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Department of Plant and Soil Sciences, Univ. of Delaware, Newark, DE 19717-1303
* Corresponding author (jtsims{at}udel.edu)
Received for publication December 17, 2001.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: alum, aluminum sulfate • BMP, best management practice • ICP, inductively coupled plasma • MR, determined colorimetrically by the Murphy–Riley method • WS, water soluble
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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While these state and federal laws and regulations address a wide range of environmental concerns related to animal production operations and the land application of animal manures, one of the major changes proposed (or already mandated in some states) is the need for improved P management. Reducing P losses by erosion (particulate P) and by surface runoff and leaching (primarily soluble P) is now viewed as an essential component of BMPs for animal agriculture. This has stimulated an intensive research effort to develop innovative approaches that can minimize the potential for P losses from the land application of animal manures.
One advance in manure management that has received considerable interest, particularly by the poultry and swine industries, is the use of litter amendments to stabilize P in manures in less soluble forms, thus decreasing the risk of soluble P losses by runoff and leaching. The main approach evaluated to date has been the addition of metal salts (e.g., aluminum sulfate, aluminum chloride, ferric chloride) or by-products containing Al, Fe, or Ca to solid or liquid manures, similar to the methods used by municipal wastewater treatment facilities to remove P from wastewaters (Codling et al., 2000; Dao, 1999; Dao et al., 2001; Moore and Miller, 1994; Smith et al., 2001). The most widespread, on-farm application of this BMP has been the use of alum [aluminum sulfate; (Al)2(SO4)3] as an amendment for poultry litter (litter: a mixture of bedding, usually woodshavings or sawdust, and manure). Most of the research on the use of alum as a poultry litter treatment has been conducted by Moore and coworkers and was recently summarized by Moore et al. (2000). They cited several reasons why alum treatment of litter should be recommended as a BMP for poultry operations: (i) alum decreases the soluble P concentration in litters and in runoff from pastures fertilized with alum-treated litter compared with normal litter (Shreve et al., 1995); (ii) alum reduces NH3 emissions from poultry houses, which decreases the potential for health-related problems for poultry and for humans working in the houses as well as the environmental effects of NH3 emitted from the houses on air, soil, and water quality (Moore et al., 1995, 1996); (iii) improved poultry performance (reduced mortality, increased weight gain and feed efficiency) and lowered fuel and electricity costs due to less need to ventilate poultry houses for NH3 control purposes (Moore et al., 2000); (iv) higher litter N and S concentrations, and thus increased fertilizer value (Moore et al., 2000); and (v) reductions in runoff of dissolved carbon, trace metals, and growth hormones (e.g., estrogen) when litter is used as a fertilizer (Moore et al., 1998; Nichols et al., 1997).
The Delmarva (Delaware–Maryland–Virginia) peninsula is one of the most highly concentrated poultry production regions in the USA. About 600 million broiler chickens are produced annually on this peninsula and nutrient surpluses exist in most counties where poultry production is located (Cabrera and Sims, 2000; Sims et al., 2000; Sims and Coale, 2002). As mentioned above, concerns about the environmental effect of the poultry industry on water quality led to the passage of state nutrient management laws in all three states in 1998–1999. A key component of all of these laws was the requirement for some form of P-based nutrient management planning. Because of the research of Moore and coworkers, one of the BMPs for P that has been of considerable interest to the poultry industry and the state agencies in this region that are charged with enforcing these laws has been the potential to use alum as a poultry litter amendment. Consequently, in 1999 we initiated a large-scale, on-farm study evaluating the use of alum by poultry operations on Delmarva. Our specific objectives were to determine the effect of alum treatment of poultry litter on (i) the properties and elemental composition of poultry litters and (ii) the solubility of several elements in litter that are of particular concern for water quality (Al, As, Cu, P, and Zn).
