COMPARATIVE-STUDY OF TITRIMETRIC AND GRAVIMETRIC METHODS FOR THE DETERMINATION OF ORGANIC-CARBON IN SOILS

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 Cr2O72- and MnO4- 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 Cr2O72- oxidation and dry combustion with a mean conversion factor of 1.109, while a new conversion factor of 1.841 between wet acidified MnO4- 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.