| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a USDA-ARS, Pasture Systems and Watershed Management Research Unit, Curtin Road, University Park, PA 16802
b Agricultural Analytical Services Laboratory, The Pennsylvania State University, University Park, PA 16802
c Dep. of Crop and Soil Sciences, The Pennsylvania State University, University Park, PA 16802
* Corresponding author (Peter.Kleinman{at}ars.usda.gov)
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: DM, dry matter • DRP, dissolved reactive phosphorus • TN, total nitrogen • TP, total phosphorus • WEP, water-extractable phosphorus
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Water-extractable P in manure has been linked to dissolved P (<0.45 µm) concentrations in runoff from manure-amended soils. Moore et al. (2000) showed that treating broiler chicken litter with alum (aluminum sulfate) reduced WEP concentrations in the litter relative to untreated chicken litter. Similarly, when alum-treated and untreated litters were broadcast onto pastures, differences in dissolved P concentrations of runoff corresponded with differences in litter WEP. Withers et al. (2001) found that concentrations of dissolved P in runoff from soils amended with mineral fertilizer, cattle manure, and biosolids were proportional to the concentration of WEP in the different amendments.
Water-extractable P in manure can also serve as a quantitative predictor of dissolved P in runoff when expressed as a concentration (e.g., g kg–1) on a dry weight equivalent basis. Kleinman et al. (2002b) applied dairy, chicken, and swine manures at equivalent total P (TP) rates (100 kg ha–1) to three acidic soils with different P concentrations. They found that when manures were broadcast, the WEP concentration of broadcast manure was strongly related to concentration of dissolved reactive P (DRP) in runoff (r2 = 0.86). For all soils, slopes of the regressions between DRP in runoff and WEP in manure were similar. In that study, manure WEP and runoff DRP were greatest in swine slurry, intermediate in layer chicken manure and lowest in dairy manure. Studies by Ebeling et al. (2002), Kleinman and Sharpley (2003), Brandt and Elliott (2003), Vadas et al. (2004b) and Kleinman et al. (2004) have confirmed that WEP concentration in manure and biosolids is a consistent indicator of DRP in runoff when P sources are recently applied to soil. While the fraction of total P that is water extractable (WEP TP–1) is correlated to runoff dissolved P concentrations within certain categories of manures (e.g., dry biosolids as shown by Brandt and Elliott, 2003), expressing manure WEP on this basis does not provide accurate estimation of runoff P concentrations across manures of varying properties. For instance, in Kleinman et al. (2002b)( 2004), concentrations of WEP (g kg–1) in dairy manure were lower than in layer chicken manure, corresponding with lower runoff dissolved P concentrations when the two manures were broadcast to soils at the same aerial rate of total P application (kg ha–1). However, because total P concentrations in dairy manure were also low, a higher proportion of total P in dairy manure was water extractable than in layer chicken manure. As a result, WEP TP–1 was higher in the dairy manure than in the layer chicken manure, making WEP TP–1 a poor predictor of runoff dissolved P concentrations across these manure categories.
Given the strong relationship between manure P and dissolved P in runoff, a number of U.S. states now include P source coefficients, formerly termed P availability coefficients, in site assessment indices (Sharpley et al., 2003; Leytem et al., 2004). These coefficients allow P sources (mineral fertilizers, manures, biosolids) that are applied to agricultural soils to be weighted on the basis of their relative availability to enrich runoff DRP when applied to agricultural soils. For instance, findings from the studies of Kleinman et al. (2002b) and Brandt and Elliott (2003) served as the initial foundation for developing P source coefficients in initial drafts of the Pennsylvania P Index, with the expectation of refining coefficients as more information on WEP in different P sources become available (Weld et al., 2003). Indeed, states in the mid-Atlantic region of the USA are adopting this approach to developing P source coefficients (Coale and Elliot, 2004).
