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SHORT COMMUNICATIONS

Alum Treatment of Poultry Litter

Decomposition and Nitrogen Dynamics

^a HazMert, Inc., 2633 Laural Circle, Rogers, AR 72756
^b Department of Crop and Soil Science, University of Georgia, Athens, GA
^c Jr., USDA-ARS, Poultry Production and Product Safety Laboratory, University of Arkansas, Fayetteville, AR 72701

^* Corresponding author (gilmour{at}uark.edu).

Received for publication March 5, 2003.

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Conclusions REFERENCES

 
While the poultry industry is a major economic benefit to several areas in the USA, land application of poultry litter to recycle nutrients can lead to impaired surface and ground water quality. Amending poultry litter with alum [Al₃(SO₄)₂·14H₂O] has received considerable attention as a method of economically reducing ammonia volatilization in the poultry house and soluble phosphorus in runoff waters. The objective of this study was to characterize the effect of alum on broiler litter decomposition and N dynamics under laboratory conditions. Litter that had been amended with alum in the poultry house after each of the first four of five flock cycles (Experiment I) and litter that had been amended with alum after removal from a poultry house after the third flock cycle (Experiment II) were compared with unamended litter in separate studies. The litters in Experiment I were surface-applied to simulate application to grasslands, while the litters in Experiment II were incorporated to simulate application to conventionally tilled crops. The only statistically significant differences in decomposition due to alum occurred early in Experiment II and the differences were small. The only statistically significant differences in net N mineralization, soil inorganic N, and soil NH⁺₄–N in either experiment was found in Experiment I after 70 d of incubation where soil inorganic N was significantly greater for the alum treatment. Thus, alum had little effect on decomposition or N dynamics. Results of many of the studies on litter not amended with alum should be applicable to litters amended with alum to reduce P availability.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Conclusions REFERENCES

 
POULTRY LITTER refers to a mixture of bedding and poultry manure, a by-product of poultry production. Bedding materials such as wood shavings, rice hulls, or sawdust are added to the floors of poultry houses and several flocks of birds are grown on it for up to one year. At the end of this time, the litter is removed and land-applied (Moore et al., 1995).

Potential health and environmental effects associated with land application of litter have received increasing attention since the early 1990s (Sharpley et al., 1994). Nitrogen in litter applied to pastures may be nitrified, potentially entering ground and surface waters as NO^–₃–N. Furthermore, land-applied litter can increase soluble reactive and particulate phosphorus concentrations in surface waters through runoff and erosion. Phosphorus contamination does not pose a direct health hazard, but instead degrades water quality by contributing inorganic P to surface water leading to eutrophication. Phosphorus is generally seen as the limiting nutrient in this process, and litter often contains greater than 2000 mg kg^–1 water-soluble P (Moore and Miller, 1994).

Because soluble P in litter poses a significant threat to water quality in areas with intensive poultry production, the conversion of this P to less soluble forms has received increasing attention. One method that has come to the forefront is the addition of alum to bedding material or litter before birds are grown on the litter. Alum not only lowers levels of available P by precipitation with aluminum, but reduces NH₃ volatilization in poultry houses and runoff losses of soluble organic C as well (Moore and Miller, 1994). The reduction in NH₃ levels has the twofold effect of improving bird health and raising the fertilizer value of the litter (Moore and Miller, 1994; Sims and Luka-McCafferty, 2002). With these benefits to growers and water quality, alum use represents an environmentally and economically attractive method for controlling nutrient losses from land-applied poultry litter.

The objective of this study was to characterize the effect of alum on broiler litter decomposition and N dynamics under laboratory conditions. Litter that had been amended with alum in the poultry house after each of the first four of five flock cycles (Experiment I) and litter that had been amended with alum after removal from a poultry house after the third flock cycle (Experiment II) were compared with unamended litter in separate studies. The litters in Experiment I were surface-applied to simulate application to grasslands, while the litters in Experiment II were incorporated to simulate application to conventionally tilled crops.

	Materials and Methods

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Conclusions REFERENCES

 
Experiment I
Captina silt loam soil (fine-silty, siliceous, mesic Typic Fragiudult) at the University of Arkansas Main Station Farm was collected from the Ap (0–10 cm) horizon. Soil was sieved through a 4-mm mesh screen to remove foreign materials such rocks and roots, and refrigerated at 4°C before use.

