| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Department of Soil Science, North Carolina State University, Raleigh, NC 27695
b Department of Plant and Soil Science, University of Delaware, Newark, DE 19716
c Department of Animal and Food Science, University of Delaware, Newark, DE 19716
d Soil and Water Science Department, University of Florida, Gainesville, FL 32611
e Department of Animal and Avian Science, University of Maryland, College Park, MD 20742
f Department of Animal Sciences, Purdue University, West Lafayette, IN 47907
* Corresponding author (rory_maguire{at}ncsu.edu)
Received for publication January 15, 2004.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: 25OH-D3, vitamin D3 metabolite 25-hydroxycholecalciferol • ICP–AES, inductively coupled plasma–atomic emission spectrometry • M3-Al, M3-Ca, M3-Fe, and M3-P, Mehlich 3–extractable aluminum, calcium, iron, and phosphorus, respectively • M3-PSR, Mehlich-3 phosphorus saturation ratio calculated as the molar ratio of M3-P to (M3-Al + M3-Fe) • NMR, nuclear magnetic resonance • NPP, non-phytate phosphorus • WSP, water-soluble phosphorus in litters or soils
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
A promising approach to reduce manure P surpluses is to decrease the P concentration of animal diets, which, in turn, leads to lower P concentrations in manures. One option is to decrease the "insurance" levels of P in animal feeds, where more P than required for optimum animal nutrition is fed to ensure that P deficiency does not limit animal productivity (Council for Agricultural Science and Technology, 2002). About two-thirds of the P in the major feed ingredients [corn, Zea mays L., and soybean, Glycine max (L.) Merr.] for swine (Sus scrofa) and poultry (Gallus gallus) (nonruminant animals) diets is in the form of poorly digestible phytate P (myo-inositol hexakisphosphate; Ravindran, 1996). The remaining P that is considered more highly digestible is termed non-phytate phosphorus (NPP). To overcome the low digestibility of phytate P in nonruminant diets, and ensure that P deficiency does not limit animal performance, mineral forms of NPP (normally some type of calcium phosphate such as defluorinated phosphate) are often added to diets.
Avoiding "insurance" use of mineral supplements in diets can reduce manure P concentrations. Feed additives are a second option. Much research has been conducted on feed additives, mainly microbial phytase (derived from the fungus Asperigillus niger), but citric acid (C6H8O7) and the vitamin D derivative 25-hydroxycholecalciferol (25OH-D3) have also been shown to increase dietary P uptake efficiency and decrease the need for dietary P supplements (Council for Agricultural Science and Technology, 2002; Cromwell, 1996; Harper et al., 1997; Huff et al., 1998). For example, Huff et al. (1998) examined the influence of phytase in broiler diets and concluded that dietary P could be decreased 11% when phytase was added to the diet, without affecting broiler performance. Nahm (2002) reported that phytase in diets with simultaneous decrease in dietary P supplementation could decrease P excretion by 25 to 35% in chickens and 25 to 60% in swine. Similarly, by supplementing swine diets with phytase and reducing dietary P, Yi et al. (1996) decreased fecal P excretion by 25 to 50%.
While research has clearly shown the great promise of feed additives to decrease the amount of total P excreted by monogastric animals, less information is available on how their use will affect P solubility in manures and manure-amended soils. The solubility of P in manures is of considerable importance, because manures with higher WSP concentrations have been shown to have higher potentials for dissolved P losses in runoff from agricultural fields (Kleinman et al., 2002). Applegate et al. (2003) fed broiler chickens diets with and without phytase, where NPP levels were adjusted to reflect the anticipated efficacy of phytase at increasing P availability to the birds. They concluded that "WSP in fresh broiler litter is dependent upon P concentration fed, but not on fungal phytase supplementation." Baxter et al. (2003) reported that diets containing phytase and low phytic acid corn reduced fecal P from pigs by 17 to 40% and either decreased, or did not increase, dissolved inorganic and organic P. Maguire et al. (2003) reported that turkey diets with decreased supplemental P and phytase led to lower WSP in manures and manure-amended soils. Gilley et al. (2001) and Moore et al. (1998) reported that adding phytase to swine and broiler diets did not significantly change dissolved or total P losses in runoff from indoor soil boxes and grassland field plots, respectively. These studies suggest that modifying monogastric diets to reduce the total amount of P excreted will probably decrease, and certainly not increase, the risk of P losses to water by runoff or leaching.