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Alum Application
Alum was applied over a period of 16 mo (January 1999 to May 2000), with most houses participating in the project receiving seven applications. The alum rate used was a modification of the approach recommended by Moore et al. (1999a) who recommended that alum be applied after each flock of chickens at a rate of approximately 0.09 kg alum per bird. For a standard 20 000-bird poultry house (typical size = 12 x 150 m, or 1800 m2) this would be equivalent to approximately 1800 kg alum flock-1 or 1.0 kg alum m-2 flock-1. This application rate would result in a final alum concentration in the litter of approximately 10% alum by weight. However, Moore et al. (1999b) also recommended that "... if growers skip several flocks without applying alum then the application rate should be increased accordingly." The nature of the Delmarva project required that this recommendation for initially higher alum application rates be followed because the poultry houses in the project began with different amounts of litter present in each house, due to the fact that the number of flocks grown before initiation of the project varied from 2 to 35 flocks per house (average = 12 previous flocks; Table 1). It was not feasible to remove all of the existing litter from all of the participating houses and begin the project with new litter. Thus, it was decided to increase the first two alum application rates to compensate for the varying amounts of untreated litter present in each house at the beginning of the study. However, because of concerns about the effects of very high rates of alum on bird health, it was also decided that the first two alum applications would not exceed 0.135 kg alum per bird (actual average value for the first two applications in the 97 alum-treated houses was 0.13 ± 0.01 kg alum per bird). After two alum applications at the increased rate, all subsequent applications were made at the recommended rate of 0.09 kg per bird. Sufficient alum was applied to each house during the project to give a final average alum application rate (based on the total number of birds grown and alum applied in all 97 houses during the 16 mo project) of 0.11 ± 0.01 kg alum per bird (equivalent, based on the actual size of the houses used in this project, to 1.4 ± 0.01 kg alum m-2 flock-1).
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Poultry Litter Collection and Analyses
At the start of the project, before any alum was applied, poultry litter samples were collected from all houses designated to receive alum and from all of the control houses. All litter samples were collected following a standard protocol developed by the University of Delaware. Ten, 10-cm-diameter cores were collected with a PVC litter coring device, from the full depth of the litter (to the underlying soil floor) in a zig-zag manner in each house and then composited in a large plastic container. The bulk litter sample was weighed on-site and mixed thoroughly, and a subsample was removed, placed in a plastic bag, and returned to the University of Delaware for analysis. An information sheet providing specific information on the sample (location, litter depth, date of sampling) was included with each sample. Initial estimates of the amount of litter present were prepared for all alum-treated and control houses based on the weights of these litter samples and the total area sampled. At the end of the project, immediately after the removal of the final flock in the study and the crusted litter from that flock, litter samples were collected from all of the alum-treated houses and the control houses by the same method that was used to obtain the initial litter samples.
All litter samples (initial and final) were stored in a cold room at 4°C until analysis. Litter pH was determined with a 1:4 litter to deionized water ratio and litter moisture content was measured by drying a subsample of the litter at 65°C. The dried litter was then ground to pass an 0.8-mm screen in a stainless steel Wiley mill. Total P, Al, As, Cu, and Zn were determined by digesting a 0.5-g dried litter sample with 7 mL of concentrated HNO3 and 3 mL of 30% H2O2 in a CEM1 (Matthews, NC) MARS 5 Microwave Accelerated Reaction System. Water-soluble (WS) P, Al, As, Cu, S, and Zn were extracted by shaking "as is" (undried) litter with deionized water (1:10 litter to water ratio) for 1 h, followed by centrifugation and filtration through 0.45-µm Millipore (Bedford, MA) filter paper. The P and Al concentrations in all filtrates were determined by inductively coupled plasma (ICP) emission spectroscopy; for the samples collected from the control and alum-treated houses at the end of the project we also determined WS-P colorimetrically with a Technicon (Tarrytown, NY) Autoanalyzer III (Murphy and Riley, 1962). Ammonium N (NH4–N) in the dried, ground litters was determined by extraction with 2 M KCl (1:40, w/v), filtration through Whatman (Maidstone, UK) #42 filter paper, and colorimetric analysis with a Latchat (Milwaukee, WI) Quikchem 8000 autoanalyzer system. Total C, N, and S were determined on dried, ground litter samples by a dry combustion method with a Model 2000 LECO (St. Joseph, MI) CNS analyzer.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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In general, we found very good similarity in the poultry operations selected to receive alum and those used for controls. For example, as summarized in Table 1, on average, the control houses were 20 yr old, 1475 m2 in size, and had a production capacity of 20 500 birds per flock. In comparison, the average values for the same parameters in the houses designated to receive alum were 20 yr, 1485 m2, and 21 000 birds per flock. Both sets of houses typically averaged 5.7 flocks per year; in this 16-mo project an average of seven flocks were grown in each house. The average number of previous flocks and litter weight in the control houses at the start of the project were 11 flocks and 89 wet Mg versus 12 flocks and 66 wet Mg for the houses where alum was to be applied.
