Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 7/1/2011
Publication Date: 10/19/2011
Citation: Sharpley, A., Beegle, D., Bolster, C.H., Good, L., Joern, B., Ketterings, Q., Lory, J., Mikkelsen, R., Osmond, D., Vadas, P.A. 2011. Phosphorus indices and the 590 Revision: Why we need to take stock of how we are doing .. ASA-CSSA-SSSA Annual Meeting Abstracts. Abstract Only. Interpretive Summary:
Technical Abstract: Since its inception nearly 20 years ago, the phosphorus (P) Index has morphed from an educational tool to a Best Management Practice targeting and implementation tool, a manure-scheduling tool, and in many cases, a regulatory tool. A great deal of research has been conducted across the U.S. to derive, validate, and support components of the P Indexing concept, particularly those related to source factors. As different versions of the P Index have emerged, ostensibly to account for local topography, hydrology, soils, land use, and individual state policies and agendas, so too have differences in the P management recommendations that are made using the P Index. As a result, there are many variations in P Indices now in use as part of the NRCS 590 Nutrient Management Conservation Standard. This variation is both a strength and weakness of the P Indexing concept. However, the inconsistency among P Indices in terms of level of detail and scientific underpinnings among states, as well as in recommendations and interpretations based on site risk, prompted a review and possible revision of the 590 Standard and P-Indexing approach. The need for revision has been heightened by a slower than expected decrease in P-related water quality impairment and, in some cases, an increase in soil P to levels several fold greater than agronomic optimum due to the inability of the P Index to prevent the continued over-application of P to soils. While the basic scientific foundations of the P-Indexing approach are sound, these concerns are real. In this presentation, we propose the use of lower and upper boundaries of P Index use and describe an approach to evaluate individual State P Indices.