Enriched Phosphate of Soil Utilization from Modified Agricultural Waste Hydrochars and Their Potential as a Heavy Metal Stabilizer

Large amounts of agricultural waste that are not properly disposed of will result in resource wastage and environmental pollution. Herein, a series of agricultural waste hydrochars (AWHs) were prepared from hydrothermal cogasification of rice husk and chicken manure and used as a phosphorus (P) and heavy metal (HM) stabilizer for improving soil quality. Crop growth could be promoted at 1% AWH addition. AWH-V provided a renewable alternative for poor and hardening soil, and the available phosphorus effectively increased from 29 to 85 mg/kg. AWH-III was especially suitable for application in Cd-contaminated soil. The accumulation of Cd in crops also decreased by 46.10% under HM stress. An increased abundance of HM-tolerant rhizosphere microbial communities combined with adsorption of AWHs promoted HM passivation and stabilization. Interaction effects on phosphate and HMs could be summarized as competitive adsorption, cation and anion balance, and P & HM retention. This work provides a promising multiobjective pathway for agricultural waste management, soil quality improvement, and crop growth promotion.