Identifying P forms in litters will aid the understanding of how this P will behave following land application. Little work has been performed on solution 31P NMR spectroscopy of poultry litters, although Crouse et al. (2000) showed that orthophosphate was the major NMR signal in NaOH + EDTA extracts of turkey litters. Using solid-state 31P NMR, Hunger et al. (2004) were able to identify Ca- and Al-associated P in poultry litter, some of which was alum treated. These studies demonstrate the potential for 31P NMR to identify specific forms of P in manures.
As feed additives to improve dietary P efficiency are currently under development (and even mandated by law in Maryland; Simpson, 1998), information on the effects of dietary manipulation on the forms, solubility and hence potential mobility of P in litters from modified diets is required. Furthermore, the environmental implications of dietary amendments can be fully evaluated only by understanding how P behaves in soils following amendment with litters from these modified diets. Therefore, the objective of this study was to evaluate how feeding closer to animal requirement and using additives such as phytase and 25OH-D3 affected the forms of P in poultry (broiler and turkey) litter and the solubility of P in litters and litter-amended soils.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Litters (mixture of feces and wood shavings used as bedding) were collected after the performance trials for analysis and use in soil incubation studies. Litter samples were collected from each replicate pen immediately after birds were removed and composited by dietary treatment by thoroughly mixing equal weights of samples from each pen. All composited litters were then spread thinly in forced air ovens, dried at 40°C, and ground to pass a 0.5-mm stainless steel screen.
The National Research Council (1994) NPP recommendations are closer to known turkey requirements than known broiler requirements. Therefore, the turkey and broiler experiments had different designs, with National Research Council (1994) recommendations being closer to the birds' NPP requirements in the turkey trial and University of Maryland (UMC) being closer to the birds' NPP requirements in the broiler study (Table 1). To avoid confusion, the NRC (turkey trial) and UMC (broiler trial) diets will be referred to as "low" in NPP, compared with the industry turkey diets and NRC broiler diets that will be referred to as "high" in dietary NPP (Table 1). When comparing diets and litters they produce, the low diets and litters will be referred to as "feeding NPP closer to requirement," as the high diets tend to overfeed dietary NPP.
|
Broiler Trials
Three flocks were grown consecutively on wood shavings, with no litter removal between flocks. A total of 56 male broilers was assigned to each pen (0.08 m2 bird–1) and each treatment was assigned to nine replicate pens. In each flock, broilers were fed from 1 d of age (hatch) for a 49-d growing period, divided into four feeding phases. The feeding phases were from 1 to 18, 18 to 32, 32 to 42, and 42 to 49 d. The broiler study compared National Research Council (1994) versus UMC recommendations of NPP with and without phytase and/or 25OH-D3, with the UMC diets having lower NPP levels than the NRC diets (Table 1). The NRC levels of NPP in the four feed phases were 0.45, 0.35, 0.35, and 0.30% NPP, while the UMC levels were 0.45, 0.31, 0.23, and 0.18% NPP. When phytase was included in the diet, NPP content was decreased by 0.10% in all feeding phases in the NRC treatments and 0.064% in all feeding phases in the UMC treatments. The NPP content was further reduced by 0.024% in all feeding phases when 25OHD3 was included in a diet.
Characterization of Litter Phosphorus
The following analyses were conducted in triplicate on the composited litter sample from each dietary treatment. Total P in litters from each dietary treatment was determined by microwave-assisted digestion of a 0.5-g dried litter sample with 7 mL of concentrated HNO3 and 3 mL of 30% H2O2. The P in these litters was also chemically fractionated by the method of Sharpley and Moyer (2000) that was based on the soil P fractionation method of Hedley et al. (1982). Samples of dried litter (0.2 g) were extracted sequentially with 40 mL of (i) deionized water for 1 h, then for 16 h each with (ii) 0.5 M NaHCO3, (iii) 0.1 M NaOH, and (iv) 1.0 M HCl. Extracts were centrifuged at 1000 x g for 1 h and the supernatant was filtered through 0.45-µm membranes (Millipore, Billerica, MA). Phosphorus detection in all digests and extracts was by inductively coupled plasma–atomic emission spectrometry (ICP–AES); the 0.5 M NaHCO3 extracts were diluted fivefold before analysis to avoid interference from the high salt concentration in this extractant.
