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

A Review of thePennsylvaniaPhosphorus Index:Version 2Joseph RudekJune 2011Submitted to:PennFutureHarrisburg, PA

A Review of the Pennsylvania Phosphorus Index: Version 2IntroductionFor many years the dogma in soil science was that it didn’t matter how much phosphorus (P)was put on soils because all in excess of crop needs would adhere to the soil. The only Ptransport mechanism of concern was erosion of soil. However, in the latter half of the 1990’s, itwas realized that at high soil concentrations, P could remobilize off the soil and move in runoffwater. The runoff of P from some crop lands to waterways became a concern as levels of soil Pbecame elevated due to high levels of manure application over extended periods especially fromconcentrated animal operations which have large amounts of manure to manage. The runoff ofP from agricultural lands contributes to other sources of P, resulting in eutrophication especiallyin lentic waters (i.e. non-running waters.) In response, the USDA added a P managementrequirement to its 590 Nutrient Management Standard, and states across the country followedup with plans to implement this standard.The Pennsylvania (PA) P-Index is divided into two parts, A and B (Beegle et al 2009.) Part A is asimple screening tool to determine whether nitrogen (N) based nutrient management plans aresufficient or if a farmer needs to complete Part B which calculates a P-Index to determinewhether nutrient management plans need to take into consideration the potential for P runoff.The Part A screening is based upon 4 criteria, an affirmative answer to any one of whichdetermines the need to complete Part B and, if appropriate, a P based nutrient managementplan. The criteria are as follows:1. Is the crop management unit in a Special Protection Watershed?2. Is there a significant farm management change as defined by Act 38?3. Is the soil test Mehlich-3 P greater than 200 ppm?4. Is the Contributing Distance from the crop management unit to receiving waters lessthan 150 ft.?In addition, the USDA’s Natural Resources Conservation Service requires P-based evaluationsfor farms receiving technical or financial assistance for manure-related issues (Kogelman et al2006.)Part B of the P-Index is divided into 2 factors: source and transport. The source factor accountsfor P availability from the soil, fertilizer and manure. The transport factor considers erosion,runoff potential, subsurface drainage, distance to waterways (known as contributing distance),and any management practices that modify P transport (known as modified connectivity.)From the source and transport factors is derived the P-Index. The P-Index is divided into 4rating categories: Low, Medium, High and Very High. Phosphorus Index ratings of Low orMedium do not require nutrient management plans to consider potential P runoff and nutrientmanagement plans can be nitrogen based. A High P-Index rating requires that P can only beapplied at crop removal rates. A Very High P-Index rating means no P can be applied.Page 1

The P-Index source factor uses a Mehlich-3 soil test to estimate the amount of P at risk forrunoff from the soil. Phosphorus availability from fertilizer depends on the amount of fertilizerand the manner in which it is applied, whether applied in spring or fall and whether and when itis incorporated into the soil. The P available from manure, like fertilizer, is dependent on whenapplied and whether incorporated but also includes a P source coefficient (PSC.) The PSC canbe taken from a chart provided by the state (e.g., in the P-Index Fact Sheet), known as the Bookvalue. Alternatively, the PSC can be determined by submitting the manure sample for a waterextractableP (WEP) analysis. The WEP test option was added to Version 2 of the PA P-Index.The Part A screening test was also modified in Version 2 with the addition of two conditions; theSpecial Protection Waters, and the significant change in farm management. The conversion toVersion 2 was described as a natural evolution of the P-Index, recommended by a group ofscientists at the USDA-ARS Pasture Systems and Watershed Management Research Unit atUniversity Park, PA and the Pennsylvania State University College of Agricultural Sciences(Beegle. pers. comm., Beegle et al 2009.) This group conducts an ongoing review of the P-Indexcalculation. While the use of a WEP analysis-based PSC likely lowers the P-Index, the additionalPart A conditions likely result in more farms calculating a P-Index. Dr. Beegle mentioned thatPA was considering a third version of the P-Index which might come out this year. A preview ofpotential recommended adjustments in the P-Index might be presaged in the SERA-17recommendations on the revisions to the 590 Nutrient Management Standard (Sharpley et al2011.)Assessments of the Affect of the Phosphorus Index on Pennsylvania AgricultureDuring the development of the PA P-Index, efforts were made to assess the impact onagriculture. In a statewide survey of over 220,000 soil samples collected in PA between 1996and 2001, Kogelmann et al (2002) found 4.8% exceeded 200 ppm P and 1.5% exceeded 300ppm P. Several counties located in the southeastern part of the state had a higher than averagepercentage of excessively high soil P samples. Lancaster, Schuylkill and Montgomery Countieshad the highest proportion above 200 ppm P (17.6%, 16.7% and 16.1%, respectively.) Additionalhotspots were noted in Wyoming, Wayne and Lackawanna Counties in the northeast and ErieCounty in the northwest (Kogelmann et al 2004.) Also of note, statewide, 48% of the soilsamples had soil P test values of 50 ppm P or more. The optimum range of soil P for crops is 30– 50 ppm P. Lancaster County had 81% of soil samples exceeding crop P needs. Seventeen outof the 67 counties statewide had greater than 60% of soil samples exceeded crop P needs. Thissuggests the possible widespread over fertilization of P. Not surprisingly, a positive relationshipwas found between animal density and high soil P concentrations.Besides high soil P concentrations and animal densities, Kogelmann et al (2002) also found thata greater percentage of the agricultural lands in the north and south-central parts of the statewere in close proximity to streams (within 150 feet), elevating the risk of P loss to streams inthose areas. Modeling of runoff in hilly areas indicated that nearly all the P runoff wasgenerated from about 10% of the watershed areas, within about 98 to 197 feet of the channel(Kogelmann et al 2004). These areas, known as variable source areas (VSA’s), are likely thePage 2

