J APPL POULT RES 2006. 15:447-456
© 2006 Poultry Science Association
In-House Composting of Layer Manure in a High-Rise, Tunnel-Ventilated Commercial Layer House During an Egg Production Cycle
A. B. Webster*,1,
S. A. Thompson
,
N. C. Hinkle
and
W. C. Merka*
* Departments of Poultry Science, Biological and Agricultural Engineering, and Entomology, University of Georgia, Athens 30602
1 Corresponding author: bwebster{at}uga.edu
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SUMMARY
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In-house composting has the potential to improve the viability of the high-rise house for commercial egg production by producing a value-added product from the manure without requiring a separate composting facility. The feasibility of in-house composting depends in part on having the ability to handle the manure mass that accumulates over an extended period. This field study showed that in-house composting is possible for the length of an egg production cycle. Beginning with windrows of a carbon source, fresh pine sawdust or shredded yard waste, upon which manure fell from the cage rows above, compost volume grew rapidly in the first few weeks, but slowed after composting activity peaked, as indicated by compost temperatures. In cold weather, when ventilation rates were low, compost remixing temporarily produced high ammonia levels in the house, but ammonia levels at other times were comparable to or lower than those in an undisturbed house. The final compost was friable and nutrient-rich, although the handling quality of the yard waste compost was reduced by persistence of elongated woody pieces of the original carbon source. The ability to access the manure storage area of a high-rise house over a cycle of production gives potential to deliver manure amendments to improve nitrogen retention in the compost, which would have the effect of improving its fertilizer value and reducing ammonia emission from the house.
Key Words: commercial layers • in-house composting • manure
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DESCRIPTION OF PROBLEM
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For many years, the trend in the commercial egg industry has been to build larger houses for laying hen flocks and to construct production complexes having a number of houses at 1 location. It is not unusual for these complexes to hold more than 1 million hens. Although achieving efficiencies of scale in egg production, this trend has also resulted in the production of large amounts of manure on individual farms. With urban encroachment and growing regulatory requirements for nutrient management planning, it has become increasingly difficult to access a sufficiently large land base upon which to apply manure with economic feasibility. Furthermore, land application of unprocessed layer manure near populated areas can produce complaints of objectionable odors. High-rise layer houses also can produce great numbers of flies from stored manure, which can irritate neighbors and create a negative public reaction against the egg producer.
In-house composting has been developed in an attempt, on the one hand, to improve the characteristics and value of layer manure to make it more marketable [1], and, on the other, to reduce fly production from the manure [2]. Both attempts have produced promising results. Until recently, however, a composting machine with sufficient capability has not been available to conduct an in-house composting trial in a modern commercial layer house for an extended period. In the present study, in-house composting of the entire manure output of a modern commercial high-rise house was evaluated over the first egg production cycle of a flock of laying hens. Two different carbon sources were compared and the effects of composting on the house environment were monitored.
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MATERIALS AND METHODS
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The in-house composting trial was conducted on a South Carolina commercial layer farm in high-rise houses designed to support bidirectional tunnel ventilation during warm weather and cross-ventilation through side-wall inlets during cooler parts of the year. Two adjacent houses were selected, holding young replacement flocks at about the same age. Both houses were 550 ft long and 60 ft wide with capacity to hold 103,000 hens at the stocking density accepted at the time. The ground floor of each house was poured concrete. The original intent was to compost the manure in both houses, 1 without a carbon source (house 1) and the other with a carbon source (house 2). After about 3 wk, the fly production from house 1 was so great that the company abandoned the composting effort in that house and the manure was left undisturbed thereafter. House 1, therefore, ceased to be the intended control, but occasional measures were taken in it thereafter for comparative purposes. Six rows of cage batteries ran the length of each house in its upper level (bird level), with the 2 stacks of cages in each battery in a 4-tier, semistair-step arrangement. Each battery was about 6 ft wide at its base. Thirty-six light hybrid hens were housed per linear foot of cage battery. Manure fell from the cages to form windrows on the ground floor (manure level) underneath the cage rows. The hens in both houses were managed in accordance with the egg company’s standard husbandry procedures.
