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a Animal Waste Management Research Unit, USDA-ARS, 230 Bennett Lane, Bowling Green, KY 42104
b Dep. of Plant and Soil Sciences, Oklahoma State Univ., 368 Agricultural Hall, Stillwater, OK 74078-6028
c Dep. of Environmental Science and Technology, Univ. of Maryland, 0214 H.J. Patterson Hall, College Park, MD 20742
* Corresponding author (Jason.warren{at}ars.usda.gov).
Received for publication May 11, 2007.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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Abbreviations: EDTA, ethylenediamine tetraacetic acid (C10H16N2O8) • NMR, nuclear magnetic resonance • ICP–OES, inductively coupled plasma–optical emission spectroscopy
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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Therefore, efforts have been made to reduce soluble P concentrations found in poultry litter. Such efforts have focused primarily on adding chemical amendments containing Fe, Al, and/or Ca to litter (Shreve et al., 1996; Moore and Miller, 1994). Alum (Al2(SO4)3·18H2O) has generally been found to be most cost effective as a litter amendment due to the added benefit of reduced NH3 emissions in the production house (Moore et al., 1999). Alum reduces litter pH, resulting in decreased NH3 emissions in the production house, which provides cost savings through lowered propane and electricity use (Moore et al., 1999).
Various studies have evaluated the impact of alum additions on the solubility of P in litter. Laboratory incubation showed that addition of 100 g alum kg–1 litter lowered soluble P by 75% (Moore and Miller, 1994). Pen trials conducted by Miles et al. (2003) showed that soluble P concentrations could be reduced by 30 to 60% depending on diet formulation when alum was applied at a rate of 0.091 kg bird–1. Sims and Luka-McCafferty (2002) conducted a farm scale study in which 97 houses received alum at a rate of 0.09 kg bird–1 and 97 houses received no alum. The researchers found that, on average, alum additions reduced soluble P concentrations in poultry litter by 72%.
Multiple studies have demonstrated that land application of alum-treated poultry litter decreases extractable P concentrations in litter-amended soils and soluble P concentrations in runoff compared with untreated litter applications (Moore and Edwards, 2007; Warren et al., 2006a). In some instances, the reductions in runoff P concentrations have been substantial. For example, Moore et al. (2000) showed that pastures amended with alum-treated litter generated 73% lower soluble reactive P in runoff compared with untreated litter applications.
Research on the mechanisms by which alum addition to litter lowers P solubility has historically emphasized transformations in inorganic P forms. Peak et al. (2002) used X-ray adsorption near edge structure spectroscopy analysis to determine that alum applied to poultry litter precipitates as amorphous Al(OH)3, which adsorbs inorganic P. Hunger et al. (2004) analyzed alum-treated litter with solid-state 31P nuclear magnetic resonance (NMR) spectroscopy and found that P associated with Al was likely in the form of poorly ordered wavellite or surface complexes with Al(OH)3. Dou et al. (2003) sequentially extracted poultry litter by the method of Hedley et al. (1982) before and after alum addition and found that P migrated from H2O and 1.0 mol L–1 HCl fractions to 0.5 mol L–1 NaHCO3 and 0.1 mol L–1 NaOH fractions during a 3-d incubation.
In addition to altering inorganic P solubility in poultry litter, alum additions may affect the mineralization of organic P found in poultry litter, which is primarily comprised of phytic acid (Turner and Leytem 2004). Data evaluating the influence of alum on organic P are limited. However, Dao (2003) found that increasing the mole ratio of Al to phytate-P in liquid dairy manure to 1:6 decreased the phytase-hydrolyzable phosphorus by 30%. They concluded that intermolecular bonding resulted in the formation of insoluble Al-phytate, which limited the activity of the phytase enzyme. This lower availability of Al-phytate to phytase hydrolysis may explain why Warren et al. (2006b) found greater concentrations of organic P extracted using 0.1 mol L–1 NaOH from soils that had received alum-treated poultry litter during a 4-yr field study. However, there is no direct evidence indicating that alum addition to poultry litter influences organic P transformations in decomposing litter during storage or after incorporation into soil.
Therefore, the objectives of this study were to determine (i) the impact of adding alum to poultry litter on phytate hydrolysis during litter storage, (ii) the distribution of inorganic and organic P forms in poultry litter during simulated storage using a sequential chemical P fractionation, and (iii) the stability of organic P in litter-amended soils.