asis for the 150 foot buffer condition in the screening portion of the P-Index. Kogelmann et al(2004) stated that the 150 foot buffer should encompass most runoff from VSAs. Perhaps thebenefits of extending the contributing distance to 200 feet should be examined as a modificationof the P-Index Part A screening test conditions.However, the above findings regarding the areas of elevated risk of P loss overestimates theacres likely to require P nutrient management. The initially calculated P-Index is not fixed andnutrient management planners can revisit the source and transport components of the P-Indexand determine what changes or additional practices may be needed to reduce the risk of P loss(Kogelmann el al 2006.) Kogelmann et al (2006) examined the affect of P-Indeximplementation in 2 counties of the state that were likely to be highly impacted, Lancaster andSnyder Counties. Based upon screening results, 45.9% and 19% of the farms fields examined inLancaster and Snyder Counties (respectively) were required to calculate their P-Indices. Ofthese, 31.2% and 12% of the fields in Lancaster and Snyder Counties had P-Index rankings thatrestricted P application rates based upon initial nutrient management plans. Kogelmann et al(2006) then focused on 4 farms they defined as highly impacted (i.e. more than one third of thefarm acreage with P restrictions) to examine what types of management measures could beimplemented to ease P restrictions. Two of the four highly impacted farms appeared to requireoff-farm manure transport to comply with P based nutrient management. If this ratio were toapply to all the farms that required P-Index calculation in Lancaster and Snyder Counties, thepercentages prohibited from applying P would drop to about 16.5% and 6%, respectively.Overall, based upon this example, more than 60% of the farms that were required to calculate aP-Index would have been able to adjust management practices or add BMPs to lessen or removeP restrictions. However, this percentage is still likely to overestimate the farms impacted as thefour farms examined were selected as worst case scenarios in counties with a higher thanaverage percentage of P problems. In addition, this example was based upon P-Indexcalculations using PSC Book values. If WEP-based PSC values were used, it is likely that thepercentage of farms with P restrictions would be even lower still.Phosphorus Source Coefficient: Lab AnalysisThere have been numerous publications regarding analytical tests to determine the availabilityof manure P and its contribution to P runoff (Kleinman et al 2007; Kleinman et al 2005; Elliott,H.A. 2006; Sharpley et al 2004; Studnicka et al 2011). It stands to reason that a specific test of amanure sample would be a better determinant of its available P relative to a generalized factor.The question then becomes how good are the analytical tests at accurately determining manureP availability? The PA P-Index uses a WEP analytical protocol described in Kleinman et al(2007.) This test essentially dissolves water soluble P out of manure samples by swirlingmeasured quantities of manure in certain volumes of water for set periods of time. The Pconcentration in the water extract is then analyzed to yield the water extractable P (or WEP.)Studnicka et al (2011) reviewed the Kleinmann et al (2007) extraction protocol and determinedthat pre-analysis manure handling could affect WEP results but reported that those effects wereminimized and extractions better predicted spring P runoff concentrations when the manure towater extraction ratio was 1:1000 (i.e. 0.25 g of manure in 250 ml of water). These contrast withPage 3

