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Atmospheric Environment 42 (2008) 3351–3363 Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends $ D.M. Miles a, , D.E. Rowe a , P.R. Owens b a Waste Management and Forage Research Unit, USDA– ARS, MS State, MS, USA b Purdue University, West Lafayette, IN, USA Received 27 September 2006; accepted 29 November 2006 Abstract Understanding how animal activities, management, and barn structure affect litter gases and nutrients is fundamental to developing accurate emission models for meat-bird facilities. This research characterized the temporal and spatial variability of litter ammonia (NH 3 ) and nitrous oxide (N 2 O) flux via a chamber method, as well as determined litter nitrogen (N) compounds by intensive sampling in two commercial broiler houses on aged litter. Thirty-six grid samples were taken during a winter flock in Mississippi on days 2, 22, and 45. On day 45, eight additional samples were taken near the feeders and waterers (F/W). Geostatistical contour plots indicate NH 3 flux on day 2 was elevated in the brood area of house one (H1) where litter and air temperatures were highest; a commercial litter treatment held the NH 3 flux near zero for approximately 45% of the brood area in house two (H2). Day 45 NH 3 fluxes were similar, averaging 694 mg m 2 h 1 in H1 vs. 644 mg m 2 h 1 in H2; both houses exhibited greater NH 3 flux near the cooling pads. Ammonia flux, litter moisture and pH were diminished at the F/W locations. Heavy cake near the exhaust fans provided the lowest recorded litter pH, highest litter moisture and ammonium (NH 4 ) with no NH 3 flux at the flock’s end. Trends in litter condition based on bird activity were evident, but individual differences persisted between the houses. The importance of cake formation over the litter surface and differences based on location, both related to bird activity and house structure, should be considered in NH 3 mitigation strategies. Published by Elsevier Ltd. Keywords: Ammonia; Broiler; Cake; Litter 1. Introduction In US commercial poultry production, meat-type birds or broilers are usually reared on an organic bedding material (i.e. wood shavings, rice hulls). The combination of deposited manure and urine, bedding material, feathers, spilled feed, and water is called ‘‘litter.’’ In high traffic areas, near the feeders and waterers or near the exhaust fans, a compacted layer, usually high in moisture, forms over the litter, ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.atmosenv.2006.11.056 $ Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture. Corresponding author. Tel.: +1 6623207481; fax: +1 6623207544. E-mail address: [email protected] (D.M. Miles).

Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends

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Page 1: Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends

ARTICLE IN PRESS

1352-2310/$ - se

doi:10.1016/j.at

$Mention o

publication is

information and

by the US Dep�Correspond

fax: +1662320

E-mail addr

(D.M. Miles).

Atmospheric Environment 42 (2008) 3351–3363

www.elsevier.com/locate/atmosenv

Winter broiler litter gases and nitrogen compounds:Temporal and spatial trends$

D.M. Milesa,�, D.E. Rowea, P.R. Owensb

aWaste Management and Forage Research Unit, USDA– ARS, MS State, MS, USAbPurdue University, West Lafayette, IN, USA

Received 27 September 2006; accepted 29 November 2006

Abstract

Understanding how animal activities, management, and barn structure affect litter gases and nutrients is fundamental to

developing accurate emission models for meat-bird facilities. This research characterized the temporal and spatial

variability of litter ammonia (NH3) and nitrous oxide (N2O) flux via a chamber method, as well as determined litter

nitrogen (N) compounds by intensive sampling in two commercial broiler houses on aged litter. Thirty-six grid samples

were taken during a winter flock in Mississippi on days 2, 22, and 45. On day 45, eight additional samples were taken near

the feeders and waterers (F/W). Geostatistical contour plots indicate NH3 flux on day 2 was elevated in the brood area of

house one (H1) where litter and air temperatures were highest; a commercial litter treatment held the NH3 flux near zero

for approximately 45% of the brood area in house two (H2). Day 45 NH3 fluxes were similar, averaging 694mgm�2 h�1 in

H1 vs. 644mgm�2 h�1 in H2; both houses exhibited greater NH3 flux near the cooling pads. Ammonia flux, litter moisture

and pH were diminished at the F/W locations. Heavy cake near the exhaust fans provided the lowest recorded litter pH,

highest litter moisture and ammonium (NH4) with no NH3 flux at the flock’s end. Trends in litter condition based on bird

activity were evident, but individual differences persisted between the houses. The importance of cake formation over the

litter surface and differences based on location, both related to bird activity and house structure, should be considered in

NH3 mitigation strategies.

Published by Elsevier Ltd.

