Multi-nutrient leaching dynamics and phosphorus speciation in soil columns amended with fungal (Talaromyces adpressus) biomass

Waste-derived fertilizers can contribute to circular nutrient management when nutrient availability is coupled with reduced leaching. This study evaluated a 1:1 sewage sludge ash (SSA)-fish meal (FM) formulation applied to soil at 1% (w/w), with or without 0.1% (w/w) macerated Talaromyces adpressus preparation. Soil column leaching assays demonstrated that fungal bioaugmentation significantly reduced cumulative nutrient losses, particularly for phosphorus (P), potassium (K), and sodium (Na) indicating enhanced retention. Soil columns (n = 3 per treatment) were leached for four weeks wherein event mass release was calculated, and treatment-by-time responses were evaluated by repeated-measures analysis. Kinetic modelling showed that fungal amendment produced smoother nutrient-release trajectories, particularly for phosphorus, whose event release declined consistently throughout the four-week period. Potassium and sodium displayed moderate later-event contributions, indicating temporal redistribution rather than abrupt early mobilization. Fungal preparation reduced cumulative release of P by 35.0%, K by 41.1%, and Na by 44.2%. Strong treatment effects were obtained for P, K, and Na, with treatment-by-time interactions confirming distinct temporal profiles. Cd and Cu release decreased by 61.8% and 83.8%, respectively. Post-leaching Hedley fractionation showed that absolute labile P was maintained (737 ± 60 vs 757 ± 156 mg kg −1 ), while its share of post-leaching total P increased from 8.19 ± 0.43% to 10.48 ± 0.97%, supporting improved availability within the retained P. The complementary seedling bioassay showed that the combined fungal-waste treatment achieved the highest germination percentage (100%), significantly exceeding soil-only (≈67%), waste-only (50%), and fungi-only (75%) treatments. Similarly, seedling vigor index and biomass accumulation were maximized under the combined treatment, indicating synergistic effects between fungal activity and organic amendment. Ni and Cr showed element-specific mobilization, identifying clear targets for formulation optimization. Together, the results support fungal-fortified SSA-FM as a promising circular fertilizer platform that combines nutrient conservation, maintained labile P, and strong early plant performance.