Broiler litter with a bedding of wood shavings was obtained from six separate poultry houses. The poultry houses were located on the same farm using the same production practices. Litter in three of the houses had been treated with alum, while litter in the remaining three houses was untreated. Thus, there were three replicates of the two treatments: litter alone and litter plus alum. For the three alum-treated houses, the litter was decaked after each batch of birds and alum was applied at a rate of 1360 kg per house following the first batch and 1820 kg per house for the remaining batches. Each house contained approximately 18 Mg of litter after each flock. After the fifth flock and before clean out, alum was not applied. Several samples of litter were collected from each house and frozen. These samples were thawed, foreign materials such as pebbles and feathers removed, and then mixed to produce one composite sample for each of the six houses. The composite sample was frozen.

Total nitrogen content for the dry soil and litters was determined with a LECO (St. Joseph, MI) CNS 2000 Elemental Analyzer. Carbon content of the soil and poultry litter was determined using a carbon train furnace at 900°C (Nelson and Sommers, 1996). Gravimetric water content for the soil was determined by placing 10 g of moist soil in a weighed porcelain crucible and drying in a microwave oven until a constant weight was reached. Water-holding capacity (WHC) of the soil was determined by saturating the soil in a weighed Gooch crucible from below and measuring gravimetric water content after initial, rapid drainage had ceased. Water content of the litters was determined in a drying oven at 46°C until a constant weight was reached.

Mason jars (710 mL) were used as incubation vessels. One hundred grams (dry equivalent) of soil were placed in each jar. The soil was then brought to 40% WHC with deionized water and mixed thoroughly for uniform soil moisture. Two grams of frozen litter were evenly spread on the soil surface and slightly wetted with deionized water. Base traps containing 20 mL 1 M NaOH were placed in each jar and the jars were sealed tightly and placed in an incubator at 25°C. Every 3 d, the incubation vessels were opened and aerated. The CO₂–C evolved was determined periodically by titration of the base traps with 1.0 M HCl after the addition of 1.5 M BaCl₂ (Zibilske, 1994). New base traps were placed in the incubation vessels each time CO₂–C was determined. The experiment was split into two parts due to space limitations in the incubator. Litters from Houses 2, 4, and 6 and a control (soil alone) were randomly chosen to be run first. Litters from Houses 1, 3, and 5 were run second including a second control.

Additional samples were set up for each run for inorganic N analysis. On Days 0, 42, and 70, a duplicate set was extracted with 1 M KCl using a 1:2 soil to water (w/v) extract. Jars were shaken every 15 min for 2 h. The jar contents were then vacuum-filtered using a disposable Nalgene (Rochester, NY) filter (0.45-µm) unit until 40 mL of filtrate was collected. Filtrates were refrigerated at 4°C before analysis. Ten-milliliter aliquots were analyzed for NH₄–N and NO₃–N using steam distillation (Mulvaney, 1996)

Experiment II
The soil was collected from the upper 15 cm of an area mapped as Cecil sandy loam (clayey, kaolinitic, thermic, Typic Kanhapludult) in the Georgia Piedmont. The sample was passed through a 2-mm sieve and wetted to 0.198 g water g^–1 before use (–0.02 MPa). Poultry litter (wood shavings bedding) was collected from a poultry house that had housed three flocks of birds before cleanout.

Treatments included a soil alone (120 g, dry equivalent), soil mixed with poultry litter (0.5 g fresh litter), and soil mixed with poultry litter amended with aluminum sulfate (0.1 g aluminum sulfate mixed with 0.5 g fresh litter). The soil or soil–litter mixture was packed into acrylic cylinders (4.45-cm i.d., 10-cm length) to a bulk density of 1.29 g cm^–3, and each cylinder was placed inside a 0.95-L glass jar. There were seven sets of experimental units, each set containing two replicates of the control treatment and three replicates of the litter treatments. The jars were placed inside an incubator at 25°C for 30 d. A 3-mL headspace sample was taken from one set of experimental units at various times during the experiment. The concentration of CO₂ in these air samples were determined with a Varian (Palo Alto, CA) Star 3600 CX gas chromatograph equipped with a thermal conductivity detector and a ⁶³Ni electron capture detector. At 0, 1, 3, 7, 17, 23, and 30 d, each experimental unit in one set was extracted with 1200 mL 1 M KCl for 30 min. The concentration of (NO^–₂–N + NO^–₃–N) in the extracts was determined by the Griess–Ilosvay technique after reduction of NO^–₃ to NO^–₂ with a Cd column (Keeney and Nelson, 1982). The concentration of NH⁺₄–N was determined by the salicylate–hypochlorite method (Crooke and Simpson, 1971).

