ABSTRACTS FROM THE ENVIRONMENTAL SOIL MANAGEMENT
RESEARCH GROUP

Coale, F.J., J.T Sims, and A.B. Leytem. 2002. Accelerated deployment of an agricultural nutrient management tool: The Maryland phosphorus site index. J. Environ. Qual. 31:1471-1476. 

In 1998, the Maryland legislature mandated nitrogen (N) and phosphorus (P) nutrient management planning for nearly all of Maryland's commercial agricultural operations. State regulations required that a phosphorus indexing tool (P Index) be used for determining the potential for P losses from agricultural land, even though a reliable P Index did not exist. The development and assessment of the P Index as a dependable tool for the evaluation of the potential for P losses was constrained by a very aggressive implementation schedule imposed by state regulations. The Maryland Phosphorus Site Index (PSI) was evaluated on 646 state-representative field sites beginning in the spring of 1999 and continuing through the spring of 2000. Of the representative fields, 69% were determined to have a "low" P loss rating, 19% were in the "medium" P loss rating category, 8% were determined to be a "high" risk for P loss, and 4% rated as "very high" P loss potential. Fifty-five percent of the fields evaluated had soil test phosphorus (STP) levels less than the 75 mg kg^-1 Mehlich-1 P environmental threshold established by state regulations. The frequency distribution of PSI performance was evaluated for several subcategories of the statewide data set. The Maryland PSI will be deployed for use in constructing farm nutrient management plans well before its predictive capabilities can be objectively and rigorously validated. Field validation is essential. In the meantime, the Maryland PSI should function adequately as a tool to assist in the prioritization of field P loss risk potential.

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Phytoextraction, a remediation strategy for lead (Pb)-contaminated soils that removes soil Pb through plant uptake and harvest, may be enhanced by use of synthetic chelates that increase soil Pb solubility and plant Pb uptake. We evaluated seven chelates (CDTA, DTPA, EDDHA, EGTA, HEDTA, HEIDA, and NTA) applied at three rates (5, 50, and 500 mM, equivalent to 0.2, 2.0 and 20 mmol total chelate kg soil^-1) for their effectiveness in desorbing Pb from four Pb-contaminated soils (total Pb 1278 to 14349 mg kg^-1). The three most effective chelates (CDTA, DTPA, and HEDTA) were then used in greenhouse studies with an uncontaminated soil and a Pb-contaminated soil (total Pb=3212 mg kg^-1) to evaluate the effect of chelate type and rate on growth, Pb uptake, and plant elemental composition. Lead desorption varied with chelate and soil and increased with chelate rate, averaging 948 mg Pb kg^-1 at the 20 mmol kg^-1 rate vs. 28 mg Pb kg^-1 by the control. The general ranking of chelate effectiveness, based on the mass of Pb desorbed, was HEDTA > CDTA > DTPA > EGTA > HEIDA > EDDHA ~ NTA. Greenhouse results with the uncontaminated soil showed that the highest chelate rate resulted in lower plant dry weights, increased plant P, Ca, Mg, Cu, Fe, Mn, and Zn, and decreased plant K. Plant uptake of Pb from the Pb-contaminated soil was enhanced by CDTA, DTPA, and HEDTA, but with even the most effective treatment (corn, high CDTA rate) the amount of Pb removed was rather low (0.4 kg Pb ha^-1 ). Lead extractable by TCLP (Toxicity Characteristic Leaching Procedure) was increased from 9 mg L^-1 in the control to from 47-174 mg L^-1 in soils treated with 20 mmol kg^-1 CDTA or DTPA and chelates generally caused a shift in Pb from resistant to more soluble chemical fractions. Future research should focus on optimizing the soil, plant, and water management practices needed to achieve adequate plant biomass for significant Pb removal, while avoiding off-site transport of Pb by leaching and surface runoff.

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Dentel, S.K., J.T. Sims, and J.T. Mah. 2001. Nutrient limitations - An update on issues with phosphorus. Presented at the symposium, "Innovative processes to produce useful materials and energy from biosolids and animal manure," June 6-8. 

Legislation in the mid-Atlantic area, and elsewhere globally is shifting nutrient management planning efforts in the direction of mandating controls on phosphorus (P) losses to surface waters and shallow ground waters, in addition to the established focus on potential nitrogen (N) losses. A systematic assessment of the risks of biosolids-P application to soils becomes essential. When biosolids are applied to soils, it is apparent that the availability of the P should be considered when determining appropriate loading, but this may vary according to the type of biosolids used. Accordingly, this study examined various biosolids samples to compare these properties, including many different biosolids and a set of P fractionations. An initial drying procedure at 60^oC instead of 105^oC was first developed in order to preserve fractionation characteristics. Findings include the general uniformity of P fractionation in terms of total P, across a suite of samples, but variability of soluble vs. insoluble fractions according to the use of biological P removal vs. chemical precipitant usage. A cationic polymer was indicated to remove some P from the soluble fraction.

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A study was conducted to develop conversion equations between the five soil test extractants commonly used by public and private soil testing laboratories serving clients in the mid-Atlantic United States. Three hundred soil samples were selected from among the samples submitted to the University of Delaware Soil Testing Program for routine fertility analysis. The samples were extracted with Mehlich 1, Mehlich 3, Bray P1, 1 N  pH 7.0 ammonium acetate and 0.1 N HCl and analyzed for phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), zinc (Zn), copper (Cu), and iron (Fe), as appropriate to the method. 

Significant linear relationships suitable for use as conversion equations were obtained between all extractants across a wide range of soil concentrations. Analysis of the 95% confidence bounds around the predictive equations showed large confidence intervals for some nutrient-extractant combinations (e.g., P, Mn, and Fe). Separation of the data into sub-populations based upon nutrient concentration (e.g., Mehlich 3P < or > 200 mg P dm^-3) and subsequent statistical analysis reduced the width of the confidence interval for some, but not all, relationships. For nutrient-extractant combinations where multiple relationships have been produced for specific concentration ranges, selection of the appropriate equation should be made based upon the intended application of the resulting data and the relevant concentration range (e.g., development of agronomic nutrient recommendations would require accuracy at "low P" concentrations versus limiting P application might require accuracy at "high" P concentrations). 

Statistical analysis of the data set using regression analysis with the "no intercept" option produced simple conversion factors that could be used to rapidly and easily convert the results obtained with one soil tst to those of another extractant. These "simple conversion factors" had slopes and confidence intervals that were comparable to those produced using standard regression analysis. The absence of an intercept component in the resulting relationship, however, would make these conversion factors more simplistic and less cumbersome for clients to use when comparing soil test results.

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Effective nutrient management requires an accurate accounting of nutrients removed from soils in the harvested portion of a crop. Because the typical crop nutrient values that have historically been used may be different under current production practices, a study was conducted to measure nutrient uptake in grain harvested in 1998 and 1999 from 23 site-years in the Mid-Atlantic region of the USA. There were 10 hybrids included in the study, but each site grew only one hybrid each year. Corn (Zea mays L.) production practices followed local state extension recommendations. Minimum, maximum, and mean corn grain yields were 4.9, 16.7, and 10.3 Mg ha^-1. Nutrient concentrations were determined on grain samples oven-dried at 70°C for 24 h. Minimum, maximum, and median nutrient concentration values were as follows: 10.2, 15.0, and 12.9 g N kg^-1; 2.2, 5.4, and 3.8 g P kg^-1; 3.1, 6.2, and 4.8 g K kg^-1; 0.13, 0.45, and 0.28 g Ca kg^-1; 0.88, 2.18, and 1.45 g Mg kg^-1; 0.9, 1.4, and 1.0 g S kg^-1; 9.0, 89.5, and 33.6 mg Fe kg^-1; 15.0, 34.5, and 26.8 mg Zn kg^-1; 1.0, 9.8, and 5.3 mg Mn kg^-1; 1.0, 5.8, and 3.0 mg Cu kg^-1; and 2.3, 10.0, and 5.5 mg B kg^-1. Median nutrient uptake values found in this study are similar to commonly used book values, but there was considerable variation among samples of corn grain. Concentrations of P and K in grain were positively associated with yield level, and concentrations of grain P were positively correlated with Mehlich-3 soil test P. The variability in nutrient removal values seen in this study, even for the same hybrid, raises questions about the usefulness of average values for estimating crop nutrient removal across a range of cropping conditions. Research is needed to identify or develop a means to correct for the sources of variability

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Heckman, J.R., T. Morris, J.T. Sims, J.B. Sieczka, U. Krogmann, P. Nitzsche, and R. Ashley. 2002. Pre-sidedress soil nitrate test is effective for fall cabbage. Hort Sci. 37:113-117. 

The pre-sidedress soil nitrate test (PSNT) was evaluated in 27 fields in New Jersey, 6 in Connecticut, 5 in Delaware, and 2 on Long Island in New York for its ability to predict whether sidedress N is needed to grow fall cabbage (Brassica oleracea var.) capitata) as a double crop. Soil NO₃-N concentrations measured on 20 field sites on the day of transplanting and 14 days after transplanting indicated that NO₃-N concentrations over this time period increase, and that residues from the previous crop were not causing immobilization of soil mineral N. The relationship between soil NO₃-N concentration measured 14 days after transplanting and relative yields of marketable cabbage heads was examined using Cate-Nelson analysis to define the PSNT critical level. Soil NO₃-N concentrations > 25 mg kg^-1 were associated with relative yields >92%. The success rate for the PSNT critical concentration was 84% for predicting whether sidedress N was needed. Soil N concentrations below the PSNT critical level are useful for inversely adjusting sidedress N fertilizer and the practice of soil NO₃-N testing may be extendable to other cole crops with similar N requirements.

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Leytem, A.B., J.T. Sims, and F.J. Coale. 2003. On-farm evaluation of a phosphorus site index for Delaware. J. Soil Water Conserv. 58:89-97. 

The contribution of phosphorus (P) to non-point source (NPS) pollution of surface and groundwaters is a serious environmental problem in Delaware. In 1999, the Delaware Nutrient Management Act was passed limiting application of P on "high" P soils to a "three year crop removal" rate or to the amount recommended by a University of Delaware P site index. The Delaware P site index was developed and evaluation on seven farms in Delaware, through a joint effort between the universities of Delaware and Maryland. Results showed that 78% of fields evaluated were in the "low" risk category, with the remaining 22% falling into the "medium" (6%), "high" (7%), and "very high" (9%) risk categories. The components of the index found to have the greatest influence on P site index ratings were soil erosion, subsurface drainage, leaching potential, distance from field to surface water, soil test P and organic P application rates and methods. P site index ratings were found to vary by year, depending on manure applications, suggesting a need for yearly P site index evaluations or averages over a cropping rotation. The P site index worked well for identifying fields with differing relative potential risks of P loss; however, validation of these P loss assessments is needed to ensure that the risk categories assigned are sufficiently protective of water quality. Continual monitoring, analysis, and improvement of the P site index are needed to ensure that it remains a useful tool for P based nutrient management planning in the future.

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Maguire, R.O., J.T. Sims, and T.J. Applegate. 2005. Phytase supplementation and reduced-phosphorus turkey diets reduce phosphorus loss in runoff following litter application. J. Environ. Qual. 34:359-369. 

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Diet modification to decrease phosphorus (P) concentration in animal feeds and manures can reduce surpluses of manure P in areas of intensive animal production. We generated turkey and broiler litters from two and three flock trials, respectively, using diets that ranged from "high" to "low" in non-phytate phosphorus (NPP) and some of which contained feed additives such as phytase. Phosphorus forms in selected litters were analyzed by sequential chemical fractionation and solution ³¹P nuclear magnetic resonance (NMR) spectroscopy. Selected litters were also incubated with four contrasting soils. Reducing dietary NPP and using phytase decreased total P in litters by up to 38%. Water-soluble phosphorus (WSP) in litters was decreased 21 to 44% by feeding NPP closer to animal requirement, but was not affected by phytase addition. Solution ³¹P NMR spectroscopy showed that feeding NPP closer to requirement decreased orthophosphate in litters by an average of 38% and that adding phytase to feed did not increase the concentration of orthophosphate in litters. Phytase also decreased phytate P in litters by 25 to 38%, demonstrating that it increases phytate P hydrolysis. Incorporation of litters with soils at the same total P rate increased WSP in soils relative to the control; this increase was correlated to soluble P added with litters at 5 d, but not by 29 d. Changes in soil Mehlich-3 phosphorus (M3-P) were related to total P added in litter, rather than soluble P. We conclude that feeding NPP closer to requirement and using feed additives such as phytase decrease total P concentrations in litters, while having little effect on P solubility in litters and amended soils.

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Strategies to Reduce the Phosphorus Concentration in Animal Feeds

Intensification of animal agriculture has led to the production of more P in manure than is required in local crops. Concerns over excessive losses of P from manured soils have now led to interest in manipulating animal diets to lower P concentrations in diets, and subsequently P excretion in manure, while sustaining animal production. Phosphorus in animal diets comes from the P present in basic feed ingredients and from mineral P supplementation. There are two main strategies for lowering P concentrations in animal diets: (i) reducing P over-feeding, which is a common practice (often called insurance feeding or safety margin), and (ii) increasing the bioavailability of feed P and improving P utilization efficiency by the animals. Reducing the over-feeding of P can apply to all animal species, while increasing the digestibility of P applies mostly to monogastric animals (swine and poultry) that lack the ability to digest the phytate-P that makes up about two thirds of the P in corn and soybean meal. Reducing over-feeding of P involves clearly identifying critical levels of P for all species and then formulating feeds as closely as possible to these recommendations. As animals age, they generally require less P as their bone development matures. Increasing the number of feeding phases, with a lowering of the P concentration in each successive phase as the animals mature, can also reduce over-feeding of P. To increase the utilization of P fed to monogastrics there are several strategies that include, (a) adding the enzyme phytase to increase digestion of phytate-P, (b) adding citric acid to lower gut pH and increase the effectiveness of phytase, (c) Adding vitamin D3 or its derivatives to increase uptake of P from the gut, and (d) breeding of high available P (low phytate-P) crops for animal feeds.

Impact of Diet Modification on Phosphorus in Manures and Losses in Runoff

Using currently available diet modification strategies, total P concentration in manure can be decreased by 40 % for poultry, 50 % for swine and 30 % for dairy cattle (CAST, 2002). For dairy cattle fed with diets containing a lower amount of P, not only is total faecal P decreased but more importantly the decrease is mostly in the water soluble fraction (Dou et al., 2002). Reducing the overfeeding of P in poultry diets will reduce the P concentration and solubility in manures generated (CAST, 2002; Maguire et al., 2004). However, for monogastric animals, the use of the feed additive phytase has raised some concern due to its effect on the solubility of P in manure, as changes in manure soluble P may affect soluble P losses in runoff. Most of the literature shows that phytase in diets does not increase the concentration of soluble P in manures generated (Baxter et al., 2003; Maguire et al., 2004). However, in a broiler study, Vadas et al. (2004) found that phytase formulation in the diet increased soluble P in litters, although this did not translate into significantly greater soluble P losses in runoff. More research on the impact of phytase is needed to clarify the situation.

Concerns over soluble P losses following manure applications are generally short-term as soluble P additions usually affect only the first runoff event (Maguire et al., 2004). Over the long-term total P application controls changes in soil test P that, in turn, exerts a strong influence on P losses in runoff. Diet modification can be used to decrease P surpluses and hence soil test P increases, therefore diet modification can go a long way towards decreasing P losses from manure-amended soils.

Baxter, C.A., B.C. Joern, D.Ragland, J.S. Sands, and O. Adeola. 2003. Phytase, high-available-phosphorus corn, and storage effects on phosphorus levels in pig excreta. J. Environ. Qual. 32:1481-1489.

CAST (Council for Agricultural Science and Technology). 2002. Animal diet modification to decrease the potential for nitrogen and phosphorus pollution. Issue paper no. 21.

Dou, Z., K.F. Knowlton, R.A. Kohn, Z. Wu, L.D. Satter, G. Zhang, J.D. Toth, and J.D. Ferguson. 2002. Phosphorus characteristics of dairy feces affected by diets. J. Environ. Qual. 31:2058-2065.

Maguire, R.O., J.T. Sims, W.W. Saylor, B.L. Turner, R. Angel, and T.J. Applegate. 2004. Influence of phytase addition to poultry diets on phosphorus forms and solubility in litters and amended soils. J. Environ. Qual. Submitted.

Vadas, P.A., J.J. Meisinger, L.J. Sikora, and J.P. McMurtry. 2004. Effect of poultry diet on phosphorus loss in runoff from soils amended with poultry manure and compost. J. Environ. Qual. 33:749-756.

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It has become common to use feed additives (such as phytase) to increase the digestibility of phytate-P to monogastric animals, decreasing the need for P supplements to diets, and decreasing the total P content in manures. In this study, the effect of incorporating phytase / and 25-hydroxycholecalciferol (25OH-D3) in turkey diets on the solubility of P in turkey manures (TMs) and TM amended soils was investigated. Turkey manures were collected from turkeys fed (i) a normal diet, and three diets containing reduced non-phytate P (nPP) called (ii) P deficient, (iii) phytase, and (iv) phytase+25OH-D3. The TMs were added to five soils at the same total P rate (150 kg P ha-1) and incubated for 42 d. The dried TMs were analyzed for water soluble-P (WS-P) and total P, while the incubated soils were analyzed for pH, organic matter (OM), Mehlich-3 P, Al and Fe (M3-P, M3-Al and M3-Fe), water soluble-molybdate reactive P (WS-MRP) and organic-P (WS-OP). The normal diet produced TMs that had six times higher WS-P and >40% greater total P than any of the reduced nPP diets. Adding phytase to the reduced nPP diets did not increase the percentage of total P that was water soluble. As a result of its greater P content, TM from the normal diet increased soil WS-MRP, but not M3-P or WS-OP, to a greater extent than the reduced nPP diets. All TMs increased WS-MRP relative to the unamended soil, and these increases were inversely related to the M3 [Al+Fe] content of each soil. Converting from a normal turkey diet to one that contains reduced nPP and phytase / and 25OH-D3 shows potential for reducing total and soluble P in manures and soluble P in manure amended soils. As reduced nPP, phytase / and 25OH-D3 in diets lead to reduced TM total P, long-term applications of these reduced P TMs using nitrogen-based management, would be expected to reduce total P and Mehlich-3 P in soils, compared to TMs from normal diets.

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At any time, the phosphorus (P) concentration in surface waters is determined by a complex interaction of inputs of soluble P and sorption-desorption reactions of P with sediments. This study investigated what factors control P in solution when various soil aggregates were mixed, seen as being analogous to selective soil erosion events, transport, and mixing within river systems. Fifteen soils with widely differing properties were each separated into three aggregate size fractions (2-52 μm, 53-150 μm, and 151-2000 μm). Resin P, water-soluble phosphorus (WSP), and the phosphorus buffer capacity (PBC = resin P/WSP) were measured for each aggregate size fraction and WSP was also measured for 11 mixes of the aggregate fractions. The smallest aggregates tended to be enriched with resin P relative to the larger aggregates and the whole soils, while the opposite was true for WSP. As the PBC was a function of resin P and WSP, the PBC was greatest in the 2- to 52- μm aggregate size fraction in most cases. When two aggregate size fractions were mixed, the measured WSP was always lower than the predicted WSP (i.e., the average of the WSP in the two individual aggregates), indicating that WSP released by one aggregate fraction could be resorbed by another aggregate fraction. This resorption of P may result in lower than expected solution P concentration in some surface waters. The strength with which an eroded aggregate can release or resorb P to or from solution is in part determined by that aggregate's PBC.

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Maguire, R.O., and J.T. Sims. 2002. Measuring agronomic and environmental soil phosphorus saturation and predicting phosphorus leaching with Mehlich 3. Soil Sci. Soc. Am. J. 66:2033-2039. 

The role that soil testing can play in identifying agricultural soils with an increased potential for P loss is an important topic. Our research compared the Mehlich 3 P saturation ratio (M3-PSR) to the ammonium oxalate degree of P saturation (DPS_ox), and the M3-PSR was then evaluated for predicting agronomic and environmental soil P saturation thresholds. Intact soil columns (15-cm diameter, 20 cm deep) and soil samples were collected from five soil series that ranged in soil texture, chemical properties, and Mehlich 3 P. The soils were analyzed for pH, organic matter (OM) and oxalate and Mehlich 3 extractable P, Al and Fe. Each intact column was leached with the equivalent of 5 mm of rainfall and resulting leachate analyzed for P. Mehlich 3 extractable Al, Fe and P were closely related to oxalate extractable Al, Fe and P, although Mehlich 3 extracted only a small amount of Fe compared with oxalate. The M3-PSRs, calculated as the molar ratios of Mehlich 3 extractable P/[Al+Fe] (ratio I) and P/Al (ratio II), were well correlated to each other and to DPS_ox. All three P saturation measurements showed a threshold or change point above which the concentration of P in column leachate increased rapidly. Both the agronomic optimum M3PSRs and the environmental limit suggested in the Netherlands for DPS_ox (25%) were below the observed change point. The M3-PSR measured in a single Mehlich 3 extraction shows excellent promise for identifying soils that represent an increased risk for P leaching losses.