Keywords: Ammonia; Broiler; Cake; Litter

e front matter Published by Elsevier Ltd.

mosenv.2006.11.056

f trade names or commercial products in this

solely for the purpose of providing specific

does not imply recommendation or endorsement

artment of Agriculture.

ing author. Tel.: +16623207481;

7544.

ess: [email protected]

1. Introduction

In US commercial poultry production, meat-typebirds or broilers are usually reared on an organicbedding material (i.e. wood shavings, rice hulls).The combination of deposited manure and urine,bedding material, feathers, spilled feed, and water iscalled ‘‘litter.’’ In high traffic areas, near the feedersand waterers or near the exhaust fans, a compactedlayer, usually high in moisture, forms over the litter,

Page 2: Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends

ARTICLE IN PRESSD.M. Miles et al. / Atmospheric Environment 42 (2008) 3351–33633352

which is known as ‘‘cake.’’ Litter and cake removedfrom broiler houses are potential fertilizer sourcesfor crops, but the conversion of N compounds inmanure to NH3 is a source of environmentalconcern. In response to this, the US EnvironmentalProtection Agency (EPA) announced the AnimalFeeding Operation Air Quality Compliance Agree-ment on January 21, 2005. Monitoring the projectmay begin early in 2007 to ensure compliance withapplicable regulations and to evaluate animalfeeding emissions.

Although the fundamental relationships amonglitter pH, moisture, and uric acid N are known(Gates et al., 1997), the lack of homogeneity of thelitter creates difficulty in accurately estimating NH3

volatilization from the litter surface. Nitrogen lossmechanisms in animal manure systems requireadditional characterization to be fully understood.Groot Koerkamp and Elzing (1996) maintain theneed for understanding the influential parametersand reactions in litter degradation that lead to NH3

volatilization.Potential damaging effects of atmospheric NH3

include eutrophication of waterways, increased soilacidity, and aerosol formation (EPA, 2004b;Mukhtar et al., 2003; Roadman et al., 2003).Elwinger and Svensson (1996) reported that animalmanures can release 40% of the total N as NH3.Sources of aerial NH3 include industry, transporta-tion, fertilizers, soils, humans, pets, wild animals,animal production, forest fires/slash burning, andwaste disposal and recycling processes (Anderson etal., 2003). Although projections differ, animalproduction appears to be a significant source. TheNational Research Council (NRC, 2003) reportslivestock’s contribution to aerial NH3 as 50–70% inthe US. Similar approximations for farm animals inEurope include 85% in The Netherlands (GrootKoerkamp et al., 1998) and 93% in Denmark (Rom,1993). Of the total NH3 emissions, the Danishreport attributed animal housing to 35%, wastestorage to 20%, and land spreading to 40% (Rom,1993). Nicholson et al. (2004) arrived at similardivisions for bird housing, litter/cake storage, andland application in a broiler study with NH3 lossesat 28%, 15%, and 57%, respectively. Recentforecasts for poultry (turkeys and chickens) emis-sions in the US anticipated generating 664,238 tonsof NH3 in 2002 of which 31% evolved from housing(EPA, 2004a).

Process-based models to project emissions mayrequire multiple years of data collection and

exploration (NRC, 2003). There is a scarcity ofscientifically derived emission factors characterizingUS animal feeding facilities. Emissions should becorrelated to specific animal species (source) activitywith details of production like type of barnstructure, air throughput, waste handling, animalmaturity, stocking density, and body weight inconjunction with prevailing interior and exterior airtemperature and humidity (EPA, 2004b). Many ofthese are interrelated factors that complicate am-monia emission rate assessments (Anderson et al.,2003; Worley et al., 2002), and the list is notexhaustive. Anderson et al. (2003) and Worley et al.(2002) report that litter characteristics such as drymatter content, pH, and NH4 concentration mustalso be considered.

The research presented here represents an initialeffort to assess trends within solid-side walledcommercial broiler houses; this work may be duallyapplicable to the macro- (emission model develop-ment by identifying parameters for inclusion) andmicro-scale (within house variability, time changesfor parameters through the flock cycle) for deter-mining litter gas evolution. In addition to develop-ing a better understanding of the pathways betweensolid waste conversion to gas phase for N com-pounds in the litter, Confined Animal FeedingOperations are required by law and within theirnutrient management plans to test litter sources atleast annually for total manure N and P. The resultsof the spatial sampling presented within couldprovide a basis for determining a representative inhouse sample when needed.

Two previous studies investigating the spatialvariability of litter composition or surface gasflux within commercial facilities were found in theliterature. Tasistro et al. (2004) assessed the littercomposition at the end of a growout in a10.5� 120m house with cross-flow ventilationand where the sawdust/wood shavings beddingwas removed after each flock (total cleanout).They associated the litter composition variationwith the extent and conditions of the litterdecomposition during the flock. Miles et al.(2006) reported litter pH, moisture, temperature,and gas (NH3, CO2, CH4, and N2O) flux ondays 1 and 21 during the 29th flock on pine shavingslitter in a 12.8� 146.3m curtain-sided house. Thehouse was operated in tunnel ventilation mode insummer conditions. Both these works will becompared to the two commercial houses sampledfor this report.

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The objectives of this research were twofold: (1)to determine the magnitude of irregularity amonglitter parameters by intensive sampling and con-current measurements at the beginning, middle, andend of a flock; and (2) to investigate the spatialvariability of selected litter N species and litter gasflux within commercial broiler houses, hypothesiz-ing that trends in variability could enhance under-standing of litter changeability for futureidentification of housing/management strategiesfor reducing NH3 emissions.