The trial began in mid August and was completed in the middle of the following July. Both houses had recently been filled with flocks of replacement pullets at the beginning of the study. House 1 had 2 in. (maximum depth) of manure under the cage rows at the start of the trial. The test house had been cleaned out and a carbon source was laid down by company personnel in a 6-ft-wide band under each cage row. For most of the house, the carbon source was fresh pine sawdust (sawdust compost) laid down at an average depth of 5.5 in. (2.73 ft3/ft), except for 2 sections, each approximately 25 ft long, which received shredded limbs, brush, and other vegetation (yard waste) obtained from a local municipality (yard waste compost) placed at an average depth of 9.3 in. (4.65 ft3/ft). The bulk densities of the sawdust and yard waste materials were measured to be 20.4 and 19.8 lb/ft3, respectively. The particle size of the yard waste was larger and more variable than that of the sawdust.
Remixing of the compost began on d 20 after the carbon source was laid down, using a "Compost Cat" machine [3]. This machine is designed to drive the length of a compost windrow using a horizontal auger to remove material from the cross-section of the windrow and deposit it onto a broad conveyor that carries the compost through the machine and drops it behind. Because the egg company intended, in part, to use composting as a means to control flies, the schedule for compost remixing was set at twice per week to interrupt the fly life cycle by incorporating eggs and pupae into the hot zone of the compost where they would not be able to survive. Remixing the compost was terminated after about 310 d because the compost volume and mass had begun to slow the compost machine too much for the company to consider it worth the effort to continue.
Most of the data were collected during 10 visits to the farm on d 20, 37, 47, 78, 142, 184, 212, 240, 268, and 331 after the establishment of the compost windrows. These visits took place the day after the compost had been remixed, except for d 20, 78, and 240 when remixing was done the day of the visit, and d 331, which was 3 wk after the last remixing. All measurements on sawdust compost were taken in one half of the house in the windrow under the second cage row at various points between the end of the house (where exhaust fans were located) and the center (the location of the tunnel inlet). Observations on yard waste compost were in sections of the third and fourth windrow at the house end and center, respectively. The locations at which measurements were taken were designated by site number, with a site corresponding to the interval between successive support posts in a row, 3 rows of which ran the length of the house. Site 1 was nearest the exhaust fans and site 31 was at the house center.
Compost volume was monitored by measuring the cross profile of the windrows. During the first 4.5 mo of the trial, the x and y coordinates of the compost surface were measured at 8- to 10-in. increments along the transverse plane of the windrow, thereby allowing an accurate estimate of the cross-sectional area of the windrow. This procedure was done at 5 locations in the front half of the house, 3 in areas with sawdust as the carbon source, and 2 in sections with yard trash. From these measures, estimated compost volumes were calculated for the 2 carbon sources. The time-consuming nature of this method limited the number of sites that could be sampled. As the compost windrows grew, it became apparent that the company driver of the composting machine tended to leave the compost uneven over the lengths of the windrows, making many sampling points necessary to estimate compost volume. Therefore, during the latter 6.5 mo of the study, a different technique was adopted wherein only the peak height of the windrow and its half width were measured and the compost cross-sectional area estimated from these 2 measures. A similar method was used by Miner et al. [4]. In each session, compost dimensions were measured at 15 evenly spaced sites along the sawdust-based windrow from 1 end of the house to the center, and at 6 evenly spaced sites in the sections containing yard waste. The last volume measurement session took place 3 wk after the company had stopped remixing the compost.
Temperatures were obtained at regular intervals along the length of the sawdust compost windrow and at representative locations in the yard waste compost. Normally, these measurements were taken 1 d after the compost had been remixed because a previous study had indicated this to be the time that core temperature peaks after a remixing event [1]. Thermocouple probes were thrust about 10 in. into the core of the windrow to obtain the temperature reading.