Solution Phosphorus-31 Nuclear Magnetic Resonance Spectrometry of Litter Extracts
Phosphorus was extracted in triplicate by shaking 2.00 ± 0.01 g of litter with 40 mL of a solution containing 0.5 M NaOH and 0.05 M EDTA for 4 h at 20°C. This provides maximum P recovery from poultry litter and optimum spectral resolution in solution 31P NMR spectroscopy (Turner, 2004). Extracts were centrifuged at 10000 x g for 30 min, and aliquots (5 mL) were diluted 20-fold and analyzed for total P by ICP–AES. The remaining solutions from the triplicate extracts were combined, frozen rapidly at –80°C, lyophilized, and ground to a fine powder. Immediately before NMR spectroscopy, each freeze-dried extract (approximately 100 mg) was redissolved in 0.9 mL of 1 M NaOH and 0.1 mL of D2O (for signal lock) and transferred to a 5-mm NMR tube. The addition of NaOH adjusts the solution to a pH > 13, necessary to ensure consistent chemical shifts and optimum spectral resolution.
Solution 31P NMR spectra were obtained using a Bruker (Billerica, MA) Avance DRX 500 MHz spectrometer operating at 202.456 MHz for 31P and 500.134 MHz for 1H. We used a 5-µs pulse (45°), a delay time of 5.0 s, an acquisition time of 0.8 s, and broadband proton decoupling for all samples. The relatively long delay time allowed sufficient spin–lattice relaxation between scans for P compounds in these extracts with low paramagnetic ion concentrations (Turner, 2004). The number of scans varied between 9000 and 14000, and spectra were plotted without line broadening. Temperature was regulated at 20°C to minimize degradation of P compounds and ensure consistent signal intensities (Cade-Menun et al., 2002; Turner et al., 2003).
Chemical shifts of signals were determined in parts per million (ppm) relative to 85% (w/v) H3PO4 and assigned to individual P compounds or functional groups based on literature reports (Turner et al., 2003). Signal areas were calculated by integration and P concentrations calculated by multiplying the proportion of the total spectral area assigned to a specific signal by the total P concentration (mg P kg–1 dry litter) in the original extract. A strong signal appearing around 6.1 ppm was assigned to inorganic orthophosphate, while signals between 4.0 and 6.0 ppm were assigned to orthophosphate monoesters (Fig. 1) . A number of individual signals were detected within this region, including those at approximately 5.95, 5.06, 4.70, and 4.54 ppm in the ratio 1:2:2:1, which were assigned to phytate P (Fig. 1). Other trace signals in this region probably represented lower-order inositol phosphate esters. A signal at approximately –4.3 ppm was assigned to pyrophosphate, a specific inorganic polyphosphate with chain length n = 2. We did not detect signals from orthophosphate diesters (usually occurring between 2 and –1 ppm), phosphonates (20 ppm), nor long-chain inorganic polyphosphates (–4 ppm and –18 to –21 ppm).
|
Incubation Methodology and Soil Analysis
Each of the poultry litters was incorporated into 50 g of air-dried soil, in triplicate, using a completely randomized experimental design. A rate of 150 kg total P ha–1 (assuming 2242 Mg topsoil ha–1) was chosen, as this is similar to the P rate when litters are applied to meet crop N requirements. Field capacity of soils was determined by the method of Tan (1996). Amended and unamended control soils (no litter added) were incubated at 70% of field capacity in polyethylene containers for 29 d at 25°C. Two holes were cut in the tops of the incubation containers to allow gaseous exchange and prevent anaerobic conditions during the incubation. Soil moisture content was maintained on a weight basis by adding deionized water at weekly intervals.
