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TECHNICAL REPORT

Waste Management

Effect of Chemical and Microbial Amendments on Ammonia Volatilization from Composting Poultry Litter

^a Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701
^b USDA-ARS, Fayetteville, AR 72701
^c USDA-NRCS, Fort Worth, TX 76115

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

Received for publication March 5, 2003.

	ABSTRACT

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

 
Research has shown that aluminum sulfate (alum) and phosphoric acid greatly reduce ammonia (NH₃) volatilization from poultry litter; however, no studies have yet reported the effects of these amendments on field-scale composting of poultry litter. The objectives of this study were to (i) evaluate NH₃ volatilization from composting litter by measuring both NH₃ volatilization and changes in total nitrogen (N) in the litter and (ii) evaluate potential methods of reducing NH₃ losses from composting poultry litter. Poultry litter was composted for 68 d the first year and 92 d the second year. Eleven treatments were screened in Year 1, which included an unamended control, a microbial mixture, a microbial mixture with 5% alum incorporated into the litter, 5 and 10% alum rates either surface-applied or incorporated, and 1 and 2% phosphoric acid rates either surface-applied or incorporated. Treatments in Year 2 included an unamended control, a microbial mixture, alum (7% by fresh wt.), and phosphoric acid (1.5% by fresh wt.). Alum and phosphoric acid reduced NH₃ volatilization from composting poultry litter by as much as 76 and 54%, respectively. The highest NH₃ emission rates were from microbial treatments each year. Compost treated with chemical amendments retained more initial N than all other treatments. Due to the cost and N loss associated with composting poultry litter, composting is not economical from an agronomic perspective compared with the use of fresh poultry litter.

	INTRODUCTION

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

 
LARGE CONCENTRATED VOLUMES of manure produced and applied to nearby relatively small land areas has led to environmental concerns. As a result of increasing environmental awareness, best management practices have been implemented to ease this imbalance. Composting has received increasing interest as a method for handling various types of animal manures. Composting manure results in 30 to 50% reductions in mass and a material more uniform in nutrient composition (Dao, 1999). Composting results in pathogen kill and produces a stabilized product that can be stored or spread with little odor or fly breeding potential (Sweeten, 1988). The biodegradation that occurs during composting makes the material more desirable by improving physical and biological conditions, including improved aeration, greater ease of seedbed preparation, improved water holding capacity, and stimulation of soil microorganism activity (Henry and White, 1993). One of the most negative effects of composting animal manures is the loss of N via NH₃ volatilization.

Ammonia volatilization increases with an increase of pH, moisture content, wind speed, NH₃ concentration, or temperature (Reddy et al., 1979). High moisture contents (up to 60%), high pH, and elevated temperatures are characteristic of composting. As pH increases, the NH₃ to NH₄ ratio increases, resulting in increased volatilization rates. Both Reece et al. (1979) and Moore et al. (1997) found that NH₃ volatilization from poultry litter dramatically increases once the pH rises above 7.0.

Furthermore, poultry litter composting has a high potential for NH₃ volatilization because of the high N concentrations in poultry litter and low C to N ratios. Ammonia volatilization during manure transport and storage reduces the agronomic value of the end product, and contributes significantly to environmental pollution (Witter and Kirchmann, 1989). Henry and White (1993) found that N concentrations in broiler litter decreased significantly due to composting. Eghball et al. (1997) reported that as much as 40% of total manure N can be lost during feedlot manure composting, while Kirchmann and Witter (1989) reported that 44% of the initial N present in a poultry manure–straw mix was lost via NH₃ volatilization. Hansen et al. (1989) reported losses up to 33% of the initial total N during composting of poultry manure. Kithome et al. (1999) reported that NH₃ loss was 47 to 62% of the initial total N after 25 d of composting poultry layer manure. Kithome et al. (1999) questioned the economical feasibility of composting low-C-to-N-ratio manures such as poultry manure, as did Eghball et al. (1997), who stated that beef feedlot manure should be land-applied without composting unless weed seeds, better manure handling, odor, or other factors are of concern.

Atmospheric NH₃ plays an important role in producing acid rain (ApSimon et al., 1987). Ammonia raises the pH of rainwater (Pearson and Stewart, 1993) which allows more SO₂ to dissolve. This leads to the formation of ammonium sulfate, which can oxidize in the soil and release nitric and sulfuric acid (van Breemen et al., 1982; Behra et al., 1989). ApSimon et al. (1987) indicated that livestock waste was the dominant source of NH₃ in Europe, with long-term trends showing a 50% increase in NH₃ volatilization from 1950 to 1980. Ammonia volatilization can also contribute to eutrophication (Schuurkes, 1986). Nitrogen deposited via wet fallout has been shown to triple over a 25-yr period and correlate to increasing N losses from agriculture, as well as increased nitrate concentrations in streams (Schroder, 1985).

