Bio-Based Fertilisers (BBFs) derived from nutrient recovery are increasingly promoted as sustainable alternatives to synthetic inputs. However, their effects on greenhouse gas (GHG) emissions remain poorly understood, especially how carbon quality interacts with phosphorus (P) availability and soil moisture to influence CO2, N2O, and CH4 fluxes. A 28-day incubation experiment was conducted using a low-phosphorus agricultural sandy loam soil amended with two pig slurry–derived BBFs that differ in