Integrated phytoremediation and MgO Si HAP biochar for heavy metal remediation and maize productivity

Heavy metal contamination in agricultural soils limits crop productivity and presents food safety risks. This study explores an integrated approach combining phytoremediation (PHY) and biochar amendments, specifically a Magnesium Oxide–Silicon–Hydroxyapatite (MOSi-HAP) biochar system, to improve soil health and agricultural output. A 120-day pot experiment was conducted, consisting of two phases: Phase 1 compared different phytoremediation plants ( Brassica juncea L, Vetiveria zizanioides L, Helianthus annuus L), MOSi-HAP biochar (3% w/w), and their combination; Phase 2 assessed maize growth in treated soil versus control. Results indicated that the integrated treatment significantly enhanced soil quality by boosting parameters such as porosity (+ 5.8%), water-holding capacity (+ 12.9%), organic carbon (to 1.10%), and cation exchange capacity (to 12.0 cmol kg⁻¹), while reducing heavy metals (Cd, Pb, As, Ni) by 93.8%, 94.3%, 94.2%, and 94.1%, respectively. Maize growth improved, with increases in plant height (from 103 ± 2 cm to 137 ± 3 cm), biomass (from 305 ± 5 g to 528 ± 8 g), and grain yield (from 4.2 ± 0.2 t ha⁻¹ to 7.1 ± 0.3 t ha⁻¹, a + 69.0% increase). Nutrient uptake of nitrogen, phosphorus, and potassium also rose significantly, alongside enhancements in antioxidant enzyme activities and a reduction in oxidative damage (malondialdehyde levels decreased by 69.1%). Grain concentrations of heavy metals fell by 98.0–98.5%, remaining below international food safety standards. Overall, the PHY + MOSi-HAP biochar method effectively reduced heavy metal bioavailability and accumulation, while improving soil quality and maize productivity under pot-culture conditions.