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Abstract. The active fraction of soil organic carbon is an important component of soil health and often isquickly assessed as the pulse of CO2 released by re-wetting dried soils in short-term(24–72 h) assays. However, soils can lose carbon (C) as they dry and, if soil samples vary in moisture content at sampling, differential C loss during the pre-assay dry-down period maycomplicate the assay's interpretations. We examined the impact of pre-assay CO2 loss ina long-cultivated agricultural soil at initial moisture contents of 30 %, 50 %, and 70 %water-filled pore space (WFPS). We found that 50 % and 70 % WFPS treatments lost more C duringdrying than did those in the 30 % WFPS treatment and that dry-down losses led to a 26 %–32 % underestimate of their CO2 pulses. We developed a soil-specificcorrection factor to account for these initial soil moisture effects. Future C mineralizationstudies may benefit from similar corrections.