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Background and objective <p>Heavy metal contamination in calcareous fluvo-aquic soils poses a significant threat to agricultural safety and human health. While modified biochar shows promise for remediation, field studies on its mechanisms and ecological effects under such conditions are still lacking.</p> <p>This study aimed to synthesize a novel silicon-phosphorus biochar-based compound fertilizer (BCF) and evaluate its efficacy in immobilizing heavy metals, influencing soil microbial communities, and promoting wheat growth in a calcareous fluvo-aquic farmland soils contaminated with heavy metals.</p> Methods <p>A Si-P biochar-based compound fertilizer (BCF) was synthesized from maize straw biomass, diatomite, triple superphosphate and urea at different pyrolysis temperatures (300℃, 450℃, 600℃) and mixture ratios (5:1:1:x (B5PN<sub>x</sub>) and 10:1:1:x (B10PN<sub>x</sub>)). A field experiment with 11 treatments was conducted on contaminated calcareous fluvo-aquic soil to assess the effects of BCF types and application rates (450, 900, and 1800&#xa0;kg&#xa0;ha⁻<sup>1</sup>) on soil properties, the availability of Cd, Zn, and Pb, heavy metal accumulation in wheat grains, wheat yield, and soil microbial community structure. Structural equation modeling (SEM) was used to analyze the pathways of Cd immobilization.</p> Results <p>The application of BCF significantly increased soil cation exchange capacity (CEC) and soil organic matter (SOM). It also markedly reduced the bioavailability of Cd, Zn, and Pb in soil, primarily due to the increased surface area, pore volume, and functional groups (e.g., N–H, PO₄<sup>3</sup>⁻, Si–O-Si) of BCF. BCF application, particularly the B5PN<sub>x</sub>, significantly decreased the concentrations of Cd, Zn, and Pb in wheat grains and enhanced wheat growth. This was linked to the enrichment of beneficial soil microorganisms such as <i>Proteobacteria</i>, <i>Gemmatimonadetes</i>, and <i>Actinobacteria</i>. SEM analysis supported that B5PN effectively immobilized soil available Cd, thereby reducing grain Cd accumulation and increasing yield.</p> Conclusion <p>The Si-P biochar-based compound fertilizer, especially the B5PN<sub>x</sub> formulation, is an effective, low-cost, and environmentally friendly amendment for remediating heavy metal-contaminated calcareous fluvo-aquic soil. It works by immobilizing heavy metals, improving soil health, and enriching a beneficial microbial community, offering a promising strategy for mitigating heavy metal bioavailability and reducing metal transfer in calcareous soil-wheat system.</p>

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Effect of Si-P biochar-based compound fertilizer on immobilization of heavy metals and wheat growth: a field study in calcareous fluvo-aquic soil

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月13日

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  • Di Wu,
  • Anqi Ren,
  • Zijie Shang,
  • Renqi Ding,
  • Lei Gu,
  • Zhifan Chen

摘要

Background and objective

Heavy metal contamination in calcareous fluvo-aquic soils poses a significant threat to agricultural safety and human health. While modified biochar shows promise for remediation, field studies on its mechanisms and ecological effects under such conditions are still lacking.

This study aimed to synthesize a novel silicon-phosphorus biochar-based compound fertilizer (BCF) and evaluate its efficacy in immobilizing heavy metals, influencing soil microbial communities, and promoting wheat growth in a calcareous fluvo-aquic farmland soils contaminated with heavy metals.

Methods

A Si-P biochar-based compound fertilizer (BCF) was synthesized from maize straw biomass, diatomite, triple superphosphate and urea at different pyrolysis temperatures (300℃, 450℃, 600℃) and mixture ratios (5:1:1:x (B5PNx) and 10:1:1:x (B10PNx)). A field experiment with 11 treatments was conducted on contaminated calcareous fluvo-aquic soil to assess the effects of BCF types and application rates (450, 900, and 1800 kg ha⁻1) on soil properties, the availability of Cd, Zn, and Pb, heavy metal accumulation in wheat grains, wheat yield, and soil microbial community structure. Structural equation modeling (SEM) was used to analyze the pathways of Cd immobilization.

Results

The application of BCF significantly increased soil cation exchange capacity (CEC) and soil organic matter (SOM). It also markedly reduced the bioavailability of Cd, Zn, and Pb in soil, primarily due to the increased surface area, pore volume, and functional groups (e.g., N–H, PO₄3⁻, Si–O-Si) of BCF. BCF application, particularly the B5PNx, significantly decreased the concentrations of Cd, Zn, and Pb in wheat grains and enhanced wheat growth. This was linked to the enrichment of beneficial soil microorganisms such as Proteobacteria, Gemmatimonadetes, and Actinobacteria. SEM analysis supported that B5PN effectively immobilized soil available Cd, thereby reducing grain Cd accumulation and increasing yield.

Conclusion

The Si-P biochar-based compound fertilizer, especially the B5PNx formulation, is an effective, low-cost, and environmentally friendly amendment for remediating heavy metal-contaminated calcareous fluvo-aquic soil. It works by immobilizing heavy metals, improving soil health, and enriching a beneficial microbial community, offering a promising strategy for mitigating heavy metal bioavailability and reducing metal transfer in calcareous soil-wheat system.