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Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that had a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water-soluble phosphorus (WSP), 0.01 M CaCl₂ P (CaCl₂-P), iron-strip phosphorus (FeO-P), and Mehlich-1 and Mehlich-3 extractable P, Al, and Fe. The Mehlich-3 P saturation ratio (M3-PSR) was calculated as the molar ratio of Mehlich-3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl₂-P, and FeO-P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich-1 P, Mehlich-3 P, and the M3-PSR), although the M3-PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich-3 P and M3-PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.

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Maguire, R.O., R.H. Foy, J.S. Bailey, and J.T. Sims. 2001. Estimation of the phosphorus sorption capacity of acidic soils in Ireland. Eur. J. Soil Sci. 52:479-487. 

The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Al_ox + Fe_ox), where Al_ox and Fe_ox are the amounts of aluminum and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil^-1 and a value of 0.5 is commonly used for the scaling factor in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (P_ox) so that DPS = P_ox/PSC.

The relation between PSC and Al_ox, Fe_ox, and P_ox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Al_ox and Fe_ox extracted, but there was also a negative correlation with P_ox. When PSC was calculated as the sum of the measure sorption after 252 days and P_ox, the multiple regression of PSC on Al_ox and Fe_ox gave the equation PSC = 36.6 + 0.61 Al_ox + 0.31 Fe_ox with a coefficient of determination (R²) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Al_ox and Fe_ox did not overlap, indicating a significantly larger regression coefficient of P sorption on Al_ox than on Fe_ox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Al_ox and Fe_ox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P<0.001), the impact of this variable was small as its inclusion in the multiple regression increased R² by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0 - 3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water-soluble P than either the Olsen or Morgan tests for P in soil.

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Soil testing to determine phosphorus (P) availability to crops is a well established process. Today, however, there is increasing emphasis on relating existing or new soil tests to the potential for P loss from soils to surface waters. The objective of this study was to determine how well short-term soil P measurements (water soluble P (WSP), Mehlich-1 P, degree of P saturation (DPS), and 1-day desorbable P) predicted long-term P release and P sorption in relation to soil properties. Topsoils and subsoils with widely differing properties were collected from four sites in Northern Ireland, the Republic of Ireland, and the U.S. mid-Atlantic coastal plain, with topsoils and subsoils sampled at each site. All soils were analyzed for water soluble P, Mehlich-1 P, oxalate extractable Al, Fe, and P (Al_ox, Fe_ox, P_ox), degree of P saturation (DPS = (P_ox/0.5[Al_ox +Fe_ox]) x 100, free [Al_ox + Fe_ox] = 0.5[Al_ox +Fe_ox]-P_ox), long-term desorbable P (using Fe-oxide-filled dialysis membranes), and long-term P sorption for "remaining P sorption capacity" (from a solution maintained at 5 mg P L^-1). Long-term desorbable P followed a pattern of initial fast P release followed by a slower release of P that was still in progress after 39 days. Water soluble P, Mehlich-1 P, and the DPS were all correlated with the cumulative amount of P desorbed in 39 days (r = 0.82*, 0.79*, and 0.83*, respectively). However, for short-term (1-day) desorbable P, correlations followed the order WSP (r = 0.94***) > DSP (r = 0.83*) > Mehlich-1 P (r = 0.72*). When P was added to the soils, all of the soils exhibited an initial period of rapid P sorption, followed by a period of slower sorption still in progress after 38 days. The soil components found to be related most closely to remaining P sorption capacity were free [Al_ox + Fe_ox] (r = 0.73*) and free Al_ox (r = 0.80*), indicating that amorphous Fe and Al are the major soil components responsible for long-term (38 days) P sorption. Overall, a single oxalate extraction for Al, Fe, and P proved to be most useful for predicting both long-term P release, through calculation of the DPS and for predicting the ability of the soils to sorb more P by calculating free [Al_ox + Fe_ox].

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Maguire, R.O., J.T. Sims, S.K. Dentel, F.J. Coale, and J.T. Mah. 2001. Relationships between biosolids treatment process and soil phosphorus availability. J. Environ. Qual. 30:1023-1033.

Laws mandating phosphorus (P)-based nutrient management plans have been passed in several U.S. Mid-Atlantic states. Biosolids (sewage sludge) are frequently applied to agricultural land and in this study we evaluated how biosolids treatment processes and biosolids P tests were related to P behavior in biosolids-amended soils. Eight biosolids generated by different treatment processes, with respect to digestion and iron (Fe), aluminum (Al), and lime addition, and a poultry litter (PL), were incubated with an Elkton silt loam (fine-silty, mixed, active, mesic Typic Endoaquult) and a Suffolk sandy loam (fine-loamy, siliceous, semiactive, thermic Typic Hapludult for 51 d. The amended soils were analyzed at 1 and 51 d for water-soluble P (WSP), iton-oxide strip-extractable P (FeO-P), Mehlich-1 P, and pH. The biosolids and PL were analyzed for P, Fe, and Al by USEPA 3050 acid-peroxide digestion and acid ammonium oxalate, Mehlich-1, and Mehlich 3 extractions. Biosolids and PL amendments increased extractable P in the Suffolk sandy loam to a greater extent than in the Elkton silt loam throughout the 51 d of the incubation. The trend of extractable WSP, FeO-P, and Mehlich-1 P generally followed the pattern: [soils amended with biosolids produced without the use of Fe or Al] > [PL and biosolids produced using Fe or Al and lime] > [biosolids produced using only Fe and Al salts]. Mehlich-3 P and the molar ratio of P to [Al + Fe] by either the USEPA 3050 digestion or oxalate extraction of the biosolids were good predictors of changes in soil-extractable P following biosolids but not PL amendment. Therefore, the testing of biosolids for P availability, rather than total P, is a more appropriate tool for predicting extractable P from the biosolids-amended soils used in this study.

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Phosphorus has been identified as a major factor involved in decreasing water quality through its role in eutrophication, and there is now a focus on controlling nonpoint agricultural P sources. This work was conducted to identify how biosolids applications under current regulations have affected the forms and release potential of P in agricultural soils. We collected samples from eight farms with a history of biosolids amendments, selecting fields that had setback areas (where biosolids applications were not permitted) to allow comparison of amended and unamended soils. We analyzed these soils for P fractions (soluble P, Al-P, Fe-P, reductant soluble P, and Ca-P; their sum equals total P), sequentially desorbable P (Fe-strip), oxalate P, Al and Fe, Mehlich-1 P, and the degree of P saturation. Our results show that following a N-based biosolids nutrient management plan can significantly increase total P (from 403 to 738 mg kg^-1) and initially desorbable P (from 32 to 61 mg kg^-1). The main soil components associated with P retention (Al_ox and Fe_ox) also tended to be increased by biosolids amendment and this may help mitigate P release. Biosolids amendment significantly increased Fe-P (from 137 to 311 mg kg^-1), probably due to Fe added to biosolids during production, and there was also a strong trend for higher Al-P where biosolids had been applied. Desorbable P was initially greatest from biosolids sites, but with increasing extractions, the release converged towards that from the setback areas. Mehlich-1 P and P_ox were good predictors of desorbable P release, as measured by one and five sequential extractions with Fe-strips. Desorbable P, by both one and five Fe-strip extractions, was more closely correlated with Al-P than Fe-P, especially in setback areas, indicating that Al-P is probably the most important source of desorbable P independent of biosolids amendment. This work indicates the importance of considering P availability at agricultural biosolids application sites and of maintaining setback areas near water bodies, where no biosolids may be applied, to reduce the risk of P losses.

Contact jtsims@udel.edu

There have been increased environmental concerns about agricultural P management, including land application of biosolids (municipal sewage sludge). This study investigated the influence of current N-based land application practices for biosolids on soil P. We collected soil samples from 11 biosolids application sites and from adjacent setback areas that had never received biosolids. These samples were analyzed for oxalate-extractable P (P_ox), aluminum (Al_ox), and iron (Fe_ox); degree of P saturation (DPS = (P_ox / 0.61[Al_ox + Fe_ox] x 100), Mehlich-1 P; iron-oxide strip-extractable P (FeO-P); and water-soluble P (WSP). In many cases Mehlich-1 P was excessive (>50 mg kg^-1), but this occurred in both application sites and setback areas. Biosolids application sites had significantly greater P_ox in the topsoils (0 to 20 cm) when averaged for all sites, with means of 589 and 296 mg kg^-1 in the application sites and setback areas, respectively. However, biosolids applications also increased [Al_ox + Fe_ox], which meant that the DPS was not always increased. There was a trend for higher P_ox and FeO-P in the biosolids-amended soil profiles (60-cm depth) and highest P concentrations were consistently found at the 0- to 5-cm depth. The net effect of biosolids applications on P_ox, relative to [Al_ox + Fe_ox], was related to FeO-P. Our data suggest that adding biosolids according to current N-based guidelines will lead to an accumulation of P in soils, but the release of this P may be mitigated by the associated increases in soil [Al_ox + Fe_ox].

Contact jtsims@udel.edu

Methods to identify agricultural soils that contribute to nonpoint source pollution of surface waters by phosphorus (P) are of increasing importance, particularly in areas with high animal densities (animal units per hectare of crop land). Our objective was to determine the relationship between agronomic soil test P (STP=Mehlich 1) and other soil P tests proposed to measure the potential for P loss by erosion, runoff, and leaching. We compared STP with soluble P, P in the "fast desorbing pool" (strip P), and soil P saturation for 127 soils (122 from Delaware and five from the Netherlands). Soil test P was significantly correlated with total P (r=0.57***, significant at the 0.001 level), soluble P (r=0.71***), strip P (r=0.84***), and oxalate-extractable P (P_ox; r=0.84***). Strip P was a better predictor of soluble P than STP (r²=0.76***). The ratio of strip P/P_ox (the percentage of reversibly sorbed P in the fast desorbing pool) increased as P sorption capacity, estimated from oxalate-extractable aluminum and iron (Al_ox + Fe_ox), decreased. We also determined the degree of P saturation (DPS) using three methods: Langmuir P sorption isotherms; oxalate extractions of P, Al, and Fe; and STP plus a single-point P sorption index (PSI). Soluble P, STP, and desorbable P increased for DPS values > 30%, similar to upper DPS limits used in the Netherlands and Belgium. Soils rated agronomically excessive in STP (>50 mg kg^-1) had higher ratios of soluble P, strip P, and P_ox to total P than those in agronomically optimum or lower categories.

Contact: mpautler@udel.edu

Non-agronomic environments, as well as agronomic settings are affected by soil phosphorus (P) levels. Soils that are over-fertilized with P defy principles of sustainable agriculture and increase the risk of non-point source pollution of surface waters. Delaware - especially Sussex County, site of a large, coastal watershed - has one of the most intensive poultry industries in the eastern United States and long-term application of animal wastes as fertilizers has elevated P levels in many soils to values well beyond those needed for crop production. To protect the quality of surface waters, it is necessary to minimize P accumulations to excessive levels in soils and the transport of P from soil to water bodies. Thus, establishing quantitative, predictive relationships between soil test P (i.e., Mehlich 1 P) and potentially desorbable P could be extremely useful in ongoing efforts to prioritize non-point source pollution control. Our specific objectives were to evaluate rapid analytical methods to assess desorbable P in soil and answer the following: Which rapid tests correlate well with the degree of P saturation (DPS) in soils? From an environmental standpoint, what is the best way to quantify the potential for P to be desorbed from soil?

Contact: mpautler@udel.edu

While alum amendments have shown to be effective in lowering water-soluble phosphate levels in poultry litter, the mechanism by which this occurs is not fully known. To determine the solid-state speciation of phosphate in litter samples, experiments were conducted with X-ray absorption near edge structure (XANES) spectroscopy. XANES analysis reveals that, in unamended samples, phosphate is present as weakly bound inorganic was well as some organic phosphate, with some dicalcium phosphate-type calcium phosphates also present. When alum is applied in the houses, XANES results suggest that it precipitates out as amorphous Al(OH)₃ and then reacts with phosphate via an adsorption mechanism. No evidence was found of aluminum phosphate precipitation in any samples.

Contact: jtsims@udel.edu

Penn, C.J., and J.T. Sims. 2002. Phosphorus forms in biosolids-amended soils and losses in runoff: Effects of wastewater treatment process. J. Environ. Qual. 31:1349-1361.

Continuous application of municipal biosolids to soils based on plant nitrogen (N) requirements can cause buildup of soil phosphorus (P) in excess of crop requirements; runoff from these soils can potentially contribute to nonpoint P pollution of surface waters. However, because biosolids are often produced using lime and/or metal salts, the potential for biosolids P to cause runoff P losses can vary with wastewater treatment plant (WWTP) process. This study was conducted to determine the effect of wastewater treatment process on the forms and amounts of P in biosolids, biosolids-amended soils, and in runoff from biosolids-amended soils. We amended two soil types with eight biosolids and a poultry litter (PL) at equal rates of total P (200 kg ha^-1); unamended soils were used as controls. All biosolids and amended soils were analyzed for various types of extractable P, inorganic P fractions, and the degree of P saturation (acid ammonium oxalate method). Amended soils were placed under a simulated rainfall and all runoff was collected and analyzed for dissolved reactive phosphorus (DRP), iron-oxide-coated filter paper strip-extractable phosphorus (FeO-P), and total phosphors (EPA₃₀₅₀ P). Results showed that biosolids produced with a biological nutrient removal (BNR) process caused the highest increases in extractable soil P and runoff DRP. Alternatively, biosolids produced with iron only consistently had the lowest extractable P and caused the lowest increases in extractable soil P and runoff DRP when added to soils. Differences in soil and biosolids extractable P levels as well as P runoff losses were related to the inorganic P forms of the biosolids.

Contact: jtsims@udel.edu

Introduction

Organic P sources vary widely in their P solubility and consequently, when applied to the soil, will have different relative risks for P loss to surface waters (Maguire et al. 2001; Codling et al. 2001). In the U.S., some P Site Indices have included P Source Coefficients (PSCs) to account for differences in P solubility between organic P sources. Preliminary research to develop PSCs has been conducted in the Mid-Atlantic (Leytem et al., 2004; Brandt and Elliott, 2003; Kleinman et al., 2002), however, final PSC values have not yet been widely adopted. Our objectives were to (i) compare the effects of animal manures and biosolids (sewage sludge) that varied in P solubility on P release from eight soils varying in properties important to P sorption and desorption; and (ii) develop a simple protocol that could be used by soil testing laboratories to determine field specific PSC values for the wide range of organic P sources now land applied in this region.

Materials and Methods

Six biosolids, two poultry litters, a dairy manure, a liquid swine manure, and inorganic P were incorporated into eight representative agricultural soils from DE, MD, PA, and VA at a rate of 135 kg ha-1 total P and incubated in 250-mL cups at 80% field capacity. Subsamples were analyzed for water soluble P (WSP) at 48 h and 30 d, pH, organic matter (OM), and Mehlich 3 (M3-) P, Ca, Fe, and Al at 30 d. Mehlich 3 P saturation ratio (M3-PSR molar ratio of M3P/[M3Fe + M3Al]) was also calculated. Effects of soil or P source could not be assessed individually due to significant soil by P source interactions. Therefore, soil/P Source pair means were compared to determine statistical differences between treatments for each soil, and between soils for each treatment.

Results and Conclusions

Biosolids and metal-salt treated manures generally contain higher concentrations of Al and Fe and consequently have lower WSP than untreated manures. When organic P sources are incorporated, it is believed that properties of these materials will control the solubility of added P. The influence of soil properties on P solubility in amended soils should not be overlooked. Incorporation of P sources into soils with low initial M3-PSR values caused no significant increases in WSP with respect to unamended soils and other P sources. However, when P sources were incorporated into soils with high M3-PSR values, untreated manures and inorganic P sources lead to increases in WSP that were significantly larger than when biosolids and treated manures were applied. This indicates that when soils become

increasingly saturated with respect to P, properties of the P source become more influential in the control of P solubility than soil properties. In all cases, soil properties influenced WSP after incorporation of organic P sources. Our results showed that application of organic P sources increased M3-P in all soils after 30 d when compared to unamended soils. In general, application of untreated manures and inorganic P lead to larger increases in WSP and M3P than biosolids or treated manures for all soils, regardless of initial soil P saturation. Regression analysis shows that measurement of organic P source WSP and initial soil M3-PSR could predict soluble P when organic P sources are incorporated into soils (R2=0.66). Analytical testing labs could use a 48 h incubation protocol to assess P solubility of organic P sources when incorporated with a variety of regional soils.

References

Brandt, R.C., and H.A. Elliott. 2003. Phosphorus runoff losses from surface-applied biosolids and dairy manure. Joint Residuals and Biosolids Mgmt Conf. Water Environ. Federation. February 19-22, Baltimore, MD.

Codling, E.E., R.L. Chaney, and C.L. Mulchi. 2001. Use of aluminum- and iron-rich residues to immobilize phosphorus in poultry litter and litter-amended soils. J. Environ. Qual. 29:1924-1931.

Kleinman, P.J.A., A.N. Sharpley, B.G. Moyer, and G.F. Elwinger. 2002. Effect of mineral and manure phosphorus sources on runoff phosphorus. J. Environ. Qual. 31:2026-2033.

Leytem, A.B, J.T. Sims, and F.J. Coale. 2004. Determination of phosphorus source coefficients for organic phosphours sources: Laboratory studies. J. Environ. Qual. 33:380-388.

Maguire, R.O., J.T. Sims, S.K. Dentel, F.J. Coale, and J.T. Mah. 2001. Relationships between biosolids treatment process and soil phosphorus availability. J. Environ. Qual. 30:1023-1033.

Contact ashober@udel.edu

The application of biosolids (sewage sludge) to agricultural soils provides phosphorus (P) in excess of crop needs when applied to meet the N needs of most agronomic crops. These over-applications can result in the buildup of P in soils to values well above those needed for optimum crop yields and also may increase risk of P losses to surface and ground waters. Because of concerns regarding the impact of P on water quality in the USA, many state and federal agencies now recommend or require P-based nutrient management plans for animal manures. Similar actions are now under consideration for the land application of biosolids. We reviewed the literature on this subject and conducted a national survey to determine if states had restrictions on P levels in biosolids-amended soils.  The literature review indicates that while the current N-based approach to biosolids management does result in increases of soil P, some properties of biosolids may mitigate the environmental risk to water quality associated with land application of P in biosolids. Results of the survey showed that 24 states have regulations or guidelines that can be imposed to restrict land application of biosolids based on P. Many of these states use numerical thresholds for P in biosolids-amended soils that are based on soil test P (STP) values that are much greater than the values considered to be agronomically beneficial. We suggest there is the need for a comprehensive environmental risk assessment of biosolids P. If risk assessment suggests the need for regulation of biosolids application, we suggest regulations be based on the P site index, which is the method being used by most states for animal manure management.

Contact ashober@udel.edu

Modern agricultural management practices for phosphorus (P), including soil testing, can no longer focus exclusively on soil fertility and agricultural productivity but must also address the role of agricultural P in nonpoint source pollution of surface waters. The eutrophication of streams, rivers, lakes, and bays as a result of P loss from soil to water points to the need for advances in soil testing that can contribute to water quality protection. A concerted research effort to modify, refine, and advance soil testing for P to achieve environmental as well as agronomic objectives has been underway for the past decade; unfortunately, little of this research has been adopted by soil testing programs in the U.S. The intent of this paper is twofold. First, to briefly review some of this research, illustrating its potential value in soil P management programs that, by necessity, must today have both agronomic and environmental components. And, second, to provide recommendations as to how soil testing laboratories can be more proactive at integrating advances in research on the environmental uses of soil P testing into their programs and, by doing so, in re-shaping their roles in sustaining a productive, environmentally sound agriculture.

