©2009 Poultry Science Association, Inc.
Efficacy of urease inhibitor to reduce ammonia emission from poultry houses1 A. Singh,* K. D. Casey,*2 W. D. King,† A. J. Pescatore,†3 R. S. Gates,*4 and M. J. Ford† *Department of Biosystems and Agricultural Engineering, University of Kentucky 128 CE Barnhart Building, Lexington 40546; and †Department of Animal and Food Sciences, University of Kentucky, 604 WP Garrigus Bldg., Lexington 40546 Primary Audience: Farm Managers, Environmental Managers, Researchers, Nutrient Management Planners SUMMARY
As the poultry industry has grown, so have concerns about the environmental management aspects of these industries, including air and water quality. Poultry operations continue to expand and are large contributors to farm income. There is increased concern related to ammonia emission from poultry operations. Various abatement methods, including dietary manipulation, chemical amendment of litter, and improvement in ventilation system management have been used to control ammonia concentrations from livestock facilities, but these methods are perceived to be too expensive, to impair bird growth, or to add to pollution in some other form. Alternative strategies include reduction of ammonia emissions by arresting N in the litter. An alternative approach to decrease ammonia emissions in poultry facilities is to block the enzyme activity in the litter because ammonia is the by-product of a 5-step enzymatic degradation of uric acid. Our preliminary study with layer feces, which were allowed to accumulate on a layer of broiler litter, indicated that a commercially available urease inhibitor resulted in a significant reduction in equilibrium ammonia concentration over time. Based on the results of the preliminary experiment, further studies were conducted to study the effect of the urease inhibitor on broiler litter and layer feces directly. The results showed that the urease inhibitor did not have any effect on equilibrium ammonia concentration when applied to drier broiler litter. The reduced moisture content in the broiler litter may have inhibited urease inhibitor activity. With layer feces, urease inhibitor reduced equilibrium ammonia concentration. The effect of the first application lasted for 1 wk, after which the equilibrium ammonia concentration in the treated trays rebounded to exceed that of the control trays. Upon a second application of urease inhibitor, the effect lasted for 14 d. The difference in the effect of the urease inhibitor on equilibrium ammonia concentration upon first and second application could have been influenced by a change in manure characteristics over time. Layer manure is a dynamic environment with continued change; therefore, more research is warranted in the area of stored layer manure. Key words: ammonia, air quality, urease inhibitor, broiler litter, layer manure 2009 J. Appl. Poult. Res. 18:34–42 doi:10.3382/japr.2008-00046 1
The information reported in this paper (no. 08-05-057) is part of a project of the Kentucky Agricultural Experiment Station and is published with the approval of the director. 2 Present address: Texas Agrilife Research Experiment Station, Texas A&M System, Amarillo, TX. 3 Corresponding author:
[email protected] 4 Present address: Agricultural and Biological Engineering, University of Illinois, Urbana, IL.
Singh et al.: Efficacy of urease inhibitor DESCRIPTION OF PROBLEM Air quality and potential gaseous emissions from livestock facilities are a concern. According to the United States Environmental Protection Agency, about 86% of the national ammonia emissions are from miscellaneous sources, which include livestock, poultry, and fertilizer [1]. An inventory of aerial pollutant emissions emanating from US poultry buildings estimated ammonia emissions to be 664 kt/yr (731,927 US tons/yr) in 2002 and will rise to 720 kt/yr (793,656 US tons/yr) in 2015 [1]. Broiler litter is used repeatedly through several flocks in the United States and is replaced approximately once a year. Layer feces is allowed to accumulate for weeks or months before it is removed from high rise layer houses, but is removed periodically from layer houses equipped with manure belts. Accumulation of this built-up litter and layer feces results in aerobic and anaerobic activity. Subsequently nitrification and denitrification processes can contribute greatly to ammonia volatilization. Various abatement methods, including dietary manipulation, chemical amendment of litter, and improvement in ventilation rates have been used to control ammonia concentrations from livestock and poultry facilities. Studies have shown dietary manipulation to be a useful tool to reduce air contaminants, especially ammonia emissions from livestock facilities [2–8]. Other dietary studies have shown no effect on ammonia emissions [9] or an increase in ammonia emissions [10]. Various chemicals amendments, including zeolites [9], superphosphate [7], phosphoric acid [11], ferrous sulfate [11], alum [11], and acetic acid and propionic acid [12], have reduced ammonia emissions from animal manures. Although these chemical amendments seem to reduce ammonia emissions, they may add to pollution in some other form. As an example, the addition of phosphoric acid may increase the phosphorus content of the litter. Blocking the enzyme activity (urease) in the litter or feces is an alternative method to decrease ammonia formation [13–15]. Ammonia is the by-product of a 5-step enzymatic degradation of uric acid. Urease inhibitors have been used as a soil additive to control urease activity when
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urea-based fertilizers are applied [16]. These inhibitors act by inhibiting the urease enzyme that converts urea to ammonia, thus decreasing the loss of N as ammonia. Among the known urease inhibitors, the most commonly used are phosphorodiamides and phosphorotriamides. N-(n-Butyl)thiophosphorictriamide (NBPT) is one of a class of phosphorotriamide inhibitors. According to Manunza et al. [17] the NBPT molecule acts as a strong urease inhibitor due to its ability to hook the active site in 3 points: the 2 Ni atoms and 1 O atom. The O atom and 1 amide group of the NBPT molecule form a bridge between the 2 Ni atoms. It is the stability of these bonds that prevents the conversion of uric acid to ammonia. More recent research on urease inhibitor has been focused on its ability to reduce ammonia emissions and conserve N in cattle feedlots [14, 15, 18]. Laboratory studies by Varel [13] showed that urease inhibitor (phosphorodiamidate), when applied on a weekly basis, prevented up to 70 and 92% of the urea from being hydrolyzed after 28 d. Both NBPT and cyclohexyphosphoric triamide successfully reduced ammonia emissions from cattle feedlot pens [14]. A study by Parker et al. [15] showed that 1 and 2 kg of NBPT/ha of beef feedlot every 8 d resulted in 49 and 69% reduction in ammonia emission rates, respectively. There are limited studies on the effect of urease inhibitor on ammonia emissions in broiler litter and layer feces [19]. The objective of this research was to investigate the effectiveness of urease inhibitor (NBPT) in reducing ammonia emissions from layer feces and broiler litter. A preliminary experiment was conducted to determine if the recommended dosage of urease inhibitor was appropriate for use in poultry systems. Based on the results of the preliminary study, 2 experiments were designed to evaluate urease inhibitor effectiveness.