2. Materials and methods

Two commercial broiler houses, side-by side andbetween the two other houses on a Mississippi farm,provided the site for determining litter gas flux andlitter N species composition. Approximately 26,000broilers were placed in each house. The research,representing the 13th consecutive flock, was con-ducted during a winter growout (January–February)where pine shavings were the original beddingmaterial. Routine litter management between flocksincluded decaking and occasionally tilling the litterprior to decaking, where the latter is used more insummer conditions. Unlike decaking which removesthe compacted layer at the litter surface, tilling thelitter would mix the entire litter base releasing moremoisture and NH3 between flocks as well as into thenext flock without sufficient drying time. Onlydecaking was performed prior to chick placementof the 13th flock.

The solid sidewall houses were approximately 2.5years old, measuring 12.8m by 146.3m (42 ft by480 ft) with evaporative cooling pads on each side ofthe west end. The half of the house, length-wise,from the center to the cooling pads represents thebrood area of the house, the area that the chicksoccupy from placement until they can maintaintheir own body temperature or until more floor/feeder space is required. Typically, the decision toutilize the full house is made by the grower and thebrood period ends between 5 and 12 days afterplacement. The opposite end of the house, the fan ornon-brood end, contained one 91 cm (36 in) fan andeight 122 cm (48 in) fans of which four were in theend wall and four nearby in the sidewalls. Thesefans were operated alone or in combination witheach other and intermittently to maintain minimumventilation early in the flock or a focal housetemperature later in the growout. Vent boxes werelocated at regular intervals near the ceiling in the

sidewalls of the house and were computer controlledto work in conjunction with the ventilation stage.The house contained no baffles or mixing fans. Gasfired brooders (heaters) were hung down the centerof the house to provide heat as needed. Thebrooders were only used during the brood period(to approximately 10 days of age).

Twenty-four hours after chicks were placed(sampling day 2/the beginning of the flock), littersamples were taken along a grid, were chilled, andtransported to the laboratory for further analyses.Gas flux was estimated, at the same locations aslitter sampling, using inverted plastic chambers anda photoacoustic multigas analyzer (Innova 1312;California Analytical, Orange, CA). In H2, a litteramendment (PLTs; Jones-Hamilton Co., Wal-bridge, OH) had been added to the brood area. Inthe middle of the growout (day 22) and near the end(day 45), grid samples for litter and gas flux wererepeated.

Litter samples (n ¼ 36 on days 2 and 22; n ¼ 44on day 45) were collected along the grid depicted inFig. 1. Three sampling points, 5m apart, wereplaced across the house and 12 sites down thehouse, 12m apart, to make up the grid. On day 45,eight additional samples were taken in a zigzagpattern down the house to investigate litter and gasflux properties in high traffic areas where greatermanure deposition would be expected to influencelitter composition and gas evolution. These addi-tional samples are called feeder/waterer (F/W)samples because they were obtained equidistantbetween the water line and the feeder line. The F/Wsample locations have been approximated in Figs. 2and 3 using circles for the parameters havingespecially high or low values at these sites. Nipplewaterer lines were 1m on either side of thefeeder lines. The location of the two feeder lineswere approximately 1.3m towards the center of thehouse from the outer grid samples. Litter sampleswere taken from the upper 5 cm at each samplelocation. Litter properties determined at thelaboratory included moisture by loss in weight afterdrying for 48 h at 65 1C, and pH using a litter:deio-nized water ¼ 1:5. The litter was water extracted fordetermining NH4 and NO3 using flow injectionanalysis (QuikChem 8000; Lachat Instruments,Milwaukee, WI). Total Kjeldahl Nitrogen(TKN) was determined by block digestion andsubsequent auto-distillation/titration (2300 KjeltecAnalyzer; FOSS in North America, Eden Prairie,MN). Relative humidity and air temperature,

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Fig. 1. Grid sample layout in broiler house.

D.M. Miles et al. / Atmospheric Environment 42 (2008) 3351–33633354

approximately 1m above the litter surface, weremeasured using a pocket weather meter (Kestril3000; Nielsen Kellerman, Chester, PA) at eachsample location.

A static chamber method was used to determinelitter gaseous flux (Miles et al., 2006). Similar fluxmethods have been used in nutrition trials and forevaluation of litter amendments (Ferguson et al.,1998a, b; Moore et al., 1997). Deriving NH3 fluxfrom a source can include theoretical relationshipsor measurements of N mass balance such as modelsor emission factors, micrometeorological techniques(usually outside the house) or chamber methods(Arogo et al., 2003). The accuracy of each typedepends on many assumptions in addition to theaccuracy of measurements and the care employed tomeet desired objectives. At each sample site in thepresent study, a flux chamber (cylindrical with35 cm height, 14.3 cm radius, containing a small

electric fan) was inverted over the litter as theanalyzer drew in the time zero gas sample. Thechamber fan mixed the air within for 10 s prior to thesecond sample, captured at 70 s after time zero. Thechamber area, elapsed time, concentration difference,and the ideal gas law were used to approximate littergas flux at each location. Litter surface temperaturewas measured concurrently with gas sampling usingan infrared thermometer (Raynger ST; RaytekCorporation, Santa Cruz, CA).