Litter properties were also very similar for the control and alum-treated houses at the start of the project (Table 1). In general, as reported in past summaries of litter composition, the litters were rather dry, alkaline materials with low C to N ratios (Sims and Wolf, 1994). Initial total P, Al, and S concentrations in the litters averaged 2.25, 0.13, and 0.74% in the control houses and 2.24, 0.14, and 0.74% in the alum-treated houses. About 7% of the total P in the litters was water soluble. As would be expected in an alkaline material, WS-Al was very low, <0.01% of total Al.
Effect of Alum Applications on Poultry Litter Properties
Properties of the litter samples from the control houses at the end of the project had changed little relative to initial values (Tables 1 and 2). Some variability would be expected given the fact that additional flocks of chickens had been grown and that from one to two Mg of "crusted" litter (the uppermost 2–5 cm of wet litter) were regularly removed from the houses after the growth of each flock of chickens. Note that removal of crusted litter is a standard industry practice and is primarily done to minimize the incidence of various poultry diseases. Average values for total As, Cu, and Zn in the control litters (45, 962, and 644 mg kg-1, respectively; not measured for initial litter samples) were similar to those reported in past studies (Natural Resource, Agriculture and Engineering Service, 1999; Sims and Wolf, 1994; Williams et al., 1999). For example, Sims and Wolf (1994) summarized the results of a number of extensive studies of poultry litter composition and reported litter concentrations ranging from 1 to 77 mg kg-1 for As, from 25 to 1003 mg kg-1 for Cu, and from 105 to 669 mg kg-1 for Zn. None of these studies, however, reported values for WS-As, -Cu, and -Zn, which we found to average 19, 272, and 29 mg kg-1, respectively, in the litter from the control houses (Table 2). The As concentrations in these litters are of some concern, given the fact that the USEPA has established "ceiling concentration limits" and "pollutant concentration limits" of 75 and 41 mg kg-1, respectively, for the land application of municipal biosolids (sewage sludge); however, Cu and Zn concentrations were well below the USEPA limits (4300 and 1500 mg kg-1 for Cu and 7500 and 2800 mg kg-1 for Zn; USEPA, 1995).
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In terms of water solubility of elements in the alum-treated litters, we observed increases in WS-Al and WS-S and marked decreases in WS-P when alum was applied (Table 2). Higher concentrations of WS-Al and WS-S would be expected due to the regular additions of both elements in the alum. Lower litter WS-P concentrations were consistent with past research and could be caused either by the precipitation of sparingly soluble compounds of Al-P or the sorption of WS-P by amorphous Al hydroxides that formed when Al3+ dissolving from the alum hydrolyzed in the alkaline litters (Moore et al., 2000). Note that we measured WS-P in all litters at the end of the project by two methods, colorimetrically (WS-PMR; Murphy and Riley, 1962) and by ICP (WS-PICP). We found the two methods to be very well correlated (r = 0.97, significant at the 0.001 probability level) and that concentrations measured by ICP were higher than those determined colorimetrically (Fig. 1 ; Table 2). Higher WS-PICP values were probably due to the presence of dissolved organic phosphorus (DOP) that passed the 0.45-µm filter; the DOP would be measured by the ICP but not by the colorimetric method, which primarily measures ortho-P. We also found lower WS-As, WS-Cu, and WS-Zn concentrations and lower ratios of WS to total P, As, Cu, and Zn in the alum-treated litters than in litters from the control houses (Table 2; Fig. 2) . Decreased concentrations of these elements could also have resulted from their sorption by amorphous Al hydroxides formed when the alum reacted in the litters.
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Effect of Aluminum to Phosphorus Ratio on Litter Properties
One of the questions that has arisen during the consideration of the use of alum as a poultry litter amendment has been the alum rate required to optimize poultry performance and minimize the potential environmental effects of land-applied litters. Alum has been used for many years in poultry houses as an NH3 control agent, typically at application rates of approximately 0.25 kg m-2 (General Chemical, 2000). However, Moore et al. (1999a) recommended higher alum application rates (approximately 1.0 kg m-2, equivalent to approximately 10% alum concentration in the litter) to achieve the reductions in litter WS-P needed to significantly decrease soluble P losses in runoff from pastures receiving surface applications of poultry litter. An alum concentration of 10% in litter would result in a final Al to P ratio in litters of approximately 0.7 to 0.9, depending upon litter P concentration (e.g., 10% alum by weight is approximately 1.6% Al by weight and litter total P concentrations typically range from 1.8–2.2%; Sims and Wolf, 1994). The costs of increasing the alum rate from one based on NH3 control to one designed to reduce soluble P losses in runoff have generated interest in the relationship between litter Al to P ratio and elemental solubility.
