Phosphorus (P) losses from agricultural soils are a major cause of fresh water quality impairment. The objective of this study was to validate, at the field level the Caribbean Phosphorus Index (CPI) a tool developed for the identification of agricultural soils with high risk of P losses to surface waters. We applied the CPI to various plots of a dairy and poultry farm in Puerto Rico, and compared those values with P runoff concentration generated under natural rainfall condition. Average soil tests P (STP) values were 41 mg P kg-1 and 152 mg P kg-1 for the dairy and the poultry farms, respectively. A average total phosphorus (TP) concentration losses in runoff was 2.29 and 5.87 mg L-1 for the dairy and poultry farm, respectively. The CPI, ranked both dairy farm plots as Medium and both poultry farm plot as High potential for P movement. However based or a criteria that indicates that runoff losses greater 1 mg L-1 from plots with less 30 m of a surface water body should rank in the Very High category; we concluded that the current CPI version underestimates the impact of the animal manure plots on the surrounding waters. Results suggest that modifications are needed to better reflect field conditions. Suspended sediment results from our experiments indicate that particular P losses were minimal from our plots. A modification of the CPI excluding soil erosion from the CPI matrix yielded results that were more attuned to the runoff concentration losses observed