Soil carbon (C) content is a sensitive indicator of agricultural management impact. Different methods are usually adopted to determine soil C content, which can lead to variable results and therefore hinder the correct interpretation of management impacts. In this study, we tested three commonly used soil C determination methods (dry combustion with elemental analysis, dry combustion with loss-on-ignition, and wet combustion) with soil samples from agricultural sites under different management conditions (fire and fire-free land preparation) and forest. The wet combustion method underestimated soil C content in relation to the standard method (dry combustion with elemental analysis). We found high determination coefficients of predictive equations of total C (dry combustion with elemental analysis) based on concentration values determined either through wet combustion or loss-on-ignition. Thus, we recommend the use of the loss-on-ignition method, which is cheap, fast, and of low environmental impact, to predict total soil C concentration under the studied management conditions.