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Materials and Methods |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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A Hartsells, fine sandy loam (Fine-loamy, siliceous, subactive, thermic Typic Hapludults) was selected for the soil incubation experiment. The soil was collected at the Alabama Agricultural Experiment Station located at Crossville, AL, from a cultivated field with no recent history of manure application. This soil was selected because of its prevalence in northeastern Alabama where poultry operations are concentrated. The initial pH of the soil was 5.7; the Mehlich-1 P concentration was 40 mg P kg–1; and the sand, silt, and clay contents were 60, 30, and 10%, respectively
Litter Incubation
Incubation containers measured 9 (diameter) by 11 cm with a single 1-mm hole in the lid for ventilation. Containers were filled with 360 g of litter and 40 g of reagent-grade alum for alum-treated litter, and untreated litter containers possessed 400 g of unamended litter. All litter was added on a dry weight basis and replicated six times. All experimental units were shaken vigorously to mix their contents, and a 50-g litter subsample was initially removed from each container (d zero samples). Deionized H2O was added to each container to adjust the gravimetric moisture content to 0.30 g g–1 before placing them in an incubator at 25°C. At 14 d, a 10-g sample was collected from each container to assess pH and moisture. At 27, 63, and 93 d, 50 g (wet weight) of litter was removed from each container. Twenty-five grams of each sample was dried at 65°C for moisture determination and ground before chemical analysis. The remaining 25 g was frozen at –20°C to allow for the possibility of future analysis of litter microbial characteristics.
Litter Analysis
Wet Chemistry
All analyses were conducted on litter dried at 65°C and ground to pass a 4-mm sieve. Litter pH was determined using a 5:1 deionized H2O/solid ratio. The concentration of total P and other selected elements were measured in litter using microwave-assisted acid digestion of 0.5 g of litter with 9 mL of concentrated HNO3 and 3 mL of HCl followed by inductively coupled plasma–optical emissions spectroscopy (ICP–OES) (Varian, Vista Pro; Varian Analytical Instruments, Walnut Creek, CA).
Chemically defined litter P fractions were determined using a method modified from Hedley et al. (1982) by Dou et al. (2000) and Sharpley and Moyer (2000) for use with various manures. Litter samples were sequentially extracted using (i) deionized H2O, (ii) 0.5 mol L–1 NaHCO3, (iii) 0.1 mol L–1 NaOH, and (iv) 1.0 mol L–1 HCl, using a litter/solution ratio of 1:200 (0.4 g:80 mL). The litter samples were shaken for 16 h with each extractant, centrifuged at 15,000 x g for 10 min, and filtered through a 0.45-µm filter. Any residue remaining on the filter was washed back into the centrifuge bottle using the next extractant. After the sequential extraction, residual-HCl P in the sample was determined by adding 10 mL of concentrated HCl and heating to 80°C in a water bath for 10 min; then an additional 5 mL of concentrated HCl was added, and the mixture was allowed to cool for 1 h. This mixture was centrifuged at 15,000 x g for 10 min and decanted into a 50-mL volumetric flask without filtration. The remaining litter was washed twice using deionized H2O and centrifuged, and the H2O was decanted into the 50-mL volumetric flask. The final solution was brought to 50 mL volume using deionized H2O. The residual P remaining in the litter was determined by microwave-assisted acid digestion and ICP–OES analysis as described previously.
Total P and molybdate-reactive P in each sequential extract and the residual-HCl extract were determined by ICP–OES and the method of Murphy and Riley (1962), respectively. Consistent with previous studies, molybdate-reactive P (Murphy and Riley, 1962) is referred to as inorganic P (Sharpley and Moyer, 2000; McGrath et al., 2005), although it is possible that other forms of P can be hydrolyzed by the method when used on H2O extractions of soil (Turner et al., 2004). Before inorganic P determination, the 0.5 mol L–1 NaHCO3 and 0.1 mol L–1 NaOH extracts were neutralized with 0.9 mol L–1 H2SO4. The 1.0 mol L–1 HCl extracts and the residual-HCl digestion solutions were neutralized with 10 mol L–1 NaOH. Organic P in each extract is presented in this paper as the difference between total P and inorganic P. In addition to total P, ICP–OES was used to determine select elemental composition of the H2O extractions.