Variograms (contour plots) were developed usinggeostatistical software (Golden Surfer 8.0; Golden,CO) to visually survey the spatial variability amongmeasured parameters and gas flux estimates for thebeginning, middle, and end of the flock. Thesoftware uses kriging, a statistical method, tocomplete the surface feature estimates over thefloor of the commercial houses. Kriging estimatesthe best value for a parameter by applying weightedlinear combinations of nearby values while trying tolessen the error variance between samples. Colorprogression from dark blue (low values) to red(upper limit values) enables extremes in parametersacross the floor area to be located quickly. Becausethe grid sampling imposes bias (samples are notrandom), traditional statistics were not applied tothe assessed litter N compounds, the litter para-meters, the air properties, or the gas flux estimates.

3. Results

3.1. Air and litter properties

The variograms for air relative humidity andtemperature, litter temperature, litter moisture, andpH are given in Fig. 2. The air and littertemperatures are reported using the same scale sothat they can be compared directly. Omitting pH onday 2, air and litter properties followed similarpatterns in both houses. The heat supplied to warmthe chicks in the brood half of the houses kept therelative humidity somewhat low (average 47%);whereas in the non-brood portions, the relativehumidity was greater (average 64%). As expected,the air temperature was elevated in the brood areas,31.1 1C vs. 22.4 1C in the non-brood. In the non-brood regions, the litter temperature was similar tothe air temperature. The litter temperature profilesindicate the hottest litter lies down the center of thehouse in the brood areas, just over 40 1C.

At the mid-growout measurement (day 22), therelative humidity ranged from 62 to 85% in both

Page 5: Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends

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Air Properties Litter Properties

Day

2D

ay 2

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ay 4

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0 5

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10 0 5

10

H1 H1 H1 H1

Relative Humidity (%) Temperature (˚C) Temperature (˚C) Moisture (%) pH

Bro

odN

on-b

rood

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odN

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rood

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rood

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H2 H2 H2 H2 H2

H1H1 H1 H1H1 H2 H2 H2 H2 H2

H1H1 H1 H1H1 H2 H2 H2 H2 H2

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Fig. 2. Variograms of air and litter properties in two commercial broiler houses (H1 and H2) at the beginning, middle, and end of the 13th

consecutive flock on pine shavings.

D.M. Miles et al. / Atmospheric Environment 42 (2008) 3351–3363 3355

Page 6: Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends

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ay 2

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Gas Flux (mg m-2 hr-1) Litter N Species (mg/kg)

NH3 N2O NH4 NO3

Bro

odN

on-b

rood

Bro

odN

on-b

rood

Bro

odN

on-b

rood

H1 H1 H2

H2

H2

H2

H2

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40

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0120

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Fig. 3. Ammonia and nitrous oxide litter gas flux and litter N species as contour plots from two commercial broiler houses (H1 and H2) at

the beginning, middle, and end of the 13th consecutive growout on pine shavings.

D.M. Miles et al. / Atmospheric Environment 42 (2008) 3351–33633356

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houses. No exceptional patterns were noted in thecontour plots, but slightly higher bands of relativehumidity appear near portions of the sidewalls. Theair temperature at this date cooled to about 25 1C orless across most of the brood area of H1 and isapproximately 25 1C down 75% of the center of H2.The air temperature was held at a nominal 26–27 1Cin the remainder of the houses. The litter tempera-ture appears greater than the air temperature on day22; lacking notable trends on the variograms, thelitter temperature averages 29.2 1C in each house.

Near the end of the growout (day 45), anunexplained and unusually high region of near100% relative humidity was observed in front of theright cooling pad in H1, which did not correlate toan extreme in any other measurement for that placeand time. This house had a greater overall relativehumidity down the length of the center of the house(60–75%) than neighboring H2 which was at45–55%. Time of day might explain the grossdifference in relative humidity between the houses,because H1 was sampled earlier in the morning thanH2. Corresponding to the time of the measure-ments, local climatic data indicate that relativehumidity decreased from 100% at 7 a.m. to 54% atnoon. Air temperatures in both houses decreasedfurther, as expected with flock age, to range19–23 1C. Alternatively, the day 45 litter tempera-tures lingered close to those of the mid-flock at27.7 1C, where the variograms show an increasednumber of smaller, cooler regions over the floorarea of both houses.

Litter moisture, pH, temperature, TKN, NH4,NO3, and N2O and NH3 flux for the two broiler

Table 1

Pooled litter properties, gas flux, and N species for two solid sidewall co

Bird age (day)

House 1

Litter properties 2 22

Temperature (1C) 27.0 29.2

Moisture (%) 22.6 27.0

pH 8.61 8.24

Gas flux (mgm�2 h�1)

NH3 400 412

N2O 7.9 18.4

Litter N species (mgkg�1)

Total Kjeldahl N 21,734 22,114

NH4 3631 4157

NO3 1145 456

houses at the beginning, middle, and end of thegrowout are given as means in Table 1. Because thechicks were in half house brood during the day 2sampling, it is recognized that the report for averagetemperature is misleading. The range of littertemperature was similar for both houses in thewinter conditions on day 2 at approximately18–42 1C. On day 45, the average litter temperaturesfor both houses were greater than on day 2, 27.7 vs.27.1 1C.

