Struvite-loaded biochar beads fertilizer for different soils: nutrient slow release, soil properties improvement and heavy metal remediation

Highlights

	● Ca/MgBC + NP showed satisfactory slow-release properties in various soils.
	● Ca/MgBC + NP effectively promoted crop growth in various soil types and pH levels.
	● Ca/MgBC + NP improved soil properties in a variety of soil types and pH levels.
	● Ca/MgBC + NP effectively immobilized heavy metals, particularly Cr and Hg (over 80%).

Abstract

This study investigates the use of struviterient-loaded magnesium-modified biochar beads (Ca/MgBC + NP) as a slow-release fertilizer and soil amendment, comparing its performance with commercially available slow-release fertilizers (SRF) in different soils and crop types. The results demonstrate that Ca/MgBC + NP exhibited satisfying swelling, water retention, and slow-release properties in all tested soils. In sandy soil, which showed the most significant differences (p < 0.05), Ca/MgBC + NP enhanced the growth of Brassica chinensis L. and Spinacia oleracea L. after 90 d, with shoot and root lengths, as well as fresh and dry weights, 1.25–2.84 times higher than those treated with SRF. The cation exchange capacity and organic carbon content of sandy soil were significantly improved (by 38.55% and 265.38%), overcoming its natural limitations in water and fertilizer retention. Principal Component Analysis (PCA) confirmed that soil properties played a crucial role in crop growth (52.67% variance explained). Spectroscopic analysis indicated that magnesium-related compounds, including struvite and Mg(PO₄)₃, contributed to the observed growth promotion. Furthermore, Ca/MgBC + NP effectively immobilized heavy metals, particularly Cr and Hg, with immobilization rates exceeding 80%. This study highlights the potential of Ca/MgBC + NP as a sustainable, low-cost fertilizer that not only enhances crop growth but also improves soil health and remediates heavy metal contamination, providing a promising alternative for green agriculture.

Graphical abstract

Keywords

Sustainable development / Slow-release fertilizer / Release behavior / Pot experiment / Soil property improvement / Heavy metal remediation

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CRediT Authorship Contribution Statement

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Hanbing Li, Li Wang and Yiwen Wang. The first draft of the manuscript was written by Hanbing Li and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Conflict of Interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Nos. 51908457 and 52070155). The authors thank Jiamei Liu and Dan Li from Xi’an Jiaotong University (China) for assistance with XPS and XRD tests respectively.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-025-1993-8 and is accessible for authorized users.

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