31P NMR Analysis
Litter samples collected at 0, 27, 63, and 93 d were analyzed by solution 31P NMR spectroscopy based on the methods of Turner (2004). The six treatment replications were combined before analysis, and samples were extracted by shaking 2 g of dried and ground litter with 40 mL of 0.5 mol L–1 NaOH and 0.05 mol L–1 ethylenediamine tetraacetic acid (EDTA) for 4 h at 20°C. Extracts were centrifuged, and 2-mL aliquots were taken for analysis of solution total P by ICP–OES; reactive P was analyzed by the method of Murphy and Riley (1962). The remainder of the extract was freeze-dried and ground into a powder using a mortar and pestle. Before NMR analysis, 100 mg of freeze-dried extract was redissolved in 1 mL of 1.0 mol L–1 NaOD (deuterated sodium hydroxide) and transferred into a 5-mm NMR tube. Solution 31P NMR spectra were obtained using a UNITY INOVA 400 NB (400 MHz) operating at 161.82 MHz with a 5-µs pulse (45°), delay time 5 s, acquisition time of 0.8 s, temperature control at 20°C, and broadband proton decoupling for all samples. Depending on the quality of spectra, the number of scans varied from 1000 to 2048. Chemical shifts of signals were determined in ppm relative to 85% phosphoric acid assigned to individual P compounds (Turner et al., 2003). Signal areas were calculated by integration, and P concentrations were estimated by multiplying the proportion of the total spectral area assigned to a specific signal by the total P concentration in the original extract. In addition, molybdate-reactive P was determined for the same NaOH-EDTA by the Murphy and Riley (1962) method. Unreactive P was determined by subtracting the reactive P from the total P determined by ICP–OES.
Soil Incubation
The soil incubation experiment included four treatments (three P sources and a no-P control) with six replications. The three sources of P amended at 60 mg P kg–1 soil were reagent-grade KH2PO4, alum-treated litter, and untreated litter. The litter samples were collected at 27 d into the litter incubation experiment and stored at –20°C until initiation of the soil incubation. The 27-d litter samples were selected because this was assumed to be adequate time for alum to react with the litter. This assumption was based on previous studies that have reported the pH of alum-treated litter to stabilize approximately 4 wk after alum addition (Moore et al., 1999). The KH2PO4 was dissolved in deionized H2O to make a solution with a concentration of 2400 mg P L–1, which was then added to the soil. Litter samples were forced through a 4-mm sieve and applied to the dry soils. The P sources were thoroughly mixed in the incubation containers with 400 mg of air-dried and ground (2 mm) soil. The amended soil was brought to 50% of field capacity, as determined using the method of Tan (1996), using deionized H2O. Container weights were recorded to allow moisture to be monitored during the incubation period. The containers were then placed in an incubator at 25°C in a randomized, complete-block design, with location in the incubator used as a blocking factor. Containers were weighed every 3 to 5 d, and sufficient deionized H2O was added to maintain the moisture content.
Soils collected after 31 and 61 d of incubation were analyzed for Mehlich 1–extractable P and pH (soil/solution ratio, 1:1). Soils were also subjected to the sequential P fractionation described previously for litter. However, a soil/solution extraction ratio of 1:60 was used instead of the 1:200 ratio used for the litter fractionation.
Statistical Analyses
Data collected from the litter incubation were analyzed as a complete randomized design with repeated measures, and data collected from the soil incubation were analyzed as a randomized, complete-block design. Analysis of variance and regression analysis were performed using SAS PROC GLM and PROC REG, respectively (SAS Institute, 2001). Fisher's protected LSD was used to separate soil incubation treatment means.
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Results and Discussion |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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Addition of alum to the poultry litter shifted organic P from the 1.0 mol L–1 HCl–extractable and H2O-extractable fractions to the 0.1 mol L–1 NaOH–extractable and 0.5 mol L–1 NaHCO3–extractable fractions (Table 1). Of these organic P transformations, the increase in 0.1 mol L–1 NaOH–extractable organic P and the decrease in 1.0 mol L–1 HCl–extractable organic P were the most dramatic. Alum additions also substantially lowered the H2O-extractable inorganic P. This decrease was associated with increases in 0.1 mol L–1 NaOH–extractable and 0.5 mol L–1 NaHCO3–extractable inorganic P. These results are similar to those of Dou et al. (2003), who found that treatment of poultry litter with alum decreased H2O-extractable and 1.0 mol L–1 HCl–extractable P. These reductions were associated with increases in the 0.1 mol L–1 NaOH–extractable and 0.5 mol L–1 NaHCO3–extractable P. However, they did not distinguish between organic and inorganic P. Hunger et al. (2005) confirmed that 0.1 mol L–1 NaOH–extractable and 1.0 mol L–1 HCl–extractable P were primarily associated with Al and Ca, respectively. Not surprisingly, addition of alum shifts water-extractable P and Ca-associated P to Al-associated P pools.
