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TECHNICAL REPORTS

Waste Management

Reducing Phosphorus Runoff from Swine Manure with Dietary Phytase and Aluminum Chloride

^a USDA-ARS, National Soil Erosion Research Laboratory, Purdue University, 275 South Russell Street, West Lafayette, IN 47907
^b USDA-ARS Poultry Production and Product Safety Research Unit, University of Arkansas, Fayetteville, AR 72701
^c Department of Animal Science, University of Arkansas, Fayetteville, AR 72701
^d Department of Crop, Soil and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701

^* Corresponding author (drsmith{at}horizon.nserl.purdue.edu).

Received for publication November 7, 2002.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Phosphorus (P) runoff from fields fertilized with swine (Sus scrofa) manure has been implicated in eutrophication. Dietary modification and manure amendments have been identified as best management practices to reduce P runoff from manure. This study was conducted to compare the effects of dietary modification and aluminum chloride (AlCl₃) manure amendments on reducing P in swine manure and runoff. Twenty-four pens of nursery swine were fed either a normal diet or a phytase-amended diet. Each pen was connected to a separate manure pit, which was treated with AlCl₃ to give final concentrations in the liquid manure of 0 (control), 0.25, 0.50, or 0.75% (v/v). Manure was collected and applied to plots cropped with tall fescue (Festuca arundinacea Schreb.), and simulated rainfall was applied at 50 mm h^–1, sufficient to generate a minimum of 30 min of continuous runoff. Samples of manure and runoff were analyzed for P and Al concentrations. Phytase reduced manure soluble reactive phosphorus (SRP) by 17%, while AlCl₃ reduced manure SRP by as much as 73% compared with normal manure. Phosphorus runoff was reduced from 5.7 to 2.6 mg P L^–1 (a 53% reduction) using AlCl₃. The mean SRP concentration in runoff from phytase diets without AlCl₃ was 7.1 mg P L^–1 during the first rainfall simulation. When phytase and AlCl₃ were used together, both manure SRP and P runoff were reduced more than if either treatment were used without the benefit of the other. Use of AlCl₃ did not increase soluble Al in manure or Al lost in runoff. Results from this study indicate that producers should use dietary manipulation with phytase and AlCl₃ manure amendments to reduce potential P losses from fields fertilized with swine manure.

Abbreviations: SRP, soluble reactive phosphorus

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
WHILE THE NUMBER of swine has remained constant over the last 35 yr, the number of animals per farm has increased (USDA National Agriculture Statistics Service, 2002). Manure from these confined animal feeding operations (CAFOs) is often field-applied to pastures at agronomic rates appropriate to supply sufficient N to the crop. A low N to P ratio results in an overapplication of P to these pastures, thereby unnecessarily increasing the risk of P runoff, which has been implicated in the accelerated eutrophication of U.S. surface waters (Schindler, 1977).

Soluble P, which is the form most readily available for algal uptake, can be the dominant fraction in runoff, accounting for as much as 80 to 90% of total P lost from pasture systems (Edwards and Daniel, 1993). Many compounds have been studied to aid producers in reducing P runoff from fields where manure is applied. Moore and Miller (1994) showed that Ca, Fe, and Al amendments to poultry litter could reduce P solubility. However, Ca phosphate minerals have been shown to dissolve under slightly acidic conditions, while similar results could occur with iron amendments under saturated conditions, where the ferric iron (Fe³⁺) was reduced to ferrous iron (Fe²⁺). Aluminum was found to precipitate P into forms that are stable under a wide range of physicochemical conditions considered normal in most soil environments. Manure amendments such as alum [Al₂(SO₄)₃·14H₂O] and aluminum chloride (AlCl₃) have been shown to reduce P solubility in manure and hence P runoff from fields fertilized with treated manure. Treatment of poultry litter with alum can reduce P solubility up to 99% (Moore et al., 1999), and has been shown to reduce P runoff from plots cropped to tall fescue by as much as 87% (Shreve et al., 1995; Moore et al., 1999, 2000). Both alum and AlCl₃ reduced P solubility by as much as 99% in swine manure, and reduced P runoff by 84% in small plot research (Smith et al., 2001). Aluminum chloride was the preferred treatment in liquid manure, because in highly reducing environments such as swine manure, sulfate could be reduced to hydrogen sulfide (H₂S), compounding problems associated with odor from swine facilities.