Initial inorganic N in field-moist soil was determined by extracting 5 g soil with 40 mL 1 M KCl for 30 min and measuring NH⁺₄–N and NO^–₂–N plus NO^–₃–N as described above. Initial inorganic N in poultry litter was extracted by shaking 0.2 g litter with 40 mL 1 M KCl for 30 min. Total C and N in soil and total C in poultry litter was measured by dry combustion with a LECO 2000 CNS analyzer. Total N in moist poultry litter was determined with a micro-Kjeldahl method (Baker and Thompson, 1992).

Decomposition
Litter decomposition was defined using Eq. [1]:

[1]

where C_t is the CO₂–C evolved from the litter amended soil at time t, C_c is the CO₂–C evolved from the control soil at time t, and C_total is the total C added to the soil in the litter, all in units of mg C kg^–1 soil.

Nitrogen Dynamics
Net N mineralization was determined using Eq. [2]:

[2]

where % N_min is percent net N mineralization, N_t is inorganic N in the litter amended soil at time t, N_c is the inorganic N in the control soil at time t, N₀ is the inorganic N in the litter at time zero, and N_org is the initial organic N in the litter, all in units of mg N kg^–1 soil.

The extent of nitrification was determined using Eq. [3]:

[3]

where % NH⁺₄–N is the percentage of total soil inorganic N in the ammonium form, NH⁺₄–N is soil ammonium N, and NO^–₃–N is soil nitrate N, all in units of mg N kg^–1 soil.

Statistics
The compare each pair feature of the fit Y by X platform (SAS Institute, 1996) was used to determine least significant differences.

	Results and Discussion

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Conclusions REFERENCES

 
Litter and Soil Characteristics
Analytical data for soils and litters are presented in Table 1. The Captina silt loam had a total carbon content of 7.1 g kg^–1. This soil has a C to N ratio of about 10 (Gale and Gilmour, 1986). Initial ammonium and nitrate N concentrations were 9 and 4 mg kg^–1, respectively. The Cecil sandy loam total C and N contents were 5.2 and 0.38 g kg^–1, respectively, to give a C to N ratio of 13.7. Initial ammonium and nitrate concentrations were 1.1 and 1.6 mg kg^–1, respectively.

Decomposition
Percent decomposition versus time is shown in Fig. 1 . Percent decomposition for litter amended with alum and unamended litter was not significantly different at any time for Experiment I. In Experiment II, small but statistically significant differences were noted early during the decomposition process (0–9.1 d). After that time, no significant differences in decomposition were found. At 30 d, 34% of the litter total C had been converted to CO₂–C in Experiment I, while 50% of the litter total C had been converted to CO₂–C in Experiment II. The two studies used different soil (Captina versus Cecil) and application method (surface versus incorporated) as well as litters from different flock cycles (five versus three), which had different C to N ratios. In addition, the number of alum applications varied. Any or all of these factors could have contributed to the differences in decomposition rate between the two studies.

View larger version (23K): [in this window] [in a new window]   Fig. 1. Percent decomposition versus time.

Net Nitrogen Mineralization, Soil Inorganic Nitrogen, and Ammonium Nitrogen
No effect of alum on net N mineralization in Experiment I was found (Table 2). At 42 d, the values ranged from 22 to 26%, while at 70 d the values ranged from 22 to 33%. Net N mineralization for Experiment II was from 15 to 17% at 17 d and from 12 to 15% at 30 d, again with no statistical differences due to alum addition. Thus, alum does not appear to affect net N mineralization of organic N in poultry litter in any consistent way.

In Experiment I, at 42 d there were no consistent differences in soil inorganic N due to alum application, which contrasts with Moore et al. (1995), who reported that after 42 d, alum litter produced significantly higher levels of inorganic N compared with litter alone. At 70 d, there was a statistically significant increase in inorganic N due to alum treatment in agreement with the Moore et al. (1995) study. In Experiment II, alum did not lead to increases in soil inorganic N.

At 42 d, NH⁺₄–N was from 89 to 92% of the inorganic N (NH⁺₄–N plus NO^–₃–N) in Experiment I. At 70 d, the NH⁺₄–N ranged from 61 to 81% of the inorganic N. Alum did not significantly affect NH⁺₄–N percentage in Experiment I. In Experiment II, alum also did not significantly affect NH⁺₄–N percentage, although values were much lower than in Experiment I. These results suggest that other factors such as litter placement, litter type, litter treatment, or soil and not alum addition are important in nitrification of N mineralized from poultry litter during decomposition.

	Conclusions

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Conclusions REFERENCES

 
Decomposition and N dynamics for alum-amended litter differed little. Overall, results of many of the studies on litter not amended with alum should be applicable to alum litters.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Conclusions REFERENCES

 

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