During the 7 farm visits spanning d 47 to 268, compost accumulation by weight was assessed by weighing the material in 16-in. cross-sections of windrows at 3 locations in the sawdust compost (near the row end, midway to the house center, and at the house center) and at 2 locations in the yard waste compost. The bulk density of the compost was calculated by dividing the compost weight by its volume. Compost was sampled for analysis of nutrients and minerals by taking and mixing thoroughly several handfuls of material from the compost that had been dug out and weighed earlier the same day. From the mixed samples, 1-pint volumes were drawn, sealed in zip-lock bags and delivered to the University of Georgia Soils Analysis Lab for determination of moisture, carbon (C), nitrogen (N), phosphorus (as P2O5), potassium (as K2O), and calcium carbonate (CaCO3). Carbon was measured by infrared detection of carbon dioxide gas after combustion of samples in an oxygen atmosphere.
Ammonia concentrations within the house were measured using a Matheson-Kitagawa 8014- 400A gas sampler [5] with Kitagawa 105SC ammonia detector tubes during a number of farm visits. These measurements were obtained along the midline of the house in both the manure storage area and the living space of the hens at the end of the cage row, midway to the center of the house, and at the house center.
Logarithmic and linear regression analyses were used to characterize changes in compost volume, weight, and bulk density during the in-house composting trial [6]. The data for compost temperature and manure and compost analyses were subjected to ANOVA to evaluate the effects of different carbon sources [7].
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RESULTS AND DISCUSSION
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The pine sawdust used as a carbon source in this study was higher in moisture, lower in nitrogen, and similar in carbon level to the yard waste on an as-sampled basis (Table 1
). The sawdust had a much higher C/N ratio. It happened that the company applied less mass of sawdust than yard waste per linear foot of windrow (Table2). The carbon-only application rate for sawdust was just 36% of that for yard waste.
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Table 1. Analyses of materials (as-sampled basis ± SE) used as carbon sources during the in-house composting field trial
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Table 2. Calculated application rates (lb/linear ft of compost windrow) of the carbon sources at the beginning of the in-house composting trial
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Compost core temperatures measured on the days following remixing events are shown in Table 3. Compost temperatures had not peaked by d 37. Sometime before d 142, core temperatures had stabilized around 130°F for the sawdust compost, and around 140°F for the yard waste. The temperatures for the 2 compost types generally did not differ significantly except on d 212 when the sawdust compost averaged 4°F cooler, and on d 268 when the yard waste compost averaged 5°F cooler. The reason for the decline in core temperature of the yard waste compost on d 268 is not known. At 331 d, after compost remixing had been stopped for about 3 wk, core temperatures had declined 15 to 30°F from peak levels. On d 240 of the trial, core temperatures were measured in the sawdust and yard waste composts immediately before and after compost remixing. These temperatures averaged 133°F before remixing and 108°F afterward. The data are consistent with the profile of temperature changes occurring after compost remixing reported by Thompson et al. [1]; that is, that core temperatures rise to peak levels within a day after remixing and decline only a few degrees over the next few days. Thus, once high compost temperatures were achieved, they remained high as long as remixing occurred every few days. It is evident that composting would continue indefinitely as long as manure was added and appropriate aeration and moisture were maintained. The material would have to go through a final stage of composting without addition of manure to produce a stable end product.
Inhibition of fly production in manure using the heat generated by composting can be one of the benefits of in-house composting [2]. However, even though the compost machine used in the current study was capable of handling the increasing volume of material for many months, there was a period at the beginning of the study when core compost temperatures would have been too low to inhibit flies. The compost machine type [8] and methods used in the studies by Pitts et al. [2] and Miner et al. [4] allowed rapid buildup of heat in compost but could not support long-term in-house composting without cleanout because the volume of material exceeded the capacity of the machine too quickly [4]. If long-term composting with a large initial volume of carbon source is desired, and it is intended to use the process to control fly production, it would be important to amend the carbon source with sufficient nitrogen and moisture to promote activity of thermophilic microbes and heat the compost as quickly as possible. This amendment could be manure or in-house compost left behind from the previous clean-out.