Alum and phosphoric acid (H₃PO₄) have both been shown to greatly reduce NH₃ volatilization from animal manures (Moore et al., 1995, 1996; Al-Kanani et al., 1992). Alum produces H⁺ when it dissolves, which reacts with NH₃ to form ammonium. Ammonium can then react with the sulfate to form ammonium sulfate. Phosphoric acid can react directly with NH₃ and form ammonium phosphates. Moore et al. (1995) found that the addition of alum reduced NH₃ volatilization and resulted in the doubling of N concentrations in the litter, which would greatly increase the value of poultry litter as a fertilizer source. Kithome et al. (1999) found that alum additions to simulated composting poultry manure resulted in higher total N concentrations than unamended controls.

Alum and phosphoric acid have been shown to reduce NH₃ volatilization as well as affect P availability; however, no studies have shown the effect of these amendments on composting poultry litter in a large-scale composting process. The objectives of this study were to (i) evaluate NH₃ volatilization from composting litter by measuring both NH₃ volatilization and changes in total nitrogen (N) in the litter and (ii) evaluate potential methods of reducing NH₃ losses from composting poultry litter.

	MATERIALS AND METHODS

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

 
Composting Procedure
Composting studies were conducted in 1997 and 1998 at EarthCare Technologies, a commercial composting facility in Lincoln, AR. Due to permit restrictions regarding the amount of waste permitted on site, an observational (screening) study was conducted the first year to determine the most effective application methods and application rates. Chemical amendments used in the study included alum [Al₂(SO₄)₃·14H₂O] and 75% technical-grade phosphoric acid (H₃PO₄), which were applied at equivalent cost (i.e., the low H₃PO₄ rate costs the same as the low alum rate). Turkey litter was obtained by EarthCare and windrowed into 12 rows the first year, with each windrow weighing approximately 3628 kg. An empty truck was weighed using truck scales, then litter was added using a front-end loader until the appropriate weight was obtained. In Year 1, the weight of the first four windrows were recorded to determine the number of front-end loader buckets needed for the appropriate weight, and the remaining windrows were not weighed out. The 11 treatments were normal composted litter (no amendment) and litter composted with 1% H₃PO₄ (surface-applied), 2% H₃PO₄ (surface-applied), 1% H₃PO₄ (incorporated), 2% H₃PO₄ (incorporated), 5% alum (surface-applied), 10% alum (surface-applied), 5% alum (incorporated), 10% alum (incorporated), 5% alum (surface-applied) plus a microbial mixture, and microbial mixture (as directed by EarthCare). The control treatment was duplicated. The microbial mixture was property of EarthCare and details of the various types of organisms were not disclosed. The microbial mixture was advertised to potentially reduce ammonia volatilization and odor and enhance the composting process. The microbial mixture was applied in both a liquid and dry form. The composting litter was monitored daily for temperature and ammonia volatilization. Each individual row was turned when a 1.11°C drop in the temperature was noted and/or the moisture content dropped below 30%. A soil probe (2.5 x 25 cm) was used to take eight cores from each windrow, which were then composited. Litter samples were taken from each windrow at Day 0, 1, 2, 4, 8, 16, 22, 28, 35, 42, 49, 56, 63, and 68 for determination of pH and moisture content.

Broiler litter was obtained by EarthCare and windrowed into twelve rows the second year, with each windrow weighing approximately 3628 kg. Broiler litter was collected from a house that had six flocks grown on it. Exact windrow weights were determined using portable truck scales. There were four treatments replicated three times in a randomized complete block design. The treatments included normal composted litter (no amendment), litter composted with 1.5% H₃PO₄ (incorporated), litter composted with 7% alum (incorporated), and litter composted with a microbial mixture (as directed by EarthCare). The composting litter was monitored daily and each individual row was turned in the same day once a week throughout the composting process to ensure each windrow was managed the same. Litter samples were taken immediately after each turning. Samples were analyzed for pH and moisture content after each turning on Days 0, 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, and 92.

All chemical amendments were applied on a fresh-weight basis. At the beginning of the composting process, water was added to each windrow to increase the moisture content to approximately 60% while mixing the windrow. Incorporated amendments were added with the addition of water. Amendments that were surface-applied were applied over the top of the windrow after the addition of water.