After 5 and 29 d, 2-g subsamples of each soil were removed and analyzed for WSP using moist soils and a soil to deionized water ratio of 1:10 (dry-weight basis), 1-h shaking time, 15-min centrifugation at 1000 x g, and filtration through a 0.45-µm Millipore membrane. Molybdate reactive P in the extract was determined by the method of Murphy and Riley (1962). These subsamples, and bulk soils, were also air-dried, extracted with Mehlich 3 (0.2 M CH3COOH + 0.25 M NH4NO3 + 0.015 M NH4F + 0.013 M HNO3 + 0.001 M EDTA) at a soil to solution of 1:10, filtered through Whatman (Maidstone, UK) no. 2 filter paper, and analyzed for M3-P, M3-Al, M3-Ca, and M3-Fe (Mehlich, 1984). All water and Mehlich-3 extracts were analyzed by ICP–AES. All soils were analyzed for pH (1:1 soil to water) and organic matter (loss on ignition) by standard methods of the University of Delaware Soil Testing Program (Sims and Heckendorn, 1991). The Mehlich-3 P saturation ratio (M3-PSR) was calculated by the following equation, with values for P, Al, and Fe in mmol kg–1 (Maguire and Sims, 2002b; Sims et al., 2002):
 | [1] |
Statistical Analyses
Separation of means was performed using least significant differences calculated using the PROC GLM procedure in the Statistical Analysis System, Version 8 (SAS Institute, 1998). All other statistical analyses were performed using the Data Analysis tool pack in Microsoft Excel 2000 (Microsoft, 2000).
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
More striking and consistently significant effects on litter P were observed due to reducing NPP concentrations in diets alone (i.e., feeding closer to requirement), or in combination with phytase use. Total (Table 1) and WSP (Fig. 2) were significantly greater in both the turkey and broiler litters from high NPP diets (A, C, 1, 5) than the equivalent low NPP diets (B, F, 2, 3). Feeding NPP closer to requirement decreased total P by 19 to 33% in turkey and 10 to 17% in broiler litters, while WSP decreased by 20 to 21% in turkey and 37 to 52% in broiler litters (high versus low NPP diets; Table 1). This agrees with previous research that has shown that feeding NPP closer to requirement can significantly decrease total and WSP in litters (Applegate et al., 2003). Adding phytase to diets, with a corresponding decrease in dietary NPP, significantly decreased total P by 7 to 24% in turkey and 17 to 24% in broiler litters relative to non-phytase diets (Table 1). Combining feeding NPP closer to requirement and using phytase decreased total and WSP by 38 and 22% in turkey litter and by 31 and 43% in broiler litter, respectively, relative to unmodified diets. In a review, the Council for Agricultural Science and Technology (2002) suggested that the concentration of P in poultry litter could be decreased by at least 40% by a combination of feed additives and reduced NPP, similar to our values of 31 to 38%.
|
Direct comparison of diets using phytase and a reduction in dietary NPP (C, F, 5, 3) and the same diets without phytase (A, B, 1, 2) showed that differences in WSP were not significant when respective litters with and without phytase were statistically compared (Fig. 2). In fact, WSP was lower (although not significantly) in the phytase than the equivalent non-phytase litter in three out of four comparisons. Further, with only one exception (NaHCO3–P for broiler diets), concentrations of NaHCO3–P, NaOH-P, and HCl-P decreased significantly when diets were formulated using phytase (Fig. 2). Lower concentrations of NaHCO3–P and HCl-P in litters probably reflect the reduced concentrations of inorganic NPP (Ca-P) contained in phytase-based diets. Reductions in litter NaOH-P concentrations when phytase was used suggest that organic P in diets (e.g., phytate P in corn and soybean) was hydrolyzed by phytase during digestion and either absorbed by the animals or excreted in an inorganic form. Clearly, more work is needed to better define the effect of feed additives and other feeding strategies on the exact chemical species present in litters and manures. However, our data suggest that feeding closer to requirement and using phytase or 25OH-D3 will reduce the environmental risk of poultry litter application by decreasing the amount of total and inorganic P applied and having little or no effect on the amount of WSP added. For example, if comparable litters from diets without (A, B, 1, 2) and with (C, F, 5, 3) phytase + reduced NPP were applied at 9 Mg ha–1, a typical N-based rate for non-leguminous crops, the amount of total P added would range from 106 to 160 kg ha–1 (no phytase) and from 87 to 122 kg ha–1 (with phytase); inorganic P (NaHCO3–P + HCl-P) added would range from 31 to 49 kg ha–1 (no phytase) and from 25 to 37 kg ha–1 (with phytase); and WSP added would range from 20 to 58 kg ha–1 (no phytase) and from 24 to 57 kg ha–1 (with phytase). These findings are consistent with results from other studies and literature reviews on this subject (Applegate et al., 2003; Baxter et al., 2003; Maguire et al., 2003; Waldroup, 2002).