Total compost volume and volume accumulation of the sawdust compost rose relatively rapidly until about 84 d, after which the rate of volume increase was lower until the end of the study (Figure 1). This trend in volume increase was a little less evident for the yard waste compost (Figure 1), wherein the logarithmic regression of volume growth over time had less predictive value than was the case for sawdust compost (R2 = 0.88 vs. 0.98, respectively). By the end of the study at 331 d, the volume (volume increase) of the sawdust compost was estimated to be 9.2 ft3/ft (6.5 ft3/ft) and that of the yard waste compost 10.2 ft3/ft (5.6 ft3/ft). The undisturbed manure in house 1 had an average volume exceeding 13 ft3/ft at the end of the study, so that despite the added carbon sources, the final volumes of the composts were 22 to 29% reduced by comparison. These volume reductions are somewhat less than the 34% relative volume reduction reported for in-house compost in a naturally ventilated, curtain-sided, high-rise house [1]. The higher rate of increase of compost volume at the beginning of the trial reflects a slow start to the composting process. A similar pattern of volume growth was noticed during an in-house composting study in a naturally ventilated, curtain-sided, high-rise house [1]. It is unlikely that starting windrow volume in itself played much of a role in the slow initiation of compost action because this was larger than needed to develop peak compost heating [4]. The slow startup of composting probably was due to the initially low supply of nutrients necessary for composting to occur. These nutrients evidently did not reach concentrations sufficient to support high activity of thermophilic microorganisms throughout the compost until weeks into the trial. Miner et al. [4] were able to achieve active in-house composting in less than 10 d after forming compost windrows in which the manure content was high enough to reduce the C/N ratio to less than 20.
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Figure 1. Total volume (TV) and volume increase (VI) expressed as cubic feet per linear foot of compost windrow of sawdust and yard waste compost during the in-house composting trial. Logarithmic regressions of sawdust compost volume on day of trial (TV = –2.98 + 2.16 ln(day), R2 = 0.98; VI = –5.71 + 2.16 ln(day), R2 = 0.98). Logarithmic regressions of yard waste compost volume on day of trial (TV = –1.86 + 2.15 ln(day), R2 = 0.88; VI = –6.44 + 2.12 ln(day), R2 = 0.87).
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After d 47, when compost weight measurement began, bulk density increased similarly for both sawdust and yard waste compost in a linear fashion on a DM basis (Figure 2). The final bulk densities of the 2 compost types were close, being 29 lb of DM/ft3 and 28 lb of DM/ft3 for the sawdust and yard waste composts, respectively. In studies by Thompson et al. [1] and Webster et al. [9], final DM mass of undisturbed manure did not differ appreciably from that of in-house compost. If the same were true in the current study, the undisturbed manure must have had lower bulk density than in-house compost. Frequent compost remixing had the effect of breaking up the material. Thus, although friable, the compost remained relatively compact. In contrast, the undisturbed manure had a porous, rigid structure particularly in the dry material comprising the sides of the windrow. The total amount of compost produced from a house of this capacity was estimated to be 510 tons of sawdust compost or 590 tons of yard waste compost after 268 d.
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Figure 2. Linear regressions of dry weight compost bulk density increase (lb of DM/ft3) on day of in-house composting trial. Bulk density (BD) sawdust compost = 10.3 + 0.068(day), R2 = 0.98; BD yard waste compost = 10.8 + 0.0615(day), R2 = 0.85.
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Figure 3 shows the crown height and volume profile of the sawdust compost along windrow 2 from its end (site 2) to the center of the house (site 31) after 268 d of the trial. The unevenness of the windrow was primarily due to shifting of material at the location where the compost machine had to cross the windrow to access other parts of the house, but also was due to operation of the machine at uneven speeds along the windrow.