Dietary modification has been used to reduce the total P added to animal diets. Most grains used in animal diets, such as corn, wheat, or soybean, store as much as 80 to 90% of the total P in the form of inositol hexaphosphate (phytate) (Turner et al., 2002). Phytate-bound P is relatively unavailable to animals, especially monogastrics, that do not benefit from the aid of the microflora and microfauna of the rumen in releasing of P from phytate. Phytase, an enzyme released by certain microorganisms (e.g., Aspergillus niger), has the ability to cleave the P from the phytate molecule (Nelson et al., 1968; Kornegay, 1996).

Due to the poor availability of phytate-bound P to monogastrics, nutritionists have used dicalcium phosphate (dical), monocalcium phosphate (monocal), defluorinated phosphate, and other phosphatic minerals to supplement P requirements in feed rations. Use of P supplements in the diet can lead to increased total P in manure, and possibly increase the risk of P runoff from fields fertilized with animal manure. Use of phytase in diets increases the availability of phytate bound P in grain, and reduces the need for supplemental P, thereby reducing the total P load in manure.

Some studies have suggested that diets containing phytase may increase the soluble P component of manure, thereby increasing soluble P in runoff (Delaune and Moore, 2001). Soluble P in manure is the most important factor that determines the P runoff losses from fields fertilized with animal manures (Delaune et al., 2001). With this in mind, coupling phytase with manure amendments, such as AlCl₃, might contribute a best management practice that would reduce both the total P excreted by animals, as well as reduce the potential loss of soluble P in runoff. Some authors have interpreted data from DeLaune et al. (2001) and speculated that changes in manure chemistry or some other factor were causing elevated levels of P runoff when fertilization occurred using litter from animals fed phytase diets compared with fertilization with normal diet manure (Waldroup, 2002).

This study was conducted to compare the effectiveness of phytase and AlCl₃ at reducing P in manure, and to determine the effects of combining these best management practices on P in manure applied to fields and the subsequent runoff.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Twenty-four pens with six nursery pigs each were used for two trials. A manure collection pit measuring 1.8 x 1.3 x 0.5 m was constructed from stainless steel and located under each pen. Manure from each pen could then be analyzed separately. The pigs were weighed and weaned at approximately 19 d of age, randomized by litter, and grouped by weight for placement into nursery pens. Each trial was 6 wk long and used a three-phase diet, with each diet phase lasting 2 wk.

A 2 x 4 factorial design was used with two levels of phytase in the diet and four levels of AlCl₃ treatment of manure in the pits. There were three replications within each trial for a total of six replications of each treatment. Phytase was either not included in the diet (normal diet), or applied to the ration after pelleting as Natuphos (BASF Corp., Mt. Olive, NJ) at 500 IU kg^–1 feed. The normal diet was based on National Research Council (NRC) available phosphorus (AP), and the phytase diet was based on NRC AP – 0.1%. Table 1 shows a list of ingredients used in diets for each phase, and total P content of each diet.

Total solids in manure were determined by APHA Method 2540-B (American Public Health Association, 1992). Twenty milliliters of manure were dried in an aluminum weighing dish at 103°C for 12 h or until a constant weight was achieved, and total suspended solids was analyzed using APHA Method 2540-D (American Public Health Association, 1992), which involves filtering 3 mL of manure through a glass fiber filter and drying at 60°C for 72 h or until a constant weight was observed. A 200-mL sample of manure was centrifuged at 15000 x g for 20 min, then filtered through a 0.45-µm vacuum filter. A centrifuged, unfiltered sample was used to determine manure pH and alkalinity. Soluble reactive P was determined colorimetrically using a Technicon Autoanalyzer II (Technicon Instruments Corp., Tarrytown, NY) on a filtered sample acidified to pH 2 with concentrated HCl. Soluble metals were analyzed on filtered, acidified samples using inductively coupled argon plasma (ICAP) spectrophotometry with a Spectro Model D ICP (Spectro Analytical Instruments, Fitchburg, MA). Manure total metals were determined using ICAP spectrophotometry on an unfiltered sample digested with HNO₃ and H₂O₂ (Zarcinas et al., 1987). Total P and metals were also analyzed on a feed sample digested using APHA Method 3030E (American Public Health Association, 1992) using ICAP spectrophotometry.