1:100 extraction ratio (i.e. 2.5 g of manure in 250 ml of water or an equivalent ratio) which is thecurrent standard procedure approved for use in calculating the PA P-Index (based uponKleinman et al. 2007). Studnicka et al (2011) found the 1:1000 water extraction ratio producedWEP estimates significantly higher than found with the 1:100 extraction ratio. Additionally,Studnicka et al (2007) found that WEP analysis of available manure P applied in the fall werenot well correlated with P runoff rates but were better predicted by the rate of available manureP applied. Further, they found that the runoff-to-rainfall ratio was the best predictor of runoff Pconcentrations across all seasons. In springtime, more rainfall infiltrates the soil relative to thefall and hence could help to explain why fall runoff P rates were higher than those during springapplication. However, as the runoff-to-rainfall ratios would not be known during the time ofmanure application, this relationship is not useable to determine allowable manure Papplication rates but rather would be valuable for modeling P runoff after the fact.Studnicka et al (2011) used a relatively small sample (0.25 g) relative to Kleinman et al (2007:0.5 – 100 g sample sizes evaluated). While Kleinmann et al (2007) found no relationshipbetween the weight of the sample and the relationship to dissolved P runoff, small sample sizescould be a problem with heterogeneous samples such as poultry litter (because of wood chips.)Phosphorus Source Coefficient: Influence on Allowable Manure PhosphorusTo determine the influence of the PSC value on allowable manure P application rates, anexample from the Pennsylvania Phosphorus Index: Version 2 Users Guide (Beegle et al 2009)was modified and the maximum allowable manure application rates were calculated at 4different PSC values (Figure 1). Phosphorus solubility coefficients used in the calculation rangedfrom 0.8, which is the book value for dairy manure, to 0.2, which resulted in manure applicationbased upon crop nitrogen needs (i.e. no P application limits.) The specific conditions in themodified example P-Index calculations are provided in Table 1. As the Mehlich-3 soil test Plevels were above 200 ppm (201 ppm in this example), the need to calculate a P-Index wastriggered 1 . Under the example conditions, the P-Index calculation for manure application basedupon crop nitrogen needs resulted in a Very High P-Index rating (129) which would not allowany phosphorus to be applied.The P-Index was recalculated to find the maximum allowable manure P application rates foreach of the PSC values. Based upon the PSC Book value for dairy manure (0.8), the maximumallowable P rate was equivalent to crop removal (50 lbs P2O5/A) with a P-Index ranking of High(P-Index =86). The maximum allowable P application rates for PSC values of 0.6, 0.4, and 0.2were 52, 79 and 117 lbs P2O5/A, respectively. The P-Index ratings for the three PSC valuesbelow the Book value were in the Medium category (79, 79, 72, respectively) allowing nutrientsto be applied at nitrogen crop requirements (or at least as high a P application rate as wouldmaintain a P-Index below 80.) Only at the PSC of 0.2 did the P application rate actually equalthe rate at the maximum allowable nitrogen application rate.1 Actually the example in Beegle et al 2009 shows a Mehlich-3 soil test concentration of 195 ppm whichwould not trigger the part B requirement although a P-Index was calculated for this farm field. For thepurpose of the exercise in this report, a soil test concentration of 201 ppm was assumed.Page 4

Thus in this example, the allowable application rate of manure P was sensitive to the PSC value.While no centralized repository of PSC values are available for review, based upon a personalcommunication with Dr Beegle, the WEP-based PSC values he has seen are quite a bit lowerthan the Book values. According to Dr. Beegle, the PSC Book values were set at the upperbounds of the expected PSC values so it was not surprising to him that the WEP-based PSCvalues were lower.140Allowable Manure Phosphorus(lbs P2O5/A)1201008060402000.8 (H) 0.6 (M) 0.4 (M) 0.2 (M)Phosphorus Solubility Coefficient (P-Index Rating)Figure 1. An example of the influence of the Phosphorus Solubility Coefficient on the allowableapplication rate of manure phosphorus. This example is adapted from Beegle et al (2009),Appendix 5, Scenario 3. The conditions are summarized in Table 1.Page 5