Solution Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy of Litter Extracts
The turkey and broiler studies had slightly different designs and 25OH-D3 generally had little effect on the speciation of litter P. Therefore, dietary treatments that were very similar in formulation and that directly compared the effects of phytase + NPP reduction on litter P (A, B, 1, 2) with currently recommended diets (industry or NRC; C, F, 5, 3) were selected for analyses by 31P NMR spectroscopy and for use in soil incubation studies. These correspond with the high and low NPP diets with and without phytase identified in Table 1.
The NaOH + EDTA extract used for the solution 31P NMR spectroscopy recovered >94% of total P from litters, except for the high turkey diet (87% recovery) (Table 2). Signals from P attached to the six carbons (C-1 to C-6) of the phytate molecule were identified (Table 2; Turner et al., 2003). Total phytate P concentrations were calculated from the NMR spectra in two ways: (i) summation of the peaks or (ii) by multiplying the C-2 peak by six (in poor-quality spectra, this signal is sufficiently well-resolved to be quantified). These two methods yielded similar results with r2 = 0.99 (significant at the 0.001 probability level) and a slope close to 1, probably as the solution 31P NMR spectra for these litters were extremely well-resolved. Total phytate P ranged from 3.65 to 7.83 g kg–1 and accounted for 26 to 63% of acid digest total P, depending on dietary treatment. Relatively small concentrations (4–14% of total P) of pyrophosphate and other monoesters were identified, while large concentrations of inorganic orthophosphate (31–63% of total P) were clearly evident in the NaOH + EDTA extract.
|
|
Comparison of Chemical Fractionation to Solution Phosphorus-31 Nuclear Magnetic Resonance Spectroscopy of Litter Extracts
Sharpley and Moyer (2000) stated that NMR was expensive but that "chemical fractionation is cheap and can provide a rapid estimate of P solubilities and labilities." As noted above, our results support this contention and suggest that using chemical methods of analysis can provide a good understanding of the forms of P in manures and thus their fate and transport in soils, once the P forms they extract have been identified by spectroscopic methods. More detailed comparison of the NMR data (Table 2) to the chemical fractionation results (Table 1) showed that statistically significant correlations existed between the concentrations of orthophosphate identified by NMR and all chemical fractions of P except NaOH-P (Table 3). The closest relationship for an individual extract was between WSP and orthophosphate (r = 0.91, P < 0.01), indicating that a simple water extract is a reasonable surrogate means to estimate the total orthophosphate content of NaOH + EDTA litter extracts, as determined by NMR. The greatest correlation coefficient (r = 0.96, P < 0.001) observed was between orthophosphate and the three extractants that primarily measure inorganic P (WSP + NaHCO3–P + HCl-P). However, the sum of the P concentrations in these three extractions averaged 147% of orthophosphate, indicating that organic P was removed by some of these extractants (Table 3). It is likely that ICP analysis of the water extract of litters also measures dissolved organic P. Sims and McCafferty (2002) analyzed 200 broiler litters and reported that values for WSP determined by ICP were approximately 15 to 20% higher than those measured colorimetrically. Further, Sharpley and Moyer (2000) reported that inorganic and organic P concentrations in the NaHCO3 extracts of dairy, poultry, and swine manures ranged from 360 to 7180 and 70 to 1100 mg kg–1, respectively. Our results also suggest that HCl extracted organic P, as the average percentage of orthophosphate extracted by (WSP + NaHCO3–P + HCl-P) was 147%, compared with 102% for (WSP + NaHCO3–P). Recent research using the same litters as in the present study has provided additional evidence that HCl extracts organic P from broiler litters and should not be assumed to only extract inorganic forms of P (McGrath, 2004). That study investigated the effects of long-term storage on P speciation using the same chemical fractionation procedure and found that, depending on storage conditions, from 71 to 90% of the P in the HCl fraction was organic P.
