Knowledge for Development

Evaluation of phosphorus indices after twenty years of science and development


Date: 20/11/2012


The P Index was proposed as a nutrient management tool in 1992 and has been implemented as such in the USA for the past decade. The goal of P Index use today is to help producers manage P, particularly manure-based P, while minimizing P losses and the associated environmental impacts. Included within this goal is the identification of critical source areas and strategic placement of best management practices. However, lack of water quality improvement in agricultural watersheds and discrepancies in P loss ratings between P indices have raised questions about continued use of the P Index.

The papers reviewed in this Special Section of the Journal of Environmental Quality conclude that P indices can provide accurate assessments of P loss but must be evaluated appropriately. Evaluation will require compiling large regional P loss datasets at field and small watershed scales. Simulation models may be used to generate P loss estimates; however, models must be calibrated and validated to ensure their accuracy. Further development of P indices will require coordinated regional efforts to identify common P Index frameworks and standardized interpretations. Stringent P Index evaluations will expand the utility of P indices for critical source area identification and strategic best management practice implementation by regulatory, education, and scientific communities alike.

(Journal of Environmental Quality 41, 09/2012 via the Soil Science Society of America, 23/10/2012)   

» Visit this site