In recent decades, traditional animal agriculture has shifted towards confined animal feeding operations marking the effects of social, political, and economic pressures towards increased specialization. While the goal of animal producers is to operate in a sustainable manner, nutrient management plans are implemented to prevent over-application of animal waste. However, historically excessive applications of animal wastes applied to agricultural land as a disposal strategy, rather than solely as a source of crop nutrients, have greatly increased Mehlich-3 phosphorus (M3P) in some situations. As a result, some North Carolina (NC) soils now have M3P above the agronomic optimum for crop production. As M3P is an indicator of the solubility of P in soils, this raises concerns about the effects of potential P losses on water quality. The NC Phosphorus Loss Assessment Tool (PLAT) estimates potential P losses from fields through various pathways and is used to help minimize non-point P transport to freshwaters. In PLAT, M3P serves as a critical component in estimating P losses in both soluble and particulate-bound forms. Current PLAT critical environmental M3P thresholds are set at 50, 100, 200, 500 mg P kg-1 soil for organic, sandy, loamy, and clayey soils, respectively, above which water-soluble P (WSP) increase rapidly. Our objectives were to validate the M3P thresholds in PLAT using M3P versus WSP relationships, and to determine the change in WSP following phosphorus fertilization of soils with a broad range of initial M3P. These results will help assess the environmental impact of nutrient management plans redirecting manure applications from high to low M3P soils. The implications for nutrient management on farms with confined animal feeding operations will then be discussed.