Purpose <p>Climate models project more frequent and severe soil dry–wet (DW) events in semi-arid regions, but whether historical moisture stress leaves lasting effects on soil carbon (C) and nitrogen (N) transformations upon new organic inputs remains unclear.</p> Methods <p>We investigated the legacy effects of four successive DW cycles on microbial C and N dynamics in a semi-arid cropland soil. After the pre-treatment, both continuously moistened (CM) and DW-exposed soils were rewet to the same moisture level with addition of concentrated oat straw leachate as a complex organic substrate. Soil respiration rates, microbial and soil C and N pools, metabolic quotient (qCO₂), enzyme activities, and phospholipid fatty acid profiles were determined on days 0, 3, and 14.</p> Results <p>A history of DW cycles increased cumulative CO₂-C release by 29% over the entire 14-day incubation period, with the legacy effect being more pronounced during the first 3 days (43.98% increase) than during the subsequent 3–14 days (16.25% increase). DW legacy elevated qCO₂, reduced dissolved organic C, microbial biomass C, and the ratio of cumulative mineralized C to net mineralized N, but did not affect total inorganic N, microbial biomass N, and net N mineralization. These responses were accompanied by decreased abundances of Gram-negative bacteria and saprophytic fungi, and increased microbial stress indicators.</p> Conclusion <p>Our results suggest a decoupling pattern in which historical DW cycles create a persistent microbial legacy that enhances C mineralization upon new substrate addition while leaving N transformations largely unaffected. Such positive C legacy effects, if persistent under field conditions, could reduce the capacity of these semi-arid cropland soils to sequester new organic C inputs under future precipitation regimes with intensified DW cycles; however, this possibility warrants longer-term field validation.</p>