Partial Root-zone Alternate Irrigation with Reclaimed Water Mitigates Cadmium Risk by Reducing Pathogenic Bacillus and Modulating Soil Microbiome

(Introduction) Agricultural water scarcity and cadmium (Cd) contamination threaten global food security. While reclaimed water (RW) offers a nutrient-rich alternative water source, and partial root-zone alternate irrigation (PRA) enhances water use efficiency, their synergistic effects on Cd-contaminated soils remain unexplored. (Methods) We investigated PRA with RW in tomato-grown soils with gradient Cd contamination (0.30–2.74 mg/kg). Soil physicochemical properties, enzyme activities, Cd speciation, and rhizosphere microbial communities were analyzed. (Results) PRA with RW significantly increased rhizosphere pH (P < 0.01) and catalase activity (+ 27.47% vs. uncontaminated soil), while decreasing electrical conductivity (EC) and organic matter with rising Cd. Notably, it reduced pathogenic Bacillus abundance and elevated beneficial Actinobacteria (+ 8.26%) and Proteobacteria (+ 4.64%). Redundancy analysis identified Flavisolibacter and Nocardioides as keystone genera driving microbial shifts, positively correlated with pH (r > 0.80, P < 0.001) but negatively with nutrients. (Conclusion) PRA with RW mitigates Cd contamination risks by suppressing pathogens ( Bacillus ) via pH/EC modulation and enriching beneficial microbes. This strategy offers a sustainable approach for safe crop production in mildly/moderately Cd-polluted soils.