DAL Leelamanie*, TDP Liyanage and IMLV Rajarathna
Department of Soil Science, Faculty of Agriculture, University of Ruhuna, Mapalana, Kambu-rupitiya 81100, Sri Lanka
Abstrsact
Determination of organic matter in soils and sediments is typically requested with contaminant analysis as a part of ecological risk assessments. However, reliable and sensitive methods are required to enable the research and extension work to substantiate the expected outcome. The purpose of this study is to provide a comparison between weight loss and carbon (C) analysis methods in determining soil organic matter (SOM) content considering their usability with potential merits and demerits. Soil samples were collected from 20 locations representing various agro-ecological regions ranging from Jaffna to Matara, Sri Lanka. The samples were analyzed for the SOM content using the Walkley-Black (WB), hydrogen peroxide digestion (H2O2), and loss on ignition (LOI) methods. The SOM content by different methods were compared using C conversion factors of 1.724, 2.2, and 3.3 for the WB method. The SOM contents determined by H2O2 and the WB methods showed linear relationships (moderate correlation) with those determined by LOI method, where the coefficients of determination (R2) were 0.58 and 0.61, respectively. The LOI method provided the highest or comparably similar SOM content with the H2O2 and the WB methods except at very low SOM contents. Use of C conversion factors 2.2 and 3.3 made SOM content estimated by WB method closer to values obtained by H2O2 and LOI methods, respectively.
Key words: Carbon analysis, hydrogen peroxide digestion, loss on ignition, soil organic matter, Walkley-Black method
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