Contact: jtsims@udel.edu

Water quality concerns have caused many U.S. states to pass laws or establish guidelines that restrict manure applications based on phosphorus (P) (Coale et al., 2002). The widespread changes in P management for manures have brought attention to the need for similar approaches for the land application of biosolids. Most states regulate the agricultural use of biosolids in accordance with federal rules that follow the standard, long-term approach used with animal manures, requiring biosolids to be applied at a rate that is equal to or less than the agronomic N rate for the crops to be grown (Shober and Sims, 2002). Recent research suggests that some of the factors that lead to the more restrictive approaches now used for animal manure P also apply to biosolids. Stehouwer et al., (2000) reported that biosolids applied to meet the N requirements for corn added from 93 to 294 kg P ha-1, much more than is removed in harvested corn grain (~25 kg P ha-1) which could lead to the buildup of P in soils and increase the risk of P loss to water. Some research, however, has shown that the risk of P loss to water is lower with biosolids than manures. This has been attributed either to the lower solubility of biosolids P, relative to manure and fertilizer P, due to the chemical amendments added at some wastewater treatment plants or to organic matter added in biosolids which improves soil structure and reduces soil erosion (Penn and Sims, 2002; Withers et al., 2001). We have conducted 5 years of laboratory and field research to determine if there are fundamental differences in the forms of soil P or the physical properties of biosolids-amended soils that mitigate the risk of P loss and require a different approach to P management than is needed for manures and fertilizers. This presentation reviews that research and its relationship to emerging environmental policies for biosolids P in the USA.

Laboratory studies were initially conducted to evaluate the effect of biosolids type on forms and solubility of P in soils of the Mid-Atlantic USA. These studies led to rainfall simulation experiments that compared soil P with P lost in runoff, using runoff boxes and a 3-year field study at two locations. Other studies compared soil P forms and desorption in fields and setback areas from a range of farms where biosolids had been used for crop production.

Results and Conclusions

Our research, at all scales, has consistently shown that soils amended with certain types of biosolids, such as those treated with metal salts, have lower soluble P concentrations and produce lower P concentrations in runoff than most manures and fertilizers. Results of these studies have been combined with data from >900 field scale P Site Index evaluations to assess the impact of assigning different risks of P loss to biosolids compared to manures. Environmental policy-makers in the mid-Atlantic and other states are now debating whether or not to assign lower risk to land-applied biosolids than animal manures. We present, based on our data and other studies, a framework that could be used to asses the risk of P loss and guide improved P when biosolids are used by agriculture.

References

Coale, F.J., J.T. Sims, and A.B. Leytem. 2002. Accelerated deployment of an agricultural nutrient management tool: The Maryland phosphorus site index. J. Environ. Qual. 31:1471-1477.

Penn, C.J., and J.T. Sims. 2002. Phosphorus forms in biosolids-amended soils and losses in runoff: Effects of wastewater treatment process. J. Environ. Qual. 31:1349-1361.

Shober, A.L. and J.T. Sims. 2004. Phosphorus restrictions for land application of biosolids: Current status and future trends. J. Environ. Qual. In review.

Stehouwer, R.C., A.M. Wolf, and W.T. Dotie. 2000. Chemical monitoring of sewage sludge in Pennsylvania: Variability and application uncertainty. J. Environ. Qual. 29:1686-1695.

Withers, P.J A., I.A. Davidson, and R.H. Foy. 2000. Prospects for controlling nonpoint source phosphorus loss to water: A U.K. perspective. J. Environ. Qual. 29:167-175.

Contact: jtsims@udel.edu

Soil testing has been an accepted agricultural management practice for decades. Interpretations and fertility recommendations based on soil analyses and the information obtained with soil samples on cropping systems, tillage practices, soil types, manure use, and other parameters have contributed to the increased efficiency of agricultural production. Recently, however, analyses of long-term trends in soil test phosphorus (P) values have shown that soil P in many areas of the world is now excessive relative to crop P requirements. The role of P in eutrophication of surface waters and emerging concerns about the human health impacts of toxic algal/dinoflagellate blooms have heightened public awareness of nonpoint source pollution by agricultural P. The greatest concerns are with animal-based agriculture where farm and watershed scale P surpluses and over-application of P to soils are common. The need for nutrient management plans based on nitrogen (N) and P is now an issue of intense debate in the U.S. and Canada. This paper addresses three issues. Should the applications of organic wastes and fertilizers be based on soil P and, if so, what is the most appropriate testing method to assess environmental risk? How can our knowledge of soil P chemistry be integrated with the expertise of hydrologists, agronomists, aquatic ecologists and others to assess the risks that P in agricultural soils poses to surface waters? And, finally, how can we use soil P testing to evaluate new "best management practices" now being developed to reduce P transport from soil to water?

Contact: jtsims@udel.edu

Agriculture’s impacts on water quality have been the focus of basic and applied research in Delaware for more than 25 years. Research has examined nutrient cycling in soils, nutrient transport from soils to water, and the environmental consequences of ground water contamination and surface water eutrophication by nutrients. Much of the research has specifically been oriented towards the development of agricultural management practices to prevent the degradation of water quality by nutrients. Other research has focused on increasing our understanding of the chemical, physical, and biological processes that control nutrient cycling and transport and improving the monitoring techniques needed to document how changing management practices affects water quality. Agencies responsible for water quality protection have sought to integrate this research into environmental policy, but have often been frustrated by the fragmented and sometimes contradictory nature of the information provided to them. This paper reviews key advances in research on nutrient management and water quality in Delaware and discusses the obstacles faced in translating research into widely accepted management practices and environmental policies.

Contact: jtsims@udel.edu

Sims, J.T., A.B. Leytem, and F.J. Coale. 2000. Adapting the Phosphorus Site Index to the Delmarva Peninsula: Delaware's experience. Presented at the NRAES (Natural Resource Agricultural and Engineering Service) symposium, "Managing Nutrients and Pathogens from Animal Agriculture," Camp Hill, PA, March 28-30.

Agriculture on the Delmarva Peninsula is heavily dependent on animal based agriculture, which is dominated by poultry production. Over 6000,000,000 broiler chickens are produced annually on the peninsula, primarily in four counties in Delaware and Maryland which have, in total, ~175,000 ha of cropland (Sims, 1997a). The poultry industry provides a stable market for commercial growers of corn, soybeans, small grains, and sorghum. This "poultry-grain agriculture" has the potential to be a completely self-contained system, in which the animal manures generated provide virtually all of the fertilizer nutrients needed to be a completely self-contained system, in which the animal manures generated provide virtually all of the fertilizer nutrients needed to produce the grain consumed by the poultry. Unfortunately, a comprehensive, workable, manure management program has not been developed on the peninsula.

Contact: jtsims@udel.edu

Agriculture is the predominant land use on Delmarva. Of the 15,500 km² total land area on the peninsula about 48% is in agriculture (soybeans, corn, small grains, grain sorghum, hay/alfalfa, commercial vegetables, and fruits), 31% is in woodlands, 13% is in wetlands (fresh and tidal), 7% is in urban and residential use, and 1% is in barrier beaches and islands. Economically, Delmarva's agriculture is dominated by a large and geographically concentrated poultry industry that is vital to the overall economy of the region. Approximately 600 million broiler chickens are produced each year on Delmarva and the total value of broilers "processed and delivered" in 1999 was $1.63 billion; the industry as a whole had an annual payroll of >$350 million (DPI, 1999). Poultry production increased markedly on Delmarva from the 1960's to early 1990's but has stabilized in recent years. Today on Delmarva, there are about 2,700 contract poultry growers working with five integrated poultry companies. On average, each grower has 2.1 poultry houses and each house has a production capacity of ~23,000 broilers.

Contact: jtsims@udel.edu

Laws and guidelines limiting P applications to cropland based on soil P exist in the Mid-Atlantic U.S. because of water quality concerns. We evaluated Mehlich 3(M3) as an environmental soil P test using 465 soils typical to the Mid-Atlantic region and found M3-P accurately predicted water soluble P, desorbable P (iron oxide strip P), and total sorbed P (oxalate P). The M3 P saturation ratio (M3 [P/(Al+Fe)]) was linearly related to the well-established oxalate P saturation method (DPS_ox) and a M3 [P/(Al+Fe)] range of 0.10-0.15 corresponded to reported environmental limits for DPS_ox (25-40%). Rainfall simulation and column leaching studies showed M3 [P/(Al+Fe)] predicted runoff and leachate P concentrations better than M3-P. We suggest consideration of the following approach now used in Delaware for agri-environmental interpretation of M3-P and M3 [P/(Al+Fe)]: (i) "Below optimum" (crop response likely; M3-P<50 mg kg^-1; M3 [P/(Al+Fe)]<0.06); (ii) "Optimum" (economic response to P unlikely, recommendations for P rarely made; M3-P=51-100 mg kg^-1; M3 [P/(Al+Fe)]=0.06-0.11); (iii) "Above Optimum" (soil P will not limit crop yields, no P recommended; M3-P>100 mg kg^-1; M3 [P/(Al+Fe)]>0.11); (iv) "Environmental" (implement improved P management to reduce potential for nonpoint P pollution - in Delaware M3-P>150 mg kg^-1; M3 [P/(Al+Fe)]>0.15 is now used); and (v) "Natural Resource Conservation" (no P applied even if potential water quality impact is low in order to conserve P, a finite natural resource).

Contact: jtsims@udel.edu

Sims, J.T., and N.J. Luka-McCafferty. 2002. On-farm evaluation of aluminum sulfate (alum) as a poultry litter amendment: Effects on litter properties. J. Environ. Qual. 31:2066-2073. 

Contact: jtsims@udel.edu

Nutrient management planning is an integral part of modern production agriculture but is hardly a new concept. The key steps in the development of profitable and environmentally sound nutrient management plans - setting realistic yield goals, using soil testing and agronomic research to identify crop nutrient requirements, applying fertilizer nutrients and manures in a timely and efficient manner, and monitoring the success of nutrient management decisions - have been well-established and widely accepted agricultural practices for decades. Despite this, we now face in many U.S. states and European countries political and legal pressures to institute mandatory nutrient management planning. For example, in 1998 the state of Maryland passed the Water Quality Improvement Act mandating that any agricultural operation with a gross income > $2500 or > eight animal units must ".have and implement a nitrogen (N) and phosphorus (P) based nutrient management plan" (Simpson, 1998). Individuals using only chemical fertilizers must implement a plan by December 31, 2002; those using sludge or animal manure by July 1, 2005. What has caused this movement away from the use of voluntary practices to manage nutrients? Why are nutrient management plans now being based on N and P, instead of N? And, most important, what are the implications of mandatory N and P based plans and how can agriculture adapt to this new direction in nutrient management planning?

Contact: jtsims@udel.edu

Delaware, located on the Delmarva Peninsula (Delaware-Maryland-Virginia) I the Atlantic Coastal Plain of the United States, is bordered by two large and extremely important estuaries, the Chesapeake and Delaware Bays. It is also the location of a national estuary, the Inland Bays. Water quality in all these estuaries has been impaired by years of point and nonpoint source pollution, particularly by inputs of nitrogen (N) and phosphorus (P). While point source discharges of nutrients have been reduced, due to improvements in municipal wastewater treatment facilities, agricultural contributions of N and P via nonpoint source pollution (runoff and groundwater discharge) remain substantial. For example, 44-55% of the N and from 29-53% of the P entering Delaware's Inland Bays was attributed to agriculture by Ritter (1992). Point sources contributed less than 12% of the N and from 0 to 25% of the P. The importance of the Inland Bays for fishing, recreation, tourism, and as a vital estuarine ecosystem has stimulated numerous research and educational programs over the past 25 years. Many have focused on the development and implementation of "best management practices" (BMPs) that could be used to minimize the impact of agricultural nutrients on water quality. Despite these efforts little improvement has been observed in water quality in the Inland Bays, prompting increased public concern and demands for greater restrictions on agriculture. Most recently, questions have arisen about the impact of the intensive animal agriculture practiced on this peninsula on ground and surface water quality. More than 700 million broiler chickens are produced on Delmarva each year and land application of the wastes from this industry has been identified as a potentially major source of N and P to the Chesapeake Bay and Delaware's Inland Bays. Our objectives are to describe the water quality problems in the Inland Bays watershed, review the challenges faced by agriculture in reducing nonpoint source pollution, and outline some immediate and long-term solutions that should be considered if we are to restore the health of the Inland Bays.

Contact: jtsims@udel.edu

Nutrient management has always been a key component of agricultural planning. Decades of research have developed and refined efficient, economic means to optimize plant nutrition and thus increase crop yields. Government advisory agencies (e.g., Cooperative Extension, USDA Natural Resources Conservation Service) and private agricultural consultants have been able to transfer much of the nutrient management research into best management practices (BMPs) that are well-accepted by farmers today. Concepts such as realistic yield goals, soil testing and plant analysis as predictive and diagnostic tools, selection of the best nutrient sources, nutrient application methods and timings for different crop rotations, and monitoring the success of a nutrient management plan are widely regarded as sensible, cost-effective practices by most farmers. Unfortunately, despite the long-term efforts in research and technology transfer to improve the efficiency of nutrient management, federal and state analyses of ground and surface water pollution consistently identify agriculture as a major nonpoint source of nutrients. These reports, in combination with a series of of local or regional events, such as fish kills, nuisance algal blooms, accidental discharges of manures from lagoons into streams and rivers, high nitrate concentrations in aquifers and rivers used as drinking waters, and soil test summaries showing large and increasing percentages of soils rated as "excessive" in P, have heightened public awareness about agriculture’s role in nonpoint source pollution. Questions are now arising about the effectiveness of voluntary BMPs in protecting the environment. Close upon these questions has come debate about the need for regulatory programs to ensure that the impacts of agricultural nutrients on water, air, and soil quality are reduced to environmentally acceptable levels. We summarize in this paper some recent changes in the U.S. with regard to nutrient management and the challenges agriculture faces in implementing these changes.

National Efforts to Improve Nutrient Management: Historically, nutrient management planning at the national level has had two major thrusts. First, federal support of research at land grant universities and government research agencies (USDA Agricultural Research Service, US Geological Survey) has been expected to produce the science-based solutions needed to maximize agricultural productivity while minimizing environmental impacts on air, soils, and waters. Second, advisory agencies, primarily Cooperative Extension and USDA-NRCS have been expected to review the research, extract and modify the most practical and useful options, and transfer this technology to the farm. More recently, due to reductions in the size and the changing mission of government advisory agencies, a greater reliance has been placed on private industry to provide advice on which new BMPs will be most useful to farmers. Advisory agencies continue to play a role, but are clearly moving more in the direction of broader scale nutrient management education and away from individual planning. Further, researchers are ever more reliant upon private industry for funding, which affects not only the direction of their research programs, but the duration. Consequently, it is increasingly difficult to sustain the long-term experiments that are vital to the evaluation of nutrient management BMPs, particularly those that seek to examine innovative practices that may not be practical or profitable in the short-term. Similar changes in the mission of research and advisory agencies have occurred in other countries, such as Canada, the Netherlands, and the U.K.

National legislation and policies to reduce agricultural nonpoint source pollution have also been proposed recently. Most of this legislation has been focused on animal agriculture, which is perceived to be of greatest immediate national concern for water and air pollution (Sharpley et al., 1998). However, it also has ramifications for other nutrient users and producers. Three examples of proposed legislation are: (i) the Animal Agriculture Reform Act (Senator Harkin, Iowa); (ii) the Farm Sustainability and Animal Feedlot Enforcement Act (Representative Miller, California), and (iii) the Poultry Electric Energy Power (PEEP) Act (Senator Roth, Delaware). A central theme is all this legislation has been the desire to address, at a national level, the water quality problems caused by the geographic intensification of animal production. One legislative goal has been to create a "level playing field", through national policies and regulations, that would prevent large animal operations from moving from their current location, often where environmental problems currently exist, to areas with less restrictive local environmental standards. Other goals have been to include more large animal operations, particularly poultry and swine, in permitted, regulatory programs; to assign responsibility for animal waste management to the large integrating companies, as well as to the farmer/contract grower; and to provide alternatives to land application of animal wastes, such as use for energy production (e.g., the PEEP Bill). To date, national legislation addressing nutrient management by animal agriculture, or any other major sources of nutrients (e.g., commercial fertilizers, municipal biosolids and composts) has not passed in the U.S.

National policy initiatives are also underway, again primarily addressing animal agriculture. By far the most significant is the USEPA-USDA Unified National Strategy for Animal Feeding Operations (AFOs), adopted in March of 1999 after lengthy discussion and public review. The nine "guiding principles" in this joint effort between the nation’s lead regulatory agency (USEPA) and its lead technical agency for agriculture (USDA) reflect the changing national attitude towards agriculture and nonpoint source pollution:

Guiding Principles in the Unified National Strategy for AFO’s

1) Minimize water quality and public health impacts from AFOs.

2) Focus on AFOs that represent the greatest risk to the environment and public health.

3) Ensure that measures to protect the environment and public health complement the long-term sustainability of livestock production in the U.S.

4) Establish a national goal and performance expectations for AFOs.

5) Promote, support, and provide incentives for the use of sustainable practices and systems.

6) Build on strengths of federal agencies and their state/local partners and make appropriate use of diverse tools including voluntary, regulatory, and incentive-based approaches.

7) Foster public confidence that AFOs meet performance expectations and that federal and state/local governments are ensuring the protection of water quality and public health.

8) Coordinate activities among USDA, USEPA, and state agencies and other organizations that affect or influence the management and operation of AFOs.

9) Focus technical and financial assistance to support AFOs in meeting national goal and performance expectations established in the Unified National Strategy.

One new theme that is found in the Unified Strategy and in other emerging policies is the need not only to protect water quality but also public health. The perception that pollution from AFOs will affect public health is based on at least two factors. First, long-standing concerns about nitrate contamination of drinking waters. And, second, more recent concerns about toxic dinoflagellates, such as Pfiesteria, which have been implicated as the causative organism for massive fish kills and human health problems in individuals directly exposed to waters where these organisms proliferate. A second theme is the perception that the large integrating companies that contract with farmers to produce poultry and swine should bear some responsibility for the management of animal wastes, which is currently solely up to the farmer/contract grower.

In addition to legislative actions, several national agencies have begun to develop new policies related to nutrient management. USDA-NRCS has recently released its "national nutrient policy" which will require more comprehensive nutrient management planning and implementation of plans for farmers receiving technical assistance and cost-sharing funds. Several agencies involved in the development of renewable energy sources (e.g., Department of Energy’s Regional Biomass Energy Programs) have initiated studies of the use of animal wastes as fuel sources. The U.S. Geological Survey is expanding research and monitoring efforts to investigate water quality and "ecotoxicological" effects of animal pharmaceuticals, microorganisms, nutrients, and trace elements in feeds. Their goal is to develop preventive and remediation strategies that would be used by AFOs to protect water quality and ecosystem health.

State Efforts in Nutrient Management: Many U.S. states have been more aggressive in their efforts to address the issue of nonpoint source pollution by agricultural nutrients. State legislatures can act much more quickly and be more (but not less) restrictive than the federal government. Three examples of recent actions taken by U.S. states to legislate policy that regulates nutrient management are: (i) Maryland’s Water Quality Improvement Act. This act mandates that any agricultural operation with a gross income > $2500 or $ eight animal units must "..have and implement a nitrogen (N) and phosphorus (P) based nutrient management plan" (Simpson,1998). Individuals using only chemical fertilizers must implement a plan by December 31, 2002; those using biosolids or animal manures by July 1, 2005. The Maryland act is the first legislative effort in the U.S. to require N and P-based nutrient management planning by such a wide range of agricultural operations; (ii) the Pennsylvania Nutrient Management Act. This act, passed in 1993, resulted in regulations, in 1998, that establish criteria, planning requirements, and implementation schedules for certain agricultural operations in Pennsylvania (Beegle et al., 1997). At present the act requires N-based nutrient management planning only for concentrated animal operations, those exceeding two animal units (AEUs) per acre (5 AEUs per ha); and (iii) Virginia’s Poultry Waste Management Act. This act focuses specifically on the poultry industry and requires the development and implementation of nutrient management plans for any person owning or operating a confined poultry feeding operation. Land application of poultry wastes will be based, as in Maryland, on N and P.

