Setting Targets for the Phosphorus Index Using Whole-Farm Phosphorus Balances.

The revised New York phosphorus index (NY-PI) is a framework and tool that ranks relative risk of soil phosphorus (P) loss from agricultural fields, and incentivizes implementation of best management practices (BMPs) known to reduce P runoff risk from individual fields. In the newly proposed NY-PI, landscape factors are combined to obtain a transport score for relative risk of P loss from agricultural fields. Best management practices, like the use of cover crops, setbacks, or manure incorporation or injection, are then used to lower the NY-PI score (credit system) and allow for greater manure management flexibility, depending on the soil P status. This transport × BMP approach is designed to incentivize BMPs where runoff risk is high. However, for enhanced P management over time, the landscape and BMP scores should take into account P nutrient use efficiency across the entire farm, which can be estimated using whole-farm nutrient mass balances (NMBs). The two management tools (NMB and PI) provide unique and complementary information to determine relative risk of P loss, yet have thus far never been combined. Linking the NY-PI and NMBs will allow for a more consistent and scientific P management that will improve whole farm P management, soil P conservation, and water quality. Integration of these two tools is essential for setting of scores and targets for the PI. Here we present a concept that combines the two management tools, as well as findings of PI comparisons for a select number of case study farms with NMB records.