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Figure 3. Profiles of crest height and volume of the sawdust compost windrow from house end (site 2) to center (site 31) on d 268 of the in-house composting trial.
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On d 20 of the study, fresh manure collected from the windrow surface was high in moisture (68 ± 1.2%) and had 3.2 ± 0.4% N and 10.0 ± 0.6% C (as-sampled ± SE, n = 3); its carbon to nitrogen (C/N) ratio was 3.0 ± 0.8. Table 4 shows data for compost moisture, nitrogen, and carbon content. Compost moisture was in the upper 40% levels when first measured and declined to mid to low 30% levels by the end of the trial. The sawdust compost at 331 d was about 5% drier than blended samples of undisturbed manure from house 1. It has been our experience that in-house compost tends to be drier than undisturbed manure produced in the same situation. The difference was greater in a naturally ventilated, curtain-sided house, which would have relatively lower ventilation rates in the manure storage area than in a tunnel-ventilated house. For example, such a moisture difference, indicated as compost moisture less than manure moisture, ranged from 20 to 24% in a naturally ventilated, curtain-sided house vs. 3 to 12% in a tunnel-ventilated house [1, 10]. The heat of the compost and frequent remixing probably accelerated drying of the compost. Compost nitrogen content was initially below 1% (sawdust compost, as-sampled), and rose gradually to around 1.5% while compost remixing was taking place, but did not reach the nitrogen level found in samples of undisturbed manure. Nitrogen content of sawdust compost increased to 2% by d 331, when remixing had been stopped for about 3 wk. Carbon contents of the composts were close to 20% on an as-sampled basis when first measured, then appeared to decline slightly before rising to 17 to 18% at the last measurement taken while compost remixing was still being done. Thereafter, the carbon content of the sawdust compost rose to 24%. Some of the variation in carbon content was influenced by changes in moisture content. Dry matter carbon content of both compost types stabilized around 27% while compost remixing was still taking place. The C/N ratios in the compost declined to about 10 by d 184 of the trial and were 11 to 12 at the end of the study, at which time undisturbed manure in house 1 had a C/N ratio of 8. After d 184 the C/N ratio was lower than ideal for composting; however, it did not get as low as the C/N ratio of undisturbed, stored manure, indicating that the carbon amendment was retained to some degree until the end of the trial. A considerable proportion of manure N typically is lost from stored, undisturbed manure [11]. In-house composting with the remixing frequency in this study may have accentuated N loss, because high ammonia production (an avenue for N loss) is to be expected from compost with high manure content [12]. This would diminish the value of the compost in regard to the balance of the plant nutrients N, P2O5, and K2O. However, the in-house composting method, itself, with a compost machine capable of driving through the compost windrows, may provide an opportunity to apply amendments to the compost that can suppress ammonia production and produce a product with higher retained N than undisturbed manure.
The percentages of the various components of the 2 compost types were quite similar for the most part, probably because the mass of manure added over time would have greatly exceeded the initial mass of the carbon source, causing the compost content to be determined primarily by the manure, regardless of the carbon source. For instance, estimating a rate of 0.05 lb of DM manure output per hen day [13], 482 lb DM of manure would have been deposited per foot of windrow in 268 d. The DM mass of carbon source laid down at the beginning of the trial was only 29 and 70 lb/linear ft for sawdust and yard waste, respectively. The different carbon sources did, however, affect the physical characteristics of the compost. The shredding process applied to the yard waste tended to produce elongated pieces of woody material. Many of these did not break down completely during the trial, making the yard waste compost more difficult to shovel. This difference in handling quality could affect acceptance of yard waste compost in some markets.