To date, one obstacle to comparing information on WEP in different manures has been the lack of a standard laboratory test for WEP. To be an effective environmental indicator, a WEP test must reflect differences in runoff dissolved P while also meeting reproducibility and other service laboratory analytical criteria. Kleinman et al. (2002a) showed that controlling manure-DM/distilled water ratio and length of shaking period were keys to consistent determination of WEP in manures and estimation of DRP in runoff. As manure DM was diluted with distilled water, P and Ca extracted from manure increased, consistent with increasing dissolution of calcium phosphates. Concentrations of WEP were logarithmically related to shaking time, so that after 1 h of shaking, WEP concentrations were at least 70% of WEP concentrations observed after 24 h of shaking (Kleinman et al., 2002a). Based on these analyses, Wolf et al. (2005) have developed a WEP test for commercial analytical laboratories with a manure DM/solution ratio of 1:200 and a shaking time of 1 h.
Despite analytical differences between studies evaluating WEP of manures and biosolids, existing literature provides a strong indication that WEP varies substantially within and between P sources. In a survey of WEP in biosolids (manure DM/distilled water ratio = 1:250; 1 h shaking), Brandt et al. (2004) found that WEP ranged from <0.1 to 8.9 g kg–1, with systematic differences in WEP based on treatment method (e.g., anaerobic digestion vs. biological P removal). Studies by Dou et al. (2002), Sharpley and Moyer (2000), Kleinman et al. (2002a), Kleinman and Sharpley (2003) employed WEP protocols sufficiently similar to Brandt et al. (2004) to allow comparison. Combined, these studies reported WEP concentrations of 2.7 to 7.4 g kg–1 for layer chicken manures, 2.1 to 4.0 g kg–1 for untreated broiler chicken litters, 1.9 to 10.5 g kg–1 for dairy manures and 6.0 to 9.0 g kg–1 for swine slurries.
Although WEP is increasingly used as an environmental indicator, there is a paucity of published information on WEP in manures. This study reports the finding of a survey of WEP in livestock manures submitted to Pennsylvania State University's Agricultural Analytical Services Laboratory over approximately a 2-yr period. Objectives of the study were to determine whether WEP varied systematically across manure categories, and assess trends in manure constituents that provide insight into mechanisms controlling WEP in manure. Results of this study will support the refinement of P Source Coefficients in site assessment indices.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Laboratory Analyses
Manures were refrigerated at 4°C on receipt and analyzed within 7 d of receipt. Dry matter was determined gravimetrically after drying manure samples at 105°C for up to 14 h. Total P, Al, Fe, Ca, and Mg were analyzed by USEPA Method 3051 using a microwave digestor (USEPA, 1986), with elements determined by inductively coupled plasma atomic emission spectroscopy (ICP).
Water-extractable P was analyzed on fresh samples (i.e., in the condition they were submitted) with DM/solution ratio of 1:200 and a shaking time of 1 h (Wolf et al., 2005). Following centrifugation (1000 x g), extract P was determined by ICP. In addition, water extractable Mg, Ca, and Fe were determined from the same extract on 74 samples. Concentrations of water-extractable elements were calculated on a dry weight equivalent.
Total N was determined by either Elementar Vario Max CN Analyzer (Elementar Americas, Inc., Mt. Laurel, NJ; combustion, chromatographic separation, and thermal conductivity detection of N) or semi-micro Kjeldahl digestion (Bremner, 1996). Watson and Galliher (2001) found Kjeldahl N and N determined by CN Analyzer to be very similar (Kjeldahl N = 0.56 + 0.94 CN Analyzer N; r2 = 0.95). This was confirmed by a comparison of both methods on manure and biosolid samples submitted to Pennsylvania State University's Agricultural Analytical Services Laboratory (Kjeldahl N = –0.02 + 1.00 CN Analyzer N; r2 = 0.91).
Statistical Analyses
Differences in manure properties were assessed by General Linear Model, with Duncan's pair-wise comparison of means. Differences discussed in the text were significant at 
0.05. Data are summarized by box and whisker plots that present (a) first, second (median), and third quartiles as horizontal lines in the box; (b) adjacent upper and lower values as "whiskers" extending from the boxes; (c) means as dashes; and (d) outliers as "*." Associations between manure properties were assessed by Pearson's correlation analysis and modeled by least squares regression (Neter et al., 1996). All analyses were conducted using SAS, Version 8 (SAS Institute Inc., 1999).