Transformations in the distribution of inorganic and organic P during decomposition of the alum-treated and untreated litters are presented in Fig. 5 . In the untreated litter, organic P initially found in the 1.0 mol L–1 HCl extract was released as inorganic P into the H2O, 0.5 mol L–1 NaHCO3, and 1.0 mol L–1 HCl fractions (Fig. 5A and 5B). After initial transformations, changes in the distribution of P within the alum-treated litter were minimal compared with changes in the untreated litter (Fig. 5). During decomposition, the total inorganic P in the alum-treated litter rose from 27 to 38% of the total litter P. This inorganic P was distributed primarily into the H2O, 0.5 mol L–1 NaHCO3, and 1.0 mol L–1 HCl extracts, which increased by 150, 33, and 78%, respectively. In contrast, the proportion of inorganic P extracted with 0.1 mol L–1 NaOH increased by only 17% (Fig. 5D). This suggests that the adsorption/precipitation reactions between added Al and inorganic P occur shortly after alum application and that interactions between Al and mineralized inorganic P are minimal. Additionally, reactions involving mineralized inorganic P are dominated by the formation of acid-extractable inorganic P compounds such as Ca-phosphates in untreated and alum-treated litter.
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Results of the current study confirm that lower H2O-extractable P in alum-treated litter does not entirely result from the formation of insoluble inorganic Al-P compounds. Instead, it is apparent that alum addition to poultry litter also decreases H2O-extractable P by limiting organic P mineralization. This indirect impact on H2O extractable P may help to interpret the results of other studies, such as Sims and Luka-McCafferty (2002), who observed that the decline in H2O-extractable litter P after alum treatment was poorly correlated with the Al:P ratio.
Soil Incubation
Sequential fractionation of soils that received the incubated poultry litter (collected at 27 d) showed that applying alum-treated litter resulted in lower H2O-extractable inorganic P compared with applications of untreated litter and KH2PO4 (Table 2
). Mehlich 1–extractable P concentrations showed similar trends. Previous research has also found that alum-treated litter applications minimized extractable soil inorganic P compared with untreated litter applications (Warren et al., 2006a; Moore et al., 1999). The lower concentration of H2O-extractable inorganic P was the only significantly different inorganic P fraction when comparing the two litter sources. This is consistent with findings of Warren et al. (2006b), who found that, after 4 yr of alum-treated litter and untreated litter application to tall fescue, the only significantly different inorganic P concentration was in the H2O fraction.
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Concentrations of soil organic P extracted after 31 and 61 d of incubation using 0.1 mol L–1 NaOH were elevated in the treatment receiving alum-treated litter compared with the 0-P control and KH2PO4 treatments (Table 2). This fraction was also elevated in the soils receiving untreated litter but was not significantly different from the 0-P control. In contrast, organic P in the residual-HCl digests was elevated in the soils amended with untreated litter above that found in the control at 31 d but not after 61 d. These data suggest that the treatment of poultry litter with alum not only limits the mineralization of organic P during poultry litter decomposition but that the Al-phytate in the alum-treated litter seems to be more stable when applied to soils than the organic P present in untreated litters. This mechanism seems to contribute to the lower solubility of P in soil amended with alum-treated litter, as evidenced by the elevated 0.1 mol L–1 NaOH–extractable organic P compared with the 0-P control. Similarly, Warren et al. (2006b) found elevated concentrations of 0.1 mol L–1 NaOH–extractable organic P in soils subjected to 4 yr of alum-treated litter application.
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Conclusions |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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Sequential fractionation of litters confirmed the persistence of organic P in the alum-treated poultry litter during the 93-d incubation. The persistent organic P in the alum-treated litter was present in 0.1 mol L–1 NaOH–extractable and 1.0 mol L–1 HCl–extractable organic P fractions. This indicates that the mechanism by which alum minimizes organic P mineralization during litter storage may not simply be the formation of Al-phytate compounds but also may be due to reductions in the mineralization of acid-extractable organic P compounds, such as Ca-phytate.
Elevated levels of 0.1 mol L–1 NaOH–extractable organic P in soil amended with alum-treated litter suggest that this organic P form is more stable in the soil environment than the 1.0 mol L–1 HCl–extractable organic P found in the alum-treated and untreated litter. This finding provides an additional mechanism by which treatment of poultry litter with alum allows for reduced P solubility on incorporation to soil.
This laboratory study confirms that chemical amendments such as alum can affect not only the form and solubility of inorganic P found in poultry litter but also the mineralization of organic P. Thus, it is likely that alum's influence on organic P in litter persists beyond the storage period, even continuing after litter is applied to soils.
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMaterials and MethodsResults and DiscussionConclusionsREFERENCES |
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