Other efforts to restrict or regulate nutrient management by animal agriculture have occurred at the state level. In Delaware, a consortium of environmental groups won a lawsuit against USEPA in 1996 for failing to discharge its duties under the U.S. Clean Water Act and protect the surface waters of Delaware. As a result, a Total Maximum Daily Load (TMDL=maximum allowable daily load of a pollutant; if exceeded waters will not be fishable or swimmable) agreement was negotiated in 1997 between USEPA and the state of Delaware. This agreement requires the state to develop pollution control strategies to reduce nutrient, sediment, and pathogen losses to surface waters below TMDL levels by 2007. In North Carolina, a legislative moratorium was imposed on the swine industry in 1997 prohibiting the construction or expansion of swine farms for two years. The goal was to allow local governments time to develop zoning ordinances and animal waste management systems for the rapidly growing swine industry. And, finally, in Oklahoma an AAnimal Waste and Water Quality Protection Task Force@ was appointed by the governor in 1997 to ensure the protection of Oklahoma=s water supply from the Aburgeoning confined animal production industry@ (State of Oklahoma, 1997).

While most legislative and policy actions at federal and state levels are now targeting animal agriculture, there are indications, such as in Maryland=s Water Quality Improvement Act, that other nutrient users will be affected to some degree by these changes (i.e. in Maryland, biosolids generators, commercial horticultural operations, cash-grain farming and vegetable production systems must follow the same regulations as animal agriculture). As another example, in Delaware, farmers have become increasingly reluctant to accept animal wastes from neighboring farms with manure surpluses. They have concerns that importing surplus P from another farming operation may eventually cause them to have to adopt more intensive, and expensive, P-based management practices on their own farm.

Adapting to Changes in Nutrient Management Planning: The move to more comprehensive, N and P based nutrient management plans is the first step in recognizing that water quality cannot be protected by N management alone. It means we must also devise best management practices that prevent the accumulation of P in soils to excessive values and the transport of P to surface waters, by all pathways, not just soil erosion. Reducing the unnecessary use of purchased chemical fertilizers is an obvious and relatively easy first step in this direction. However, what strategies are available to animal agriculture and municipalities, where the use/disposal of manures and biosolids is a requirement, not an option? Sims and Moore (1998) outlined the following approach:

• Develop a N and P based nutrient management plan: The principles involved in developing a N and P based nutrient management plan for animal wastes (or municipal biosolids) are conceptually straightforward but very difficult to implement in many agricultural settings today. First, the N and P requirements of the crop to be grown are identified based on a realistic yield goal. Next, an application rate of manure is selected that does not over-apply either N or P. Identifying the correct application rate to provide the amount of available N required is a well-developed process that basically requires knowledge of the expected mineralization of organic N and recovery of inorganic N in the particular manure for a given soil and cropping system, information that is readily available in most states (Sims, et al., 1995). Finally, timely and efficient application of the manure is made taking into consideration crop N uptake patterns and the potential pathways of N loss that must be avoided. Phosphorus application rates are normally based on soil test P values, with most manures regarded as being approximately equivalent to fertilizer P in terms of plant availability. However because the soils in most areas with intensive animal agriculture are often well above the critical soil test P value recommended for optimum yields, the P-based manure application rate is essentially zero, thus land application is a moot point. This requires farmers to not only identify alternatives to land application for their manures, but to purchase chemical fertilizers to meet the N needs of their crops. Today, for many farmers, this approach is economically impossible. Alternatives to land application are not developed and the costs of purchasing fertilizer N to replace manure N already present on the farm will be a significant economic burden. Additionally, the current state of knowledge on P transport suggests that P-based management is not necessary in all situations where soil test P values are excessive, at least not in the near term. The use of risk assessment tools, such as the P Index, to identify areas on farms with the greatest likelihood of impacting surface waters based on hydrology, soil P, and management practices, is now being regarded as a more effective approach to identify areas where P-based management should be required (Lemunyon and Gilbert, 1993; Sims, 1996; Sharpley, 1995). At the same time it must be recognized that simply because the risk of P transport is low now, the buildup of soil P to grossly excessive values is unlikely to be a sustainable practice in the long term.

• Develop alternatives to land application: There is a pressing need for alternatives to land application of animal wastes. The most prominent suggestions have been to use manures as bioenergy sources or as components of value-added products that can be economically re-distributed to areas with nutrient deficits(composts, pelletized fertilizers). While with economic incentives, these may be promising options for dry manures (e.g. poultry), they are unlikely to be useful for industries that rely on liquid treatment systems (swine, dairy). National or regional efforts are required to identify the best technologies available and promote new research in these areas, to carefully assess other environmental impacts that might occur(e.g. air quality problems from burning manures), and to foster private investment in large-scale solutions such as these.

• Improve the efficiency of land application programs: While long-term solutions are debated, there is a near-term need to implement the practices identified by researchers in the past decade to improve nutrient management when manures are land applied. It is beyond the scope of this paper to describe all of these, but examples are: greater use of soil and plant N tests such as the pre-sidedress soil nitrate test, the leaf chlorophyll meter, and the stalk nitrate test; the adoption of Aenvironmental soil P tests@ by soil testing laboratories to aid, along with the P Index, in identifying soils that are Asaturated@ with P and located in hydrologically sensitive areas (Sibbesen and Sharpley, 1997; Sims, 1998); the modification of animal diets using phytase enzymes and high available P corn, which can reduce P excretions by poultry and swine by 30-50%; and the use of municipal wastewater technologies for animal wastes, such as the amending poultry litters with alum to stabilize P in a form that is less susceptible to runoff and leaching (Moore, 1998).

Literature Cited

Beegle, D. 1997. Nutrient management legislation in Pennsylvania: Who will be affected? Agron. Facts 40. Pennsylvania State Univ., University Park, PA.

Lemunyon, J.L., and R.G. Gilbert. 1993. Concept and need for a phosphorus assessment tool. J. Prod. Agric. 6:483-486.

Moore, Jr., P. A. 1998. Best management practices for poultry manure utilization that enhance agricultural productivity and reduce pollution. P. 89-124. In J. Hatfield and B. A. Stewart (eds.) Animal waste utilization: Effective use of manure as a soil resource. Ann Arbor Press, Chelsea, MI.

Sharpley, A.N. 1995. Identifying sites vulnerable to phosphorus loss on agricultural runoff. J. Environ. Qual. 24:947-951.

Sharpley, A. N., J. J. Meisinger, A. Breeuswma, J. T. Sims, T. C. Daniel, and J. S. Schepers. 1998. Impacts of animal manure management on ground and surface water quality. p.173-242. In J. Hatfield and B. A. Stewart (eds.) Animal waste utilization: Effective use of manure as a soil resource. Ann Arbor Press, Chelsea, MI.

Sibbesen, E., and A. N. Sharpley. 1997. Setting and justifying upper critical limits for phosphorus in soils. p. 151-176. In H. Tunney et al., (eds.). Phosphorus Loss from Soil to Water. CAB International, London.

Simpson, T. W. 1998. A Citizen's Guide to Maryland's Water Quality Improvement Act. Univ. of MD Coop. Extension, College Park, MD.

Sims, J. T. 1998. Phosphorus soil testing: Innovations for water quality protection. Commun. Soil Sci. Plant Anal. 29:1471-1489.

Sims, J. T. 1996. The Phosphorus Index: A Phosphorus Management Strategy for Delaware's Agricultural Soils. Fact Sheet ST-05. College of Agricultural Sciences and Cooperative Extension. University of Delaware, Newark, DE.

Sims, J. T., B. L. Vasilas, K. L. Gartley, B. Milliken, and V. Green. 1995. Evaluation of soil and plant nitrogen tests for maize on manured soils of the Atlantic Coastal Plain. Agron. J. 87:213-222.

Sims. J. T. and P. A. Moore, Jr. 1998. Nutrient management planning: Phosphorus or nitrogen based? p. 84-93. Proc. Natl. Poultry Waste Mgt. Symp., October 19-21, Springdale, AR.

State of Oklahoma. 1997. Report of Governor Frank Keating=s Animal Waste and Water Quality Protection Task Force. Office of the Environment, Oklahoma City, OK.

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The importance of phosphorus (P) originating from agricultural sources to the nonpoint source pollution of surface waters has been an environmental issue for decades because of the well-known role of P in eutrophication. Most previous research and nonpoint source control efforts have emphasized P losses by surface erosion and runoff because of the relative immobility of P in soils. Consequently, P leaching and losses of P via subsurface runoff have rarely been considered important pathways for the movement of agricultural P to surface waters. However, there are situations where environmentally significant export of P in agricultural drainage has occurred (e.g., deep sandy soils, high organic matter soils, or soils with high soil P concentrations from long-term overfertilization and/or excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present overviews of ongoing research in the Atlantic Coastal Plain of the USA (Delaware), the midwestern USA (Indiana), and eastern Canada (Quebec). Our objectives are to illustrate the importance of agricultural drainage to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P losses in subsurface runoff.

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Reducing phosphorus (P) in dairy diets may result in different types of manure with different chemical composition. Application of these manures to soils may affect the soil P solubility and lead to different environmental consequences. A laboratory incubation study determined the impact of 40 dairy manures on P dynamics in two soil types, Mattapex silt loam (Aquic Hapludult) and Kalmia sandy loam (Typic Hapludult). The manures were fecal samples of lactating cows, collected from commercial dairy farms located in Northeastern and Mid-Atlantic United States, with a wide range of dietary P concentrations (from 2.9 to 5.8 g P kg^-1 feed dry matter, DM). Dried and ground fecal samples were mixed with surface horizon (0-15 cm) of soils at 150 kg P ha^-1 and the mixtures were incubated at 25^oC for 21 days. At the end of incubation, water soluble P (WS-P) and Mehlich-3 P (M3-P) in the soil-manure mixtures were substantially higher than the control (soil alone) but were lower than soils receiving fertilizer KH₂PO₄ at 150 kg P ha^-1. Similarly, the reality extractability of P in soils amended with low- and high-P manures was always lower (<93%) than KH₂PO₄ suggesting that fertilizer P is more effective at increasing soil solution P in the short-term. Concentrations of WS-P or M3-P in soil-manure mixtures did not differ regardless of the source of manure (i.e., different farms and different diets). This suggests that when the same amount of P is added to soil through manure applications, the solubility or bioavailability of P in soils will be the same. However, P concentrations in feces correlate significantly with that in diets (r=0.82**); and when the manures were grouped into high-P diets (averaging 5.1 g P kg^-1) versus low-P diets (3.6 g P kg^-1), manure P was 40% greater in the high-P group (10.6 g kg^-1 DM). Thus, lowering excess P in diets would reduce P excretion in manures, P accumulation in soils, improve P balance on farms, require less area for land disposal, and decrease potential for P loss to waters.

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Intact soil monoliths (70 cm deep, 50 cm diameter), collected from a free draining Lismore silt loam soil (Udic Haplustept) under grassland, were used to evaluate phosphorus (P) leaching for two years. The objective of the study was to investigate the effect of the application of mineral P fertilizer (at 45 or 90 kg P ha^-1 y^-1) and/or farm dairy effluent (FDE) (30 to 60 kg P ha^-1 y^-1) on P losses by leaching. Annual mean total P (TP) concentrations and losses were higher from the treatments that received both FDE and P fertilzer (203-429 μg L^-1; 1.4-2.5 kg ha^-1) compared with P fertilizer alone (77-151 μg L^-1; 0.6-1.3 kg ha^-1). The form of applied P influenced the pattern of P forms leached. For example, significantly higher P losses in different P forms were observed for the combined mineral P fertilizer and FDE treatment (P45/FDE200) than fertilzer alone (P90/N200/U). This is due to the inclusion of liquid FDE in the former treatment although the total P inputs were similar for both treatments. This illustrates the potential of these soils to adsorb soluble inorganic P applied from mineral P fertilizer, while FDE contained unreactive P forms that were mobile in the soil profile. There was a distinct pattern of P forms leached in the following order: particulate unreactive P (PUP; 40-70%) > dissolved unreactive P (DUP; 14-53%) > particulate reactive P (PRP: 5-12%) > dissolved reactive P (DRP: 1-11%). Results also suggest that changing the irrigation method from flood to spray may be the most effective means to reduce P loss in these stony, free-draining soils.

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Vadas, P.A., J.T. Sims, A.B. Leytem, and C.J. Penn. 2002. Modifying FHANTM 2.0 to estimate phosphorus concentrations in runoff from Mid-Atlantic Coastal Plain soils. Soil Sci. Soc. Am. J. 66:1974-1980. 

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Vadas, P.A., and J.T. Sims. 2002. Predicting phosphorus desorption from Mid-Atlantic Coastal Plain soils. Soil Sci. Soc. Am. J. 66:623-631.

Pollution of surface waters by P from agricultural areas is a water quality issue in Delaware. The FHANTM 2.0 computer model can help identify areas with a high potential for P loss, but the model's representation of P desorption from soils to runoff waters needs re-evaluation. The equation, P_d = K P_o t^α  W^β, has been proposed to predict such P desorption, but equations originally proposed to predict values for the constants K, α, and β from the ratio of soil clay content/soil organic C content may not  be accurate for Delaware soils. Therefore, we measured P desorption for 23 sandy Delaware soils for times of 5 to 180 min, water/soil rations of 10 to 1000 L kg^-1, and three initial levels of soil desorbable P. Values for the constants K, α, and β were calculated and related to soil properties. We found that K, α, and β values were not well related to clay/OC, but were better related to the ratio of oxalate-extractable Fe/OC content (α) or the sum of oxalate-extractable Fe and Al (β and K). These results can be used to help refine the FHANTM 2.0 model in predicting P loss from agricultural areas in Delaware and similar landscapes in the Mid-Atlantic Coastal Plain.

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Artificially drained, agricultural soils that are high in phosphorus (P) and have seasonally fluctuating water tables may be significant nonpoint sources of P to Delaware’s Inland Bays. Topsoil, unamended and amended with 4 g kg^-1 poultry litter (PL), and subsoil horizons from two soil series in the Inland Bays watershed were flooded for 28 days and drained for 14 days at 25^oC. Soil pH and redox potential (Eh) were measured (mV) and P sorption isotherms were constructed for each horizon under oxidized, flooded, and drained conditions. For each isotherm, P sorption maxima (b_max), P sorbed at a solution P concentration of 1.0 mg L^-1 (b_1.0), and the equilibrium P concentration at zero sorption (EPC₀) were calculated. Flooding decreased Eh and increased pH, and draining returned Eh and pH to near initial values. Flooding and draining decreased b_max in all horizons. The b_1.0 values were always significantly less than b_max values; however, flooding and draining had inconsistent effects on b_1.0 values. Flooding increased EPC₀ in the unamended Pocomoke A horizon, but decreased EPC₀ in the same PL-amended horizon. Draining reduced EPC₀ values in both Pocomoke A horizons. Flooding and draining had little effect on EPC₀ in other horizons. Our data suggest that land application of PL and fluctuating water tables may increase the potential for P loss from soils through both a decrease in soil P sorption capacity and an increase in solution P concentrations in topsoils.

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Artificially drained, agricultural soils in Delaware’s Inland Bays watershed are high in phosphorus (P) from poultry litter and fertilizer applications. The potential loss of P from these soils to drainage waters during soil reduction and reoxidation was investigated. Soil from three artificially drained, cultivated fields and two wooded areas was collected and characterized as Fallsington sandy loam (fine-loamy, mixed, mesic Typic Ochraquult), Pocomoke loamy sand (coarse-loamy, siliceous, thermic Typic Umbraquult), and Osier loamy sand (siliceous, thermic Typic Psammaquent). Topsoils, unamended and amended with poultry litter (PL), and subsoils were reduced for 28 days and reoxidized for 14 days at 25 and 35^oC. The soils were analyzed for pH, redox potential (Eh), soluble P and Fe²⁺, and P fractions unoccluded Fe-P and Al-P, occluded Fe-P and Al-P, and Ca-P) under oxidized, reduced, and reoxidized conditions. Reduction decreased Eh to moderately reduced (200-350 mV) and reduced (-100 to 100 mV) values, and increased pH (0.8 + 0.1) and soluble Fe²⁺ (44 + 24 mg kg^-1). Reoxidation returned Eh, pH, and Fe²⁺ to near initial values. Reduction increased soluble P in unamended cultivated topsoils (0.69 + 0.42 mg kg^-1), decreased soluble P in amended cultivated topsoils (1.42 + 1.31 mg kg^-1), but had little effect in subsoils or wooded soils. Reoxidation decreased soluble P in cultivated topsoils, but increased soluble P in subsoils and wooded soils. Reduction increased the extractability of all P fractions in cultivated topsoils (20 + 12 mg kg^-1), but increased only Ca-P extractability in subsoils and wooded soils (9 + 3 mg kg^-1). Reoxidation decreased the extractability of these fractions to near initial values.

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Poultry products are consumed by most ethnic populations worldwide. In recent years, the global production of poultry meat and eggs has increased at an annual rate of approximately 5% with the United States, China, the former Soviet Union countries, Brazil, France and Japan representing dominant production countries. In 1991, nearly 40 million metric tons of poultry meat and 600 billion eggs were produced globally (Sims and Wolf 1994). In the United States, poultry production increased by 44% between 1982 and 1994 representing a recent annual production inventory of nearly 8 billion broilers, 300 million layers and 300 million turkeys (Bagley et al. 1996; U.S. Senate Committee on Agriculture, Nutrition and Forestry 1997). There is little doubt that the consumption, and thus, production of poultry will continue to increase relative to the world’s population and economy. Consequently, environmental parameters impacted by waste by-products resulting from the production and processing of poultry products are of increasing importance, worldwide. Although various options are available to producers for managing poultry wastes, the most commonly utilized practice involves land application as the final step for utilization of manures and bedding material. This practice, when managed properly is environmentally sound and results in little or no discharge of environmental contaminants to surface and groundwaters. However, under certain environmental conditions and / or poor management practices, the disposal of poultry wastes has long been recognized as a potential detriment to the environment. Fish kills, animal and human health impacts resulting from improper disposal of poultry wastes were noted several decades ago (Loehr 1968). Zindel and Flegal (1970) reported that mineral imbalances can occur in soils receiving excessive poultry wastes. Pratt (1979) and Fontenot et al. (1983) identified nitrate nitrogen (NO₃-N) leaching in soils as a result of over application of poultry wastes. Currently, the debate over the contribution of modern animal agriculture to environmental pollution is a central issue in the U.S. and many parts of the world. Although science-based evidence is often limiting, reports often note that agriculture in general is one of the major contributors to environmental pollution (Sutton 1994). For example, a recent report by the U.S. Senate Committee on Agriculture, Nutrition and Forestry (1997) noted that: agricultural runoff and nutrients from livestock and poultry are the greatest pollutants in 60% of the rivers and streams identified by the U.S. Environmental Protection Agency as impaired; manure from feedlots is blamed by the U.S. Fish and Wildlife Service for impairing fisheries along 60,000 miles of streams; animal waste is degrading nearly 2,000 bodies of water in 39 states; pollutants from concentrated animal feeding operations (CAFOs) impairs more miles of U.S. rivers than all other industry sources and municipal sewers combined; nutrient runoff from CAFOs has depleted oxygen in the Gulf of Mexico, near the mouth of the Mississippi River to concentrations so low that aquatic life is depleted, and; the U.S. Environmental Protection Agency determined that manure from CAFOs containing streptococci and coliform bacteria had contaminated groundwater in a total of 17 states. In addition, fish kills in 1997 attributed to toxic blooms of Pfiesteria piscicida in rivers proximate to the Maryland-Virginia Eastern Shore focused attention on the management of wastes from nearby poultry operations. The contribution by poultry production to each of these statistics, relative to livestock and row crop agriculture, as well as to contribution from non-agricultural enterprises including municipal discharge and urban runoff is the subject of much unresolved scientific debate. However, there is little debate that worldwide trends are towards fewer farms and geographic intensification of poultry facilities. Under these conditions, the production of poultry meat and eggs results in tremendous quantities of by-products such as hatchery wastes, manure, litter and on-farm mortalities. The subsequent processing of poultry products also results in large quantities of offal, processing waste waters and biosolids (sludge). Each of these by-product categories represent potential organic and inorganic nutrients as well as trace elements and pathogenic microorganisms of environmental concern.