Ammonia volatilization was measured on a daily basis using Sensidyne (Clearwater, FL) NH₃ detector tubes and flux chambers as described by Moore et al. (1997). Ammonia flux calculations were based on the difference in NH₃ concentrations in the chamber at time zero and at 5 min using the ideal gas law and the dimensions of the chamber (radius = 13.34 cm, height = 31.15 cm). With a known volume of the chamber and area of measurement, the NH₃ flux can be calculated using the ideal gas law:

[1]

where P is the pressure (assumed to be 1 atm), V is the volume of gas, n is the number of moles of gas, R is the gas constant (0.08206 L·atm/mol·degree), and T is the temperature in kelvin (273.15 + °C). The volume V of gas (NH₃) was calculated by multiplying the change in concentration by the volume of the chamber. Once the volume is calculated, the number of moles of NH₃ may be calculated and therefore the mass of NH₃ produced. The calculations were put on a rate basis by dividing the mass by the area of measurement and the time. Ammonia fluxes were also measured immediately before and after turning; the mean of these values was used for the daily loss on days in which the windrows were mixed. Since the area of the windrows constantly changed, the total mass of N lost was not calculated. The ammonia data in this paper are presented as a mass per measured area. This method allows for an adequate relative comparison among treatments.

Litter samples were taken from each treatment at the beginning and ending of each study and analyzed for total N, total C, and pH. At the end of each compost study, each windrow was placed onto a truck and weighed using certified scales to determine ending windrow weights. Upon return to the laboratory, 20 g of litter from each sample was placed in a 250-mL polycarbonate centrifuge tube and extracted with 200 mL of deionized water for 2 h on a mechanical shaker (Self-Davis and Moore, 2000). The sample was then centrifuged at 8000 rpm (10314 x g) for 20 min. Aliquots of the supernatant were taken and pH was measured immediately. Compost samples were also analyzed for total N and total C using a LECO (St. Joseph, MI) CNS-2000 elemental analyzer, and C to N ratios were determined.

Statistical Analysis
Analysis of variance was used to determine significant treatment effects (SAS Institute, 1990). When significance was indicated, means were separated using Fisher's protected least significant difference (LSD, P < 0.05). Linear regression analyses were performed using JMPIN to test if the slope was significantly positive (SAS Institute, 1996).

	RESULTS AND DISCUSSION

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

 
Ammonia Volatilization
Year 1
Regardless of the chemical amendment, when applied at the same rate, the amendments surface-applied resulted in lower ammonia volatilization rates compared with incorporated amendments (i.e., 10% alum surface-applied lower than 10% alum incorporated; 1% H₃PO₄ surface-applied lower than 1% H₃PO₄ incorporated). Chemical amendments surface-applied at the highest rates had the lowest NH₃ volatilization among respective treatments (Fig. 1a and 1b) . The high rate of H₃PO₄ surface-applied lost 190 g NH₃ m^–2, 50% lower than observed from unamended controls (Fig. 1a). The lowest NH₃ volatilization rates among all treatments were from the surface application of alum at the high rate, with a loss of 91.3 g NH₃ m^–2, a 76% reduction over the unamended controls (Fig. 1b). The pH of compost treated with a surface application of H₃PO₄ at the high rate remained below 8 for the first 28 d of the study (data not shown). In contrast, the pH of compost treated with a surface application of the high rate of alum remained below 8 for the first 63 d of the study (data not shown).

View larger version (33K): [in this window] [in a new window]   Fig. 1. Cumulative ammonia loss for the 68-d composting process in Year 1 from (a) phosphoric acid–treated compost and the controls; (b) alum-treated compost and the controls; and (c) controls, microbially treated compost, and microbially treated compost with alum.

Measured NH₃ volatilization was 406 g NH₃ m^–2 from the microbially treated compost, a 6% increase over the controls (Fig. 1c). The addition of alum to microbially treated compost markedly reduced NH₃ emission rates (Fig. 1c). The addition of alum at the 5% rate reduced NH₃ volatilization by 59% compared with compost treated with microbes alone (Fig. 1c).

Results of the Year 1 experiments are summarized in Fig. 2a . An average of 382 g NH₃ m^–2 was lost from the controls (untreated compost) during the 68-d composting process (Fig. 2a). Ammonia volatilization rates were higher from compost treated with microbial amendments than all other treatments (Fig. 2a). The means of all the chemical treatments were grouped together to observe treatment effects. Chemical amendments greatly reduced NH₃ volatilization. Mean cumulative NH₃ volatilization rates were 44% lower from H₃PO₄ treatments and 62% lower from alum treatments compared with the unamended controls (Fig. 2a).

View larger version (27K): [in this window] [in a new window]   Fig. 2. (a) Mean cumulative ammonia loss and (b) mean pH values of composting poultry litter with time in Year 1.

