A COMPARISON OF WEIGHT LOSS AND C ANALYSIS METHODS IN DETERMINING ORGANIC MATTER CONTENT IN SRI LANKAN SOILS

Abstract

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 be tween 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 vari ous 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.