Most poultry manure, worldwide, is applied to land and applications of nutrients, regardless of source, in excess of the receiving land’s agronomic potential to utilize the nutrients increases the potential for environmental contamination in one form or another. Characterizing poultry production by-products as resources, as opposed to a waste, has been the focus of much discussion and debate on the subject of on-farm best management practices. Many producers, in fact, take exception to the terminology farm wastes. In recognizing the pollution versus resource value of poultry wastes, especially for utilization as a crop nutrients, there needs, however, to be an equal recognition of field, farm and regional environmental balance. Within the field where poultry waste is applied as fertilizer under circumstances where the receiving area has a theoretical capacity to utilize the nutrients, environmental contamination may result due to factors involving timing and method of manure application which could lead to nutrient losses due to leaching, erosion, runoff, or volatilization. At the farm unit level, the availability of cropland to biologically utilize the nutrients produced is critical. The input of feed nutrients to a poultry production operation often exceeds the nutrients in the primary products produced (meat, eggs, and harvested crops resulting from land applied manure nutrients excreted by the birds on the site in question). The mass nutrient balance for N and P is illustrated (Table 1) for a typical medium-sized poultry operation containing100 ha of cropland and three poultry houses producing 6 flocks of meat type birds per year for an annual production inventory of approximately 180,000 birds. Under the illustrated calculations and assumptions (crop rotations of corn, soybeans, double-cropped wheat, and some vegetable crops) results show an annual excess of N and P of approximately 220 and 80 kg/ha/year, respectively. The same mass balance principals are true for an agricultural economy based region or state, where total nutrient contribution from all sources to the water basins and atmosphere within the region must be considered for ecological balance.

The issue of environmental balance is more complex considering recent trends in animal production. It has been estimated that nearly all poultry operations in the U.S. are conducted under confined conditions (Fogg 1980; Overcash et al. 1983) and many of these operations are in clustered geographic areas. For example, the majority of U.S. poultry production occurs in a few southern and mid-Atlantic states and California. In Arkansas, where over 900 million meat-type birds are produced annually, 2 counties which contain approximately 3.5% of the state’s total land area produce over 20% of the total (Edwards and Daniel 1992). In North Carolina, which is considered one of the leading states in livestock and poultry production, nearly 30 million tons of fresh manure, from all livestock and poultry, containing 205,000 tons of nitrogen, 138,000 tons of phosphorus, 1,700 tons of zinc and 290 tons of copper were generated in 1993 (Barker and Zublena 1995). It was calculated that statewide, approximately 20% of the nitrogen and 66% of the phosphorus crop needs could be met with these livestock and poultry manure resources. However, within certain North Carolina livestock and poultry production counties, three counties produced enough manure to exceed their total nitrogen crop requirements and 18 counties had an excess of phosphorus. Since 1993, the swine industry has experienced tremendous growth while the poultry industry has continued a moderate growth in North Carolina, often in the same counties referenced above. Even with the best management practices for land application of animal wastes in such concentrated livestock and poultry producing regions, it is questionable that such situations can be sustainable in the long term due to environmental impacts.

As a consequence of concentrated poultry production operations and limited land area for crop growth, producers in many areas are faced with few options other than removing surplus animal wastes from their farms. These, and emerging environmental issues, such as ammonia volatilization from animal wastes, are currently challenging established best management practice guidelines for producers in many areas. In the near future, the protection of airsheds may be as important an environmental issue to producers as the protection of watersheds. Addressing these environmental concerns represents a serious threat to the long term sustainability of many poultry producers worldwide. This review will focus on the management and agricultural land application of poultry manure resulting from laying hen operations and litter resulting from meat-type chicken and turkey production. Dead bird disposal, also a critical environmental issue facing poultry producers, is not covered. Reviews published earlier this decade (Edwards and Daniel 1992) and (Sims and Wolf 1994) addressing the topic of environmental impacts of poultry waste, including dead bird management and disposal, are noted and recommended.

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Characterizing labile phosphorus (P) forms in animal manure is a challenge due to their susceptibility to hydrolysis. Harsh assay conditions commonly applied for characterizing P, such as sequential fractionation and 31P NMR analysis, can underestimate labile P in animal manure. In this study, we characterized dairy manure P under relatively mild assay conditions. Fresh dairy manure was separated into soluble part(s) and residual components. The hydrolyzable organic P in these fractions was then characterized by enzymatic hydrolysis at pH 5.0 and categorized as simple monoester P, polynucleotide P, phytate-like P, and nonhydrolysable P. Autoclaving released residual P in a level similar to that observed with spontaneous hydrolysis over 54 h. Ultrasonication, intended to release inorganic (Pi) and organic P (Po) trapped in the manure matrix, released a little residual P. About 75% of total manure P was characterized by the approach used. The remaining 25% could be regarded as recalcitrant P. In water extracts, 77% was Pi, 11% hydrolyzable Po and 12% enzymatically nonhydrolyzable Po. In the residual resuspension, 25% was spontaneous labile P, 32% was simple monoester P, 7% was polynucleotide P, 9% was phytate-like P, and 26% as nonhydrolysable P. This study indicates mild enzymatic hydrolysis is useful for quantifying labile (or hydrolyzable) forms of Po in dairy manure.

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Sims, J.T., G.S. Toor, R.O. Maguire, J.M. McGrath, and A.L. Shober. 2003. Advances in the management of organic phosphorus sources in the Chesapeake Bay watershed, USA: Implications for agriculture and the environment.

Nonpoint source phosphorus (P) pollution of the Chesapeake Bay by agriculture has been recognized as a serious environmental problem for more than 30 years. However, decades of research education and technical assistance have failed to significantly reduce agricultural P inputs to this nationally important estuary. Serious water quality problems in the late 1990s prompted passage of nutrient management laws in several states in the watershed that now regulate land application of organic P sources (manures, biosolids, composts) and mandate improvements in organic P management. Federal regulations and guidelines also require P-based management for certain agricultural operations. We have conducted research on innovative approaches to reduce agricultural nonpoint P pollution for more than 10 years and have actively worked with state and federal advisory and regulatory agencies to implement improved P management practices. This presentation has two objectives. First, we synthesize our research findings from the past 5 years addressing two of the most important advances in P management in this region: (i) modifying poultry and dairy diets to reduce P excretions through the use of dietary additives and reductions in over-feeding; and (ii) use of chemical amendments to stabilize P in agricultural and municipal organic P sources (manures and biosolids). Effects of these practices on the forms and concentration of P in manures, biosolids, and soils, runoff, and leachate from soils amended with these organic P sources will be discussed. Second, the environmental implications of widespread adoption of these practices by agriculture and municipalities on the watershed will be critically analyzed.

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Agricultural nonpoint source pollution of surface waters and ground waters by nitrogen and phosphorus has been an environmental issue in the Mid-Atlantic U.S. for more than 30 years. In 1997 a series of fishkills in Maryland that were also linked to outbreaks of the toxic dinoflagellate Pfiesteria piscicida and to human health problems resulted in intense public and media pressure to control agricultural nonpoint source pollution. By 1999 nutrient management laws had been passed in Delaware, Maryland, and Virginia. Concurrent with this were total maximum daily load (TMDL) lawsuits, changing regulations for concentrated animal feeding operations (CAFOs), and new nutrient management policies by USDA-NRCS. All involved have sought "science-based" solutions and policies from the outset of these changes. We review the steps taken to integrate past and ongoing research into the development and implementation of nutrient management laws and guidelines for the Mid-Atlantic and provide a critical assessment of the current and future status of efforts to improve water quality in this region.

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The use of alum [aluminum sulfate: (Al₂)(SO₄)₃] as an amendment for poultry litter has been recommended as a best management practice to reduce the concentration of soluble phosphorus (P) in litters and in runoff from soils fertilized with alum-treated litter vs. normal litter. Alum treatment can also reduce ammonia (NH₃) emissions, lower fuel and electricity costs due to less need to ventilate poultry houses, and result in higher litter nitrogen (N) and sulfur (S) concentrations, and thus increased fertilizer value. We conducted a large-scale "on-farm" study of the use of alum as a litter amendment for commercial poultry operations on the Delmarva Peninsula. One hundred poultry houses received 7 applications of alum over an 18-month period; another 100 houses, as similar as possible in construction, management, etc., were used as a control group. Poultry litter samples were collected from all 200 houses at the beginning and conclusion of the project and analyzed for pH, and total and water soluble P, Al, N, As, Cu, and Zn. Results showed that litters treated with alum had lower water soluble P values (678 mg kg^-1) than unamended litters (1986 mg kg^-1) and higher concentrations of total N, S, and Al. Water soluble As, Cu, and Zn concentrations were lower in alum-amended litter (9, 220, 19 mg kg^-1) than unamended litter (25, 355, and 37 mg kg^-1) but soluble Al was higher (22 vs. 4 mg kg^-1).

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Sims, J.T. 2000. Phosphorus leaching in agricultural soils: Source, transport, and management factors .

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Nonpoint source pollution of surface waters by agricultural phosphorus (P) is emerging as a major environmental issue in the U.S. State and federal policies, laws, and regulations under development, or in place, seek to limit P applications in manures and fertilizers based on soil P alone, or in combination with other factors (e.g., topography, drainage, management practices, proximity to surface waters). Upper critical limits for soil test P, sometimes referred to as environmental thresholds, are now being established in the U.S. and in other countries. Approaches under consideration include agronomic soil P tests, measures of the degree of P saturation, and water soluble P. This presentation (i) reviews recent research on the use of soil P measurements as indicators of environmental risk and (ii) critically analyzes the approaches now being proposed in the mid-Atlantic region of the U.S. to identify soils sufficiently high in P to be of concern with respect to nonpoint source pollution of surface waters.

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Land application of animal manures and municipal biosolids based on crop nitrogen (N) requirements will build soil phosphorus (P) to values beyond crop requirements. Recent water quality concerns about P movement from biosolids-amended soils to surface waters have resulted in mandated, P-based management plans in some states, creating serious problems for municipalities seeking to beneficially re-use biosolids in crop production. We characterized the forms, solubility, and degree of saturation of P in soils from 17 sites in DE, MD, and VA where biosolids had been applied to crop land in accordance with state regulations. Data are compared with results from nearby setback areas managed similarly but without biosolids applications. Implications of the changes in soil P from biosolids use for water quality will be presented.

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Nutrient management (NM) is a critical component of land use planning. Efficient use of nutrients is not only economical, but also environmentally sound as it minimizes the loss of nutrients (e.g., nitrogen and phosphorus) which may have serious implications for sensitive surface and groundwater supplies. It is essential, therefore, that those charged with developing policy and/or writing plans have a good understanding of the issues. A training program consisting of eight modules was developed and conducted for NM planners and agency field staff in Delaware. Topics included basic principles of NM, nutrient cycling and management, soil testing/plant analysis, plan development and water quality/ecology. The format included slide-assisted lectures, interactive exercises, and panel discussions. Attendees received a training manual for later reference. A summary of the program and training materials will be presented.

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Nutrient management planning in the U.S. is changing from a voluntary agricultural practice to one that is increasingly regulated to protect environmental quality. State laws and national strategies emphasize the importance of science-based nutrient management plans, particularly for animal agriculture. Soil scientists and their colleagues in other disciplines have conducted research on the fate and transport of nutrients for decades. How can this research be used to formulate state and national policies that protect the environment and sustain agricultural profitability? The Soil Science Society of America (SSSA) has developed a position paper that outlines the process by which nutrient management policies should be developed and implemented. This position paper will be presented for discussion and debate.

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The nonpoint source pollution of surface and shallow ground waters by phosphorus (P) applied to crop lands as agricultural and municipal biosolids (manures, litters, sludges, wastewaters) is an area of intense interest and heated debate throughout the world. Agricultural biosolids management practices have historically been based on meeting crop N requirements; municipal biosolids have followed the same approach but have also had to address the environmental impacts of non-essential trace elements, organics, and pathogens. The result has been the accumulation of P in many soils to values that are excessive relative to crop needs and concerns about the relationship between soil P saturation and water quality. Basing the management of any type of biosolids on P will require a fundamental re-analysis of the agricultural use of these materials. This presentation provides a systematic, critical analysis of the development of P-based management plans for all biosolids, assuming water quality protection is of equal importance to agricultural production.

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Land application programs for organic amendments in the U.S. have historically followed either voluntary (animal manures) or regulatory (municipal biosolids) approaches. Concerns about nonpoint source pollution of surface and ground waters by P have intensified efforts in the U.S. to develop a more regulatory framework for the land application of animal manures, at both state and federal levels. At the same time questions have arisen about the absence of P criteria in regulatory programs used for the agricultural management of municipal biosolids. A survey of the current approaches used by the USEPA and state EPAs for P-based management of municipal biosolids will be presented, along with a summary of the current status of regulatory and legislative actions at the state and federal levels addressing animal wastes. A national strategy for the development of P-based management programs for organic wastes will be proposed.

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Gartley, K.L., J.T. Sims, and M.A. Flock. 2000. Soil test summary data: Valuable educational tool or invasion of privacy?

Increased computerization has improved the data processing capability of soil testing laboratories and consequently, made it possible for laboratories to develop large databases of soil test results. When combined with other information (e.g., location, management practices), these databases provide useful information in the form of soil test summaries. In their most basic form, summaries describe the distribution of soil test results within the group of samples. When combined with other information such as field location, cropping system or manure history, and compared across years, the data can be used to monitor long-term trends in soil fertility and/or highlight relationships between soil fertility and management practices. Soil test summaries, however, are not without limitation and controversy. First, summaries are only as accurtte and representative as the information and samples supplied to the laboratory. Second, and perhaps of greater importance, are confidentiality issues associated with soil test results. With increasing regulation of nutrient management, many growers have valid concerns regarding release of their results, even in a summary set format. A discussion of the development and use of soil test summaries will be presented along with perspectives and issues facing public and private laboratories.

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The addition of any new test to a soil testing laboratory’s list of services inherently raises several issues that must be addressed if the new test is to fit within the existing operation and is to be accepted and used appropriately by the laboratory’s clientele. Given the current discussion regarding the relationship between phosphorus (P) use by agriculture and the impact of P on the environment, the likelihood that a soil testing laboratory might be asked to offer a test which would provide a measure of environmental risk from P rather than just the agronomic requirement for P by a crop is increasing. Inclusion of such a test would require not only adjustments within the laboratory protocol but also the development of supporting materials such as report forms and/or fact sheets which explain how to interpret the results and offer some type of recommendation based on those results. This poster will summarize the University of Delaware Soil Testing Laboratory’s experiences with adding the Amorphous Iron and Aluminum and Oxalate-Extractable P test to its list of services as a means of estimating the degree of P saturation present in sensitive soils. Discussion will include a review of how the test is presented to the public, adjustments necessary to “fit” the test into our existing operation and interpretive materials developed to support its use.

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Little information is known regarding the availability of different organic P sources typically used as a fertilizer source in agricultural production. Thus, we investigated the relative solubilities of P in nine organic amendments consisting of four manure classes: liquid, fresh, composted, and treated. Organic P sources were incubated for 56 days with an Evesboro sandy loam (Mesic, coated Typic Quartzipsamment). The relationships between organic P source, water soluble P (WSP), Fe-oxide strip P (FeO-P), and Mehlich 3 P (M3-P) were examined. There were significant differences in WSP, FeO-P and M3-P between classes of organic P sources following the trend liquid>fresh>composted>treated sources. This data suggests that P availability coefficients can be assigned to different organic P sources to reflect differences in solubility and their potential reactivity in soils.

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The contribution of P to non-point source (NPS) pollution has become a concern in Delaware due to the degradation of water quality in the Delaware Inland Bays. Therefore, the state of Delaware has begun to create nutrient management legislation dealing with the issues of NPS pollution and focusing on agriculture lands. A Phosphorus Site Index (PSI) was developed for the state to assess the risk of potential for P losses from agricultural areas. This index was tested on six farms in Delaware, to determine how the use of the PSI would affect farmers within the region. In addition, an economic analysis was performed on these farms to determine the financial impact of using the PSI to determine where P based nutrient management planning should be used. Approximately 70% of fields fell within the "low risk" category, while approximately 8% fell into the "very high" risk category. The index seemed to be useful for ranking fields based on potential for P losses and allow the state to use the PSI to focus resources in areas where the biggest gains would be expected from investment in water quality protection measures.

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The buildup of soil phosphorus (P) to concentrations well above those needed for crop production in watersheds dominated by intensive broiler production is an issue of increasing concern. Past research has clearly shown that additions of broiler litter to soils increases soil test P and soluble P losses in runoff. However, questions still remain about the relationship between the initial soil test P value and the nature of the increase in P losses (linear or curvilinear) when soils are amended with broiler litter. we conducted an incubation study to examine the effect of broiler litter rates on (0, 2.5, 5.0, 7.5, 10 g/kg) on soil test P and soluble P in three groups of soils with similar physiocochemical properties but varying initial soil test P values (Mehlich 1 P: 9 to 340 mg P/kg). Soil moisture was adjusted to ~80% of field capacity and soils were incubated for four months with samples analyzed at one and four months. Soil test P (Mehlich 3), water soluble P, and Fe-strip P increased in a near-linear manner with increasing rates of poultry litter additions, regardless of initial soil test P concentrations. Effects of treatments on the degree of soil P saturation and desorbable P will also be reported.

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Characterizing phosphorus (P) transport from agricultural fields to surface waters has been increasingly important for water quality protection. The phosphorus site index (PI) was developed as a risk assessment tool to identify the risk of P transport from fields by integrating soil P status with transport and management parameters. We have revised and evaluated the PI in Delaware, Maryland, and Pennsylvania. The new version of the PI is separated into two parts, one addressing site transport and the other soil P and P sources. Our evaluation was conducted on more that 100 farms in Maryland and Delaware. This presentation summarizes the results of these evaluations, including a critical analysis of the method used to establish P management criteria based on the PI.

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Maguire, R.O., J.T. Sims, and T.J. Applegate. 2004. Supplementing phytase and decreasing phosphorus in turkey diets reduces phosphorus in litters and in runoff from amended soils. 

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A positive mass balance for P on many farms and regions with intensive animal agriculture has led to increased soil test P levels, and non-point losses of P that can have a detrimental effect on surface waters. Adding feed amendments, such as phytase, can increase P digestibility, lower feed and manure P contents and therefore decrease the total amount of P that must be managed in watersheds dominated by intensive animal agriculture. Despite the lowered total P content of such manures, concerns have been raised that feed additives may increase P solubility in manures and lead to a greater risk of P loss from manure amended soils. We obtained manures from several animal studies that involved feeding combinations of phytase, citric acid and 25OH-D3 with different levels of total P, to swine, broilers and turkeys, and analyzed these manures for total and water soluble P. The results will be discussed in terms of the implications for the mass balance of total P on intensive animal farms and how the feed additives and varying total P contents affected P solubility in manures.

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The use of feed additives, such as phytase, to increase the digestibility of P in animal diets has become common, in an attempt to decrease the problems associated with excessive amounts of total P in animal manures in areas with intensive animal agriculture. However little is known about how feed additives affect P solubility in manures and manure-amended soils. We generated turkey manures using several combinations of non-phytate P (nPP), phytase, and 25OH-D3. Three diets that contained reduced nPP, phytase, 25OH-D3 and both phytase and 25OH-D3 were identified as the most beneficial for reducing feed total P and maintaining bird health and weight gain. The manures from these diets, as well as control manures, were incubated with five soils from four U.S. states. Water soluble molybdate reactive P and organic P were measured after 1, 7, 21 and 42 days and Mehlich 3 P at days 1 and 42. The effects of dietary modification with reduced nPP, phytase and 25OH-D3 on the solubility of P in manure amended soils will be discussed.

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Regulations to protect surface water quality are becoming more common, and often involve changing manure nutrient management plans (NMPs) to a phosphorus (P) basis, as NMPs based on nitrogen (N) normally lead to the application of P at rates above crop requirements. It is important to understand how changing to NMPs based on P will affect P losses to surface waters via subsurface pathways. Therefore we established 12 plots (0.1 ha each) on the Delmarva Peninsula, and applied poultry manure according to a NMP based on N to 6 plots, with the remaining 6 plots receiving manure and inorganic N at rates dictated by a NMP based on P. Groundwater samplers were installed at depths of 30 cm and 75 cm in the center and down slope of each plot, with the depths of the samplers reflecting the base of the topsoil, and the depth the water table has to rise to for water to flow in the drainage ditches at the site, respectively. Concentrations of P in the groundwater at both depths under the NMPs based on N and P will be reported, and implications for P losses in subsurface pathways will be discussed.

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Concerns about phosphorus (P) concentrations in surface waters are longstanding. Attention has recently focused on P losses from diffuse sources such as agricultural soils. Considerable research has been carried out on P losses by runoff and erosion, for example under the "National P Project", but less is know about P losses from agricultural soils in leaching and subsurface flow. On the Delmarva Peninsula, sandy soils and flat topography predominate, and drainage ditches are required to lower the water table for profitable agriculture. A large proportion of rainfall infiltrates rather than flowing over the soil surface, creating a possible pathway for P leaching. We took intact soil columns with a range of soil test P values at two depths (20 cm and 40 cm), from ditched agricultural land. Soil samples were taken at corresponding depths of 0 to 20 and 20 to 40 cm and analyzed for pH, organic matter, water soluble P, iron strip P, Mehlich-1 P, and Mehlich-3 and oxalate P, iron and aluminum. The soil in the columns was brought to field capacity and leachate water was collected in response to adding a known volume of water. The leachate was analyzed for total P and molybdate reactive P. Leachate P will be related to depth, soil properties and soil test P. Implications for P losses from ditched agricultural soils on the Delmarva Peninsula will be discussed.

