Shell-Derived Ca/Mg Composites Enable Dual Phosphorus Capture and Soil Fertility Enhancement

To address the dual challenges of phosphorus (P) pollution and scarcity, a shell-derived composite (Ca/2Mg550) was developed through optimized synthesis, achieving dual phosphorus capture and enhancement of soil fertility. The hierarchically porous Ca/2Mg550 exhibited a high P adsorption capacity of 28.35 mg/g in agricultural runoff, outperforming conventional materials via synergistic mechanisms: ligand exchange between CO 3 2– /PO 4 3–, electrostatic attraction, and Ca–Mg-phosphate precipitation. In addition to adsorption, Ca/2Mg550 facilitated coagulation of colloidal P through pH- and ionic strength-mediated aggregation, while transforming iron-bound P into calcium-bound P and elevating soil available P by 20.0–50.0%. Metagenomic analysis shows enrichment of specific microbial taxa that enhance organic P mineralization. Field trials demonstrate a reduction in total P runoff by 69.96% and 79.42% from paddy fields and tea plantations, respectively, along with a >26% increase in fertilizer use efficiency. The ecological safety of the composite material is confirmed through minimal heavy metal and pesticide residues and an improvement in soil microbial diversity. This circular aquaculture-to-agriculture approach effectively transforms shell waste into a dual-functional material, providing a sustainable solution to the phosphorus scarcity-pollution paradox through closed-loop resource recovery.