Effects of mulch drip irrigation on the coupled heat-Fe drive in root zone soils and analysis of soil Cr(Ⅵ) remediation mechanism

Developing innovative agricultural remediation technologies to mitigate the threat of hexavalent chromium (Cr(VI)) to crop growth and development. In this study, four drip irrigation treatments: silver mulch (S), transparent mulch (T), black mulch (B), and no cover (CK), to investigate the mechanisms by which mulch-drip irrigation technology to drive Cr(VI) remediation through heat-Fe redox coupling in black soil. The results indicated that mulched drip irrigation alters soil thermal dynamics via photothermal regulation. Fe redox cycling exhibits color-dependent characteristics, and Cr(VI) distribution is synergistically regulated by heat-iron metabolism. The B treatment provided short-term remediation of Cr(VI) through Fe²⁺ chemical reduction facilitated by microbial activity; however, the mid-soil layer (10 ∼ 30 cm) was reactivated (CV= 0.22) due to redox shock, indicated by an Eh rebound of 71.61 mV). The T-treatment drives deep enrichment of Cr(VI) due to its high heat capacity and thermal diffusivity, whereas the S treatment establishes a pattern of “surface depletion - mid-layer locking.” This study provides a theoretical basis and technical optimization direction for the remediation of heavy metal pollution in agricultural land.