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). Core Ideas Stakeholder engagement is essential to develop improved Phosphorus Indices (PIs). A “Transport × BMP”‐based PI incentivizes BMP use where risk of P transport is high. In a “Transport × BMP”‐based PI, soil‐test P sets rate limits to enhance P balances. A “Transport × BMP”‐based PI can reduce barriers to regionalization of PIs within watersheds.