2 research outputs found
Investigating the Crustal Structure near the Mahakandarawa seismic station in Sri Lanka through the Receiver Function Method
No full textSri Lanka has a very ancient geological history that begins in the Precambrian, when it formed part of the Gondwana supercontinent. It was connected to India, Madagascar, Antarctica, and Africa, sharing the same crustal evolution. When Gondwana began to break apart around 180 million years ago, Sri Lanka drifted with the Indian plate to reach its present position in the Indian Ocean. The present work analyzes the subsurface structure beneath the Mahakandarawa (MALK) broadband seismic station using teleseismic P-wave conversions. A combination of converted wave analysis and H-κ stacking was applied to determine both Moho depth and the velocity ratio of compressional to shear waves. The approach indicates a crustal thickness of nearly 37.8 km with a velocity ratio of 1.73, giving a Poisson’s ratio close to 0.25. Such values are typical of silica-rich, felsic material rather than mafic compositions. When compared with previous studies from neighboring Gondwanan fragments such as southern India and Madagascar, which report Moho depths of ~36–39 km and similar felsic crustal compositions, the results from MALK show strong consistency. This agreement reinforces Sri Lanka’s geological affinity with East Gondwana and provides new regional constraints on its tectonic evolution, particularly regarding the preservation of ancient felsic crust across separated continental blocks.Keywords: Teleseismic Receiver Function, Gondwana, Sri Lanka, Crustal Structure, H-κ stackin
Effect of Nutrient Management and Weeds on Incidence of Fungal Diseases in Rice
No full textHigh-input, modern agriculture uses large amounts of energy, water, fertilizers, and pesticides to produce high crop yields. One of the major bottlenecks of the modern agriculture in the tropics is substantial yield losses due to fungal diseases including rice blast, leaf spots and leaf scald. The aim of this study was to compare the incidence of fungal diseases in judicious nutrient management systems, including organic, integrated, and conventional, under different weed categories during dry season (May to September 2020) and wet season (November 2020 to March 2021). Rice disease incidence were collected for both seasons from 48-84 days after sowing. Additionally, disease incidences on grasses and sedges weeds were also calculated. Brown spot, narrow brown leaf spot, leaf scald, and rice blast incidences were substantial in wet season, while the disease incidences during dry season in 2020 were negligible. The disease incidences were significantly higher (P<0.05) in organic and conventional input systems compared to the integrated input system. Disease incidences of brown spot and leaf scald were found in the dry season. Higher disease incidences were recorded in the wet season than in the dry season. The incidences of the brown spot were higher on sedges than in grasses and vice versa were observed for narrow brown leaf spot disease. Leaf scald incidences were positively correlated with the significant nitrogen status of the rice crop. Disease incidence was low in integrated input system compared to conventional and organic input systems, while weeds were reported as alternative hosts. It can be concluded that the integrated nutrient management with recommended dosage of nitrogen application with proper weed management can lead to low disease incidents, hence is ecologically more sustainable
