Carbon (C) mineralization was assessed during incubations of a Mediterranean sandy soil amended with various organic by-products covering a wide range of C and nitrogen (N) contents. The laboratory incubation systems consist in measuring continuously the soil respiration (as CO2-C) in closed chambers, or less current, in pre-storing soil containers in semi-open chambers until transferred and measured for CO2-C evolved in closed 'measuring-jars'. The latest were improved, the new designs permitting to test a much greater number of by-products with a minimum handling. No significant differences were found between the results obtained by the different incubation systems. The storage systems using pre-storage of soils gave reproducible cumulative CO2-C curves. Results obtained with the pre-storage systems could be compared confidently to C mineralization data from studies using permanent closed chambers. One of them was specially reliable and can thus be recommended for long-term incubation experiments.