Manure was applied to plots measuring 1.52 x 6.10 m that were constructed in 1998 at the University of Arkansas Agriculture Experiment Station in Fayetteville, AR. The plots were established on a Captina silt loam soil (fine-silty, siliceous, active, mesic Typic Fragiudult) with a 5% slope and cropped to tall fescue. Composite manure from each pen of pigs in the second trial was used for manure application, allowing three replications of each treatment for the rainfall simulation study. There were three days between the final collection of manure and manure application to plots. Immediately before application, manure was homogenized by stirring for 5 min in the container, a subsample of manure was withdrawn for analysis of soluble and total P (using methods described above), and the amount required for application was withdrawn and applied to the plots at a rate equivalent to 50000 L ha^–1. Plots for manure application were randomized for treatments based on Mehlich III soil test phosphorus (STP) with a mean roughly equivalent to 247 mg P kg^–1 soil (Table 3).

Phosphorus concentrations in runoff were log–normally distributed. Therefore, these concentrations were logarithmically transformed. Since many runoff P concentrations were <1.0 mg P L^–1, 1 was added to all P concentrations before logarithmic transformation so that all values obtained were positive (Neter et al., 1996).

Statistical analysis was performed using GLM procedures in SAS Version 8.2 (SAS Institute, 1985), and mean separation tests were performed using Fisher's protected least significant difference (LSD). Means and standard errors were calculated using the PROC MEANS procedure in SAS.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Manure Physical Properties
Manure treated with AlCl₃ had a higher level of manure total solids than that from control pens (Table 4). Manure in control pens contained an average of about 20 g solids L^–1 manure, while treated manure contained an average of 24.9 g solids L^–1 manure. This increase may be due to the ability of AlCl₃ to flocculate organic material suspended in manure (Timby et al., 2001). Manure from pigs fed phytase diets also tended to have slightly more total solids compared with pens fed the normal diet. The reasons for this are not clear.

Manure Chemistry
As expected, increasing levels of AlCl₃ reduced manure pH (Table 5). This effect was also noted during in-situ manure analysis, which also showed reductions in NH₃ volatilization from treated manure by as much as 50% compared with untreated manure (Smith et al., 2004). Use of phytase diets also reduced manure pH. This effect is a result of less dicalcium phosphate in the diet and, thus, less dicalcium phosphate ending up in manure.

Total P in manure was not affected by the level of AlCl₃ (Fig. 1A) . This was expected, because the manure treatment was not intended to reduce total P, but instead reduce P solubility. Manure from pigs fed phytase diets did show reductions in total P. The total P fed to pigs was reduced by 17% in phytase manure compared with normal diet manure, and overall the total P excreted was reduced by 13% (Table 1; Fig. 1A).

View larger version (25K): [in this window] [in a new window]   Fig. 1. Effect of AlCl3 treatment and dietary modification on (A) manure total P and (B) manure soluble P (different letters indicate statistical difference at P < 0.05; bars indicate standard error).

Although soluble P was not reduced to the same extent as found in previous studies, our results show that in-house treatment provides the added benefit of reduced NH₃ volatilization (Smith et al., 2004), as this would reduce ambient levels of NH₃ in the housing, and it could also lead to an increase in productivity through increased weight gains, resulting from reduced susceptibility to respiratory diseases such as conchal atrophy and atrophic rhinitis.

Dietary modification by the addition of phytase also reduced P solubility. Phytase significantly reduced manure SRP from 178 mg P L^–1 in normal diet pens to 137 mg P L^–1 in phytase fed pens without AlCl₃, a reduction of 23% (Fig. 1B). Soluble P concentrations in manure were consistently significantly less in the phytase manure compared with manure from animals fed the normal diet. When both phytase and AlCl₃ at the 0.75% rate were used in combinations, soluble P was reduced by 84% compared with that from pens where neither treatment was employed. Reduction of soluble P within an AlCl₃ treatment may be a result of an increased Al to P ratio, and hence an increased efficiency of the AlCl₃ treatment. Producers who need to reduce P solubility in manure can accomplish that goal very effectively through use of both dietary modification and manure amendment.

