Corn stalk-zeolite Co-pyrolyzed biochar modified by Mg and chitosan coating: Adsorption mechanism and nutrient slow-release properties.

The low utilization of nitrogen (N) and phosphorus (P) fertilizers causes resource waste and water eutrophication. To address this, novel biochar composites (Mg-ZSBC and CS-Mg-ZSBC) were prepared via co-pyrolysis of corn stover with zeolite, magnesium modification, and chitosan coating. Adsorption experiments showed that Mg-ZSBC efficiently immobilized N/P through struvite precipitation, achieving removal rates of 90.05% for P and 55.73% for N, with maximum adsorption capacities of 106.61 mg/g for NH4+-N and 170.55 mg/g for PO43--P. Release kinetics revealed that chitosan-coated CS-Mg-ZSBC had cumulative release rates of only 10.22% for N and 15.27% for P over 35 days in soil. Pot experiments demonstrated that compared to traditional compound fertilizers, CS-Mg-ZSBC increased Chinese cabbage height and root length by 10-15%, and boosted biomass by 28.7%. It also improved soil cation exchange capacity and microbial community structure. This study provides a feasible strategy for recovering wastewater nitrogen and phosphorus and developing low-carbon, eco-friendly biochar-based slow-release fertilizers.