In the determination of carbon contents in organic residues, analytical methods for soils are frequently employed without adequate calibration. Thus, methods capable to determine the levels of C and organic matter (OM) in organic residues must be tested and calibrated, using as a reference the dry combustion method. The objectives of this study were to evaluate methods for determining the levels of total carbon (TC), organic carbon (OC) and OM in organic residue samples; to determine mathematical equations for the conversion of OM and OC in TC quantified by the dry combustion method and to assess the viability to the muffle method for the routine of laboratories for OM quantification and to infere the TC contents in organic residues. In 2010, samples from 42 composts, crop residues, manures, sewage sludge, coffee husk, and sawdust, among others were collected in municipalities of the Southern region of Minas Gerais and in Jundiaí-São Paulo. The samples were dried at 65 °C for 48 hours, crushed and sieved (0.250 mm opening) and analyzed. The following methods were tested: modified Walkley-Black, Yeomans and Bremner (YB), dry combustion (TOC analyzer) and muffle (M) combustion at 550 ºC, for the determination of OC, TC, and OM, respectively. TC contents in organic residues varied from 8.5 to 51.4 %. The Yeomans and Bremner (YB) method underestimates the C content when compared to the dry combustion method. Based on the OM and OC contents and mathematical equations, the TC combustion method contents can be estimated.
carbon analyzer; dry combustion; modified Walkley-Black