In recent years concerns have been raised about the addition of Al to soils. Total aluminum in manure ranged from 10 mg Al L^–1 in normal diet manure without AlCl₃, to 380 mg Al L^–1 in phytase manure with the high levels of AlCl₃ treatment. Thus, while increasing levels of AlCl₃ increased total Al levels in swine manure, phytase had little effect on total Al. Aluminum is the third most abundant element in the earth's crust (Schulze, 1989). Therefore, adding Al at the rates we propose should have virtually no effect on the amount of Al found in the soil. For example, if AlCl₃ was added to manure at 0.75% and applied to land at 50000 L ha^–1 for 10 yr, the total aluminum in a hectare furrow slice would only increase by a total of 0.0095%. At this rate, it would take more than 1000 yr to increase the total Al in soils by 1%. Soluble Al was as much as three orders of magnitude less than total Al. Soluble Al ranged from 0.10 mg Al L^–1 in the normal diet manure with 0.25% AlCl₃ treatment to 0.24 mg P L^–1 in phytase diet manure without AlCl₃ treatment. Some of the highest levels of soluble Al were found in manure from pens where there was no AlCl₃ treatment, while the lowest levels of soluble Al were observed in pens with AlCl₃.

Runoff Chemistry
The use of AlCl₃ appeared to have little effect on runoff pH. Runoff pH from plots fertilized with manure from normal diets without AlCl₃ was roughly equivalent to that from plots fertilized with the high level of AlCl₃ (7.32 and 7.30, respectively). Runoff water from plots treated with phytase manure tended to have slightly lower pH compared with pens within the same AlCl₃ treatment and normal diet although these differences were not significant. With the exception of the plots treated with the 0.50% AlCl₃, the trends were very similar for manure pH and runoff pH. Fertilization with swine manure resulted in slightly higher runoff pH compared with unfertilized control plots.

In plots fertilized with manure from animals fed the normal diets, the runoff alkalinity increased slightly with increasing levels of AlCl₃, while the runoff alkalinity decreased in plots fertilized with phytase manure. As expected, runoff alkalinity from plots fertilized with manure was higher than that collected from unfertilized control plots.

Plots fertilized with manure from normal diet pens and no AlCl₃ resulted in a mean runoff SRP of 5.66 mg P L^–1 during the first rainfall simulation (Fig. 2) . Runoff SRP decreased with increasing levels of AlCl₃. A 53% reduction in SRP was noted when comparing the high level of AlCl₃ (0.75% v/v in manure) to the control treatment within the normal diet (5.66 and 2.65 mg P L^–1 respectively). Phytase manure without AlCl₃ resulted in runoff SRP concentrations of 7.14 mg P L^–1 during the first rainfall simulation. When comparing the mean for all three rainfall simulations, the normal diet, without AlCl₃ treatment, resulted in a mean runoff SRP of 2.6 mg P L^–1, and the mean runoff SRP concentration resulting from the phytase diet treatment with no AlCl₃ was 3.3 mg P L^–1.

View larger version (22K): [in this window] [in a new window]   Fig. 2. Effect of AlCl3 treatment and dietary modification on runoff soluble P (different letters indicate statistical difference at P < 0.05; AlCl3 x phytase interaction, P = 0.05).

Manure was held for 3 d between the final manure collection from the third phase of the second trial and manure application. To address potential concerns of changes in manure chemistry during this time, manure samples were collected immediately before application to plots for rainfall simulation studies, as described in Materials and Methods, above. When the soluble P concentrations in these samples were compared with a weighted average of manure SRP concentrations from the three phases (Fig. 3) , there was a very strong correlation (m = 0.98; r² = 0.95). Other researchers have noted increases in P runoff when manure from dietary modification treatments was applied to plots (DeLaune and Moore, 2001), while at least one researcher has attempted to attribute these differences to changes in manure chemistry that occurred between manure collection and application (Waldroup, 2002). Results from the current study indicate that there was very little, if any, change to manure chemistry during the 3-d holding period (Fig. 3).

View larger version (23K): [in this window] [in a new window]   Fig. 3. Soluble reactive phosphorus (SRP) concentration in composited manure samples used for application to rainfall simulation plots as a function of weighted SRP concentrations from manure samples taken during the in-house trials.

Regression equations between P concentrations in runoff and manure SRP, manure total P, and soil test P are shown in Table 6. Results from these regressions indicate that manure SRP was the most important fraction in determining P losses from pasture systems especially in the first rainfall simulation (Fig. 4) . These results are consistent with Delaune et al. (2001), who indicated that when manure or some other form of soluble P (such as triple super phosphate) is added to a pasture system, that the amount of soluble P applied has the greatest effect on P lost in runoff.