Table 1. Conditions assumed in example displayed in Figure 1. (Adapted from Beegle et al(2009)Soil Test Levels (Mehlich-3) 201 ppm PCrop; Planned YieldCorn; 125 bu/AOther P Nutrient Applied 0Manure Group: Application Dairy; SpringSeasonN Balanced Manure Rate 11,905(gal/A)Planned Manure Rate (gal/A) 9000*Manure Nutrients Applied at 76 lbs N; 117 lbs P #Planned Rate (lbs N or P)Fertilizer Application Method 0.2Factor: Placed or injected 2” ormore deepManure Application Method 0.6Factor: Incorporated >1 week ornot incorporated followingapplication in April to OctoberPhosphorus Source Coefficients 0.8, 0.6, 0.4, 0.2Erosion Factor: Soil Loss 4(ton/acre/yr)Runoff potential Factor: 6Drainage class is somewhatpoorSubsurface drainage: none 0Contributing Distance: 100 to 6199 ft. or

It is worth noting that the PSC Book values for the various manures has also changed fromVersion 1 to Version 2 (Table 2). The poultry categories as well as liquid dairy that were 0.9 inVersion 1 were reduced to 0.8 in Version 2. The biosolids catagories which had PSC’s of 0.3 inVersion 1, were all increased to 0.4 in Version 2. A PSC for horse manure is also added toVersion 2.Table 2. Organic phosphorus source availability coefficientsOrganic Source Version 1 PSC* Version 2 PSC +Swine slurry 1.0 1.0Poultry Broiler 0.8 0.8 Layer 0.9 0.8 Turkey 0.9 0.8 Duck 0.9 0.8Dairy Liquid 0.9 0.8 Bedded pack 0.8 0.8 Beef 0.8 0.8Horse Not Provided 0.8Alum treated manure 0.5Biosolids Biological nutrient removal 0.8 0.8 Alkaline stabilized 0.4 0.4 Conventionally stabilized 0.3 0.4 Composted 0.3 0.4 Heat-dried 0.2 0.4 Advanced-alkaline stabilized 0.2 0.4*Beegle et al 2006+Beegle et al 2009The Influence of Phosphorus Solubility Coefficients on Phosphorus Index ValuesGiven the lack of data on actual WEP-based PSC values, a set of hypothetical calculationsintended to show the resulting P-Index values at PSC values across the range of possibilities wasconducted. Nutrient management data from the Appendix within Kogelmann et al. (2004) wererecalculated with PSC values ranging from Book values to o.1. All the examples presented inKogelmann et al (2004) are from livestock operations in Lancaster and Snyder Counties andwere calculated with Book PSC values before any modifications in application rates or methodsor BMPs were considered. Specifically, in the hypothetical calculations, the PSC values neededto reduce P-Index values from one category to a lower P-Index category were determined andthe quantity of change in both the PSC and resulting P-Index from the original values wasPage 7

plotted (Figure 2). By lowering the P-Index ranking categories, P application restrictions wouldbe reduced or removed. For examples initially in the Very High P-Index category, PSC valuesnecessary to reduce the P-Index ranking to High and Medium were determined with thefollowing exceptions. In one case, the minimum PSC (0.1) did not reduce the P-Index categoryfrom the Very High ranking. In 3 other cases, the minimum PSC only lowered the P-Index fromthe Very High to the High ranking. For examples with P-Index values in the High rank, PSCvalues necessary to reduce the P-Index to Medium were calculated.Quantity of P-Index change120100806040200P-Index change vs. PSCchange0 0.2 0.4 0.6 0.8 1y = 83.143x + 0.0752R² = 0.5791PI changeQuantity of PSC reduction from "Book value"Linear (PI change)Figure 2. Change of P-Index (PI) versus the reduction in PSC from “Book value.” Data adaptedfrom Kogelmann et al. 2004.Based upon this analysis, the reduction in PSC values was significantly correlated with thereductions in the P-Index ratings (P>.001; R2 = 0.58.). For each reduction in PSC of 0.1, acorresponding reduction of about 8 P-Index units is predicted, on average. This relationshipseems especially well correlated for reductions in PSC values from Book values of less than 0.3units.The increase variability in the relationship between PSC reductions and change in P-Indices asthe level of PSC reduction increases may be related to the variability in the influence of thesource and transport terms. Kogelmann et al (2004) found that about 50% of the P restrictionson farms in Lancaster County were due to high P sources, either from high soil tests or highmanure P application rates. Transport factors were the primary concern in 21% of the cases andfor the remaindering 29%, both source and transport contributed equally. In Snyder County,transport factors and source factors were found to be about equal, with transport factorsshowing a slightly higher influence on P-Index rankings.Page 8