|
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
|
|
Manure Water-Extractable Phosphorus Trends by Livestock Category
Analysis of manure properties within livestock categories highlighted differences in manure properties not apparent across all manures. Significant differences in WEP, WEP TP–1, DM, and TP were clearly evident between livestock categories (Fig. 3 and 4).
|
|
As with WEP, swine and dairy manures contained statistically similar concentrations of water-extractable Ca (mean = 7.4 g kg–1 for swine; mean = 4.9 g kg–1 for dairy) and Mg (mean = 4.2 g kg–1 for swine; mean = 4.9 g kg–1 for dairy) that were significantly higher than all other manures. Water-extractable Ca and Mg exhibited negative, albeit variable, correlations with DM in swine manure (r = –0.87, p = 0.005 for Ca; r = –0.40, p = 0.324 for Mg) and dairy cattle manure (r = –0.69, p < 0.001 for Ca; r = –0.75, p < 0.001 for Mg). General similarities in WEP, water-extractable Ca, and water-extractable Mg relationships with DM support the hypothesis that the dissolution of calcium phosphates in dairy and swine manures and magnesium phosphates in dairy manures is controlled, at least in part, by manure water content. As illustrated in Fig. 5a and 5b, significant positive correlations between WEP and water-extractable Ca were observed in both dairy and swine manure and between WEP and water-extractable Mg in dairy manure. Differences in the strength of the correlations and slopes of regression equations between WEP and water-extractable Ca or Mg indicate that the role Ca and Mg play in P solubility varies between livestock types. The influence of manure water content on the dissolution of calcium phosphate compounds is corroborated by data from Kleinman et al. (2002a) who observed positive relationships with different slopes between WEP and water-extractable Ca in swine slurry and dairy manure when manure DM/distilled water ratios were varied in the laboratory (total Ca was constant in these experiments).
|
In our survey, total Ca and Mg content of manure (as opposed to water extractable forms of Ca and Mg) were negatively correlated with WEP TP–1, indicating that these elements are strongly associated with solid and solution phases of P in manures. For total Ca, which exhibited the strongest overall correlation, the relationship with WEP TP–1 was best described by a power function across all livestock manures (Fig. 2), but was generally linearly correlated when manures were separated by livestock category. In swine manures, WEP TP–1 was well correlated with total Ca and Mg (r = –0.78, p < 0.001 for Ca; r = –0.69, p = 0.012 for Mg) whereas in dairy manures WEP TP–1 was poorly correlated with total Ca and Mg (r = –0.20, p = 0.049 for Ca; r = –0.26, p = 0.039 for Mg).
Water-extractable P in swine and dairy cattle manure has also been shown to vary with dietary P intake and animal age (Dou et al., 2002; Ebeling et al., 2002; Knowlton et al., 2002; Baxter et al., 2003). In this survey, the influence of TP in manure on WEP concentration was apparent at the level of livestock category, as trends in manure TP (Fig. 4b) between livestock categories roughly coincided with trends in WEP (Fig. 3a). Within individual livestock categories, TP provided an inconsistent indicator of WEP. A significant positive correlation was observed between WEP and TP in dairy cattle manure (r = 0.73, p < 0.001), but not in swine manure. Dou et al. (2002) observed concomitant increases in manure TP and WEP from dairy cattle fed diets increasing in TP supplementation. Notably, trends in WEP TP–1 between livestock categories (Fig. 3b) were very different from those in WEP concentration (Fig. 3a). Dairy manure possessed the highest WEP TP–1 (mean = 59%), as TP concentrations in cattle manure (dairy and beef) were low. In contrast, swine manure had relatively low WEP TP–1 (mean = 35%) and was not significantly different from all livestock manures but dairy. As mentioned above, while WEP TP–1 provides insight into the fraction of TP that is readily water soluble, it can be a poor indicator of dissolved P in runoff across livestock manure categories, which is controlled by concentration of WEP in manure.