MATERIALS AND METHODS Preliminary Experiment Layer Facility. The experiment was conducted over a 21-d period at the University of Kentucky Poultry Research Facility. The experiment was performed in a caged layer room using 12
JAPR: Research Report
36 groups of 6 birds (Hy-Line W-36, 61 wk of age) housed in pairs in 36 cages (80 in.2/bird). Each group of 6 cages housed 12 birds, allowing 80 in.2/bird of floor space. A 16% CP layer diet and water were provided ad libitum. A photoperiod of 16L:8D was provided by incandescent lights. Fresh air was ducted to each of the individual cages. Fecal collection was accomplished by placing 12 containers measuring 46 × 66 × 66 cm below each of 12 groups of 6 hens such that the manure from the birds dropped in the respective containers. Urease Inhibitor Treatment. At the start of the experiment, a base of broiler litter (5 kg) was placed in each of the 12 containers to provide an absorbent surface for the urease inhibitor. The broiler litter used as the base in the containers was built-up litter (wood shavings) from 2 consecutive flocks. Urease inhibitor was applied on d 0 and reapplied at d 7. Six of the containers were treated with urease inhibitor, NBPT, at the rate of 0.08 mL/kg of litter. The 6 control containers were sprayed with deionized water at the same volume as the urease inhibitor. Freshly voided feces accumulated in the containers through a 21-d duration. Gas Sampling. Gas sampling was done using an equilibrium chamber technique in which a tight container is placed over the emitting surface and continuous concentration readings are recorded using a photo-acoustic infrared gas analyzer, until quasi steady-state conditions are achieved. It does not directly measure emission; rather, the headspace concentration is measured. This technique has been used by Gates et al. [20], Ferguson et al. [8, 21], Parker et al. [15], and Miles et al. [22] to study the effect of dietary manipulation on ammonia volatilization. Ammonia concentrations were measured on d 0, 2, 4, 7, 9, 11, 14, 16, and 21. Feces Sampling and Chemical Analysis. Fecal samples were collected from each container at the start of the experiment before urease inhibitor application and at the end of the experiment. The samples were stored on ice until they were transported for analysis. A portion of the sample was acidified for total ammoniacal N (TAN) estimation. The remaining portion was analyzed for moisture content, pH, total Kjeldahl N (TKN), and total N following standard methods [23]. For moisture content, the lit-
ter samples were dried in a convection oven at 100°C for 24 h. The pH was measured using a pH probe (Orion Ross Sure-Flow model 8765). Approximately 6 g of wet litter was mixed with 50 mL of distilled, deionized water and stirred for at least 10 min before measuring [23]. The TAN was measured using an ammonia probe (Orion model 95–12) according to the procedure outlined in Singh et al. [19]. Main Experiments Broiler Facility. Twenty-four broiler chicks (Cobb males) were housed in each of 24 floor pens (122 × 183 cm; 4 × 6 ft; 0.093 m2/bird or 1 ft2/bird). Each pen was equipped with a tube feeder and nipple drinker (3 nipples/pen). All birds had ad libitum access to feed and water. Minimum ventilation was provided at the rate of 0.75 to 1 ft3/min per bird. Broiler Experiment. The experiment was carried out over 2 flocks; flock 1 commenced in February on built-up litter from 4 flocks, and flock 2 in April on built-up litter from 5 flocks. The original bedding material was 4 in. of wood shavings, with caked litter removed between flocks and the litter stirred. Birds were removed on d 42 for each flock. Three treatments and a control were utilized during each flock as follows: T1: inhibitor applied on d 1; T2: inhibitor applied on d 21; T3: inhibitor applied on d 1 and 21; and control: only deionized water applied on d 1 and 21. Each treatment was applied to 6 replicate pens. Urease inhibitor was applied at the rate of 0.08 mL/kg of litter, and the control was sprayed with deionized water at the same rate. Gas analysis and litter samples were collected on d 0, 21, and 42 during flock 1. During flock 2, gas analysis and litter samples were collected on a weekly basis. During flock 2, after the second application of urease inhibitor (d 21), equilibrium ammonia concentrations in the pens were measured every alternate day for 1 wk. Layer Experiment. The layer experiment was conducted over a 48-d period, and the experimental design and equipment were similar to those described in the preliminary experiment. However, instead of using used broiler litter as the base material, each container was placed below a group of 3 cages with 6 hens (Hy-Line
Singh et al.: Efficacy of urease inhibitor
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Table 1. The effect of treatment, day, and their interaction on ammonia concentration during the preliminary experiment Effect Treatment Day Day × treatment
Numerator df
Denominator df
F-value
P>F
1 8 8
10.3 74.8 74.8
18.22 28.48 5.91
0.0015