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Concerns about phosphorus (P) loss from agricultural land have led to laws mandating P-based nutrient management plans being passed in several U.S. mid-Atlantic states. While much is known about the fate of P in manured soils, less is understood about the relationship between biosolids (wastewater treatment residuals) treatment process and P availability in biosolids amended soils. We incubated two soils with biosolids from a range of treatment processes, with respect to incorporation of Fe, Al, lime and digestion, for two months. Release of P from the amended soils will be related to biosolids treatment process and biosolids analyses. Implications for P mobility in biosolids amended soils will be discussed.

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Water quality concerns have caused some U.S. states to develop regulations that will limit land application of animal manures and municipal biosolids based on soil P. While much is known of the fate of P in manured soils, less information is available on the effects of biosolid treatment process, such as digestion and incorporation of Al, Fe, and lime, on the behavior and mobility of P in soils. For two months, we incubated two soils of the mid-Atlantic region of the U.S. with biosolids from four different treatment processes typical of those currently used in the area. The kinetics of P release and changes in soil P forms with time will be related to biosolids treatment process. Implications for P mobility in biosolids amended soils and for the selection of biosolids treatment process by municipalities will be discussed.

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There has been increasing concern about the impact of agriculture on the environment and in particular, the effect of the loss of nutrients such as phosphorus (P) on ground and surface water quality. Most studies of P have involved relatively short-term measurements, while in the field, processes are long-term. We investigated long-term P sorption and desorption kinetics for topsoil and subsoil pairs from areas of intensive animal agriculture in Delaware and Ireland. These kinetics will be linked to several measures of soil P content and other soil properties such as oxalate-extractable aluminum and iron, organic matter content, and pH to improve our ability to predict P loss by surface and subsurface runoff.

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Toor, G.S., J.D. Peak, B.J. Cade-Menun, and J.T. Sims. 2004. Understanding phosphorus forms in dairy and poultry manures using sdvanced spectroscopic techniques. 

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Toor, G.S., and J.T. Sims. 2004. Leaching losses of phosphorus from three benchmark soils of the Inland Bays watershed. 

In areas of intensive animal production, phosphorus (P) excreted in manures often exceeds local crop requirements. This surplus manure P is generally applied to soils and has led to the current situation where soil test P is frequently above agronomic optimum values for crop growth. The transport of P to surface waters has been studied for years, however, less is known about the leaching of P to shallow ground waters. Soils and agricultural systems in the Inland Bays watershed, USA possess a number of the hydrologic characteristics associated with regions where P leaching is a concern. In order to determine the leaching potential of three dominant soil series present in the region, we collected 9 soil columns (50-cm deep, 30-cm diameter) within each soil series, which vary in soil test P from "low-medium (50 to 100 mg Mehlich 3-P/kg)" to "excessive (>150 mg Mehlich 3-P/kg)". Columns were collected using soil coring machine, which is attached to a tractor, with each column being encased in a cylindrical PVC pipe casing as it is collected. The bottom 4-cm of the soil column was removed from the cylinder and replaced with a washed gravel and sand mixture to create a free-draining situation similar to that of the field soil. Leaching studies are being conducted using these columns to establish quantitative relationships between soil test P and P saturation in the soil profile and P concentrations in leachate.

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Toor, G.S., S. Hunger, J.D. Peak, J.T. Sims, and D.L. Sparks. 2003. Advances in the characterization of phosphorus in organic wastes. 

There is international interest today in the fate and transformations of phosphorus (P) applied to soils in organic wastes. The growing interest in this topic stems from (i) long-standing agricultural concerns about the most efficient means to beneficially recycle the P in organic wastes as a plant nutrient and (ii) increased regulation of all forms of organic P used as soil amendments in order to prevent nonpoint source pollution of surface and shallow ground waters. The typical approach used by land managers to characterize P in organic wastes is to measure total P. Most recently, there has been growing interest in measuring water soluble P to determine the potential effect of land application of organic wastes on soluble P losses via surface runoff and leaching. Most scientists involved in this research recognize that measuring total or water soluble P will provide only limited information about the fate of P in soils amended with organic wastes. Fortunately, recent research has begun to advance our knowledge of the speciation of P in organic wastes by applying new analytical methodologies to P characterization (e.g., nuclear magnetic resonance (NMR), X-ray absorption near edge structure (XANES) spectroscopy, enzymatic hydrolysis). This paper will discuss using "a case study approach" of how analytical methods such as sequential P extraction, NMR, enzyme hydrolysis and XANES spectroscopy can aid researchers in advancing knowledge of P speciation in manures.

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Toor, G.S., J.T. Sims, and Z. Dou. 2003. Phosphorus dynamics in soils amended with dairy manures from modified diets.

Phosphorus (P) losses from agricultural production systems have contributed to the widespread eutrophication of natural waters. This is especially true in areas with intensive animal farming, where repeated manure applications have led to excessive accumulation of P in soils. Recent research has begun to focus on ways to reduce P excretion in manures through dietary modification by feeding P closer to the animal requirement. On dairy farms, it has been a common practice to add inorganic P to diets due to concerns that the amount of available P in the organic ingredients may be inadequate for satisfactory cow performance. The National Research Council recommends 0.32 to 0.38 % P for lactating dairy cows. However, on many US dairy farms, P is often supplemented at rates much higher than the recommended range, sometimes reaching up to 0.80 % P. The excessive addition of inorganic P results in higher P excretion in manure, increasing the potential of P losses to waters. The objective of this study was to investigate the effect of dairy diet modification on P forms in manures and manure-amended soils. Through laboratory incubation trials, two soils were amended with dairy manures at a uniform rate of 150 kg P ha^-1. The manure samples were collected from commercial dairy farms in the Northeast and Mid-Atlantic regions and contained total P ranging from 5.5 to 14.0 g kg^-1 manure dry matter. Water extractable P, Mehlich 3 P, and sequential P fractionation data will be reported.

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Phosphorus (P) is considered a key element for promoting eutrophication of natural waters and evidence is accumulating that the degree of eutrophication in water bodies may be influenced by the P species leached/eroded from agricultural systems. Research over the last four decades has shown that organic P does move in the soil profile, however, the different forms of organic P as it is transported through the soil remain largely unknown. Understanding the different organic P forms in the leachate will help us to trace the origin of P species so that specific P mitigation strategies can be implemented at the source. Therefore, the objective of this study was to characterize the different P forms in leachate from a grassland soil using a combination of ³¹P nuclear magnetic resonance (NMR) and enzyme (phosphatase) hydrolysis techniques. Extensive physico-chemical analysis of leachate collected from intact soil monoliths (50 cm diameter, 70 cm depth) over two year period suggested that unreactive forms of P were the dominant forms (>85 %) leached from the Lismore Silt Loam soil (Udic Haplustept). The unreactive P was confirmed to consist of monoesters (67 %) and diesters (20 %) with NMR spectroscopy. A functional classification of monoesters by using specific phosphatase enzymes into labile monoester P (7-36 % of total unreactive P, TUP) and inositol hexakisphosphate (8-37 % of TUP) was achieved. This is a first direct evidence of the presence of these organic P forms in leachate and highlights a greater threat to water bodies from organic P transfer as these species has been reported to be directly utilized by algae and cynobacteria in the aquatic ecosystems.

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Water quality degradation in areas of intensive livestock production has prompted concerns about the need to better manage phosphorus (P) in organic wastes, as P is a key element for accelerating eutrophication of natural waters. To more effectively utilize and manage organic manures, a detailed understanding of different chemical forms of manure P is important. From an agronomic perspective, only total P is typically measured primarily to determine the total amount of P being added to the farmland. However, from an environmental perspective, it is equally important to know the different forms of P present in the manures. For example, it has been demonstrated that some of the organic P species (labile monoester P, inositol hexakisphosphate, diesters) are directly available to aquatic biota and thus pose a threat to the deterioration of water quality. The main objective of this study was to characterize P in dairy (produced from diets with different P levels) and poultry manures (amended with phytase or alum) using traditional (chemical P fractionation) and new (X-ray Absorption Near Edge Structure, XANES, spectroscopy) methods. Chemical fractionation of P suggested that manures were composed of inorganic (total inorganic P, 21-51 %) and organic P species (inositol hexakisphosphate type material (IHP): 25-52 %, nucleic acid type P/residual P: 18-41 %, and phospholipids (<2 %)). The XANES spectroscopic analyses at the P K-edge suggested that a relatively large fraction of the P in all manures was consistent with organic and weakly-bound phosphate. In dairy manure samples, spectral features consistent with hydroxylapatite-type calcium phosphates were observed. In the poultry litter samples amended with phytase, a 20% decrease in IHP was noted compared with unamended litter indicating that addition of phytase hydrolyzed the IHP component which culminated in 15 % higher inorganic P in phytase amended litter. In the alum amended poultry litter, there was 19 % decrease in the IHP probably due to the formation of insoluble complexes of IHP with aluminum (added with alum). Spectral features consistent with poorly crystalline calcium phosphates were observed in some poultry manures, depending on alum/phytase amendment.

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Preferential flow can result in elevated concentrations of phosphorus (P) in leachate/surface runoff particularly following application of animal waste, which in turn may contribute to accelerated eutrophication of natural waters. This study evaluated P loss from a grassland soil immediately following application of farm diry effluent (FDE). Intact monolith lysimeters (50-cm diameter, 70-cm depth) were collected from a Lismore silt loam soil (Udic Haplustept) under pasture. Treatments included applications of mineral P fertilizer (45 kg P ha^-1) with and without farm dairy effluent (FDE: 200 and 400 kg N ha^-1), and cow urine (1000 kg N ha^-1). Leachate was collected on 8 occasions following FDE application between August 1999 and May 2001. Dissolved reactive P (DRP) and total dissolved P (TDP) were determined on filtered (<0.45 mm) whereas, total reactive P (TRP) and total P (TP) were determined on unfiltered leachate and FDE samples. Of the TP losses that occurred over the two years from the FDE treatments, 44-61 % (1.9-2.6 kg ha^-1) was lost during the 8 drainage events that occurred within 24 hours following FDE application. Concentrations of TP determined in the leachate were commonly 100-400 μg L^-1, although TP concentrations immediately following FDE application were often 2500 μg L^-1. This was attributed to preferential flow, which resulted in rapid transport of unreactive P (mainly organic P) from the applied FDE. Therefore, short-term strategies for reducing P loss in this free-draining soil should aim to increase the residence time of applied P from FDE within the soil.

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Effective environmental management of intensive grassland requires detailed understanding of the amounts and forms of soil phosphorus (P) loss to the environment. Repeated applications of fertilizer and manure have led to P accumulation in soils making them long-term P diffuse sources. This study was conducted on intact monolith lysimeters (50 cm diameter, 70 cm depth), which were collected from a Lismore silt loam soil (Udic Haplustept) under pasture. Treatments included applications of mineral P fertilizer (45 kg P ha^-1) with and without farm dairy effluent (FDE: 200 and 400 kg N ha^-1), and cow urine (1000 kg N ha^-1). Flood irrigation (100 mm) was applied every three weeks between November and April. Leachate was collected after irrigation or a significant rainfall event and analyzed for dissolved reactive P (DRP) and total dissolved P (TDP) in a filtered (<0.45 mm) sample, and total reactive P (TRP) and total P (TP) in an unfiltered sample within 48 hours of collection. Examination of the seasonal pattern of P forms in the leachate indicated that total particulate P (TPP) was the dominant form in the leachate (77 % of TP) compared with total dissolved P (TDP) (23 % of TP) during the irrigation season (November - April). This was mainly attributed to greater preferential flow, which increased physical dislocation of particulate bound P. During the non-irrigation season (May - October), the proportions of TPP (51 % of TP) and TDP (49 % of TP) in leachate were similar.

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Amending poultry litter with alum [aluminum sulfate: (Al₂)(SO₄)₃] has been proposed as a best management practice to reduce soluble phosphorus (P) losses from litters and soils fertilized with litters to surface waters and shallow ground waters. Litter amended with alum, compared to normal litter, should result in decreases in soluble P and desorbable P in litter-amended soils, regardless of soil pH, and will likely have no effect on soluble or exchangeable Al, which is controlled by soil pH. The effects of soil pH on P and Al solubility were evaluated in a long-term laboratory study. Four Al:P ratios (0.3, 0.5, 0.7, and 1.0) and unamended poultry litter were applied to two soils at comparable rates of total P (150 kg TP/ha). The soils initially were brought to four different pH levels, ranging from 4.1 to 6.4. Moistened soil-litter mixtures were incubated and subsampled at 0, 7, 28, 49, and 98 days. Extractions for water-soluble P and Al were done immediately after subsampling. Another subsample was dried, then tested for pH, oxalate-extractable P, Al, and Fe; Mehlich 3-extractable P, Al, Fe, and Ca; iron-oxide strip P; KCl-exchangeable Al; and KCl-extractable NH4 and NO3. We report results for these analyses for both soils at the various pH levels.

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New soil tests are being developed to characterize the potential for phosphorus (P) loss to surface and shallow ground waters by runoff and leaching. One approach that has received interest lately is characterization of the degree of soil P saturation (DPS). The original method developed to measure DPS involved extraction of soils with acid ammonium oxalate (DPS-Ox) for P, aluminum (Al), and iron (Fe), a somewhat time-consuming approach for routine soil testing laboratories. We investigated the suitability of the widely-used Mehlich 3 soil test to characterize DPS in soils by rapid extraction of P, Al, and Fe. Relationships between DPS-Ox and DPS-M3 and between both DPS and water-soluble P, desorbable P, and soil properties will be presented. An approach to use the Mehlich 3 test for DPS in watershed-scale, P-based nutrient management planning will also be discussed.

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Nutrient management for water quality protection is one of the most important agricultural issues facing Delaware and many other states in the U.S. Atlantic Coastal Plain. The role of phosphorus (P) in surface water quality problems such as eutrophication is well known. To develop management practices that can decrease non-point source pollution of waters by soil P, we need to understand the short- and long-term kinetics of P sorption We used rapid chemical extraction methods such as water-soluble P, readily-desorbable P, oxalate-extractable P, and iron-oxide strip P to characterize the solubility and extent of P saturation in 50 soils. Short-term P sorption was measured for the same soils using standard batch methods and a P sorption index. Long-term sorption was measured by reacting the soils with a 5 mM P solution for 1,4, and 16 weeks. Comparisons of short- and long-term P sorption kinetics will be related to other soil properties to improve our ability to predict P loss.

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Soil P accumulation resulting from nitrogen based application of manure and municipal waste water treatment residuals (Biosolids) is well documented. This soil P accumulation can result in excessive P losses to surface waters. There is clearly a need to understand the impact of land application of biosolids and poultry litter on soil P levels and non-point-source pollution of surrounding water bodies. We therefore established 20 plots each on experimental sites at the Universities of Delaware and Maryland respectively. Identical experimental design consisting of five treatments (Unamended soil, poultry litter and three biosolids receiving three different treatments from three different treatment plants) and four replications were set up at both sites. Soils were sampled at 0-5 and 0-15 cm depths: 1) before amendments with biosolids and poultry litter and 2) before each rainfall simulation. All soils and biosolids were analyzed for Ammonium-oxalate-extractable-P, Mehlich I-P, Mehlich 3-P, Molybdate-Reactive-P and Soluble-P. Implications for P availability in biosolids and poultry litter amended soils at 0-5 and 0-15 cm depths will be discussed.

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There is ongoing concern that land application of poultry litter is a cause of nonpoint source phosphorus (P) pollution of surface and shallow ground waters. One means to reduce the P surpluses in watersheds with intensive animal agriculture and the amount of P applied to cropland is dietary manipulation to reduce excreted P, using phytase enzymes and high available P corn (HAPC). We grew three flocks of broiler chickens using six diets that included phytase and HAPC. A greenhouse study was then conducted to compare P uptake by corn with litter from modified diets, normal litter, and fertilizer P. Major forms of soil P (soil test, water-soluble, desorbable, and P fractions) were also determined in post-harvest soils.

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The sorption and desorption of phosphorus (P) in soils assumes a magnitude of ever greater importance as knowledge of the effects of P losses on ground and surface water quality is updated with new scientific findings. Poultry feeds produced with normal corn varieties are high in P because of the need to compensate for the low digestibility to monogastric animals of phytate-P in corn by supplementing the diets with inorganic P. Reducing P in the diets should decrease the potential environmental impacts when poultry manures and litters are applied to cropland. We investigated the effect of using a low phytate P corn hybrid and/or the phytase enzyme in six poultry diets on (i) the amount and forms of P in poultry litters and (ii) the sorption and desorption of P in litter extracts by three coastal plain soils varying in organic matter, Fe, Al, and clay. The economic value and environmental implications of changing to poultry diets using low phytate corn and phytase enzymes will be discussed.

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Many agricultural soils in southern Delaware test high in P from years of PL applications from a highly concentrated poultry industry. In some areas, seasonally high water tables in poorly drained soils can increase the potential for P loss to water by subsurface pathways and surface runoff. Stabilizing P in such soils by the addition of by-products, such as drinking water treatment residuals rich in amorphous Al oxides may reduce P losses. Our objective was to assess the effect of aluminum water treatment residuals (AWTR) on P desorbability and extractability in a poorly drained soil subjected to flooding and draining. We conducted a long-term column study using a high P soil amended with 25 g/kg AWTR, with and without PL additions of 4 g/kg. Unamended columns were used as controls. Columns were incubated at field capacity and room temperature for 28 days, flooded for 55 days, then drained and incubated at field capacity for 72 additional days. During incubation, we conducted analyses for soil solution P, anion exchange membrane P, and redox potential. Our results showed that the addition of AWTR decreased soluble P in soils. At the end of the study, for the control, PL, AWTR, and AWTR+PL treatments, respectively, soluble P concentrations in lysimeter samples were 0.80, 1.48, 0.06, and 0.16 mg P/L and in the topsoil were 92, 120, 10, and 18 mg/kg.

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Southern Delaware is the site of one of the most concentrated poultry industries in the U.S. Land application of poultry litter to cropland has always been the only economical viable alternative for this industry. Today many soils in southern Delaware are rated as “excessive” in soil test phosphorus (P) because applications of poultry litter, alone or in conjunction with inorganic fertilizers, annually add more P than is removed in harvested crops. Because nonpoint source pollution of surface waters by P is an important environmental issue in Delaware, there is need for management practices that reduce P losses in leaching and runoff. Our objective was to assess the value of amending soils considered excessive in P with municipal and industrial by-products (e.g., water treatment residuals) high in reactive Fe and Al on P solubility and sorption-desorption. Two coastal plain soils were incubated with five rates of several by-products for 7, 21, and 49 days and changes in P solubility, desorbability, and sorption capacity were determined. Effects of the by-products on soil pH, soluble salts, and non-essential trace elements will also be presented.

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Chemical amendment of poultry litter to stabilize phosphorus (P) and increase ammonia emissions has received increased interest because of the impacts of P on water quality and NH₃ on poultry performance and air quality. Alum (aluminum sulfate) has been shown to be an effective litter treatment but questions remain about the stability of Al and P in soils amended with alum-treated litter. We characterized the chemical properties of litter treated with alum at five rates throughout the growth of five flocks of broiler chickens under on-farm conditions. The litter was then used in laboratory studies investigating the effect of soil pH on the forms and solubilities of P and Al in two Atlantic Coastal Plain soils amended with alum-treated poultry litter. Changes in Al and P with time during the two-month study will be reported.

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Amending poultry litter with alum [aluminum sulfate: (Al₂)(SO₄)₃] has been proposed as a means to reduce soluble phosphorus (P) losses to surface waters and shallow ground waters. Most research on this management practice has been conducted on pastures in the southeastern U.S. Because the poultry industry on the Delmarva peninsula primarily applies litter to crop land used for the production of corn, soybeans, and small grains, there is a need to evaluate the forms and plant availability of P, and other elements (Al, As, Cu, N, S, Zn), when litters are incorporated with soils. We conducted a long-term greenhouse study comparing alum-amended (with four Al:P ratios - 0.3, 0.5, 0.7, and 1.0) and unamended poultry litter and fertilizer P, all applied to three soils at comparable rates of total P (150 kg TP/ha). Corn, wheat, and soybeans were grown for eight weeks each (litter and fertilizer P were applied prior to each crop). We report results of soil analyses for soluble and plant available nutrients and trace elements, and plant growth and elemental uptake for all three crops.

