (2014)
  • Volatile profiles of traditional aromatic rice varieties in Sri Lanka

    • Authors: Gavini D Liyanaarachchi, NS Kottearachchi, Radika Samarasekera
      Abstract: The fragrance of rice grain and the flavour of cooked rice are important quality factors that influence consumer acceptability. The principal volatile compound that contributes the fragrance in rice is 2-acetyl-1-pyrroline (2AP). Brown rice samples of six Sri Lankan rice varieties, including some traditional aromatic ones were analyzed for fragrant volatile compounds by gas chromatography (GC). Simultaneous steam distillation and solvent extraction methods were compared in the process of analysis. Leaf extracts of Pandanus latifolius, a major source for naturally occurring 2AP, was used in GC peak enrichment technique to identify the GC peaks of the tested rice varieties. In addition to 2AP, other fragrant volatile compounds were also identified in the tested varieties. They were aldehydes such as hexanal, benzaldehyde and octanal, and alcohols such as 2-butoxy ethanol, octanol, benzyl alcohol, 1-pentanol, phenol, alpha terpeneol and hexanol. The volatile profiles varied among the varieties and the majority of volatiles were detected in Lanka-Samurdhi and Suwandal. However, the highest 2AP was detected in Kuruluwee. The volatile compounds detected in rice bran and husk were not detected in the polished rice of Suwandal and vice versa. This study reveals that volatile profiling information of potential donor parents can be employed in aromatic rice breeding programmes and in quality assurance studies.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 87-93
      PubDate: 2014-03-11
      Issue No: Vol. 42 (2014)
  • Potent α-glucosidase inhibitors from the lichen Cladonia species from
           Sri Lanka

    • Authors: V Karunaratne, Vinitha M Thadhani, Shamsun Nahar Khan, M Iqbal Choudhary
      Abstract: The discovery of α-glucosidase inhibitors has been actively pursued with the aim to develop therapeutics for the treatment of diabetes and other carbohydrate-mediated diseases. This study focused on the lichen Cladonia sp., which yielded three potent α-glucosidase inhibitors, namely zeorin (1), methyl β-orcinolcarboxylate (2) and methylorsellinate (3) with several fold higher inhibitory activities than those of acarbose, an antidiabetic drug used to manage type II diabetes mellitus and the standard, 1-deoxynojirimycin. Atranorin (4) and lobaric acid (5), the other two metabolites isolated from the lichen did not show any α-glucosidase inhibitory potential. All compounds were identified on the basis of one dimentional (1D) and two dimentional (2D) NMR spectral data and with comparison to reported data.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 95-98
      PubDate: 2014-03-11
      Issue No: Vol. 42 (2014)
  • Are the people marginalized through knowledge economy'

    • Authors: Upali S Amarasinghe
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 1
      PubDate: 2014-03-10
      Issue No: Vol. 42 (2014)
  • Prototype implementation of an islanding detection relay based on pattern
           classification of current and voltage transients

    • Authors: NWA Lidula, AD Rajapakse, Jean-Paul Pham, N Denboer
      Abstract: A prototype islanding detection relay, which uses decision tree classifier to categorize the transient generating events as ‘islanding’ or ‘non-islanding’ was implemented and tested. It consisted of two basic stages of signal processing to extract the required feature vectors for the classification. The first stage involved signal filtering and in the second stage signals were processed by rectifying, summing, and lowpass filtering to get the energy content in the three phases during a selected time-frame. A simple radial medium voltage distribution system having a single distributed generator was simulated in PSCAD/EMTDC to obtain the transient waveforms, and the performance of the relay was tested with signals generated using an RTP real-time waveform playback instrument. The experimental results showed high accuracy in detecting islanding events within a response time of less than two cycles. The proposed relay can be implemented with a very low cost and is simple in construction. Therefore, this could be an acceptable low cost substitute for the expensive and complex transfer trip schemes, which are commonly in use with the distributed generation.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 03-15
      PubDate: 2014-03-10
      Issue No: Vol. 42 (2014)
  • Analysis of the behaviour of SnO2 composites of ZnO and TiO2 using
           impedance spectroscopy

    • Authors: CN Nupearachchi, VPS Perera
      Abstract: Composite semiconductor nanostructures will contribute in large measure for the future generation of cost effective optoelectronic devices. In order to advance the progress it is important to understand the mechanism of charge injection, transport and recombination in these systems. Impedance spectroscopy (IS) is a relatively old and powerful method for characterizing many of the electrical properties of materials and their interfaces. In this study, the impedance of composite porous films of SnO2/ZnO and SnO2/TiO2 have been taken into consideration and their behaviour in composite films was analyzed using IS to describe the mechanism of charge carrier transportation. The composites of SnO2 and ZnO showed higher resistivity than their pure form and when SnO2 : ZnO is in 1:1 ratio the resistivity of the composite film was the lowest (7.6 × 104 kΩ m). When the percentage of SnO2 is around 40 % and 90 % the resistivity of the films were higher where each of these cases could be explained by the depletion of electrons in the conduction band of SnO2 and ZnO at the interface. In contrast to the SnO2 and ZnO composite films, the minimum resistivity of 5.86 × 105 Ωm was obtained for SnO2 and TiO2 composite films when SnO2 is 33 %, which is lower than when they are in pure form. This low resistivity of both composite films is possibly attributed to the formation of a super structure in the composites where the electrons transport ballistically in mini bands.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 17-22
      PubDate: 2014-03-10
      Issue No: Vol. 42 (2014)
  • A multilevel Bayesian analysis of university entrance eligibility for
           selected districts in Sri Lanka: methods and application to educational

    • Authors: NI Jayawardena, MR Sooriyarachchi
      Abstract: Multilevel data structures are becoming a commonly encountered phenomenon in educational research. This type of data generates a number of statistical problems, of which clustering is particularly important. To solve the problems inherent in these, special statistical techniques are required. This study aimed to determine the factors affecting the university entrance eligibility of students from some selected districts in Sri Lanka, whilst capturing the layered structure of this educational data into pupil and school levels and determining how these layers interact and impact the dependent variable of interest. This study used university entrance eligibility of General Certificate of Education: Advanced Level (G.C.E) (A/L) student records in 3 districts of Sri Lanka. The response variable is university entrance eligibility of students, which is a binary variable. Thus a two level binary logistic model was fitted using the Bayesian Markov Chain Monte Carlo (MCMC) method as this method has some advantages over other classical statistical methods. When determining the eligibility for university entrance, GCE A/L students find Science subjects more competitive than Arts and Commerce subjects. Students with a higher IQ level (as given with the data) and students with higher English ability stand a better chance. The chance is higher for students from national schools compared to provincial and private schools, and girls show more potential than boys. Students studying in English medium have a higher chance while those studying in Tamil medium have a lower chance compared to the students studying in Sinhala medium.
      DOI : J.Natn.Sci.Foundation Sri Lanka 2014 42 (1): 23-36
      PubDate: 2014-03-10
      Issue No: Vol. 42 (2014)
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