The average litter moistures in Table 1 show anincrease from the beginning to the end of the flock.In Fig. 2, the contour plots indicate that individualareas ranged from very dry during brood (�13%) tovery moist in the high cake areas at the end of theflock (�57%). The brooder heat effectively dried thelitter in the brood areas on day 2, ranging from 12%to 26% moisture with an average of 18.6% in H1and 20.9% in H2. At the mid-flock measurement,low moisture is still prevalent in portions of thebrood area in both houses. The non-brood endsappear to have some drier regions than on day 2,but have nominal increases near the fans across thehouse width. By the end of the growout, moistureincreased in both houses, more so near the side-walls. The additional samples taken at the F/Wsites, which are approximated with circles on day 45in Fig. 2, are especially interesting; these high trafficareas were predominantly caked but had lowermoisture (�24%) than surrounding litter samples(430%). In H2, an extreme caked area (‘‘U’’shaped) was present near the fans and exhibitedthe highest litter moisture, averaging 50.7% foreight grid samples in that area. This high moisture/

mmercial broiler houses during flock 13 on pine shavings bedding

House 2

45 2 22 45

27.8 27.2 29.2 27.6

29.5 24.9 27.6 36.4

8.43 8.33 8.51 8.00

694 307 294 649

17.1 12.9 22.6 31.5

23,231 20,159 21,505 24,157

6184 5109 5850 7651

110 2350 1316 9

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caked area is denoted with a rectangle in Figs. 2 and3 to point out the high moisture, low pH, low NH3

flux, and high NH4 specific to that area of H2.Litter pH appeared to decline over the flock on

average. In H1, average litter pH dropped from 8.61to 8.43 from the beginning to the end of thegrowout. However, day 22 pH averaged 8.24. InH2, average litter pH was initially 8.3 vs. 8.0 at theend of the growout, with a mid-flock pH of 8.5. Thefreshness of the feces in the sample can reduce pH,but this would not fully explain the decline,especially considering the number of samples con-tributing to the average. New sawdust bedding has apH between 5 and 6.5 (Elliott and Collins, 1982).Although litter pH is generally projected to increasewith bird age and the number of flocks (Nahm,2003), documentation of within flock changes onbuilt up litter are sparse.

The pH down the center of the brood area in H1on day 2 was slightly lower than the surroundinglitter (8 vs. 8.2). The litter amendment applied to thebrood area of H2 produced consistently lower pH(�7) in much of that area on day 2. Reece et al.(1979) reported that modest NH3 volatilizationoccurs at pH 7 and below. On day 22, both broodareas indicate lower pH than the remainder of thehouses, but H1 was lower than H2. By day 45, muchof H1 litter had a pH48 with a lesser magnitude ofpH at the F/W locations. The pH in H2 at the endof the growout appeared to decrease from day 22 inmuch of the house, masking the appearance of lowpH in the F/W samples. The area of extreme cakethat formed near the exhaust fans in H2 on day 45resulted in the lowest recorded pH of the experi-ment, 5.44.

3.2. Litter gas flux and N compounds

Litter NH3 flux followed a trend similar to littermoisture, increasing with bird age (Table 1). On day2, the litter treatment in H2 seemed responsible for alesser overall flux estimate; 307mgm�2 h�1 vs.400mgm�2 h�1 in H1. The overall middle flockNH3 fluxes appeared to remain near those of day 2for each house: in H1, 412 vs. in H2,294mgm�2 h�1. Similar and higher values foroverall flux were evident by the end of the growout,694mgm�2 h�1 in H1 and 649mgm�2 h�1 in H2.

Variograms for NH3 flux over the floor area ofthe two houses are presented in Fig. 3. With thebeginning of the flock, the brood area of H2 (littertreatment applied) had NH3 flux that was essentially

zero over approximately 45% of the area. In thebrood area of H1, NH3 flux was elevated down thecenter of the house, which corresponded to thelocation and operation of hanging brooders. By day22 the profile for NH3 flux was primarily linearalong the length of both houses, with greater fluxevident near the sidewalls in H1. A comparabletrend was sustained at the end of the flock. Inaddition, during the final measurement, two sig-nificantly elevated regions of NH3 flux wereapparent in the brood area in the center of H2.Also on day 45, the NH3 flux was greatest near thecooling pads of both houses. The extreme cakedarea in H2 at the fan end had virtually no NH3

evolution. The circles on the day 45 variogramsapproximate the location of F/W samples whereNH3 flux was generally less than surroundingsamples.

Nitrous oxide flux from the litter was low inmagnitude throughout the growout, 0–5mgm�2 h�1 over most of the floor area in both houses(Fig. 3). However, there was a slight increasingtrend with bird age. Including a consistentlyelevated region near the right cooling pad in H2,the average N2O flux for the flock was18mgm�2 h�1. The sidewalls in H2 on day 45contributed to the increase to some extent and N2Oflux was greater in H2 than in H1.

