[Objective] In crop fields of calcareous soil, it is found that CO₂ released from rhizosphere may come from as many as three sources, i.e., root respiration, decomposition of soil organic carbon (SOC) and dissolution of soil inorganic C (SIC), so partitioning of the released CO₂ by source is the premise of quantifying soil C balance.[Method] A pot experiment was designed and carried out to have 18 pots of summer maize (Zea mays L.), of which three had maize plants treated with ¹³CO₂ pulse-labeling for 7 hours, separately, at the elongation, heading and grain-filling stages, while in the other, the crop grew in nature as CK. On the 27^thday (d) after each labeling, samples of the soils and plants were collected from the pots for analysis of total C and ¹³C in shoot, root, soil and emitted soil CO₂. Comparisons were made between the treated pots and CK, trying to partition the emitted CO₂ by source.[Result] Results show that the contribution of root respiration to soil CO₂ emission decreased from 66.7% at the elongation stage to 25.8% at the grain-filling stage. Over the whole vigorous vegetative growth period, root- and soil-derived CO₂ did not differ much in contribution to soil CO₂ emission, and the contribution of SOC decomposition and SIC dissolution to soil CO₂ emission reached about 30% and 20%, respectively. The contribution of maize growth to input of soil C in the form of roots and rhizodeposits was high enough compensate for the release of soil total C (SIC + SOC), hence the soil functioned as a C sink.[Conclusion] All the findings in this experiment demonstrate that SIC dissolution is more important than previously presumed in stabilizing the global C pool and regulating CO₂ concentration. If the contribution of SIC dissolution to soil CO₂ emission in calcareous soil were neglected, overestimation of the contribution of SOC decomposition is likely to occur, which will inevitably affect quantification of the priming effects of SOC and assessment of the soil C balance.