Bone char outperforms biochar in phosphorus-deficient soils: Comparative analysis of soil fertility enhancement and greenhouse gas mitigation

Phosphorus (P) deficiency limits crop yields globally, creating a need for sustainable alternatives to synthetic P fertilizers. This study evaluates the effects of biochar and bone char on maize growth, soil fertility, P availability, and greenhouse gas (GHG) emissions in soils with a moderate or low P content. A 42-day pot experiment was conducted with three treatments: control, conventional biochar, and bone char, each applied at 1 % (w/w). Measurements included plant growth, soil properties, nutrient levels in soil and pore water, and GHG fluxes (N2O, CH4 and CO2). The results showed that bone char significantly enhanced plant growth, especially in P-deficient soils, where shoot biomass was ten times higher than the control. Bone char also dramatically increased P availability in both soil types, outperforming biochar, which had limited effects on P levels. In terms of GHG mitigation, both biochar and bone char reduced N2O and CH4 emissions compared to the control, with bone char showing greater effectiveness in P-deficient soils, potentially due to its slow-release nutrient properties. Biochar promoted methane consumption, especially in P-rich soils. The findings suggest that bone char is an ideal amendment for P-deficient soils, offering dual benefits of nutrient enhancement and GHG reduction, while biochar's advantages lie in improving soil physical properties and mitigating emissions across different soil types. Overall, we conclude that bone char represents a viable option to improve sustainable P cycling and GHG mitigation in agronomic systems, highlighting the circular economy benefits of repurposing waste materials.