Plant nutrient and CaCO3 content of the composts are presented in Table 5. The P2O5 and K2O contents of the sawdust compost changed little after 125 d, finishing the trial at 4.9 and 3.8%, respectively, on an as-sampled basis. The CaCO3 content was 25% as sampled at the end of the trial. All of these components tended to be lower at 125 d for the yard waste compost than for the sawdust compost, although most of the differences were not statistically significant; their concentrations were equal to those in the sawdust compost on d 268. At the end of the study, the concentrations of P2O5, K2O, and CaCO3 were higher in the undisturbed manure in house 1 than in the sawdust compost, but the difference was statistically significant only for CaCO3 on a DM basis. Residual carbon source in the composts at the end of the study could have diluted these constituents relative to the undisturbed manure.
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Table 5. Plant nutrient and calcium carbonate content (% ± SE) of compost samples during the in-house composting field trial
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During warm weather, when many of the house’s exhaust fans were in operation, interior ammonia levels were low, being less than 10 ppm on the bird level and usually less than 20 ppm in the manure storage area when measured. On September 20 (d 37), for example, ammonia concentrations measured at mid morning averaged 4 and 3 ppm on the bird levels of houses 1 and 2, respectively. During cold weather, when few of the house’s fans were operated, ammonia levels were higher, but not excessively so when measured on a day when compost was not being remixed. On such days, house 2 compared favorably with house 1. For example, on February 14 (d 184), the ammonia concentrations on the bird level at the end of each house near the fans were 55 and 30 ppm in houses 1 and 2, respectively. Figure 4 shows ammonia levels measured in house 2 on January 3, 1 d after the compost had been remixed, when only 6 of the house’s 36 fans were in operation. Ammonia ranged from 25 to 70 ppm in the manure storage area, and from 15 to 25 ppm on the bird level. Excessive ammonia has a negative impact on hens, which show aversion to levels 25 ppm or higher [14]. For this reason, the United Egg Producers (UEP) animal husbandry guidelines stipulate, "Ammonia concentration to which the birds are exposed should ideally be less than 25 ppm and should not exceed 50 ppm, but temporary excesses should not adversely affect bird health" [15]. Except during compost remixing, house 2 was in compliance with the UEP guidelines when ammonia levels were checked, even during winter in a low ventilation situation.
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Figure 4. Ammonia concentrations during winter on the bird level and manure level of the house on a day following compost remixing (January 3, d 142 of the trial, 6 of 36 house fans in operation at the time of observation).
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Once enough manure had been deposited on the windrows to reduce the carbon:nitrogen ratio below 20, a significant amount of ammonia was released when the compost was remixed. The high levels of ammonia generated at the site of remixing made it imperative for the compost machine operator to wear protective eye and breathing equipment. However, during the warmer part of the year, when a substantial proportion the house’s ventilation fans were in use, the ammonia released during compost remixing was quickly removed from the house and was not objectionable except at the compost machine. In cool weather, during a remixing event in December (d 125), ammonia was measured to be 280 ppm in the manure storage area near the fans while remixing was ongoing (Figure 5). Once working of the compost was finished, ammonia declined rapidly and was 55 ppm in the same location after 3 h. The number of fans running ranged from 4 at 1000 h to 14 at 1400 h over which time the ammonia measurements were taken. On the same day, ammonia was also elevated at the bird level, being 120 to 130 ppm during remixing (Figure 5). Ammonia declined gradually on the bird level once remixing ended, except in the house center where the decline was quite rapid. After 3 h, ammonia was 15 to 25 ppm at all locations measured on the bird level. The egg company did not notice any health- or production-related consequences of these spikes of ammonia. Nonetheless, the welfare implications of such high ammonia concentrations, even if experienced only temporarily by hens, would make it desirable to ventilate the house’s bird level during compost remixing to minimize the hens’ exposure to ammonia, or to amend the compost to limit ammonia emission.
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Figure 5. Ammonia concentrations during winter on the bird level and manure level of the house during and immediately after compost remixing (December 17, d 125 of the trial, 4 of 36 house fans in operation at the start of observation, additional fans staged on as the day progressed to a total of 14 at the end of observations).
