In their national policy guidelines on nutrient management, the USDA-Natural Resources Conservation Service (NRCS, 1999), identified three strategies for managing phosphorus (P) applications to cropland on a field-by-field basis to reduce the risk of resulting surface water contamination. Two of the strategies – limiting applications to agronomic recommendations and limiting applications above specified soil test P threshold levels – rely on soil test P as the sole indicator for guiding manure management decisions. The third NRCS strategy is the use of a comprehensive P loss risk assessment, or P Index.