|
Effect of Poultry Diet on Phosphorus Forms in Litter-Amended Soils
The soils selected for the incubation study ranged in pH from 5.3 to 7.9 and in organic matter from 10 to 57 g kg–1 (Table 4). The Clime was a calcareous soil, as shown by the high pH and M3-Ca content. Soil test P (Mehlich 3) concentrations ranged from 3 to 152 mg kg–1. Sims et al. (2002) reported 51 to 100 mg Mehlich 3 P kg–1 as being optimum for crop growth, so the selected soils ranged from very low to above optimum. Soil P saturation (M3-PSR) for the three acidic soils ranged from 0.04 to 0.17. Environmental upper limits suggested for M3-P and M3-PSR range from 150 to 200 mg kg–1 and 0.15 to 0.20, respectively (Khiari et al., 2000; Maguire and Sims, 2002b; Sims et al., 2002).
|
All litters increased soil WSP significantly, relative to the unamended control soil, after 5 d, for all soils except the Clime (Fig. 4a, 4b) . Results for that calcareous soil were mixed, with WSP significantly increasing, relative to the control, for five of the eight litter treatments.
|
|
Comparison of soils amended with litters from diets formulated with and without phytase showed that, for 12 of the 16 comparisons, phytase use in diets either had no effect or decreased soil WSP at the 5-d sampling date (Fig. 4a, 4b). The amount of litter WSP added to soil was always numerically greatest for litter produced from turkey and broiler diets containing phytase. However, soil WSP at 5 d was significantly greater when amended with turkey and broiler litters produced from the phytase diets only for the Clime and Rumford soils. The Rumford soil had the highest P saturation value of all soils (M3-PSR = 0.17; Table 4) which may have contributed to the higher soil WSP values initially observed. The slightly higher WSP values observed with the litters from turkey diets using phytase in the calcareous Clime soil cannot be readily explained; however, this did not occur with broiler litters nor persist throughout the incubation. After 29 d there were no comparisons where amending a soil with a litter from a phytase diet significantly increased soil WSP relative to a litter from a non-phytase diet. These results are similar to the results of Maguire et al. (2003), who amended soils with turkey litters and observed no increase in soil WSP where phytase had been included in diets. Gilley et al. (2001) and Moore et al. (1998) also reported that adding phytase to swine and broiler diets did not significantly affect soluble P losses in runoff.
All litters significantly increased soil test P (M3-P) relative to the unamended control soils (Table 5). Significant differences in M3-P occasionally occurred between litters from different diets, but there were no consistent trends suggesting that dietary NPP level or phytase use will result in major differences in plant-available P in these soils. Dietary modification, therefore, should not have any negative effects on crop production. Understanding the effect of dietary manipulation on soil test P is also important to the environmental aspects of farm-scale nutrient management planning. In some states, M3-P is now the basis for determining when more intensive manure management is required to protect or improve water quality. For example, in Delaware and Maryland, a value of 150 mg M3-P kg–1 is used to identify soils requiring a comprehensive site assessment of the risk of P loss to water (P Site Index; Coale et al., 2002; Leytem et al., 2003). Average increases in M3-P due to litter application (across all four soils) ranged from 27 to 33 mg kg–1. Thus, on average, for these types of poultry diets, each kg of litter total P added resulted in an increase of from 0.18 to 0.22 mg M3-P kg–1 soil (Table 5). Based on the total P values of the litters (Table 1), adding a N-based litter rate (9 Mg ha–1) would result in greater increases in M3-P for high-NPP diets, compared with low-NPP diets, and lower or similar increases in M3-P when phytase was included in the diet (Table 5). This again illustrates the value of modifying poultry diets to reduce P excretion. Information such as this could also be used to determine the effect of diet on the amount of litter that could be applied to a field before M3-P exceeded a specified upper limit. As an example, for the Nicollet soil, regardless of diet, about 600 kg of litter P could be applied before M3-P would increase from 35 to 150 mg kg–1. For turkey litter, using the industry diet (A; total P = 17768), this equates to 34 Mg litter ha–1, while for the NRC diet with phytase and NPP reduction (F, total P = 10983), 55 Mg litter ha–1 could be applied.
