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The C isotopic composition (delta C-13) of pedogenic carbonates reflects the photosynthetic pathway of the predominant local vegetation because pedogenic (secondary) CaCO3 is formed in isotopic equilibrium with soil CO2 released by root and rhizomicrobial respiration. Numerous studies show the importance of pedogenic carbonates as a tool for reconstructing paleoecological conditions in arid and semiarid regions. The methodological resolution of these studies strongly depends on the time scale of pedogenic carbonate formation, which remains unknown. The initial formation rate can be assessed by C-14 labeling of plants grown on loess and subsequent incorporation of C-14 from rhizosphere CO2 into newly formed carbonate by recrystallization of loess CaCO3. We tested the feasibility of C-14 and C-13 tracers for estimating CaCO3 recrystallization rates by simultaneous C-14 and C-13 labeling and comparison with literature data. C-14 labeling was more efficient and precise in assessing recrystallization rates than C-13 labeling. This is connected with higher sensitivity of C-14 liquid scintillation counting when compared with delta C-13 measurement by IRMS. Further, assessment of very low amounts of incorporated tracer is more precise with low background signal (natural abundance), which is true for C-14, but is rather high for C-13. Together, we obtained better reproducibility, higher methodological precision, and better plausibility of recrystallization rates calculated based on C-14 labeling. Periods for complete CaCO3 recrystallization, extrapolated from rates based on C-14 labeling, ranged from 130 (125-140) to 240 (225-255) y, while it was approximate to 600 (365-1600) y based on the C-13 approach. In terms of magnitude, data from late-Holocene soil profiles of known age provide better fit with modeled recrystallization periods based on the C-14 approach.