Dynamic changes of Cd in agricultural soils with different pH under flooding–drainage–dryland alternation: Implications for soil management

Abstract The accelerated industrialization and urbanization have exacerbated soil contamination by heavy metals, particularly cadmium (Cd). While flooding–drainage–dryland alternation can improve soil structure and fertility, its effect on Cd release and migration requires further research, especially under varying pH, limiting its application in Cd‐contaminated soil remediation. This study examined the factors influencing Cd bioavailability in soils from China with different pH (acidic soils: Shangrao soil [SR] and Changshu soil [CS]; alkaline soils: Xinxiang soil [XX] and Langfang soil [LF]) under flooding–drainage–dryland alternation. Results show that flooding decreases Cd bioavailability across all soil types, with subsequent drainage leading to partial recovery. However, by the 140th day of dryland cultivation, extractable Cd in SR, CS, XX, and LF soils had reduced by 30%, 49%, 55%, and 59%, respectively, compared to pre‐flooding. Acidic soils and alkaline soils showed marked differences in Cd transformations during flooding–drainage–dryland alternation. Cd in acid soils were predominantly extractable and ion‐exchangeable Cd, while alkaline soils contained ion‐exchangeable and poorly crystalline Cd. Correlation analysis revealed that Cd bioavailability in acidic soils is predominantly influenced by Fe fractions (extractable Fe: Fe F0 , r 2 = −0.86; poorly crystalline Fe 2+ : Fe 2+ F2 , r 2 = −0.94; crystalline Fe 2+ : Fe 2+ F3 , r 2 = −0.83) and ion‐exchangeable Cd ( r 2 = 0.92). During dryland farming, pH emerges as the primary governing factor, while extractable Mn is strongly associated with changes in Cd bioavailability during the flooding phase. Conversely, in alkaline soils, Cd bioavailability is primarily dictated by pH ( r 2 = 0.73). Fourier transform infrared combined with two‐dimensional correlation spectra analyses highlighted the roles of clay minerals, iron oxides, and organic matter in Cd adsorption for acidic soils, and polysaccharide‐related organic matter in alkaline soils. This study highlights the key factors affecting Cd dynamics in the flooding–drainage–dryland alternation, offering valuable insights for soil pollution control and Cd risk management.