Poultry manure contains valuable nutrients, but excessive or poorly managed application can contribute to nitrogen and phosphorus losses and environmental contamination. This review examines how dietary protein and phosphorus management influence nutrient excretion, manure composition, phosphorus solubility, runoff, manure treatment, and soil amendment value. The reviewed studies indicate that reducing dietary crude protein with adequate amino-acid supplementation can reduce nitrogen excretion, while reducing non-phytate phosphorus and using phytase can reduce selected phosphorus fractions in poultry litter. However, lower total manure phosphorus does not consistently translate into lower runoff phosphorus because solubility, sediment transport, soil phosphorus status, rainfall, treatment, and application practices also determine losses. Stabilization through composting or anaerobic digestion may improve the suitability of poultry manure as a soil amendment, but treatment performance is process- and hazard-specific. Overall, effective management requires coordination of feed formulation, manure treatment, soil testing, application rate, and environmental monitoring. The review also identifies the need for longer-term, integrated studies in poultry systems beyond the commercial broiler, layer, and turkey evidence most commonly represented in the literature.