Agricultural Phosphorus Balance Calculator: A tool for watershed planning

Best management practices implemented to minimize agricultural phosphorus (P) water quality impacts typically focus on retaining nutrients rather than improving P use efficiencies. Although it is now well understood that long-term reduction of P loadings requires achieving a watershed level P balance, this concept is generally not incorporated in watershed planning. This paper develops a detailed P balance for the Albert Lea Lake watershed, a high production agricultural watershed in south-central Minnesota, United States. Watershed specific crop and livestock management data were acquired through personal interviews, surveys, feedlot permits, and site visits. These data, together with published resources, were used to develop an open-source Agricultural P Balance Calculator to compute P use efficiencies of livestock operations, crop production, and collectively, the watershed's agricultural system. In 2010, the P use efficiency was 1.7, indicating that more P was being exported from the watershed as agricultural products than imported, implying that crops were "mining" P from watershed soils. The Agricultural P Balance Calculator enables users to identify production areas where P use efficiency strategies could be incorporated into conservation implementation planning, thereby enhancing prospects for meeting P reduction goals.