Multi level synergistic regulation of phosphorus slow-release performance through LDH modified biochar-based slow-release fertilizer.

Addressing global phosphorus resource scarcity and low utilization efficiency of traditional phosphorus fertilizers, this study presents an innovative strategy for modifying biochar-based slow-release phosphorus fertilizer (BSPF) with Mg-Al layered double hydroxides (LDH-BSPF), to enhance phosphorus slow-release performance through multi-level synergistic regulation. A novel slow-release system was fabricated via co-pyrolysis technology integrating biomass, phosphorus sources, and LDH. The effects of Mg/Al molar ratios (2:1-5:1) and pyrolysis temperatures (400-600 °C) on material structural properties were systematically investigated. The interlayer structure of LDH significantly optimized the pore architecture of biochar, increasing the BET specific surface area by 1.48-9.94 times, while simultaneously immobilizing phosphorus through mechanisms of interlayer adsorption and chemical bonding. Phosphorus fixation in the LDH-BSPF followed a hierarchical pathway comprising "surface adsorption-interlayer adsorption-pore entrapment". Furthermore, structural evolution of LDH during pyrolysis was found to modulate the slow-release performance. Results from the 28-day static water release experiment demonstrated that 4:1-LDH-BSPF achieved a 36.8 % cumulative phosphorus release rate, representing a 44.6 % decrease relative to unmodified BSPF (66.5 %), with release kinetics primarily following diffusion mechanisms. Comprehensive characterization and phosphorus fractionation analysis confirmed that multi-level phosphate retention-transformation within LDH interlayers, coupled with the synergistic effects of LDH structural modulation on biochar pore architecture and functional groups, constitute the key mechanisms underlying the enhanced slow-release performance. Pot experiments verified that LDH-BSPF significantly outperformed conventional commercial phosphorus fertilizers in promoting pepper growth. This research provides a theoretical basis for developing high-efficiency biochar-based slow-release fertilizers and improving phosphorus utilization efficiency.