Technical Abstract: The last decade has seen major research strides in the US, highlighted by efforts in Pennsylvania and surrounding states, to develop phosphorus (P) management strategies for protecting water quality in a sustainable animal agriculture production system. The most visible outcome of this effort has been the development of state of the art phosphorus site indices (P Index). The P Index has been adopted as a component of nutrient management policy or regulations in 47 states. While research on agricultural P and the environment continues, new efforts are currently under way focusing on implementation of P- Index based policies. Significant challenges have emerged as we have transitioned into implementation. These include fundamental questions about the underlying validity of the P Index and the relationships between regional nutrient balance and BMP-based approaches such as the P Index. Also, many operational challenges have been identified such as: costs and time required for P-Index based plans; variable implementation costs due to location and type of operation; integration of P- Index based plans with other plans such as farm conservation plans; and what BMPs are available to address problems identified by the P Index. Like many other areas, we in Pennsylvania and the Mid-Atlantic region have been working to evaluate and develop practical responses to these challenges. This paper discusses some of the key challenges we face and how we are responding. Examples of intra- and interstate collaboration to address technical and policy issues are also provided.