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CONCLUSIONS AND APPLICATIONS
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- It was possible, with the type of composting machine used in this study, to maintain in-house composting activity for an extended period before exceeding the capacity of the machine; that is, about 300 d in this case. Ability to compost for a long time gives a producer flexibility as to when to clean out a house. This is important because, in some regions, land application of manure-based materials is not permitted at certain times of the year.
- The compost was a nutrient-rich product, and was friable and homogeneous compared with undisturbed manure. The improved handling characteristics should give in-house compost better acceptability over manure in some markets. However, a final stage of composting without addition of manure would be necessary to finish the product into a stable form.
- The carbon source made little difference to the moisture, nutrient, and mineral composition of the compost; however, the physical characteristics of the carbon source did affect the handling quality of the compost because larger pieces of yard waste were not broken down completely during the trial.
- Having a machine capable of accessing the manure storage area of a high-rise house gives potential to deliver manure amendments to improve nitrogen retention in the compost, which would improve its fertilizer value and reduce ammonia emission during the composting process.
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REFERENCES AND NOTES
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- Thompson, S. A., P. M. Ndegwa, W. C. Merka, and A. B. Webster. 2001. Reduction in manure weight and volume using an in-house layer manure composting system under field conditions. J. Appl. Poult. Res. 10:255–261.[Abstract/Free Full Text]
- Pitts, C. W., P. C. Tobin, B. Weidenboerner, P. H. Patterson, and E. S. Lorenz. 1998. In-house composting to reduce larval house fly, Musca domestica L., populations. J. Appl. Poult. Res. 7:180–188.[Abstract/Free Full Text]
- Farmer Automatic, Inc., Register, GA.
- Miner, F. D., Jr., R. T. Koenig, and B. E. Miller. 2001. The influence of bulking material type and volume on in-house composting in high-rise, caged layer facilities. Compost Sci. Util. 9:50–59.
- Matheson Tri-Gas, Montgomeryville, PA.
- Lotus Freelance Graphics for Windows; Version 9.5. 1999. Lotus Development Group, Cambridge, MA.
- SAS Institute. 2002–2003. General Linear Models Procedure of SAS, version 9.1. SAS Institute, Inc., Cary, NC.
- Brown Bear Corp., Corning, IA.
- Webster, A. B., W. C. Merka, and S. A. Thompson. 2000. Manure output from a tunnel-ventilated, high-rise layer house. University of Georgia Poultry Tips, Commercial Eggs, March. http://department.caes.uga.edu/poultry/tips/tipsyear.htm
- Webster, A. B., W. C. Merka, and S. A. Thompson. 2000. Strategies to improve the value of cage layer manure. Pages 175–183 in Proc. VII Seminario Internacional Production y Patologia Aviar, Universidad Austral de Chile, Valdivia.
- Patterson, P. H., and E. S. Lorenz. 1996. Manure nutrient production from commercial White Leghorn hens. J. Appl. Poult. Res. 5:260–268.[Abstract/Free Full Text]
- Elwell, D. L., H. M. Keener, D. S. Carey, and P. P. Schlak. 1998. Composting unamended chicken manure. Compost Sci. Util. 6:22–35.[Medline]
- Bell, D. D. 2002. Waste management. Pages 149–167 in Commercial Chicken Meat And Egg Production. 5th ed. D. D. Bell and W. D. Weaver Jr., ed. Kluwer Academic Publishers, Norwell, MA.
- Kristensen, H. H., L. R. Burgess, T. G. H. Demmers, and C. M. Wathes. 2000. The preferences of laying hens for different concentrations of atmospheric ammonia. Appl. Anim. Behav. Sci. 68:307–318.[Web of Science][Medline]
- UEP. 2004. United Egg Producers Animal Husbandry Guidelines for U.S. Egg Laying Flocks, 2004 edition. United Egg Producers, Alpharetta, GA.
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SUMMARY
DESCRIPTION OF PROBLEM
