A study was conducted of the effectiveness of applying various rates (0–50 g/kg) of fly and bottom ash (<2 mm and 2–4 mm) from a coal-fired power plant, and melter (AP10B and PAP5) and basic (KOBM) slags from a steel-manufacturing plant on mitigating phosphorus (P) loss from a Pallic soil sown to pasture. Measurements were made of soil pH, Olsen P, and H₂O-P (as a measure of P loss in overland flow), and soluble P and contaminants (B, As, Cd, Pb, Se) from a weekly leaching regime for 9 weeks. Results shows that H₂O-P had decreased up to 40% in soils treated at the greatest rate of melter slag (50 g/kg), and increased in KOBM and fly ash treated soils. The effect on Olsen P relative to H₂O-P was much less in metler slag and bottom ash treated soils than soils treated with fly ash or KOBM slag. The fly ash was considered unsuitable for the mitigation of P loss from soils due to B toxicity to plants, while KOBM is also unsuitable due to a liming effect and the increase in soluble P loss. At the rates applied, no treated soil leached toxic metals (As, Cd, Hg, or Se) above current guidelines. In contrast, the incorporation of melter slag and bottom ash is considered an effective P loss mitigation strategy.