Evaluating Management Implications of the New York Phosphorus Index with Farm Field Information

Phosphorus (P) loss from agricultural fields can contribute to water quality degradation. The current New York P index (NY-PI) scores fields on the basis of P sources and field characteristics that reflect risk of P transport (a source × transport approach). Recently, a transport × best management practice (BMP) approach was proposed, which first scores fields using landscape-driven transport factors and then offers various BMPs to reduce the score (i.e., risk of P transport). To analyze the score distribution of the current NY-PI and the incentivizing potential of the proposed structure, a database of 33,327 agricultural fields in New York was assembled in collaboration with nutrient management planners and farmers. Under the current NY-PI, no additional P could be applied to 2% of the fields, while for 3% the application rates should not exceed annual crop P removal. Flow distance (field to stream) was a major driver for NY-PI scores. The current NY-PI relies heavily on soil test P to assess runoff risk, allowing some low-P fields to receive manure independent of transport risk. A scenario evaluation showed that the proposed NY-PI limits P application on fields with high transport risk while simultaneously incentivizing adoption of BMPs in such areas. In the absence of farm-level water quality data, a farm field database can help set P index coefficients and assess implications of a new P index. This study emphasizes the value of involving stakeholders in assessing nutrient management tools, as well as the importance of using an incentive-driven approach for protecting water resources.