Year 2
An average of 80.0 g NH₃ m^–2 was lost from the controls during the 92-d composting study (Fig. 3a) . Ammonia volatilization rates in Year 2 were much lower than observed in Year 1, which can be explained by the litter pH. The initial pH of the litter used in Year 2 was 8.4 (Table 1). However, the pH decreased below 7 for all treatments after the addition of water. The authors do not have an explanation of why this occurred; nevertheless, the same effect was seen across all treatments. As observed in Year 1, microbial amendments resulted in the highest NH₃ volatilization rates among all treatments (Fig. 3a). Emissions from the microbially treated compost were lower than the control for most of the composting process. However, the pH of microbially treated compost became higher than the pH of the control (Fig. 3b) and subsequently resulted in a higher cumulative NH₃ loss (Fig. 3a). An average of 83.9 g NH₃ m^–2 was lost from microbially treated composts, a 5% increase over the controls. The addition of microbial amendments could have stimulated N mineralization, thereby increasing NH₃ volatilization rates.

View larger version (25K): [in this window] [in a new window]   Fig. 3. (a) Cumulative ammonia loss and (b) pH values of composting poultry litter with time in Year 2.

Alum additions significantly lowered NH₃ volatilization rates compared with the control and microbially treated compost, reducing NH₃ volatilization rates by 45 and 47%, respectively. Ekinci et al. (2000) showed that the addition of alum to broiler litter composted with short paper fiber decreased NH₃ loss, with increasing alum application rates resulting in decreasing NH₃ loss. Kithome et al. (1999) reported a 26% reduction in NH₃ loss from simulated composting of poultry manure with alum additions. The pH of alum-treated compost remained below 8.0 for the entire composting process with pH values of 6.7 at Day 50 (Fig. 3b). Results from Year 2 show that chemical amendments can significantly reduce NH₃ volatilization without the addition of a high C source.

Total Nitrogen and Carbon
Year 1
Initial characteristics of the litter composted are listed in Table 1. Total N concentrations decreased for all treatments during the composting process (Table 2). Chemically amended composts had numerically higher N concentrations than the controls and microbially treated compost. Mean ending total N concentrations were 43.6 g N kg^–1 for alum treatments and 39.7 g N kg^–1 for H₃PO₄ treatments compared with the initial N concentrations of 49.1 g N kg^–1 (Table 2).

View larger version (18K): [in this window] [in a new window]   Fig. 4. Correlation between cumulative ammonia loss and ending total nitrogen concentrations in Year 1.

As in Year 1, no significant differences were found among treatments with regard to C or mass losses (Table 3). Kithome et al. (1999) also showed that alum had no effect on the composting process. This is important since the addition of chemical amendments can significantly reduce NH₃ volatilization without affecting composting.

Fifty-six percent of the initial N was lost from compost treated with the microbial mixture, a 12% increase over the untreated controls (Table 3). Although not significant, total N losses were lower for compost treated with alum and H₃PO₄ (Table 3), due to lower NH₃ volatilization rates.

The initial C to N ratio of the litter composted in Year 2 was 7.76. Composting such low-C-to-N-ratio materials markedly increases the potential for NH₃ loss. Most studies have observed the effect of composting manures with an added C source such as straw or sawdust. Since chemical amendments were used in this study, no C sources were added to simulate on-farm composting. By increasing the C to N ratio, mineralization is slowed and NH₃ volatilization can be decreased. However, significant amounts of the initial N can be lost even when adding substantial amounts of C (Mahimairaja et al., 1994; Kirchmann and Witter, 1989; Hansen et al., 1989).

Adding a C source is another cost that must be accounted for, not only the cost of the material, but also the handling and transport of the material. Brodie et al. (2000) calculated the production cost of a machine windrow operation with the addition of C to be $57 per Mg of compost produced. This cost does not account for the value of N lost during the composting process. Due to the loss of N during composting coupled with the cost, composting poultry litter may not be economical to producers interested solely in yield production.

	CONCLUSIONS

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

 
Alum and H₃PO₄ greatly reduced NH₃ volatilization during composting of poultry litter. Composted poultry litter treated with chemical amendments resulted in higher ending N concentrations and lower mass N loss than untreated controls and compost treated with a microbial mixture. However, even with chemical amendments, as much as 47% of the initial manure N was lost during composting. Although the microbial treatment resulted in higher C losses, N losses were also higher. Furthermore, the chemical amendments did not affect the composting process. Ammonia volatilization could be further reduced with added carbon sources along with chemical amendments. However, this would increase the cost of composting. Although an economic analysis was not performed, it is unlikely that composting poultry litter, even with chemical amendments, is economically feasible from an agronomic perspective since fresh litter has more N. The addition of chemical amendments to composting poultry litter could be beneficial to meet environmental concerns or regulatory measures. Composting poultry litter could potentially increase concentrations of nonvolatile nutrients of environmental concern and subsequently elevate levels on applied land, especially if compost is applied to meet crop N requirements.

	NOTES

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

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

	REFERENCES

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

 

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