View larger version (18K): [in this window] [in a new window]   Fig. 4. Soluble reactive phosphorus (SRP) concentration in runoff from the first rainfall simulation as a function of manure SRP concentration.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Reducing nutrient losses, especially P losses from runoff, is essential to the animal agriculture industry for protection of surface water quality. Use of manure amendments and dietary modification are two methods that have been proposed for producers to use to accomplish the goal of reducing potential P losses from field-applied animal manure.

It was found in this study that AlCl₃ manure amendments could reduce soluble P as much as 73%, while dietary modification with phytase reduced SRP in manure by 17%. The use of both treatments reduced manure SRP from 178 mg P L^–1 in normal swine manure to about 28 mg P L^–1 in manure from pens using both phytase diet and AlCl₃ manure amendments at 0.75%, an 84% reduction in soluble P.

Phosphorus runoff losses were reduced when AlCl₃ was used by as much as 53% when comparing plots fertilized with manure treated with the high level of AlCl₃ to plots treated with manure from pigs fed a normal diet without AlCl₃ addition in the first rainfall simulation. There were no statistical differences between P runoff from plots fertilized with the manure treated with AlCl₃ at the high rates and the unfertilized control plots. When dietary modification and AlCl₃ were used together, P runoff in the first rainfall simulation was reduced to about 1.5 mg P L^–1, an overall reduction of 73% in P runoff. At the 0.50 and 0.75% AlCl₃ treatment levels, P runoff was reduced by 39 and 43%, respectively, when comparing the plots fertilized with phytase manure to those plots fertilized with manure from animals fed the normal diet.

Aluminum in runoff was not affected by AlCl₃ treatment, either. Results of total Al analysis in manure indicate that concerns of adding Al to soils, at the rates recommended here, are unjustified, particularly when considering that Al is the third most abundant element in the earth's crust.

This study compares the use of dietary modification and manure amendments on P losses from pasture systems fertilized with swine manure. Both phytase and AlCl₃ reduced soluble P in manure. When AlCl₃ was used alone or in cooperation with dietary modification with phytase, P runoff was reduced. The potential effects of using both treatments is very promising, and should be incorporated into commercial-sized operations on a limited scale to ensure that the benefits noted here can be reproduced under real production scenarios. A reduction of more than 50% in P runoff from fields fertilized with swine manure could make a fairly important impact on the P mass received by a surface water body, particularly in watersheds where intensive swine production occurs.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products that may be suitable.

	REFERENCES

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• American Public Health Association. 1992. Standard methods for the examination of water and wastewater. 18th ed. Am. Public Health Assoc., Washington, DC.
• DeLaune, P.B., and P.A. Moore, Jr. 2001. Predicting annual phosphorus losses from fields using the phosphorus index for pastures. Better Crops 85(4):16–19.
• DeLaune, P.B., P.A. Moore, Jr., D.C. Carmen, T.C. Daniel, and A.N. Sharpley. 2001. Development and validation of a phosphorus index for pastures fertilized with animal manure. In G.B. Havenstien (ed.) Proc. of the Int. Symp. Addressing Animal Production and Environmental Issues [CD-ROM], Research Triangle Park, NC. 3–5 Oct. 2001. North Carolina State Univ., Raleigh.
• Edwards, D.R., and T.C. Daniel. 1993. Potential runoff quality effects of poultry manure slurry applied to fescue plots. Trans. ASAE 35:1827–1832.
• Kornegay, E.T. 1996. Nutritional, environmental and economic considerations for using phytase in pig and poultry diets. p. 277–302. In E.T. Kornegay (ed.) Nutrient management of food animals to enhance and protect the environment. Lewis Publ., Boca Raton, FL.
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• Moore, P.A., Jr., M.L. Self-Davis, T.C. Daniel, W.E. Huff, D.R. Edwards, D.J. Nichols, W.F. Jaynes, G.R. Huff, J.M. Balog, N.C. Rath, P.W. Waldroup, and V. Raboy. 1998. Use of high available phosphorus corn and phytase enzyme additions to broiler diets to lower phosphorus levels in poultry litter. In J.P. Blake and P.H. Patterson (ed.) Proc. 1998 Natl. Poultry Waste Symp., Springdale, AR. 19–21 Oct. 1998.
• Nelson, T.S., T.R. Shieh, R.J. Wedzinski, and J.H. Ware. 1968. The availability of phytate phosphorus in soybean meal before and after treatment with mold phytase. Poult. Sci. 47:1842–1848.[ISI][Medline]
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