|
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
In addition to reducing total P excreted, our results show that modifying diets by reducing overfeeding and using feed additives such as phytase and 25OH-D3 often decreased and never increased WSP in poultry litters. As past research has shown that P losses in runoff and leaching from manure-amended soils are related to the P solubility in applied manures, this study suggests dietary modification would reduce the risks of P loss to water associated with land application of litters.
The solution 31P NMR results also showed that phytase in diets did not affect the concentration of total inorganic P (ortho P) in litters. However, phytase in diets did decrease phytate P where phytase was added to the diets, supporting past evidence on the effectiveness of dietary phytase for increasing phytate P hydrolysis. Applying solution 31P NMR to poultry litters is a fairly new procedure. This study showed the sensitivity and usefulness of this procedure in its ability to identify changes in P forms in poultry waste.
Adding litters to soils on a P basis rather than the more common N basis could be considered a worse-case scenario for phytase, as it is more efficient at reducing litter total P than WSP and application on an P basis can therefore result in greater application rates of litter WSP. Litters always increased soil WSP; however, when soils were amended with litters at the same total P rate, in 12 out of 16 comparisons phytase had no significant effect or decreased WSP in the soils. Treatment effects were also relatively short lived in soils, with differences in water-soluble P evident at 5 d but not at 29 d. Therefore, any potential adverse environmental effects would be short lived from adding greater amounts of water-soluble P in litter applications to agricultural soils. Changes in M3-P were related to total P applied in litters, so that if dietary modification decreases litter total P and litters continue to be applied on an N-based nutrient management plan, then dietary modification will help mitigate increases in soil test P.
In conclusion, the results of this study support feeding NPP closer to requirement and the use of phytase in feeds, as part of a system to decrease P surpluses in areas of intensive animal production without increasing the potential for P losses from litter-amended soils.
|
ACKNOWLEDGMENTS |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Related articles in JEQ:
This article has been cited by other articles:
|
|
 |
|
  T. W. Simpson, A. N. Sharpley, R. W. Howarth, H. W. Paerl, and K. R. Mankin The New Gold Rush: Fueling Ethanol Production while Protecting Water Quality J. Environ. Qual., March 1, 2008; 37(2): 318 - 324. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. B. Leytem, P. Kwanyuen, P. W. Plumstead, R. O. Maguire, and J. Brake Evaluation of Phosphorus Characterization in Broiler Ileal Digesta, Manure, and Litter Samples: 31P-NMR vs. HPLC J. Environ. Qual., March 1, 2008; 37(2): 494 - 500. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. B. Leytem, P. W. Plumstead, R. O. Maguire, P. Kwanyuen, J. W. Burton, and J. Brake Interaction of Calcium and Phytate in Broiler Diets. 2. Effects on Total and Soluble Phosphorus Excretion Poult. Sci., March 1, 2008; 87(3): 459 - 467. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. Ajiboye, O. O. Akinremi, Y. Hu, and D. N. Flaten Phosphorus Speciation of Sequential Extracts of Organic Amendments Using Nuclear Magnetic Resonance and X-ray Absorption Near-Edge Structure Spectroscopies J. Environ. Qual., October 16, 2007; 36(6): 1563 - 1576. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. O. Maguire, D. A. Crouse, and S. C. Hodges Diet Modification to Reduce Phosphorus Surpluses: A Mass Balance Approach J. Environ. Qual., July 17, 2007; 36(5): 1235 - 1240. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Kleinman, D. Sullivan, A. Wolf, R. Brandt, Z. Dou, H. Elliott, J. Kovar, A. Leytem, R. Maguire, P. Moore, et al. Selection of a Water-Extractable Phosphorus Test for Manures and Biosolids as an Indicator of Runoff Loss Potential J. Environ. Qual., July 17, 2007; 36(5): 1357 - 1367. [Abstract] [Full Text] [PDF]
|
|
