The phosphorus (P) index is a tool that was developed to assess the potential for P losses from fields to surface water bodies. In 1999, the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) issued national policy and general guidelines on nutrient management to include risk assessments for P. States were required to revise these guidelines by April 2001. These guidelines apply to nutrient management where nutrients are applied to the land, including organic by-products and animal manure. All NRCS staff will use this guidance when providing financial or technical assistance to producers. Third party vendors and other non-NRCS employees will use these guidelines when providing assistance through federal conservation programs for which NRCS has technical responsibility. The national guidelines suggested the use of one of the following risk assessments: soil-test P values, threshold limits, or a P risk index. The Iowa State Technical Committee recommended the use of the P index approach based on the advice of an interdisciplinary group that involved scientists, technical personnel, and representatives from various groups. The P index tool provides a rating of the risk of P delivery from agricultural fields to surface water supplies that can be used to prioritize fields for nutrient and soil management practices. The purpose of this presentation is to provide a brief overview of how the P index and variable-rate technology can be used to do better agronomic and environmental P management within a field.