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Alum (aluminum sulfate) has shown promise as a means to decrease the solubility of phosphorus (P) and reduce ammonia (NH₃) emissions from poultry litter. We generated alum-amended litter under on-farm conditions by adding alum to the litter produced by five flocks of broiler chickens. Alum-amended and normal litter were then used in a greenhouse study with three coastal plain soils and three crops (corn, wheat, soybeans) to determine the effects of amending litter with alum on plant growth and uptake of Al and P. Results to be reported will include plant dry matter production, elemental composition and the forms of Al and P in soils at the conclusion of plant growth.

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Approximately 900,000 Mg of poultry litter are produced in Delmarva each year, the majority of which is land-applied for crop nutrients. Commonly, a phosphorus (P) surplus results when crop removal of P is less than that applied. Best management practices should be employed to minimize this surplus and ensure that P does not leave the field and adversely affect water quality. The application of aluminum sulfate (alum) has been shown to be effective in reducing soluble P and conserving nitrogen (N) in poultry litters, in reducing P in runoff from soils amended with litters, and in improving poultry health. Poultry litters were treated with alum and applied to Atlantic Coastal Plain soils to evaluate the effectiveness of this practice in Delmarva. Sorption and desorption of P as a function of time and application rate will be discussed.

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Contact jtsims@udel.edu

Contact jtsims@udel.edu

Concern over nutrient losses from agricultural fields and their contribution to surface water eutrophication has led to research into broiler diet modification to reduce phosphorus (P) concentrations in broiler litter (BL). The addition of phytase and vitamin D metabolites to broiler diets in conjunction with reductions in supplemental non-phytate P has shown promise as a means to reduce P concentration in BL. However, little is known about the effect of dietary modification on P solubility and forms in BL or litter-amended soil. This study was conducted to determine the impact of broiler diet modification in conjunction with storage on changes in P solubility and forms in BL and litter amended soils and how this in turn will influence P losses in runoff from amended soils.

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Phytase use in broiler diets to reduce total P in broiler litter has become a common practice; however, little is known about the effect of dietary phytase on P solubility in the resulting litter, particularly when litters are stored for prolonged periods of time. This study was conducted to determine the effects of phytase in broiler diets and storage conditions on P solubility in the litter. Litters generated from four diets were stored for six months. The four diets were (i) National Research Council (NRC) recommendations, (ii) University of Maryland College Park (UMC) recommendations, (iii) UMC with 600 FTU phytase and a 0.064% reduction in non-phytate P (nPP), and (iv) NRC with 600 FTU phytase and a 0.10% reduction in nPP. Two storage containers were used for each litter type, one containing litter at its initial moisture content (M.C.) and the other was brought up to a M.C. of 40%. The litters were sampled periodically and analyzed for soluble P, M.C., and total P (initial and final samples only). Effect of diet on soluble P during storage will be discussed along with the implications for land application programs using broiler litters generated from diets including phytase.

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Phosphorus (P) lost in runoff from agricultural fields has been identified as a contributor to eutrophication in freshwater systems. The purpose of this study was to evaluate the environmental performance of four cropping systems based on their discharge of P in runoff. The Sustainable Agriculture Project was established at Chesapeake Farms in 1993 to investigate the environmental, economic, and social implications of four cropping systems commonly employed in the region. Since 1994, runoff from the cropping systems has been sampled and analyzed for various nutrients. Conventional tillage resulted in an increase in total P concentrations and a decrease in orthophosphate-P concentrations in runoff. Furthermore, the percentage of total P as orthophosphate-P in runoff was lower in the conventionally tilled systems than in the no-till or reduced tillage systems. Sediment loss and exposure of P to surface runoff, by surface application of fertilizers and manures, had the greatest impact on P loss in runoff. In addition, timing of specific activities relative to rainfall events influenced the impact of those activities on P concentrations in runoff. As a result, systems that utilized cover crops, crop rotations, and reduced tillage exhibited the least propensity for P loss in runoff.

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McGrath, J.M., and J.T. Sims. 2000. Effect of poultry diets using phytase enzymes and high available phosphorus corn on phosphorus in poultry litter, soils, and runoff.

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Application of phosphorus (P) in excess of crop needs to agricultural soils can cause an accumulation of P that increases the potential for P losses in runoff and thus the eutrophication of receiving waters. The Sustainable Agriculture Project at Chesapeake Farms (SAPCF) was established in 1993 to investigate the environmental, economic, and social implications of five cropping systems in the Chesapeake Bay watershed. The cropping systems ranged in intensity from continuous, no-till corn to a corn-rye cover-soybean-wheat-hairy vetch cover rotation that relied heavily on cultural management practices. The purpose of this study was to determine the effects of these cropping systems on soil P. Soil samples were taken in 1993 before the plots were established, and throughout the course of the project. The overall change in soil test P, a mass balance for P, and the effects of the different cropping systems on soluble P will be reported.

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Shober, A.L., and J.T. Sims. 2004. Effects of reducing conditions on phosphorus solubility in biosolids and manure amended soils.

Land application of biosolids and manures has led to buildup of excess soil phosphorus (P) thereby raising questions over the long-term stability of added P. There is concern that erosion of P-rich soil particles into surface water bodies or submergence of amended soils could lead to reducing conditions allowing for dissolution of P. Our objectives were to quantify dissolved P, Al, Fe, Ca, and As in 4 Mid-Atlantic soils amended with biosolids and manures under oxidized conditions, and determine the effects of reducing conditions on dissolved P, Al, Fe, Ca, and As release to overlying waters. Four soils were incubated for 30 d with manures, inorganic P, or biosolids. Dried soils were submerging under 0.01M NaCl in centrifuge tubes and reduced under N2. Redox potential (Eh) and pH were measured initially and then weekly until Eh reached values where Fe would be reduced. Dissolved P, Al, Fe, Ca, and As were analyzed initially and after reduction. Average soil Eh decreased from 585 mV to -52 mV, while pH increased from 5.9 to 6.9. Concentrations of dissolved P decreased for all samples as soils became more reduced regardless of increases in dissolved Fe. It is possible that P dissolution under reducing conditions was followed by sorption by Al in the reduced soils. More research must be conducted to determine if the soils are functioning as a sink for solution P once samples were reduced.

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Organic P sources vary widely in their P solubility and will have different relative risks for P loss to surface waters when applied to the soil. Phosphorus source coefficients (PSCs) were designed as a scaling factor for use in the P Site Index to account for these differences. Our objectives were to (1) quantify P solubility in Mid-Atlantic soils amended with animal manures and biosolids, (2) understand the mechanisms controlling P solubility in these soils, and (3) predict the potential for P loss to water using soil and P source properties. Ten organic P sources and inorganic P were incorporated into 8 soils. Subsamples were analyzed for water soluble P (WSP) at 48 h and 30 d, and Mehlich 3 (M3) P, Ca, Fe, and Al at 30 d. In general, application of untreated manures and inorganic P led to larger increases in WSP and M3P than biosolids or treated manures for all soils, regardless of initial soil M3-P Saturation Ratio (M3-PSR). Results indicate that when soils become more saturated with respect to P, P solubility of amended soils is increasingly controlled by source properties rather than soil properties. Analysis shows that P source %WSP and initial soil M3-PSR can predict soluble P when sources are incorporated into soils. Increasing incubation time led to decreases in WSP for soils amended with untreated manures and inorganic P.

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Shober, A.L., J.T. Sims, F. Coale, and J. White. 2003. Temporal changes in phosphorus fractionation in biosolids-amended soils: Relationships to phosphorus losses in runoff. 

Wastewater treatment processes have been shown to affect the forms of phosphorus (P) in biosolids and the potential for P loss from biosolids-amended soils. Soil samples, collected for a three-year field runoff study that received iron-treated (Fe-treated), lime stabilized, Fe/lime-treated biosolids, poultry litter, and control, were analyzed for water soluble P (WSP), iron-strip extractable P (FeO-P), Mehlich 3 P (M3P) and subjected to a sequential fractionation procedure to identify temporal changes in the forms and solubility of soil P. Results showed that soils receiving Fe-biosolids had lower WSP, FeO-P, and M3P when compared with lime stabilized biosolids and poultry litter. These results agree with runoff study data, which indicate that concentrations of dissolved reactive P (DRP) in runoff followed similar trends. Sequential fractionation trends indicated that concentrations of P associated with Fe were higher for Fe-treated biosolids while concentrations of P associated with Ca were similar for all soils. Fractionation also showed trends of decreasing sequential soluble P, while concentrations of Fe-P tended to increase with time in all soils. Other P fractions showed no definite changes with time. Results indicate that when compared with other amendments, addition of Fe-treated biosolids to soils will lead to less DRP in runoff as well as slow increases in insoluble forms of P associated with Fe.

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The application of biosolids to agricultural soils provides phosphorus (P) in excess of crop needs when applied at nitrogen based agronomic rates. This can result in the buildup of P in soils to levels above those needed for optimum crop yields and also increase risk of P loss to surface and ground waters by erosion, runoff and leaching. The Federal biosolids regulations (40 CFR Part 503) do not limit the amount of P that can be land applied. Because of concerns about the impact of P on water quality in the U.S., many state and federal agencies now recommend or require P-based nutrient management plans for agricultural operations that use animal manures. Similar actions are under consideration for the land application of biosolids. We conducted a national survey to determine if states had restrictions on P levels in biosolids and soils at land application sites. Results showed that more than 20 States have regulations or guidelines that can be imposed to restrict land application of biosolids based on P. Many of these states include numerical criteria for P in biosolids. Other states are preparing draft regulations that would include some P-based restrictions on land application.

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Hyde, J.E., G. Binford, and J.T. Sims. 2004. Using soil organic matter and phosphorus saturation to predict change in water soluble phosphorus following phosphorus amendment.

Nutrient management planning requires routine soil testing and manure management BMPs to minimize environmental phosphorus (P) loss. The objective of this study was to examine variables from routine soil test results to estimate changes in soil water soluble P (WSP) following soil P amendment. In an incubation study, 14 surface soils (0-15 cm) from the Mid-Atlantic and Northeast regions of the United States were amended with 150 kg P ha^-1 from one of two dairy manures of different P concentrations, or fertilizer (KH₂PO₄). The soils were analyzed for total P, Mehlich 3 P, Al, and Fe, organic matter (OM), pH, and soil texture. A stepwise regression procedure was developed using OM and P saturation ratio (M3 P/(Al+Fe)) to estimate changes in soil WSP from a variety of soil types and existing P levels.

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Nutrient management is an important part of diary production. New regulations have place emphasis on soil phosphorus (P) levels to reduce its loss to environmentally sensitive waters. The objectice of this study was to characterize regional; soil properties to estimate changes in soil P loss due to manure applications from different dairy diet P concentrations A total of 11 farms across five states (DE, MD, NY, PA, VA) were sampled for feed, fresh feces, stored manure, and soil. All samples were analyzed for total P, extractable aluminum, calcium, iron, and P; organic matter (OM), and pH. Preliminary results suggested a strong correlation between P content in feed and excreta extractable P (r2=0.76p=0.05). Similarly, excreta extractable P was significantly (p=0.05) correlated with manure water soluble P (r2=0.91). The soil sample results (pH, OM, and extractable elements) suggest the range of soils represent the diversity in soil characteristics necessary to develop a regional model, however further study is needed to determine if the soil P loss can effectively be predicted from diet P management.

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Gilbert, J.K., J.T. Sims, R. Lowrance, and G. Williams. 2004. Using the riparian ecosystem management model (REMM) to assess the effect of vegetated filter strips on phosphorus losses in runoff. 

Nonpoint phosphorus (P) pollution of surface and shallow ground waters is a widespread environmental concern. In Delaware, historic application of poultry litter and inorganic fertilizer has resulted in accumulation of phosphorus (P) in soils. Programs such as the Conservation Reserve Enhancement Program, (CREP) offer incentives for voluntary management practices to reduce P pollution. One of these practices, vegetative filter strips (VFS), accounts for approximately 20% of the 7500 acres under CREP in the state. While it is accepted that VFS's can control particulate P (PP) pollution, it is not known how VFS's affect dissolved reactive P (DRP) movement. The Riparian Ecosystem Management Model (REMM) quantifies the effectiveness of VFS's at reducing P loss to water, primarily by considering PP transfer via soil erosion. We evaluated the current version of REMM for high P soils of the mid-Atlantic coastal plain to determine VFS characteristics needed to minimize P loss. Simulations evaluated the influence of VFS width, nutrient management BMP's, soil moisture status, and the role of soil chemical properties (e.g., soil P saturation, soil organic matter, Al and Fe oxides) in P retention by VFS's. Model validation will be conducted by comparing REMM output to field data from VFS's in Delaware. Results will be related to ongoing efforts to design VFS's that can effectively prevent nonpoint P water pollution.

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Gilbert, J.K., and J.T. Sims. 2004. Phosphorus forms and solubility in agricultural buffers: Implications for water quality.

In the state of Delaware, CREP (Conservation Reserve Enhancement Program) subsidizes land taken out of agricultural production to install riparian buffers as a management practice to control nonpoint source pollution. The simplest riparian buffer is the vegetative filter strip (VFS). There is debate to what pollutants are efficiently managed by VFS. Runoff studies have shown that sediments and sediment bound nutrients are better managed by VFS than soluble nitrogen (N) and phosphorus (P). This study was designed to determine what mechanisms affect dissolved P retention by VFS, by characterizing the effects of VFS on soil P saturation ratios, water soluble P and organic P in agricultural fields compared to adjacent VFS. An adsorption/desorption study was also conducted on selected samples to determine whether changes in soil properties due to buffer vegetation were affecting the potential for dissolved P retention and release. Samples were taken from eight different farms in the state of Delaware. Priority watershed were identified within the state and farms with buffers within those watershed were chosen for monitoring. Buffers were also chosen to represent the five most common soil series in the state, to include narrow (7m-18m) and wider (>24m) designs, and to include both warm and cool season grasses. Performance differences over time will be evaluated, although the majority of buffers in the state are less than 5 years old. Data will be used to understand in what ways VFS can be used to manage dissolved P losses from agricultural lands.

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Boyer, L.S., G.D. Binford, D.J. Hansen, J.T. Sims, K.L. Gartley, and S.C. Tingle. 2004. Evaluating the amino sugar nitrogen test for use on Delaware soils.

Animal manures represent a significant source of fertilizer N for corn production in Delaware. Research has shown that long-term histories of manure application to soils can result in N losses from soils if N availability from these long-term applications of manure is not accounted for when making N fertilizer decisions, which can result in both environmental and human health concerns. Recently, a new soil test was developed at the University of Illinois that shows promise as a tool for improving N management decisions on soils with histories of manure applications. The objective of this two-year project was to evaluate the potential of this soil test as an N management tool in Delaware. This test measures an amino sugar N component of soils. A great advantage of this soil test is that the analyses can be performed on the same soil sample that is taken for traditional soil testing of pH, P, K, and other nutrients. Our preliminary results suggest that a high percentage of Delaware soils are quite low in this amino sugar component relative to the critical concentration that was developed in Illinois. In fact, amino sugar N concentrations of 65 fields sampled during 2003 and 2004 were all well below the critical concentration proposed by Illinois research. Fields with long-term histories of manure applications had no tendency for higher amino sugar N concentrations.

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Boyer, L., R.O. Maguire, and J.T. Sims. 2002. Phosphorus leaching from undisturbed soil columns amended with normal and alum-treated poultry litter.

The environmentally sound management of animal manures is a major problem facing U.S. agriculture today. An area of particular concern on the Delmarva Peninsula is the impact of phosphorus (P) leaching from "high P" soils on ground and surface water quality. Phosphorus leaching can occur in deep sandy soils, in high organic matter soils, and in soils where over-fertilization and/or excessive use of organic wastes, such as poultry litter, has increased soil P to values above those needed for economically optimum crop yields. One best management practice to reduce the environmental impacts of animal manures that is of particular interest to the poultry industry is the use of "alum" [Al₂(SO₄)₃] as a poultry litter amendment ("litter" is a mixture of bedding material, usually sawdust, and poultry manure). Our objective was to compare the effects of normal and alum-treated poultry litter on the leaching of P and aluminum from undisturbed soil columns varying in soil test P.

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Eaton, R.A., and J.T. Sims. 2002. Water treatment residuals as soil amendments for agricultural buffers: Effects on plant growth, soil phosphorus, and phosphorus leaching.

Recent research has shown that saturation of soil with P can not only enhance soluble P losses in runoff but also by leaching into shallow ground waters. Consequently, there is a need to develop and evaluate innovative soil conservation practices that will reduce subsurface P losses. We evaluated the use of water treatment residuals (WTRs) as soil amendments for buffer strips using laboratory and greenhouse studies. Results from lab studies clearly showed that WTRs could stabilize soil P in less soluble forms and also increase the P sorption capacity of high P soils varying in chemical and physical properties. Greenhouse studies showed that a municipal alum WTR and an industrial Fe WTR could reduce P solubility and leaching without negatively affecting the growth of either agronomic crops or plants typically grown in buffer strips. Implications of these results for long-term management strategies needed to achieve the reductions in P loading required by state nutrient management laws and USEPA Total Maximum Daily Load (TMDL ) agreements will be discussed.

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Phosphorus (P) enrichment of surface waters due to agricultural runoff has been implicated as a major cause of the degradation of water quality in the Atlantic Coastal Plain. One alternative that is currently being investigated to protect water quality is the use of municipal or industrial water treatment residuals (WTRs) as a soil amendment in buffer strips, both to stabilize soil P and reduce P losses by runoff and leaching by increasing soil P sorption capacity. We incorporated two WTRs into three high P (> 100 mg P/kg) Delaware soils at four rates (0, 15, 30, 60 g/kg) to evaluate WTR effects on P sorption/desorption. Amended soils were equilibrated for six months and sampled periodically to determine the influence of WTR rate and soil type on water soluble P, desorbable P, and total P sorption capacity. WTRs were found to effectively reduce soluble and desorbable P and increase soil P sorption capacity. WTRs were then incorporated at one rate with the same three soils used in the laboratory experiment. Orchard grass (Dactylis glomerata) was then grown in the amended soils, and early growth, emergence, and P uptake were evaluated. Soil properties that may affect plant growth in buffer strips (e.g., pH, soluble salts, trace element and nutrient availability) were also determined.

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Many soils in the Atlantic Coastal Plain are high in phosphorus (P) due to long-term over-application of manures and fertilizers. Stabilizing P in these soils by addition of drinking water treatment residuals (WTRs) may reduce P losses by runoff and leaching. We characterized WTRs from 20 treatment plants in the mid-Atlantic region for P sorption capacity and elemental composition. All WTRs were then incorporated with two high P soils and incubated for 21 days. WTRs effectively reduced soluble and desorbable P and increased soil P sorption capacity. An approach to predict the solubility of WTRs for use as soil amendments to protect water quality will be presented.

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Desorption of phosphorus (P) from soils has been described with a simplified power-type kinetic equation. The equation accounts for variations in three primary factors that influence P desorption, which are time, water to soil ratio, and the quantity of desorbable P present in the soil. The influence of each factor on P desorption is represented in the equation by a constant. Research outside Delaware has shown that the values of the constants correlate well to the ratio of clay to organic carbon (OC) for many soil types. However, these soils were not representative of most Delaware soils. We found that the constants correlate better to soil iron (Fe) and aluminum (Al) content or the ratio of Fe to OC. We will discuss the ability of the Delaware-modified equation to predict P concentrations in runoff collected during greenhouse and field rainfall simulation experiments and the intended use of the desorption equation in a future field-scale P transport simulation model.

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FHANTM2 is a field scale model developed in Florida to simulate water and phosphorus (P) movement in high water table, artificially drained soils. In Florida when a site is out of compliance with P discharge limits, FHANTM2 is used to determine what land use practices can bring the site back into compliance. A similar use is intended in Delaware.  In FHANTM2, hydrology is based on the DRAINMOD model, and P movement is based on the GLEAMS model. The GLEAMS model code was previously modified to improve model performance in the flat, high-water table, sandy Spodosols of Florida. For use in Delaware, we have modified the P model code again to more accurately represent local soils and conditions. We will present a summary of these Delaware modifications, the research involved in making these modifications and the results of the calibration and confirmation processes for the completed model.