Total Kjeldahl N from the grid litter samples washigher in the brood areas compared to the non-brood ends of the houses at the beginning of theflock (Fig. 3). In H1 the brood area averaged23,600mgkg�1 whereas the fan end was19,900mgkg�1. For H2, the brood area averagewas 21,700 and 18,700mgkg�1 in the opposite endof the house. The trend of greater TKN, approxi-mately 23,000mgkg�1, in the brood regions wasobvious into the middle of the flock. At the end ofthe flock, the higher TKN regions still remainednear the same magnitude of 23,000mgkg�1, butstretched over the entire floor region with a fewlower regions near the sidewalls. The F/W samplesrevealed the highest TKN concentrations for theflock, approximately 31,000mgkg�1. Table 1 pre-sents the whole house averages for each sampledate, indicating an increase with flock age.

Ammonium in the litter tended to increase overthe flock cycle. The H1 average NH4 concentrationsfor the beginning, middle, and end of the flock were3600, 4200, and 6200mg kg�1 as compared to H2values of 5100, 5800, and 7700mgkg�1, respec-tively. Trends within the houses are difficult to

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detect in Fig. 3 due to the relatively small differencescompared to the particularly high NH4 concentra-tions (near 24,000mgkg�1) found in the extremecaked region of H2 on day 45. For H2, litter NH4 inthe center of the brood region (approximately10,000mgkg�1) appeared greater than surroundinglitter (near 5000mgkg�1) on days 2 and 22.

Nitrate concentrations were more variable be-tween the houses than the other N species measuredin the litter. As seen in Fig. 3, H2 exhibited thehighest litter NO3 on day 2 with one small area nearthe left sidewall brood area and nearly half the fanarea from the left sidewall to the center of the house.Also, compared to litter TKN and NH4, the trendwith bird age was reversed so that NO3 levelsdropped during the flock. In H1, days 2, 22, and 45NO3 sample concentrations averaged 1150, 460, and110mg kg�1 (Table 1). For H2, these values were2350mg kg�1, 1300mgkg�1, and 90mgNO3kg

�1.The NO3 concentrations were lowest in both houseson day 45 with the exception of one elevatedarea near the right side of the fan end in H1.Although difficult to detect on the variograms, theday 45 F/W litter NO3 levels were elevated some-what compared to the remainder of the floor area.

4. Discussion

4.1. Air and litter properties

Half house brood conditions on day 2 wereobvious in the temperature and relative humidityprofiles in the brood area for both houses. Thehighest overall measured temperatures for the flockwere observed on day 2 for the litter down thecenter of the brood area which corresponds to thesupplied heat from the brooders. The results forelevated litter temperature, in addition to low littermoisture, during brooding have been previouslyshown to correspond spatially to this managementscheme in a curtain-sided commercial broiler house(Miles et al., 2006). In a southern US study onparticulate matter and NH3 emission factors fortunnel-ventilated broiler houses, Lacey et al. (2003)conducted measurements primarily in summerconditions, but reported one mean relative humidityvalue for the middle of a winter flock, approxi-mately 46%74. Compared to the spatial reportgiven here, that level of relative humidity waspresent at the beginning of the flock in only thebrood regions of the houses. However, it was alsoencountered in H2 down the center of the house at

the end of the growout. Although climatic factorslike air temperature and relative humidity arethought to impact NH3 generation within broilerfacilities, the spatial trends for these parameterspresented here do not appear to have any significantcorrelation to gas flux or N compounds in the litter.In the work by Lacey et al. (2003), neither houseambient temperature nor relative humidity wasfound to be significant influences on emissions.Still, the role relative humidity plays in the fate ofNH3 outside an animal facility may be important.For example, the formation of ammonium nitratedepends on relative humidity, and the phase of thecompound as a particulate or a gas is related toambient temperature and relative humidity (Baeket al., 2004; EPA, 2004b).

Seasonal changes in temperature necessitatecomplementary ventilation management to keepthe birds at an appropriate temperature. Seasonalvariability in temperature has been thought tocontribute to sizeable emission fluctuations (EPA,2004b). Elliott and Collins (1982) reported 1–2 1Cincreases in temperature can greatly increase NH3

volatilization. The variograms showed that littertemperatures were maintained higher than airtemperatures. External temperatures are not pro-vided and some herding of the birds existed whileaccomplishing the measurements. However, it wasobvious that the larger birds insulate the littersurface towards the middle and end of the flockwhich may be more influential on litter gas flux thanseasonal conditions.

Ventilation controls litter moisture (Gates et al.,1997) and winter fan operation rates are generallyless than warmer seasons to reduce heating costs.The objective of ventilation is to provide an optimalthermal environment for bird growth (Lacey et al.,2002). Controlling litter moisture (drying the sur-face) and house NH3 concentrations (diluting withincoming air) are subordinate effects. Increasedventilation rates are required to reasonably reduceNH3 levels within houses, which are higher thanrates needed for moisture control (Xin et al., 1996).The greater moisture near the sidewalls at the end ofthe growout could be an artifact of ventilationwhere a more fully developed air flow profile ispresent down the middle of the houses and able tostrip away litter moisture. Although emissions maydecrease at moisture extremes, appropriate relation-ships for intermediary levels have not been devel-oped (Elliott and Collins, 1982). Large increasesin aerial NH3 may occur at 430% moisture

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(Carr et al., 1990). Carey et al. (2004) suggest littermoisture ranging from 25% to 35% as favorable forreduced odor/dust, but individual house featuresshould be known to arrive at a precise level.

