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Purpose <p>Traditional fast-acting phosphorus fertilizers suffer from low utilization efficiency due to leaching and fixation, causing pollution and waste. Biochar-based slow-release phosphorus fertilizer (BSRF) offers a solution by enhancing efficiency, regulating release, extending duration. However, in order to enhance the integrated advantages of traditional BSRF in “reduced application, enhanced efficiency, soil improvement, and environmental protection”, this study mainly addresses issues such as uneven heating, energy waste, and unclear slow-release mechanisms.</p> Materials and methods <p>This study used microwave co-pyrolysis technology to prepare a novel BSRF by using waste apple wood as biomass raw material and accurately mixing it with bentonite and KH₂PO₄ in ratios of 10:3 and 10:1, respectively, to determine different ratios of bentonite and phosphate. Put the homogeneous mixture into a microwave tube oven. Under a high-purity nitrogen atmosphere, the temperature was raised to 700&#xa0;°C at a heating rate of 10&#xa0;°C/min. The residence times at 700&#xa0;°C were controlled at 1, 10, 20, 40, and 60&#xa0;min, respectively, to prepare biochar samples BC, BC10B3, BC10P1, BC10B1P1, BC10B2P1, and BC10B3P1 at different residence times.</p> Results and discussion <p> Results show microwave processing refined the BSRF pore structure via bentonite’s layers and phosphate addition, hindering direct phosphate dissolution, and generated abundant oxygen-containing and phosphorus-containing functional groups and chemical bond. The larger surface area provided more phosphate adsorption sites. This enhanced hydrophilicity, adsorption capacity, surface chemical activity, sustained P supply, and slowed P release. Optimal conditions (1 min residence, BC10B3P1) yielded reduced mass loss and higher yield. BC10B3P1 showed optimal 14-day slow-release efficiency and zero-order kinetics dominated by surface diffusion. Bentonite suppressed P migration via physical confinement and promoted chemical bonding with biochar functional groups, creating a synergistic physical-chemical slow-release system that elucidates multi-component regulation of long-term release. Field experiments have confirmed that the application of BSRF increases soil fertility and promotes plant growth.</p> Conclusions <p> This study aimed to tailor the structure of BSRF by modulating preparation parameters such as residence time and phosphate addition ratio. This optimization improved the pore architecture and increased oxygen- and phosphorus-containing functional groups of the BSRF, thereby elucidating the intrinsic relationship between these structural modifications and its slow-release performance. The results demonstrate significant enhancements in slow-release characteristics and adsorption capacity under different preparation conditions, laying the groundwork for developing highly efficient BSRF.</p> Graphical Abstract <p></p>

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Microwave-assisted modification for enhancing the slow-release performance of biochar-based fertilizer and application

  • 期刊论文

  • 发表日期：

    2025年10月13日

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  • Linlin Zhu,
  • Bingzhe Su,
  • Chen Guan,
  • Yao Chen,
  • Dongye Huang,
  • Jiayao Zhou,
  • Qiuyu Chen,
  • Xiaochen Liu,
  • Fei Tian,
  • Zhansheng Wu

摘要

Purpose

Traditional fast-acting phosphorus fertilizers suffer from low utilization efficiency due to leaching and fixation, causing pollution and waste. Biochar-based slow-release phosphorus fertilizer (BSRF) offers a solution by enhancing efficiency, regulating release, extending duration. However, in order to enhance the integrated advantages of traditional BSRF in “reduced application, enhanced efficiency, soil improvement, and environmental protection”, this study mainly addresses issues such as uneven heating, energy waste, and unclear slow-release mechanisms.

Materials and methods

This study used microwave co-pyrolysis technology to prepare a novel BSRF by using waste apple wood as biomass raw material and accurately mixing it with bentonite and KH₂PO₄ in ratios of 10:3 and 10:1, respectively, to determine different ratios of bentonite and phosphate. Put the homogeneous mixture into a microwave tube oven. Under a high-purity nitrogen atmosphere, the temperature was raised to 700 °C at a heating rate of 10 °C/min. The residence times at 700 °C were controlled at 1, 10, 20, 40, and 60 min, respectively, to prepare biochar samples BC, BC10B3, BC10P1, BC10B1P1, BC10B2P1, and BC10B3P1 at different residence times.

Results and discussion

Results show microwave processing refined the BSRF pore structure via bentonite’s layers and phosphate addition, hindering direct phosphate dissolution, and generated abundant oxygen-containing and phosphorus-containing functional groups and chemical bond. The larger surface area provided more phosphate adsorption sites. This enhanced hydrophilicity, adsorption capacity, surface chemical activity, sustained P supply, and slowed P release. Optimal conditions (1 min residence, BC10B3P1) yielded reduced mass loss and higher yield. BC10B3P1 showed optimal 14-day slow-release efficiency and zero-order kinetics dominated by surface diffusion. Bentonite suppressed P migration via physical confinement and promoted chemical bonding with biochar functional groups, creating a synergistic physical-chemical slow-release system that elucidates multi-component regulation of long-term release. Field experiments have confirmed that the application of BSRF increases soil fertility and promotes plant growth.

Conclusions

This study aimed to tailor the structure of BSRF by modulating preparation parameters such as residence time and phosphate addition ratio. This optimization improved the pore architecture and increased oxygen- and phosphorus-containing functional groups of the BSRF, thereby elucidating the intrinsic relationship between these structural modifications and its slow-release performance. The results demonstrate significant enhancements in slow-release characteristics and adsorption capacity under different preparation conditions, laying the groundwork for developing highly efficient BSRF.

Graphical Abstract