Methods of start (as a new one), reactive, basal, and long-term respiration determination in laboratory conditions were used for evaluating C_org transformation with CO₂ release from sandy soil (Haplic Luvisol) enriched in field experiments with organic (manure) and mineral (clay, lime) materials. They proved to be useful in such experiments. The objective of the investigation was to find which treatments stimulate or inhibit C_org mineralization. Of all treatments used, the least susceptible to C_org mineralization in soil appeared to be the soil enriched with manure. The most susceptible was soil enriched with soil+manure+clay+lower dose of lime.