Restructuring the P Index to Better Address P Management in New York.

The New York Phosphorus Index (NY-PI) was introduced in 2001 after the release of the state's first Concentrated Animal Feeding Operation (CAFO) Permit that required a nutrient management plan developed in accordance with NRCS standards. The stakeholder-based approach to development of the NY-PI, combined with a requirement for all regulated farms to determine a NY-PI score for all fields, ensured widespread adoption. While P management greatly improved over time, the initial NY-PI overemphasized soil-test P (STP), allowing for P addition if STP was low, even if the risk of P transport was high. Our goal was to develop a new PI approach that incentivizes implementation of best management practices (BMPs) where P-transport risk is high, building on feedback from certified planners (survey), analysis of a planner-supplied 33,000+ field database with NY-PI information, and modeling of the impacts of specific BMPs on P runoff using data from a central NY CAFO farm. We propose a new NY-PI structure that identifies landscape-driven P-transport risk if P is surface applied when crops are not actively growing to reach a raw PI score that is multiplied by credits (factors ≤ 1.0) for implementation of BMPs effective in reducing the risk of P transport. In this "Transport × BMP" approach, STP is used as P application cutoff. This approach could reduce barriers to regionalization of PIs, as states can identify landscape risk factors, soil-test cutoffs, and BMPs while maintaining the same management categories (no manure, P-removal-based rates, or N-based management).