Beef Manure
The lowest mean WEP concentrations of all livestock categories were associated with beef cattle manures, which did not differ significantly from dairy and broiler chicken manures (Fig. 3a). Beef cattle manures included in the study had significantly greater DM than did dairy manures (Fig. 4a), reflecting general differences in storage and/or handling of manures by beef and dairy producers, with a minimum DM content of 19% for beef cattle manures and 1% for dairy manures. Despite large differences in recommended P content of beef and dairy cattle diets, with beef cattle generally consuming less than dairy cattle (National Research Council, 1996, 2001), as well as strong linear correlation (r = 0.86) between dietary P intake and fecal TP in dairy cattle (Wu and Ishler, 2002), no significant differences were observed in manure TP concentration between beef and dairy cattle (Fig. 4b). Furthermore, WEP TP–1 in manure was not significantly different between these two classes of cattle (Fig. 3b). Associations between WEP and other water-extractable elements as well as between WEP and total Ca and Mg were consistent between dairy and beef cattle.
Poultry (Layer Chicken, Broiler Chicken, Turkey) Manures
Of the three poultry manures, turkey manure, represented by only five samples, had the greatest WEP concentrations, and was second only to swine manure (Fig. 3a). Dry matter content of turkey manure averaged 75%, similar to broiler chicken manure (mean DM = 71%), although WEP of turkey manures was 1.9 times that of broiler chicken manures (Table 1). Given the small sample of turkey manures included in the survey (N = 5), representing only three producers, generalizations must be tempered. However, Moore et al. (1995) observed that mean WEP of turkey litter (N = 30) was 2.4 times that of broiler chicken manure (N = 64), supporting the relative findings of this survey. Even though several studies currently report WEP in turkey manures (Moore et al., 1995; Maguire et al., 2003; Penn et al., 2004), differences in processing of manures and water-extraction procedures preclude direct comparison of WEP concentrations from those studies with this survey. Specifically, Maguire et al. (2003) dried the turkey manures before analysis and all three studies analyzed WEP at a DM/solution ratio that was much narrower than the ratio used in this survey.
As with cattle and swine manures, differences in WEP within and between the two chicken manures were related to manure DM and TP. Dry matter contents of broiler chicken manures were among the highest observed in the survey, while DM in layer chicken manures was intermediate to broiler chicken and beef cattle manures (Fig. 4a). Coincidentally, WEP of broiler chickens was lower, but not statistically so, than that of layer chickens (Fig. 3a). However, while DM helps to explain some of the relative difference in WEP between chicken manures, DM was only weakly correlated with WEP in chicken manures (r = 0.53, p = 0.006) and was not effective in explaining differences between poultry manures and other species (e.g., layer poultry vs. dairy manures).
The varying correlations between WEP and DM in the manures of different species of livestock suggest that mechanisms of P solubility are somewhat independent between species. For instance, no significant correlations between WEP and water-extractable Ca and Mg were detected in either chicken categories, but a good correlation was observed between WEP and water-extractable Fe in layer chickens (Fig. 5c). Notably, this correlation was strongly weighted by five observations at the lowest and highest water-extractable Fe concentrations. As illustrated in Fig. 2, WEP TP–1 was negatively correlated by power model with total Ca content, with the highest total Ca contents in layer poultry manure, consistent with Ca-P as a dominant fraction of TP that is not water extractable. When broiler and layer chicken manures were analyzed separately, no significant correlations were observed between WEP TP–1 and total Ca, as the slope of the regressions approached zero in these manures. It is possible, especially for layer poultry manures, which possessed the highest total Ca contents of any manures (Table 1), that the absence of a significant relationship reflects saturation of P with respect to Ca such that total Ca content does not limit P solubility.
Significant correlations between WEP and TP in manure were observed in both broiler chickens (r = 0.81, p = 0.053) and layer chickens (r = 0.66, p < 0.001). Elsewhere, Vadas et al. (2004a) found that altering supplemental TP in broiler chicken diets significantly affected concentrations of WEP and TP in manures. Both WEP and TP in layer chicken manure were greater than in broiler manure (Fig. 3a and 4b), although differences were not statistically significant for WEP. Differences in manure P between broiler and layer chickens appear to be a function of bird metabolism, rather than dietary intake of P. Rapidly growing broilers have greater efficiency in metabolizing P, and recommended dietary P intake is higher for broiler chickens than for layer chickens (National Research Council, 1994).