Phosphorus Index Ranking and Allowable Phosphorus RunoffUltimately, the importance of the P-Index and the phosphorus management it engenders isrelated to how much P is leaving the fields. Consequently, one of the most important aspects ofthe P-Index is how much P runoff it is designed to allow. Sharpley et al (2001) showed that therelationship between soil test P and runoff shows a break point at a soil test P of 200 mgP/l(mg/l = ppm) based upon a split line model (Figure 3.) Above 200 ppm P, runoffconcentrations increase at a higher rate as soil P increases relative to the rate below the 200ppm threshold. Sharpley et al (2001) noted that this break point is similar to the soil Pthreshold proposed for the Pennsylvania PI by Beegle (1999.) Sharpley et al (2001) estimatedthat on average, dissolved P represents the major portion (64%) of total P transported in surfacerunoff for soils that have not received manure within 3 weeks of measurements. When manurewas applied, however, dissolved and total P in runoff was much higher and no longer correlatedwith soil P. This can be seen in Figure 3 by looking at the symbols representing treatments withmanure applications. These data points all show much higher P runoff relative to that predictedfrom soil only. This is one of the major rationales for using a P-Index instead of the simple soiltest P threshold to manage P application.Figure 3. Relationship between the concentration of dissolved P in subsurface runoffPage 9

and Mehlich-3 extractable soil P concentration (Sharpley et al 2001)When measured farm field runoff was correlated with the P-Index, the relationship betweencombined soil and manure P runoff and P-Index was much improved over using the soil Pconcentration alone (Figs 3, 4 and 5). These results support the value of the P-Index as anappropriate estimator of runoff over using soil P levels alone. At the thresholds where the P-Index ranking increases from Medium to High, and from High to Very High, the concentrationof total P in runoff was approximately 1.0 and 1.6 mg P/l, respectively (Figure 4). The total Ploss in runoff at the threshold where the P-Index ranking increased from medium to high, andfrom high to very high, was approximately 200 and 350 g P/ha (Figure 5.) The P concentrationand loss values in Figures 4 and 5, respectively, are the levels of P allowed to be lost from thefield edge which are designed into the PA P-Index.Figure 4. Relationship between the concentration of dissolved and total P in surface runoff andthe P-Index rating for sites in fields where no P had been applied within the last six months andwhere fertilizer or manure had been applied within three weeks of rainfall. (Sharpley et al 2001)Page 10

Figure 5. Relationship between the loss of dissolved and total P in surface runoff andthe P-Index rating for sites in fields where no P had been applied within the last sixmonths and where fertilizer and manure had been applied within three weeks of rainfall.(Sharpley et al 2001)However, the relationships in Sharpley et al (2001) between P loss and the established P-Indexrankings is based upon manure P availability being calculated from total P in the manure,adjusted only by a loss factor for application and timing. No PSC, Book value or otherwise isused. If WEP-measurement based PSC are used and they are substantially lower, therelationship seen in Figures 4 and 5 may no longer hold. Granted there are numerous studieswhich show a significant relationship between WEP and dissolve P runoff. However, one wouldsuspect that at minimum, even if the relative relationship between P-Index and P loss in runoffis maintained with WEP-measurement based manure PSC’s, the curves would be shiftedupward, allowing more P runoff than previously estimated at any particular P-Index value.Based upon my survey of the literature, I have seen no studies which compare the P loss inrunoff based upon P-Indices calculated from WEP-measurement based PSCs. It seems all theanalyses upon which the P-Index rankings were established were conducted either with Bookvalue PSC’s or no PSC factor. Perhaps the Sharpley et al (2001) analyses overestimated theactual available manure P because no PSC correction was applied. However, thatPage 11