Although our on-farm study was not designed to directly evaluate the effect of litter Al to P ratio on the solubility of P and other elements, the nature of the project did result in litters with a wide range of Al to P ratios. Unlike the on-farm study of Moore et al. (2000) where alum applications were made to a control house and an alum-treated house exactly according to the currently recommended protocol, beginning with fresh litter and continuing for five flocks, the applications in our project were made to houses with a wide range in the amounts of litter initially present (Table 1). Consequently, due to variable dilution effects among the poultry houses, at the end of the study the alum-treated litters ranged in Al to P ratio from 0.14 to 1.13 (average = 0.57 ± 0.19) compared with a value of approximately 1.0 (total Al = 1.87%, total P = 1.89%) in the study of Moore et al. (2000).
In general, although there were clear trends for lower concentrations of WS-PMR, WS-PICP, WS-As, -Cu, and -Zn and higher concentrations of WS-Al in alum-treated litters than in those from the control houses, we observed only slight changes in elemental solubility as Al to P ratio in the alum-treated litters increased from 0.2 to 1.0. Statistically significant, but rather weak, negative correlations were found between litter Al to P and WS-PMR (r = -0.25, significant at the 0.05 probability level; Fig. 3a) , but not WS-PICP (Fig. 3b), and between Al to P and WS-Al, As, Cu, and Zn (r = -0.48, -0.46, and -0.35, all significant at the 0.001 probability level, and -0.21, significant at the 0.05 probability level; Fig. 4 ; note that correlation coefficients only apply to litters in alum-treated houses).
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Some questions remain about this BMP, however. Alum amendment also increased litter total and water-soluble Al relative to litters from the control houses. Since Al has the potential to be phytotoxic to plants and to have deleterious effects on aquatic ecosystems it will be important to ensure that these increases in litter Al do not result in higher concentrations of soluble Al in the soil solution or in runoff or leaching from litter-amended soils. Because Al solubility in soils is controlled by soil pH and soil solution Al concentrations are very low in soils limed to the "target pH" for crop production (pH 6.0–6.5), it seems unlikely that phytotoxicity from Al will be a major limiting factor for the use of alum-treated litters as soil amendments. This is supported by the work of Moore et al. (1998) who amended tall fescue (Festuca arundinacea Schreb.) grown on a Captina silt loam soil (fine-silty, siliceous, active, mesic Typic Fragiudult) with four rates of fertilizer N (NH4NO3: from 65–260 kg N ha-1) and alum-treated or normal litter (from 2.24 to 8.98 Mg ha-1). They found that both normal and alum-treated litter increased soil pH and slightly decreased exchangeable Al relative to fertilizer N. No significant treatment effects were noted for plant Al concentrations. With respect to Al effects on water quality, there is little information on soluble Al transport from soils amended with normal or alum-treated litters. However, research comparing Al losses in runoff from pastures fertilized with alum-treated and normal litters did not find statistically significant increases in soluble Al in runoff (Moore et al., 2000).
Another consideration is the fact that we observed only minor decreases in WS-P, -As, -Cu, and -Zn as litter Al to P ratio increased from approximately 0.2 to 1.0, but did find higher concentrations of NH4–N for litter Al to P ratios > 0.6. Therefore, it seems important to further evaluate the most effective and economic alum application rate needed to achieve different production and environmental objectives. Finally, while alum will decrease the solubility of several elements of environmental concern (e.g., P, As, Cu, and Zn) it will have little effect on total concentrations of these elements in litters. Therefore, applying litters treated with alum to meet crop N requirements will continue to increase soil P concentrations. Since many soils in Delmarva are already considered "excessive" in P relative to crop P requirements (Sims et al., 2000), research is needed on the long-term solubility, and thus potential mobility, of P and trace metals in soils amended with alum-treated litters. Specifically, will the forms of P added in alum-treated litters be more stable in the soil environment and thus less susceptible to runoff and leaching than the P in "normal" litters?
In summary, this study demonstrated that it is possible to implement, on a large scale, a BMP for poultry production that has the potential to reduce the potential environmental effect of land-applied poultry litters. Future research should focus on the fate, transformations, and mobility of soluble Al, P, and trace metals in soils where alum-treated litter is used as a fertilizer material for row crop production since a considerable body of work has already documented the agronomic and environmental effects of alum-treated litter on pastures.
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ACKNOWLEDGMENTS |
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1251 et seq. |
NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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1 Mention of any trade names does not imply endorsement by any institution or agency contributing to this research. 
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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