A Review of the Pennsylvania Phosphorus Index ... - PennFuture

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estimating available manure P using a WEP test is strong but there is evidence that the currentanalytical procedure could be improved.The real issue with agricultural P management based upon a P-Index system is at what level theallowable P losses from farm fields are set within each P-Index ranking. The model upon whichthe P-Index is based seems scientifically sound. It estimates the quantity of available P andmoves that P across the landscape. However, the model end point setting of allowable P loss isindependent of the model structure. The determination of allowable P loss from farm fields is apolicy decision. However, this critical decision has instead been made by the P-Index modeldesigners. A policy discussion about the appropriate level of allowable farm field P loss shouldbe held by policy makers with stakeholder input. However, that discussion needs to be informedby the knowledge of how the aggregate loading of P from farm fields will be affected by theallowable farm field P loss. Currently, it is not known how much P would be loaded into awatershed from agricultural fields by the current P-Index ranking structure.Furthermore, the scientific basis of the current P-Index ranking index is based upon sourceinput variables for manure P availability using Book value PSC’s or only adjusting manure Pavailability by loss factors for application and timing. The relationship between P-Indexrankings and field edge P losses needs to be updated with current manure PSC values. It may beargued that the Book value PSC’s overestimate manure P availability but the scientific basis forthe current P-Index ranking incorporates those overestimates in the formulation of itsrelationship between PI ranking and field edge P loss. If the availability of manure P is to becorrected with WEP analyses, the relationship of the P-Index ranking to field edge P loss alsoneeds to be corrected.Recommendations1. Model the P load from farmlands in aggregate across watersheds based upon current andalternate P-Index ranking thresholds.o The allowable P loss inherent in the P-Index rankings is a policy decision that isburied within the P-Index model structure. Information is needed on the impactof setting the allowable P loss at various levels before an informed policy decisioncan be made.o The research supporting the current P-Index ranking thresholds seems to bebased upon estimates of manure P availability that are higher than likely beingused today. Therefore the relationship between manure as a source of availableP, and the P runoff from farm field edge needs to be reexamined.2. Pennsylvania should collect nutrient management information in a centralized location(with protections in place for confidential business information, if needed) so acres offarmland with P restrictions can be determined. This would also provide informationabout how much P was being applied by these farms, the values of the WEPmeasurementbased PSC’s, and what activities are being employed to manage manuredifferently to avoid P loss.3. All farms applying manure should calculate a P-Index value. All P-Index informationshould be gathered at a centralized location to allow analysis.Page 13
4. Require BMPs to reduce P loss from fields with Very High P-Index rankings.5. Attend meetings of the group which evaluates and makes recommendations formodifications to the PA P-Index. This would allow a deeper insight into the workings ofthe P-Index and potentially, some input into how the PA P-Index is designed andimplemented.6. Evaluate the impact of extending the riparian buffer zone in Part A Screen of the P-Indexto 200 feet. The data seem to indicate that the active areas of P runoff extend out thatfar.7. Conduct monitoring of targeted watersheds to determine the actual loss and riverinetransport of P from farm fields.8. The long term solution to the P imbalance in watersheds with a high density of livestockoperations is to restore the P balance. The import of feed grains to areas of dense animalproduction exceeds P removal. One possible solution may be found in an effectivemanure transport program perhaps including some processing to develop value-addedmanure-based products. Another possible solution may be to decrease animal densityand substantially increased the integration of animal and crop production.ReferencesBeegle, D.B. 1999. Soil fertility management. In N. Serotkin and S. Tibbetts (eds.) TheAgronomy Guide. 1999 – 2000. Publ. Distribution Center, Pennsylvania State Univ., UniversityPark. (Reference taken from Sharpley et al 2001 as a copy could not be found in electronicsearch.)Beegle, D.B., J.L. Weld. W.J. Gbuerk, P.J. Kleinman, A.N Sharpley, and C. Kogelman. 2006.The Pennsylvania Phosphorus Index: Version 1; User Documentation (Draft).http://panutrientmgmt.cas.psu.edu/pdf/rp_PIndex_Guidance_Manual0605.pdfBeegle, D.B., J.L. Weld. W.J. Gbuerk, P.J. Kleinman, A.N Sharpley, and C. Kogelman. 2009.Pennsylvania’s Nutrient Management Act Program Technical Manual (Version 4.0) - Appendix5:The Pennsylvania Phosphorus Index: Version 2 Users Guide(http://panutrientmgmt.cas.psu.edu/pdf/Technical_Manual/Appendix%205%20-%20P%20Index%202009-10.pdf).Elliott, H.A., R.C. Brandt, P.J.A. Kleinman, A.N. Sharpley, and D.G. Beegle. 2006. Estimatingsource coefficients for phosphorus site indices. J. Environ. Qual. 35:2195-2201.Gburek, W.J., A.N. Sharpely, L. Heathwaite, and G.J. Folmar. 2000. Phosphorus Managementat the watershed scale: A modification of the phosphorus index. J. Environ. Qula. 29:130-144.Page 14
Page 1 and 2: A Review of thePennsylvaniaPhosphor
Page 3 and 4: The P-Index source factor uses a Me
Page 5 and 6: 1:100 extraction ratio (i.e. 2.5 g
Page 7 and 8: Table 1. Conditions assumed in exam
Page 9 and 10: plotted (Figure 2). By lowering the
Page 11 and 12: and Mehlich-3 extractable soil P co
Page 13: overestimation is incorporated into

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