Phosphorus that accumulates in the surface of sandy soils is susceptible to leaching and surface runoff. Converting dissolved P to less soluble forms using materials containing Fe, Al, and Ca can reduce the amount of soil P released to runoff. The dredged muck of the St. Lucie Estuary has been proposed as a manufactured soil for application on local sandy soil. It is assumed that the application of the muck will enhance soil P retention. In this study, the effects of muck sediments on water-soluble P, Olsen-P, and P fractions of some Florida sandy soils were investigated. In the muck type and rate experiment, two soils (a high P soil and a low P soil) were incubated for 30 days with the mucks at 0, 5, 15, and 30%. Application of muck reduced water-soluble P and Olsen-P significantly in the high P soil, and also reduced water-soluble P and Olsen-P slightly but consistently in the low P soil. When a high rate of muck (30%) was applied, the high Fe and Al muck reduced water-soluble P by 69 to 89% and Olsen-P by 27 to 62%, whereas the low Fe and Al muck reduced water-soluble P by 23 to 61% and Olsen-P by 22 to 34%. At low rates (15%), water-soluble P was reduced by 35 to 79% for the high Fe and Al muck and 2 to 43% for the low Fe and Al muck, whereas Olsen-P was reduced by 24 to 44% for the high Fe and Al muck and 12 to 31% for the low Fe and Al muck. The decreased P solubility resulted from the conversion of readily soluble P (H2O-P and NaHCO3-P) to less soluble pools (HCl-P and residual P). Amending the high P soils with mucks has the potential to reduce P enrichment of runoff by decreasing the solubility of soil P. These data indicate that application of muck can result in significant reductions in nonpoint-source P runoff from high P soils.