206-1 Phosphorus Indices and the 590 Revision: Why We Need to Take Stock of How We Are Doing.



Tuesday, October 18, 2011: 9:05 AM
Henry Gonzalez Convention Center, Room 217A, Concourse Level

Andrew Sharpley, Crop, Soil and Environmental Sciences, University of Arkansas, Fayetteville, AR, Douglas Beegle, Crop and Soil Sciences, The Pennsylvania State University, University Park, PA, Carl Bolster, Animal Waste Management Research Unit, USDA-ARS, Bowling Green, KY, Laura Good, UW Madison, Madison, WI, Brad Joern, Agronomy, Purdue University, W. Lafayette, IN, Quirine Ketterings, Animal Sciences, Cornell University, Ithaca, NY, John Lory, University of Missouri, Columbia, MO, Robert Mikkelsen, International Plant Nutrition Institute, Merced, CA, Deanna Osmond, Dept. of Soil Science/North Carolina State University, Raleigh, NC and Peter Vadas, USDA-ARS, Madison, WI
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.
See more from this Division: ASA Section: Environmental Quality
See more from this Session: Symposium--Evaluation and Validation of Phosphorus Indices: Part I