Usage and management alter the dynamics of soil organic carbon (SOC). The aim of this study was to compare the CO2 emissions in a Typic Humudept under different uses, and to relate the effects of CO2 emissions to the organic carbon content of the soil. Soil samples were collected from the 0-0.05, 0.05-0.10, 0.10-0.15 and 0.15-0.20 m layers under the following agricultural systems: no-tillage (NT), conventional (CT) and fruit orchard (FO). Samples were also collected from an area of native forest (NF) adopted as reference. The variables under evaluation were CO2 emissions and SOC content. Interaction between the usage or management systems and the soil layers influenced CO2 emissions in the soil. However, there was a difference in CO2 emissions between the soil layers under NF and CT only. In the 0-0.20 m layer, there was no difference in CO2 emissions under FO or CT, however these were greater than under NF or NT. In turn, the emissions under NT were lower than under NF at this layer. Furthermore, the systems with greater CO2 emissions showed less SOC. As such, in a Typic Humudept, the no-tillage management system results in reduced CO2 emissions. Greater SOC mineralisation has a direct impact on higher CO2 emissions.