Sustainable resource management with bone char—challenges and opportunities for enhancing soil health and phosphorus stocks

The global annual production of animal by-product (ABP)-derived bone, estimated at 95‒126 million tonnes, presents both an environmental challenge and an opportunity for sustainable resource utilization. We estimate that bone char (BC) could theoretically replace 13‒32% of the global phosphorus (P) fertilizer market. BC, produced through the pyrolysis of animal bones, has emerged as a promising material for use in a range of agricultural applications related to soil fertility and water quality. The conversion of ABP-derived bone into BC through pyrolysis not only eliminates potential human and animal pathogens (e.g., prions, viruses, bacteria), but also creates a valuable resource rich in P, calcium, and magnesium. This review synthesizes current research on the potential applications of BC in agriculture, focusing on its multifunctional role as a slow-release P fertilizer, a carbon (C) storage material, and an effective adsorbent for remediating contaminated soils. Field and laboratory studies demonstrate that BC's performance is strongly influenced by pyrolysis conditions, with optimal temperatures between 300 and 500 °C for nutrient release applications and above 600-800 °C for enhanced surface area and contaminant remediation. Its hydroxyapatite structure enables gradual P release and potential toxic element (PTE) immobilization, while its porous nature can provide new habitat niches for soil microorganisms and improve soil water retention. In comparison to most conventional inorganic fertilisers, BC can enhance soil fertility by releasing P slowly, thereby improving plant growth and productivity, particularly in acidic soils. The low cost, renewable nature, and ease of regeneration of BC further enhance its appeal as a viable solution for mitigating environmental pollution and promoting sustainable resource management practices. Beyond its established applications, this review identifies critical knowledge gaps, including the need to investigate BC's long-term impacts on soil health, microbial communities, and greenhouse gas emissions. We also discuss opportunities for optimizing production methods and expanding applications beyond agriculture. Given BC's potential to address multiple agricultural and environmental challenges, we emphasize the importance of interdisciplinary research to evaluate implementation barriers, including economic viability, social acceptance, and regulatory frameworks.