Optimizing ridge–furrow height to enhance soil cadmium remediation in oilseed crop rotation systems

Although oilseed crop rotation provides a safe utilization strategy for Cd–contaminated fields, its overall remediation efficiency remains limited. A two–year field experiment was conducted at two sites to investigate the effects of ridge–furrow height under four crop rotation systems on the soil environment and Cd accumulation. High ridges with deep furrows (DF) improved soil drainage and lowered soil moisture, electrical conductivity, pH, and organic matter content. These changes increased the abundance of Acidobacteria and organic–matter–degrading bacteria, thereby enhancing Cd bioavailability. In contrast, low ridges with shallow furrows (SF) facilitated the enrichment of typical anaerobic Fe– and S–reducing bacteria, which promoted Cd immobilization. Compared with SF, DF increased the proportion of available Cd in macroaggregates and Cd²⁺ in soil solution by 29.3 % and 27.3 %, respectively, leading to a 16.8 %–84.8 % increase in Cd accumulation across the four rotation modes. Under DF, rotation mode 4 reduced total and available Cd in topsoil by 18.4 %–20.2 % and 40.5 %–43.2 %, respectively. The structural equation model revealed the influence of ridge–furrow treatments on the transformation process of Cd in the soil–oilseed crop system. Moreover, Cd concentrations in all plant oils (n = 192) consistently remained below 50 μg/kg, which guaranteed the safe and reliable use of oilseed-derived products in industrial applications. Overall, increasing ridge–furrow height effectively enhanced Cd remediation through oilseed crop rotation, but the restoration of soil fertility and its synergy with phytoremediation require further investigation. • Deep furrows reshaped soil properties by altering moisture, pH, OM, and microbial structure. • Increased Cd availability in soil aggregates and solution promoted Cd uptake in rotations. • Oilseed rotation Mode 4 with deep furrows markedly reduced total and available Cd in topsoil. • Vegetable oils from contaminated soils maintained Cd levels below international safety limits. • Ridge–furrow optimization offers a low–cost and scalable strategy for Cd remediation.