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 (H 2 O 2 ), 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 H 2 O 2 and the WB methods showed linear relationships (moderate correlation) with those determined by LOI method, where the coefficients of determination (R 2 ) were 0.58 and 0.61, respectively. The LOI method provided the highest or comparably similar SOM content with the H 2 O 2 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 H 2 O 2 and LOI methods, respectively.
Highlights
Organic matter in soils and sediments is widely distributed over the earth’s surface in almost all terrestrial and aquatic environments (Schnitzer, 1978)
Results showed that when the organic matter content in soil exceeded about 6g/100 g loss on ignition (LOI) method provided significantly higher organic matter contents compared with other two techniques
Since we found this difference is demarcating, the soil organic matter (SOM) contents determined by WB, H2O2, and LOI methods are expressed in two sub figures, one below 6g/100g (Figure 1a), and the second beyond 6g/100g (Figure 1b), considering the SOM contents measured by the LOI method as the base
Summary
Organic matter in soils and sediments is widely distributed over the earth’s surface in almost all terrestrial and aquatic environments (Schnitzer, 1978). The importance of soil organic matter (SOM) in supplying nutrients, contributing to cation exchange capacity, and improving soil structure is already well recognized. Organic matter content of the soil is used to adjust nitrogen, sulfur, herbicide, and/ or lime recommendations in many parts in the world. Presence of organic matter is known to be an important factor in calculating loading rates for sewage sludge and other wastes (Bertucci and Salvador, 1992) and stimulating non-wetting conditions in soil particles (Leelamanie and Karube, 2009) and aggregates (Leelamanie et al, 2013; Leelamanie and Karube, 2014a,b). Soil and sediment total organic carbon (TOC) determinations are typically requested with con-
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