Pinewood engineered biochar as a solution to nutrient leaching management: Mitigating phosphorus and nitrate loss from poultry litter under saturated porous conditions.

Poultry litter (PL) is a valuable, inexpensive source of phosphorus (P) and nitrogen (N). However, repeated PL applications to soils cause P stratification and enhance both phosphate (PO43-) and nitrate-N (NO3--N) losses through surface runoff and leaching, which can result in the contamination of surface and groundwater. Therefore, this study evaluated pristine biochar (PBC), iron-modified biochar (Fe-PBC), and magnesium-modified biochar (Mg-PBC) for immobilizing PO43- and NO3--N extracted from PL using column and batch experiments. Column experiments demonstrated early PO43- breakthroughs in PBC and Fe-PBC, indicating limited immobilization, whereas Fe-PBC substantially immobilized NO3--N, and Mg-PBC effectively immobilized both NO3--N and PO43-. Magnesium-modified biochar exhibited experimental maximum adsorption capacity (qmax) of PO43- (1.25 ± 0.003 mgg-1) while NO3--Nqmax was nearly identical for both Mg-PBC (0.1 ± 0.001 mgg-1) and Fe-PBC (0.09 ± 0.0003 mgg-1). Phosphate adsorption kinetics on PBC and Fe-PBC were best described by Elovich model, whereas NO3--N adsorption kinetics were better explained by the pseudo-first-order, pseudo-second-order, and Elovich models. The Sips isotherm best fits for PO43- adsorption on PBC and Mg-PBC, along with NO3--N adsorption on all biochars, indicating heterogeneous multilayer adsorption. Langmuir fits described NO3--N adsorption well, but poorly described PO43- adsorption, whereas the Freundlich model better reflected the heterogeneous adsorption. Results suggest that Fe-PBC can serve as NO3--N adsorbent, while Mg-PBC can act as an effective adsorbent for both PO43- and NO3--N, suggesting potential solutions for nutrient management. This study helped understand biochar-nutrient interactions under chemically complex PL-solutions and provides insights for developing sustainable nutrient management strategies in manure-applied regions.