The presence of caked surfaces over the beddinghas been primarily characterized by high moisture,but physical effects of the cake condition havescarcely been defined. Sistani et al. (2003) found theaverage cake moisture for three farms in MS was44–47.7%, whereas litter moisture ranged from25.6% to 29.7%. In the spatial litter study byTasistro et al. (2004), average water content in thelitter bedding was 29.7% in the center of the house,17.4% at the feeders, and 54.6% below the waterers.The results of the current study are comparablewhen discussing average litter moisture within thehouses. In addition, the results presented here seemto differentiate cake based on location and moist-ure. The additional samples taken on day 45between the feeders and waterers were predomi-nantly cake. However, these samples had lowermoisture (expected to result from the addition ofdry matter from spilled feed) and lower pH than thesurrounding friable litter. The extreme caked area inH2, near the fans on day 45, was a high moisturecake. The caked samples are discussed further belowwith respect to NH3 flux.

The trend in litter pH on average was notconsistent between the houses; the dynamic natureof the pH changes may be due to the litteramendment application in only H2 prior to chickplacement. Early in the growout litter amendmentsare the primary means for altering litter pH, buttheir control does not endure through the entireflock. Although litter pH is frequently expected toincrease with the litter age, and corresponding flockage, a similar phenomenon has been reportedpreviously where litter pH decreased between days1 and 21 (Miles et al., 2006). Greater depositionand, thus inclusion of fresher excreta, later in thegrowout could explain the overall decrease in pHfrom the beginning to the end of the flock. As mostof the samples maintained pH 8 or greater on thebuilt up litter, one would not expect NH3 volatiliza-tion to be diminished due to pH. The intensivesampling demonstrates how litter characteristics canvary within the flock cycle.

4.2. Litter gas flux and N compounds

Much of the recent emphasis on gas measurementsurrounding animal facilities centers around devel-

oping process-based emission factors (the productof house concentration and ventilation rate) todetermine potential for regulatory action. The focusof this study was to look at trends in the littersurface to create baseline data for identifyingcollinear management and climatic factors duringthe flock that shapes those trends. The litter gas fluxvalues for NH3 appear reasonable compared toother chamber measurements, although many com-parisons among house specific/interrelated factors(i.e. bedding type, diet, and management) anddistinction in methodology were not feasible.Brewer and Costello (1999) reported a mean NH3

flux of 208mgm�2 h�1 after six flocks were raisedon rice hulls. Baracho et al. (2001) found day 39NH3 flux (wood chip bedding) averaged2568mgm�2 h�1.

Brood conditions on day 2 (heat supply) causedan increase in NH3 flux in H1, whereas, the litteramendment reduced the NH3 flux in H2 for aportion of the brood area. It is unknown why thereduction in NH3 flux was skewed toward the leftside of H2, whether the product was appliedunevenly or some other factors caused the productto be exhausted more rapidly near the opposite side.The magnitude of flux in both houses was essentiallyunchanged from the beginning to the middle of thegrowout, but the pattern of the flux migrated frombrood vs. non-brood to flow down the length of thehouse. This is in contrast to a previous study (Mileset al., 2006) of one, curtain-sided broiler house insummer where the litter flux (1) decreased betweendays 1 and 21 and (2) maintained a brood vs. non-brood nature of comparison from the beginning tothe mid-growout measurement. The increase inventilation under summer conditions likely dilutedthe house and litter surface NH3 concentrationsduring the second measurement (Miles et al., 2006).

The caked areas at the F/W samples and near thefans in H2 showed reduced NH3 flux. While theTKN at the F/W samples was elevated, the fan areaTKN was not as pronounced. The H2 fan area cakehad low litter pH and high litter NH4. Highmoisture can cause the cake to become anaerobic,diminishing NH3 production (Carr et al., 1990).

Additionally, the compaction of the cake frombird traffic suggests a physical barrier impedingNH3 volatilization. It is apparent that cake forma-tion during the flock can affect the accuracy ofpredicting NH3 emissions from the litter surface.The formation of cake within houses is currentlyunavoidable. Although the diminished NH3 flux

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from caked surfaces may be desirable, the cake can‘‘slick over’’ with increased deposition or moisturein the house (i.e. from improperly operated misters)creating a platform for increased contact with thelitter surface, thus excreta, for the birds.

The ambient levels of N2O within the houses(observed before, after, and between flux measure-ments) were below 2 ppm which is similar to wintermean N2O concentrations (�2.2 ppm) observed inUK houses (Wathes et al., 1997). Flux estimateswere low because the differential concentrationsmeasured (the increase in gas buildup within thechamber for a sample time and location) were low.Nitrous oxide fluxes from the houses were compar-able to a previous study over litter (Miles et al.,2006) showing generally low flux levels with slightelevations at the ends of the house and near thesidewalls. An opposing trend in this study indicatedan increase (near double) in N2O flux from day 2 today 22, whereas the previous study indicated nochange for the same time period. Further, the day45 overall results indicated a slight decrease in N2Oflux in H1, while in H2, there was a sufficientincrease.

