Comparative Study of Titrimetric and Gravimetric Methods for the Determination of Organic Carbon in Soils

Abstract

Abstract Fourty seven soil samples were collected from agriculture fields at two depths (0–15 cm and 15–30 cm). The samples were analysed to determine the total organic carbon TOC (using the dry combustion reference method), the organic carbon OC (using wet acidified Cr2−O7 and MnO− 4 oxidation) and organic matter OM (using loss on ignition). A comparison between the TOC and each of OC and OM were carried out using regression analysis. This analysis reveals an excellent linear relation between the results of wet acidified Cr2O2− 7 oxidation and dry combustion with a mean conversion factor of 1.109, while a new conversion factor of 1.841 between wet acidified MnO− 4 oxidation and dry combustion is proposed. Also, regression analysis reveals that the linear relation between loss on ignition and the dry combustion reference method gives a stronger intercept (a > 0), indicating that these are less related (the traditional equation by Walkley and Black assumed the intercept a = 0). The stronger intercept (a > 0) in our study reflects the removal of non-organic soil constituents during ignition. This linear relation was improved by inclusion of clay percentage as an independent variable using multiple regression analysis.