Precision-based augmented manure for pH-targeted soil acidification: improved phosphate-mediated cadmium immobilization and canola growth in calcareous soils

Cadmium (Cd) contamination in agricultural soils poses a significant threat to sustainable food production, necessitating innovative remediation strategies. This study introduces knowledge-based augmented manure (AM), formulated through controlled microbial oxidation of sulfur to generate H+ ions for targeted soil acidification, optimizing phosphate (P)-mediated Cd immobilization. A greenhouse experiment was conducted using B. napus in non-spiked and Cd-spiked alkaline soils (0 and 60 mg kg−1 Cd), with two P fertilizer rates (0.5% and 1% DAP) applied in combination with either normal manure (NM) or AM. The amendment rates (P40 and P80) were determined based on an incubation trial to achieve specific soil pH targets (7.5 and 6.5) while preventing over-acidification. Results showed that Cd stress severely impaired plant growth and triggered antioxidant enzyme activity. However, AM + P80 significantly improved plant physiological and agronomic traits, leading to a 90.9% reduction in Cd bioaccumulation, an 83% decrease in the Cd bioconcentration factor, and a 78.8% decline in the Cd harvest index. Additionally, the AM + P80 treatment reduced the health risk index by 83.2%, demonstrating its potential to enhance soil health, suppress Cd uptake, and safeguard food safety. These findings highlight AM as a promising, precision-based soil amendment that regulates pH, optimizes P-Cd interactions, and improves plant resilience in Cd-contaminated calcareous soils.