Manure Water-Extractable Phosphorus Trends by Storage and Handling Category
Fewer significant trends in WEP of manure were observed on the basis of storage and handling systems (Table 1). Although fresh manures, bedded pack, and litter had lower mean WEP than earthen, aboveground, and covered systems, differences were not statistically significant (Fig. 6a). Nor were differences observed in WEP TP–1 by storage and handling category (Fig. 6b). Several factors likely contributed to this result.
|
|
|
CONCLUSIONS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Results of this survey have implications to P site assessment indices that differentiate P sources on the basis of WEP (Sharpley et al., 2003; Weld et al., 2003). Specifically, this survey shows that distinction of manures within certain livestock categories is needed to accurately reflect WEP. For instance, liquid manure storage systems in dairy and poultry operations have different WEP than dry manure storage systems. Although none of the manures included in this study were reported as having been treated with P sorbing amendments (e.g., alum), application of such amendments would substantially affect the distribution of WEP concentrations found in particular livestock categories. Furthermore, growing efforts to modify livestock diets will also have an effect on WEP in certain livestock systems. Continued monitoring of WEP is needed to improve on the database evaluated in this study and to track changes in manure quality as nutrient management evolves in livestock production.
|
ACKNOWLEDGMENTS |
|---|
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Received for publication March 10, 2004.
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  R. W. McDowell, Z. Dou, J. D. Toth, B. J. Cade-Menun, P. J. A. Kleinman, K. Soder, and L. Saporito A Comparison of Phosphorus Speciation and Potential Bioavailability in Feed and Feces of Different Dairy Herds Using 31P Nuclear Magnetic Resonance Spectroscopy J. Environ. Qual., May 1, 2008; 37(3): 741 - 752. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. J. Penn and R. B. Bryant Phosphorus Solubility in Response to Acidification of Dairy Manure Amended Soils Soil Sci. Soc. Am. J., January 11, 2008; 72(1): 238 - 243. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Gungor, A. Jurgensen, and K. G. Karthikeyan Determination of Phosphorus Speciation in Dairy Manure using XRD and XANES Spectroscopy J. Environ. Qual., October 24, 2007; 36(6): 1856 - 1863. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. W. McDowell, D. M. Nash, and F. Robertson Sources of Phosphorus Lost from a Grazed Pasture Receiving Simulated Rainfall J. Environ. Qual., July 17, 2007; 36(5): 1281 - 1288. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. L. Shober and J. T. Sims Integrating Phosphorus Source and Soil Properties into Risk Assessments for Phosphorus Loss Soil Sci. Soc. Am. J., March 12, 2007; 71(2): 551 - 560. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. J. Chardon, G. H. Aalderink, and C. van der Salm Phosphorus Leaching from Cow Manure Patches on Soil Columns J. Environ. Qual., January 9, 2007; 36(1): 17 - 22. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. A. Vadas, W. J. Gburek, A. N. Sharpley, P. J. A. Kleinman, P. A. Moore Jr., M. L. Cabrera, and R. D. Harmel A Model for Phosphorus Transformation and Runoff Loss for Surface-Applied Manures J. Environ. Qual., January 9, 2007; 36(1): 324 - 332. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Jiao, J. K. Whalen, and W. H. Hendershot Phosphate Sorption and Release in a Sandy-Loam Soil as Influenced by Fertilizer Sources Soil Sci. Soc. Am. J., January 1, 2007; 71(1): 118 - 124. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. A. Elliott, R. C. Brandt, P. J. A. Kleinman, A. N. Sharpley, and D. B. Beegle Estimating Source Coefficients for Phosphorus Site Indices J. Environ. Qual., October 27, 2006; 35(6): 2195 - 2201. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. A. Vadas and P. J. A. Kleinman Effect of Methodology in Estimating and Interpreting Water-Extractable Phosphorus in Animal Manures J. Environ. Qual., May 31, 2006; 35(4): 1151 - 1159. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. A. Vadas Distribution of Phosphorus in Manure Slurry and Its Infiltration after Application to Soils J. Environ. Qual., February 2, 2006; 35(2): 542 - 547. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Wolf, P. J. A. Kleinman, A. N. Sharpley, and D. B. Beegle Development of a Water-Extractable Phosphorus Test for Manure: An Interlaboratory Study Soil Sci. Soc. Am. J., April 11, 2005; 69(3): 695 - 700. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||
