Bone char acidified with phosphoric acid as a novel phosphate fertilizer: Synthesis, characterization, and agronomic performance

Phosphorus (P) is essential for plant growth, however, global reliance on non-renewable phosphate rocks raises sustainability concerns, particularly in countries like Brazil that heavily depend on imported P fertilizers. Bone char, a byproduct of animal bone pyrolysis, has emerged as a promising alternative P source due to its hydroxyapatite content and circular economy potential. However, its moderate solubility limits agronomic efficiency for short-cycle crops. This study investigated a novel approach to enhance P solubility by acidifying bone char with phosphoric acid (H 3 PO 4 ). Bone chars were produced at different pyrolysis temperatures, characterized by X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy, and scanning electron microscopy, and compared to commercial sources with high and low solubility (triple superphosphate and Bayóvar, respectively). Solubility tests, P release and diffusivity studies, and incubation trials were conducted alongside greenhouse experiments with maize in a highly weathered clayey soil. The characterization of acidified bone char (bone char-H 3 PO 4 ) showed the peaks of the hydrated monobasic calcium phosphate, bands for the phosphate ions, high solubility of P in water, and the presence of the elements C, O, P, and Ca. Bone char-H 3 PO 4 demonstrated increased P solubility and cumulative release, with similar performance to triple superphosphate in both P uptake and biomass production. Despite lower soil P availability observed in incubation, bone char-H 3 PO 4 supported high agronomic efficiency, highlighting its potential as a sustainable and effective alternative P fertilizer. Additionally, bone char retained carbon in its structure, offering added benefits for soil health and climate-smart agriculture.