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Desorption of phosphorus (P) from soils has been successfully described by several researchers with a simplified kinetic equation. The equation accounts for variations in three primary factors that influence P desorption, which are time, water to soil ratio, and the quantity of desorbable P present in the soil. Each factor is represented in the equation by a constant. Previous research outside of Delaware has shown that the values of the constants correlate well to the ratio of clay to organic carbon (OC) for many different soil types. However, these soils were not representative of most Delaware soils. We conducted desorption experiments and calculated values for the three equation constants for twenty different Delaware soils. We found that the constants correlated well to soil iron (Fe) and aluminum (Al) content or the ratio of Fe and Al to OC, but not to the ratio of clay to OC. We will discuss our experimental results and the intended use of the desorption equation in a future P transport simulation model.

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FHANTM2 is a field-scale model developed in Florida to simulate water and phosphorus (P) movement. In Florida, when a site is out of compliance with P discharge limitations, FHANTM2 is used to determine what land use practices can bring the site back into compliance. A similar use is intended in Delaware. In FHANTM, hydrology is based on the DRAINMOD model and P movement is based on the GLEAMS model. The GLEAMS model code has been altered to improve model performance in the flat, high water table, sandy Spodosols of Florida. To be used in Delaware, the P model code must be altered again to accurately represent the soils found there. These alterations deal primarily with the relationship between P sorption and soil physical or chemical properties, and are based on data collected from years of soil P research in Delaware. A summary of this research and the resulting modifications made to FHANTM2 will be presented.

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Protecting water quality in southern Delaware’s Inland Bays is a priority because they are valuable fisheries, recreational areas, and dynamic ecosystems. Southern Delaware is dominated by poultry-grain agriculture. Phosphorus (P) inputs to poultry farms greatly exceeding outputs has lead to widespread elevation of P in soils, often to agronomically excessive levels, and an increased potential for P losses to surface waters by via runoff, erosion, and drainage. We have recently begun to use the FHANTM 2.0 field-scale simulation model, originally developed in Florida and modified for use in Delaware, to assess the nature of and the effect of management practices on P pollution. Our presentation summarizes research results and status.

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Previous work has shown that runoff from soils high in phosphorus (P) can potentially contribute to non point source pollution of surface waters. Current efforts toward developing a national P site index have additionally focused on factors other than soil test P (STP) such as rainfall intensity, slope, cropping system, management, and soil type. Although STP is a major factor in causing runoff P losses, the relationship between STP and P losses in runoff is dependent upon soil type. We conducted rainfall simulation studies with soil boxes using five Delaware soil types consisting of four STP values ranging from low to excessive in Mehlich-1 P. Simulated rainfall events were conducted, using standard protocols for intensity and duration of rainfall. Runoff was collected and analyzed for soluble P, iron strip P, and total P. Soils were characterized and will be related to the amounts of runoff P.

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Penn, C.J., J.T. Sims, and A.N. Sharpley. 2000. Effect of wastewater treatment process on forms of phosphorus in biosolids-amended soils.

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Penn, C.J., J.T. Sims, and A.N. Sharpley. 2000. Characterizing phosphorus losses in runoff from biosolids-amended soils by a rainfall simulation method.

Phosphorus (P) loss is surface water runoff from "high" P soils contributes to the eutrophication of fresh water bodies; soils become "high" in P by continuous application of P in the form of fertilizers, manures, and biosolids beyond plant needs. Recent legislation in Maryland restricts P applications to high P soils, however, under these new laws, land application of all types of municipal biosolids are regulated the same as animal manures. Since the biosolids treatment process will vary within a region, P loss in runoff from soils amended with different biosolids may also vary depending upon treatment process (e.g., liming, use of Al or Fe salts). We evaluated P losses in runoff from biosolids-amended soils using a rainfall simulation box method. Two 15-minute rainfall simulations were conducted at one week intervals at a rainfall intensity of 7.5 cm/hr, using two different soils and 10 treatments: eight different biosolids types, one poultry manure, and a control (unamended soil). All runoff was collected and analyzed for water soluble P, iron oxide strip P, total P, sediment load, and total runoff volume. The relationship between biosolids treatment process and P losses in runoff will be reported.

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Runoff from soils excessive in phosphorus (P) can represent a significant nonpoint source of P. Under nutrient management legislation in Maryland, such soils can no longer receive P in any form. This includes manure and biosolids, which fall in the same category. However, due to the biosolids treatment process, runoff P characteristics may differ greatly from manure, or between the biosolids themselves. We amended two different soils with four different types of biosolids and one poultry manure. Phosphorus was measured in runoff collected from the amended soils as well as in the amended soils themselves; this was done to correlate soil test P and biosolids treatment process to runoff P.

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Continuous addition of municipal biosolids based on plant nitrogen (N) requirements can result in the buildup of soil phosphorus (P) to values in excess of crop needs. Runoff from biosolids-amended soils high in P can potentially contribute to nonpoint source pollution of surface waters. Little is known about the effect of biosolids treatment processes on P losses in runoff. We conducted rainfall simulation studies with soil boxes using a Matapeake silt loam soil amended with four types of biosolids and one animal manure (poultry litter). Four simulated rainfall events were conducted, using standard protocols for intensity and duration of rainfall, at one-week intervals. Runoff was collected and analyzed for total P and soluble P. Runoff losses of P will be related to biosolids type and forms of P in biosolids and soils.

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Baum, K., G.M. Pierzynski, P. Kleinman, R.O. Maguire, J.T. Sims, G.S. Toor, and T. Zhang. 2003. Water-extractable P in animal waste.

Land applied manures create a potential phosphorus (P) runoff hazard. It may be possible to predict the potential hazard of surface applied manures by determining the water-soluble P content in the manure. The objective of this study was to evaluate the influence of sample handling, holding time, and type of filter paper on the water-soluble P content of manures. This was a multi-laboratory study. Water-soluble P was extracted from various manure samples using fresh, dried, and dried/ground samples; with holding times of 0, 3, and 7 days; and using Whatman #40 and 0.45 micron nitrocellulose membrane filter papers. Results varied among the different samples. A significant two-way interaction between holding time and sample handling method occurred for most samples. However, there was no consistent effect of time within or across sample handling methods, and there was no consistent effect of sample handling method within or across holding time. When significant differences due to the type of filter paper were found, Whatman #40 filter paper consistently yielded higher results.

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Surplus of nutrients (N and P) in food animal production systems contributes to accelerated water quality decline in many areas. A viable and cost-effective approach to managing nutrients on dairy farms is to minimize excessive nutrients in diets, which in turn leads to less nutrient excretion in manure without impairing animal performance. The objective of this study was to examine the N and P profiles in feed samples collected from dairy farms and elucidate major factors contributing to possible overfeeding. Data were obtained for nearly 100 commercial dairies in the Northeast and Mid-Atlantic regions. On average, these farms fed P 26% above the National Research Council recommendations. Excess P in diets is excreted in feces, contributing to potential environmental loss. Most farms overfed P because it was so formulated in the rations by nutrition service providers. Crude protein concentrations in the feed samples appear to match the formulated rations. However, the soluble protein fraction exceeded what was recommended, suggesting a possible shortage of rumen bypass proteins. This may lead to compromised milk yields as well as excretion of a high concentration of urea in urine. Urine urea-N, once excreted, is prune to volatilization losses. Concerns and challenges in optimizing feed nutrients will be discussed.

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In some areas of intensive animal operations the phosphorus (P) content of manures exceeds local crop requirements, raising concerns about the fate of this P. Efforts have recently focused on reducing the P content of manures through diet manipulation. We generated layer, broiler, turkey and swine manure using diets with reduced P and feed additives (such as phytase) to increase dietary P uptake. Soluble P was measured (i) in these manures and (ii) over a period of 29 days in soils amended with these manures. The implications of dietary amendment for P solubility in manures and manure-amended soils will be discussed.

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The use of alum (Al2(SO4)3)as a poultry litter (PL) amendment is used as a best management practice to reduce soluble phosphorus (P) and trace metal concentrations in runoff from soils treated with PL. There is evidence that a sorption mechanism between aluminum hydroxides and PO4-3 promotes P retention. It is important to understand the stability of P in the system and how aging affects distribution of phosphorus and metal availability in the litter to assess environmental fate. Sequential extractions and desorption studies are useful in trying to determine these relationships. Long-term (25d) desorption reveals that the use of alum amended litter as a soil treatment reduces the amount of P released, compared to a soil treated with unamended litter, by approximately 34, 52 and 56 mg kg-1 for Evesboro, Rumford and Pocomoke soils, respectively. While these values may be statistically significant, they may not be considerable in terms of management of PL on these soils. Sequential extractions of soils, after one PL application, show the relative amounts of P removed by each extractant follow the trend: NH4F=NH4-Oxalate>Na-DCB>NH4Cl=H2SO4, regardless of treatment. To understand these systems, the use of sequential extraction, of P in PL, in conjunction with X-ray Absorption Near Edge Structure Spectroscopy, will allow for direct evidence about how PL chemistry changes in the presence of alum.

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Reducing the amount of P in poultry litter is of great interest in many states. Diet modification is one approach for reducing P in litter. In the winter of 2000, a Delaware integrator conducted a feeding trial with four feeding scenarios that included normal corn with and without phytase enzyme and a 0.1% reduction in inorganic P, and low phytate corn with and without phytase enzyme and a 0.2% reduction in inorganic P. After two flocks of broilers, the poultry litter was collected and used in field studies during the 2000, 2001, and 2002 growing seasons at two locations. These studies consisted of 10 treatments: control (no P), the four litter samples from the feeding trial, poultry litter from a typical Delmarva poultry operation, and four rates of inorganic P fertilizer. Corn was planted to all plots and harvested for grain yield, and soil samples were taken at various times and analyzed for soil test P and water-soluble P. The various diets affected the P concentration of the litters, and the soil P levels followed trends similar to those expected from the analyses of the litter. No differences were observed in grain yields among the poultry litter treatments in 2000 or 2001.

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Dou, Z., J. Ferguson, J.D. Toth, L. Chase, K. Knowlton, R. Kohn, J.T. Sims, and Z. Wu. 2002. Phosphorus management on northeast and mid-Atlantic dairy farms: Preliminary data.

Improving phosphorus (P) management on dairy farms is critical for water quality and the sustainability of the dairy industry. Optimizing P in dairy rations is a cost-effective means to reduce the environmental impact of unfavorable P balance on animal farms; however, many dairy producers overfeed P and may be reluctant to modify their feeding strategies. A multistate, multi-disciplinary project supported by the USDA-IFAFS Program was recently initiated to develop optimal P management technologies on dairy farms. One of the objectives is to determine dietary P range that is adequate for optimal production while minimizing P excretion in manure. We have collected feed and fecal samples from nearly 100 commercial dairy operations in five states in the Northeast and Mid-Atlantic regions. Preliminary results from the initial sampling in Spring 2002 (n=53 herds) show a wide range of dietary P concentrations fed on farms, from 2.8 to 6.6 g/kg feed DM. Water soluble P in fecal samples from herds fed less than 4.0 g/kg dietary P is significantly lower than herds fed 4.0 g/kg or more dietary P (2.06 vs. 3.5 g/kg fecal DM).

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Toth, J.D., Z. Dou, J.D. Ferguson, Z. Wu, L. Chase, K. Knowlton, R. Kohn, and J.T. Sims. 2002. Phosphorus management on northeast and mid-Atlantic dairy farms: Survey results.

As the initial phase of a comprehensive project designed to develop optimal P management technologies, we surveyed dairy farmers in NY, PA, DE, MD, and VA on herd management and producer opinions on issues related to P feeding of lactating cows. Questionnaires were mailed in January 2002 to a random sample of 2500 farms. Response rate approximated 25%. Holstein was the predominant dairy breed (91%). Lactating herd size averaged 97 for MD, NY and VA and 64 for PA with similar milk yield for all five states (28 kg/d). TMR feeding was reported by 50% of respondents, component feeding by 40%, and intensive grazing by 3%. The majority (76%) reported routine forage testing. Diet P (% feed DM) ranged from 0.36% to 0.70% with a mean of 0.44% based on valid numerical values provided by 96 respondents. Use of mineral P supplements was reported by 60% of respondents. An overwhelming majority (89%) reported aware of nutrient management regulations; 47% acknowledged a general problem of P surplus on animal farms; 21% reported already reduced diet P; and 70% expressed interests in reducing P feeding if conditions are met. Reasons given for lack of interest in reducing P feeding include: current level recommended by professionals (64%), P helps with reproduction (36%), concerns over possible production loss (26%), safety margin (17%), etc. Clearly, farmers and nutrition service providers are all players impacting feeding decisions.

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Binford, G.D., D.J. Hansen, J.T. Sims, and W.R. Rohrer. 2001. Nutrient management plan: Delaware example.

Legislation was passed in June of 1999 (Title 3, Chapter 22) that requires most all entities who handle nutrients in the state of Delaware to have a nutrient management plan. This legislation also formed the Delaware Nutrient Management Commission, which is responsible for developing and implementing the state's nutrient management program. By law, the state nutrient management program must be fully implemented by January 1, 2007, with 20% of the required plans being developed each year from 2003 through 2007. The legislation outlined the main components that must be included in a nutrient management plan, while the nutrient management commission has been charged with determining the details of what must be included in a Delaware certified nutrient management plan. This paper will provide details of the required elements of nutrient management plans and animal waste management plans for Delaware.

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Agriculture is the dominant land use in Virginia, Maryland and Delaware and the dominant agricultural sector is the geographically concentrated poultry industry. On the Delmarva Peninsula for example, approximately 600 million broilers are produced annually. In addition, Virginia's Shenandoah Valley produces 187 million broilers and 34 million turkeys and milks 43,600 dairy cows annually. Approximately two-thirds of Virginia and approximately 70% of the Delmarva Peninsula drain into the Chesapeake Bay with the remainder of the Delmarva Peninsula draining into the Delaware Bay or the Atlantic Ocean. Public concern regarding non-point source pollution has recently resulted in legislation in all three states that will regulate nutrient use. Over applications of P resulting from annual applications of manure from confined animal feeding operations as well as the land application of P in biosolids from metropolitan areas is a major environmental concern for the region. Work on the national P runoff project is focusing on characterizing the relationship between soil test P and runoff P on soils impacted by the application of P as manure (especially poultry litter) and biosolids. Results from this work will be used to refine and validate the P-Index for each state.

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Phosphate contamination of the Chesapeake Bay is one of the largest environmental issues in the eastern United States today. Decades of intensive poultry litter application to sandy, low-lying soils in the Delmarva region has led to soils that contribute large amounts of phosphate to the watershed in both runoff and leaching. One possible solution to improve environmental quality is to lower water-soluble phosphate levels in poultry litter with wastewater coagulants such as alum (aluminum sulfate). It has been proven that addition of alum lowers water-soluble P levels dramatically in poultry litter, but the mechanism has never been fully addressed. We used XANES spectroscopy at the P k edge to directly determine the speciation of phosphate in poultry litter samples with varying amounts of alum amendment. No aluminum-phosphate solid phases were observed in the samples, and instead adsorption of phosphate to amorphous aluminum oxides appears to be the dominant mechanism. This has important implications for the long-term stability pf phosphate in alum-amended litters.

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Phosphorus loss via surface runoff has been recognized as a significant contributor to non-point source pollution of surface water bodies, such as the Chesapeake Bay. The growth of urban and suburban populations within the Bay's watershed has resulted in increased volumes of municipal biosolids. Due to their low N:P ratio, application of biosolids to cropland at N based rates can result in the accumulation of excessive P at the soil surface. The purpose of this study is to assess the potential for P runoff losses from soils receiving biosolids resulting from three different treatment processes. Biosolids were applied to a Chester silt loam soil (Typic Hapludult, fine loamy, mixed, mesic, 8% slope) and an Elsinboro silty clay loam soil (Typic Hapludult, fine loamy, mixed, mesic, 8% slope) at a rate to supply 200 kg/ha total P and incorporated by disking to a depth of 18 cm. The plots were planted with corn (Zea mays). Simulated rainfall (7 cm/hr) was applied and runoff collected 24 h after incorporation and at 1, 6, 12, and 13 months after application. Total runoff volumes were collected, measured, sampled and analyzed for pH, dissolved P, Fe-oxide strip P, total P and sediment load. Differences in dissolved P, Fe-oxide P, and total P were noted among biosolids generated from different wastewater treatment processes and controls at each sampling interval.

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Coale, F.J., J.T. Sims, A.B. Leytem, and E.B. Baugher. 2000. Applications of the Phosphorus Index: Mid-Atlantic U.S.

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Daniel, T.C., D.B. Beegle, F.J. Coale, W.E. Jokela, J.L. Lemunyon, A.N. Sharpley, J.T. Sims, and J.L. Weld. 2000. The Phosphorus Index: Current versions compared.

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Weld, J.L., D.B. Beegle, J.T. Sims, J.L. Lemunyon, A.N. Sharpley, W.J. Gburek, F.J. Coale, and A.B. Leytem. 2000. Comparison of state approaches to the development of phosphorus indices.

Many states are considering the use of the Phosphorus Index (PI) to address land management and water quality issues associated with phosphorus (P). The original PI, developed by Lemunyon and Gilbert as a field management tool to guide site-specific P management, was intended to be dynamic, allowing it to be modified to address the unique management, production, landscape, and climate conditions of individual states. Currently, more than 20 states and provinces of Canada are modifying the PI to meet their specific needs. These modifications have resulted in PI versions, that despite some similarities, have fundamental differences in: 1) the source and transport favors used to assess a site, 2) the method used to calculate the final PI value, 3) the range of final PI values, and 4) the management guidance associated with final PI values. Selected PI versions representative of the variety of PI's being used will be compared and contrasted based on these factors. This assessment will provide a better understanding of specific PI modifications, the potential impact of differences in PI versions on recommended P management guidelines, and the direction PI development is moving at the national level.

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Phosphorus contamination of the Chesapeake Bay watershed is a huge environmental problem. Since long-term application of poultry manure to agicultural land is one of the primary sources of excessive P levels in Delaware, efforts have been made to reduce the mobility of P in poultry litter by adding chemical amendments such as alum. This paper will present results from in situ XANES spectroscopy investigating the effect that alum amendments have on the chemical form of P in poultry litter. The effect of alum application rates and time of reaction will be discussed.

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Phosphorus (P) losses from Maryland's agricultural soils have been implicated as a contributor to eutrophication in the Chesapeake Bay. This paper investigates one aspect of the total agricultural P load - leaching P. The study consisted of five Maryland soils amended with four annual applications of animal manures. At two locations, five rates of broiler litter were applied annually in tilled and no tillage systems. At one location, five rates of broiler litter and five equivalent rates of P fertilizer were applied in a no tillage system. Total P, soluble reactive P, oxalate-extractable P, Fe, and Al, and Mehlich1 soil test P were determined at seven depth increments to 150 cm. The degree of P saturation was determined with depth. The influence of manure rates and tillage systems on P leaching will be discussed.

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The presidedress soil nitrate test (PSNT) measures the concentration of NO₃-N in the surface 30 cm of soil at an early growth stage of a crop to predict the need for supplemental N. The PSNT is widely used in field corn and sweet corn. The objective of our research was to evaluate and extend the usefulness of the PSNT to a new crop. We conducted field trials at 34 locations to calibrate the PSNT for use on cabbage that was planted after harvest of an early season vegetable crop. Cabbage response to sidedress N fertilizers was closely related to PSNT values. When PSNT values were low (<16 mg kg^-1) there were significant yield responses to sidedress N. When PSNT values were greater than 30 mg kg^-1, no significant yield responses to N were observed. The PSNT critical value is about 25 mg kg^-1, but research is continuing to more clearly define the critical level for cabbage. Our research demonstrates that the PSNT is useful for improving N management in crops other than corn.

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The general requirements of phosphorus (P) soil test methods for environmental purposes are similar to those of agronomic tests with respect to accuracy, reproducibility, speed, and cost. However, the potentially bioavailable soil P fraction of interest for environmental purposes may be different from the P pool of interest for crop production. Environmental soil P test methodology may change with soil chemistry and site-specific variables that affect the immediate and long-term fate of P lost via runoff, erosion, and subsurface transport. Challenges that relate to sample collection timing, depth, handling, and spatial variability remain unresolved for many cropping systems. We will discuss these challenges and raise the accountability issue of generating quantitative test results in light of their potential regulatory implications.

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