Phosphogypsum as a soil amendment: mechanisms, applications, and environmental risks

Phosphogypsum (PG) is a calcium sulfate-rich by-product of phosphoric acid production. Agricultural reuse can recover calcium and sulfur and improve soils constrained by sodicity, subsoil acidity, or nutrient deficiency. This review examines PG characteristics, soil interactions, agronomic responses, and environmental risks. Structured literature screening, evidence classification, bibliometric analysis, and critical narrative synthesis were combined. Phosphogypsum supplies Ca 2+ for sodium displacement and clay flocculation in saline-sodic soils and can improve subsoil calcium availability and reduce aluminum toxicity in acid soils. Responses depend on material composition, soil properties, application rate, water management, climate, and crop requirements. Evidence for greenhouse gas mitigation is concentrated in flooded rice systems, with limited validation in upland agriculture. Residual acidity, soluble salts, fluorine, potentially toxic elements, and naturally occurring radionuclides require assessment through contaminant speciation, leachability, cumulative loading, crop uptake, and exposure pathways. Inconsistent material characterization, short experimental durations, and limited long-term field, regulatory, and economic assessments constrain the transfer of published results to practice. Agricultural use requires source-specific quality control, rates matched to soil requirements and environmental limits, long-term monitoring, and economic comparison with conventional amendments and other PG management options.