overestimation is incorporated into the establishment of the P-Index ranking thresholds atcertain quantities of allowable P loss. When WEP-based PSCs are used, the P-Indices that resultare lower than those calculated using Book value P-Indices, all else being equal, however, theactual P loss would not have changed. Hence, the amount of P loss across the P-Index rankingswould be higher than that modeled by Sharpley et al (2001).While it seems appropriate that construction of the P-Index model be undertaken byagricultural technical experts, the setting of the allowable P loss from the farm field edge is apolicy decision, beyond the technical modeling of P delivery. Beegle (pers. comm.) suggestedthat the P-Index model thresholds were set with reference to the amount of P allowed to bedischarged by waste water treatment plants with strict effluent limits. Further, Beegle offeredthat the P-Index was designed to identify risk levels of P runoff not specific loss rates of P.However, it is appropriate to ask whether setting farm field runoff at a P concentrationequivalent to waste water treatment plant effluent is appropriate? (Given the use of WEPmeasurementbased PSC’s, the P losses could be even higher.) The answer to this question maybe best addressed by trying to better understand the impact of setting the P-Index rankingthresholds at certain levels of P runoff. What would be the loading impact if all the farms thathave P-Indices which require consideration of phosphorus loss, have P runoff at 200 or 350 gP/ha? The Sharpley et al (2001) model also assumes some specific volume of runoff from farms;what is that volume and how does that value influence the estimate of loss of P from farms? Toallow a better assessment of the impacts of P loading from manure application, the loss of Pfrom farm fields using WEP-measurement based PSC’s in aggregate across a watershed shouldbe modeled.Pennsylvania changed the variables by which it allows nutrient managers to determineappropriate P management but there has been no coordinated effort to monitor how this changehas affected actual P management. The Commonwealth needs to collect data on P management,P-Indices and PSC’s so it can evaluate how the current P-Index management approach isworking. Models relating P-Index rankings to P runoff need to be recalculated using the newparameters. Furthermore, targeted watershed monitoring of actual farm field P loss andtransport in rivers based upon the current management strategies should be undertaken.Over the long term, the current approach to agricultural P management is unsustainable. MoreP is being imported into counties with high livestock and poultry densities within feed grainsthan is being exported as agricultural products (Gburek et al 2000.) This imbalance means Pwill continue to accumulate in soils and the problem of loss from farm fields will continue to getworse. Attention needs to be given to a long term solution that restores the import/export Pbalance within a watershed.ConclusionsChanges in the P-Index between Version 1 and Version 2 are likely to result in: a) more farmfields assessed for risk of P loss given the addition of 2 conditions to the Part A Screening test,but; b) fewer fields having P application restrictions or having lesser P restrictions as the WEPmeasurementbased PSC’s are likely to lower P-Index rankings. The scientific support forPage 12

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

Kleinman, P.J.A., A.M. Wolf, A.N. Sharpley, D.B. Beegle and L.S. Saporito. 2005. Survey ofwater-extractable phosphorus in livestock manures. Soil Sci. Soc. Am. J. 69:701-708.Kleinman, P. and others. 2007. Selection of a water-extractable phosphorus test for manuresand biosolids as an indicator of runoff loss potential. J. Environ. Qual. 326:1357-1367.Kogelmann, W.J., R.B. Bryant, H.S. Lin, D.B. Beegle, and J.L Weld. 2006. Local assessments ofthe impacts of phosphorus index implementation in Pennsylvania. J. Soil and WaterConservation. 61:20-30.Kogelmann, W.J., H.Lin, D. Beegle, R. Bryant and J. Weld. 2004. Assessing The Impacts Of P-Index Implementation in Pennsylvania: Phase II Project Report. Submitted to: PennsylvaniaState Conservation Commission, PA Dept. of Agriculture, Harrisburg, PA.(http://panutrientmgmt.cas.psu.edu/pdf/p_index_reportII.pdf)Kogelmann, W.J., H.Lin, and R. Bryant. 2002. A Statewide Assessment of the Impacts of P-Index in Pennsylvania: Phase 1 Report. Submitted to Pennsylvania State ConservationCommission. Pennsylvania Department of Agriculture, Harrisburg, PA.(http://panutrientmgmt.cas.psu.edu/pdf/p_index_report.pdf)Kogelmann, W.J., H.Lin, R. Bryant, D. Beegle, Wolf, A.M., and Petersen, G.W. 2004. A statwideassessment of the impacts of phosphorus-index implemntationin Pennsylvania. J. of Soil andWater Conservation. 59:9-18.Sharpley, A.N., and others. 2011. Revision of the 590 Nutrient Management Standard: SERA-17Recommendations. Southern Cooperative Series Bulletin No. 412.(http://www.sera17.ext.vt.edu/Documents/590Recommends2011.pdf)Sharpley, A.N., R.W. McDowell, and P.J.A. Kleinman. 2004. Amounts, forms, and solubility orphosphorus in soils receiving manure. Soil Sci. Soc. Am. J. 68:2048-2057.Sharpley, A.N., R.W. McDowell, J.L. Weld, P.J.A. Kleinman. 2001. Assessing site vulnerability tophosphorus loss in an agricultural watershed. J. Environ. Qual. 30:2026-2036.Studnicka, J.S., L.G. Bundy, T.W. Andraski, L.W. Good, and M.J. Powell. 2011. MeasuringWater-extractable phosphorus in manures to predict phosphorus concentrations in runoff.Communications inSoil Science and Plant Analysis 42: 10712-1084.Page 15