Total Kjeldahl N concentrations were influencedby half house brood management through themiddle of the flock, indicating greater concentra-tions in the brood area of the houses(�23,000mg kg�1). The levels, ranging from10,500 to 36,500mgkg�1 in this report, appearsomewhat lower than the three-producer, one yearsurvey grand averages reported by Sistani et al.(2003). Litter and cake TKN analyzed by Sistani etal. (2003) using the same method as the currentstudy were 32,800 and 37,600mg kg�1, respectively.The spatial work by Tasistro et al. (2004) for across-flow commercial house found total N con-centrations from 30,000 to 50,000mgkg�1 (drylitter) using combustion analysis at the end of asingle growout and that decreased total N wascorrelated to increased pH. In the variograms forTKN and litter pH, the same association is evidentexcept for the application of the litter treatment inH2 on day 2.

Organic N is converted to NH4 via N mineraliza-tion. Ammonia volatilization and mineralization,commencing upon defecation (EPA, 2004a), are theN transformations in the ammonification portion ofthe N cycle (Tiquia and Tam, 2000). Conversions ofN compounds provide the pathways for emissionsto air and water. When water is present, NH3

solubilizes in it to form NH4+. Ammonium in litter

provides beneficial nutrients for plants when litter island applied. However, maintaining it in the litterand reducing NH3 losses are challenging. Litteramendments work by reducing litter pH so that theequilibrium between NH3 and NH4 favors the later,as indicated by the increased NH4 in the H2 broodarea on day 2. Ammonium concentrations in cakeand litter were reported by Sistani et al. (2003) as12.5% and 11.5% of the total N. The comparablefractions for the current study are greater. In H1, ondays 2, 22, and 45 the % NH4 of total N were16.7%, 18.8%, and 26.6%. In H2, the respectiveportions were 25.3%, 27.2%, and 31.7% NH4 oftotal N. Thus, in both houses the relative amount ofNH4 increased with bird age, but H2 had higherconcentrations than H1.

In poultry housing adsorbent litter beddingmaterials retain some N, permitting microbes theopportunity to start N immobilization, the conver-sion of NH4 to NO2 then NO3 (Nahm, 2003).Though immobilization provides a mechanism toreduce air emissions from manure, without propercare in storage and land application, water contactmay cause NO3 leaching. Nitrate levels rangedbetween 0 and 4200mg kg�1 and decreased as theflock aged, unlike NH4 and TKN. Days 22–45samples were similar to the Sistani et al. (2003)reports of 290mgkg�1 in litter and 590mgkg�1 incake. The slightly elevated NO3 concentrations atthe F/W samples (caked) were consistent with thoseof Sistani et al. (2003) indicating greater NO3 incake. However, the elevated NO3 levels did notcarry over to the extreme caked fan area in H2 atthe end of the flock.

5. Conclusions

During a winter flock, NH3 and N2O flux wereestimated to learn more about the surface chemistryof the litter and, with concurrent measurements ofair and litter parameters and litter sampling, howlitter and gas parameters change over the floor areaof commercial broiler houses. House management,feeder and waterer placement, and bird activityinfluence litter gas flux and N compounds in thelitter. Data trends agree with established relation-ships for the influence of pH, moisture, andtemperature on gas emissions. Bird age/size affectedlitter temperature; the larger birds appeared toinsulate the litter base which could potentiallynegate seasonal effects on emissions. Also, aberra-tions in the physical condition of the litter, whether

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friable or caked, should be considered regarding thelitter surface chemistry and NH3 generation.

The two most prominent litter characteristics thatemerged in this study were the presence of cake withrespect to NH3 potential and the origination of thecake (near F/W or tunnel fans). The effect of thecompaction of the cake to create a deterrent sealand, thus, a decline in NH3 generation has not beenexplored in the current literature. Caked areas in thehouse produced lower NH3 flux, but differed inmoisture content based on location. Cake moisturewas lower between feeders and waterers but highernear the exhaust fans. Also, cake from the F/Wsamples differed in moisture, pH, TKN, and NH3

flux from the surrounding litter. The F/W cake hadlower moisture, pH, and NH3 flux, but higher litterTKN. Other researchers have characterized cake bywater content and nutrients or have characterizedlitter under waterers, feeders, and in the middle ofthe house, but have not made the distinction basedon location within commercial houses while report-ing litter condition, litter moisture, and potentialNH3 flux.

Comparing the tabular averages of data to thevariograms reveals that single point measurementsmust be obtained with caution so that an upper orlower threshold value is not reported as a repre-sentative condition for the broiler flock. The trendsnoted in the litter parameters, gas flux, and littercomposition for this study should be compared toreplicate studies to establish trends related to housestructure, management, and bird activity. Furtherstudies of the spatial variability are expected to leadto new best management practices. Input frombroiler managers will be required to evaluatepotential management practices to prevent detri-mental effects on the birds. Zone litter treatmentduring the flock is one example. Sampling recom-mendations for litter nutrient analyses as part ofcomprehensive nutrient management plans shouldconsider the potential variability and areas repre-sented within commercial houses by friable litter, F/W cake, and cake from areas in other high trafficzones.

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