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Greenhouse Gas Emissions during Co-Composting of Calf Mortalities with Manure

^a Agriculture and Agri-Food Canada Lethbridge Research Centre, 5403 1st Ave S., Lethbridge, AB, T1J 4B1 Canada
^b Alberta Agriculture and Food, 5401 1st Ave S., Lethbridge, AB, T1J 4V6 Canada
^c College of Resources and Environment, China Agricultural Univ., Beijing, P.R. China 100094

^* Corresponding author (haoxy{at}agr.gc.ca).

Received for publication February 12, 2007.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Summary and Implications REFERENCES

 
Composting may be a viable on-farm option for disposal of cattle carcasses. This study investigated greenhouse gas emissions during co-composting of calf mortalities with manure. Windrows were constructed that contained manure + straw (control compost [CK]) or manure + straw + calf mortalities (CM) using two technologies: a tractor-mounted front-end loader or a shredder bucket. Composting lasted 289 d. The windrows were turned twice (on Days 72 and 190), using the same technology used in their creation. Turning technology had no effect on greenhouse gas emissions or the properties of the final compost. The CO₂ (75.2 g d^–1 m^–2), CH₄ (2.503 g d^–1 m^–2), and N₂O (0.370 g d^–1 m^–2) emissions were higher (p < 0.05) in CM than in CK (25.7, 0.094, and 0.076 g d^–1 m^–2 for CO₂, CH₄, and N₂O, respectively), which reflected differences in materials used to construct the compost windrows and therefore their total C and total N contents. The final CM compost had higher (p < 0.05) total N, total C, and mineral N content (NO₃^– + NO₂^– + NH₄⁺) than did CK compost and therefore has greater agronomic value as a fertilizer.

Abbreviations: CK, control compost (manure + straw) • CM, compost containing manure, straw, and calf mortalities • FL, front-end loader • GHG, greenhouse gas • SB, shredder bucket • TC, total carbon • TN, total nitrogen • WC, water content

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Summary and Implications REFERENCES

 
LIVESTOCK production is one of the anthropogenic activities that increase greenhouse gas (GHG) concentrations in the atmosphere. Livestock manure can be a significant source of N₂O and CH₄ emissions (Chadwick et al., 1999). In Canada, 150,000 Mg CH₄ and 17,000 Mg N₂O are emitted annually from livestock manure, accounting for approximately 2.9% of the national total CH₄ and 12.1% of national total N₂O emissions (Environment Canada, 2004).

Although most livestock manure is applied directly to land, windrow composting of manure before land application is being adopted by a growing number of feedlot producers. The composting of cattle feedlot manure produces a stabilized product that can be stored or spread on land with little or no odor, pathogens, weed seeds, or fly breeding potential (Rynk, 1992; Larney et al., 2006). Manure compost can also be trucked farther economically because volume and mass are significantly reduced during the composting process (Larney et al., 2000). On the other hand, N loss and GHG emissions known to occur during the composting process (Hao et al., 2001, 2004; Peigné and Girardin, 2004) are a concern.

Composting is a biological process in which organic matter is transformed into humus-like material. Emission of GHG is a consequence of this microbial-driven process. The amount and proportion of each GHG emitted during composting and the chemical composition of the final product can be highly variable and are influenced by several factors (Hao et al., 2004), including moisture content, C/N ratio (Shi et al., 1999), aeration method (Lopez-Real and Baptista, 1996; Hao et al., 2001), and the type of amendment used (Mahimairaja et al., 1994; Swinker et al., 1998; Hao et al., 2005).

In Alberta, Canada, the average mortality rate of calves is 2.5%, which is much higher than the 1.0% reported for adult cattle in feedlots (AAFRD, 2002). After the appearance of foot-and-mouth disease in Great Britain in 2001, along with worldwide incidents of bovine spongiform encephalopathy, fewer cattle mortalities are being rendered in Canada. Composting has advantages over other methods of livestock disposal, such as incineration or burial, which have a variety of shortcomings including expense, odor, and the risk of air and water pollution (Morris et al., 1995; Imbeah, 1998).

Co-composting calf mortalities with manure could affect the composting process and rate of GHG emission given that carcasses have much higher contents of C, N, and moisture than does most livestock manure. Indeed, Xu et al. (2007) reported a significant increase in GHG emission when adult cattle mortalities were co-composted with manure. Before livestock mortality composting can be widely adopted, its impact on GHG emissions and the final composition of compost product needs to be assessed. Thus, the objectives of this study were to investigate the rate of GHG emissions and final compost properties resulting from co-composting calf mortalities with manure.

	Materials and Methods

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Summary and Implications REFERENCES

 
Experimental Site
The study was conducted at a commercial feedlot near High River, Alberta (50° 35' N, 113° 52' W, elevation 1219 m) in a semiarid climate. The 289-d experiment was initiated on 13 Dec. 2004 and completed on 28 Sept. 2005. Air temperature and precipitation data (Fig. 1 ) were obtained from a nearby weather station (Environment Canada, 2006).

View larger version (20K): [in this window] [in a new window]   Fig. 1. Mean daily air temperature and precipitation during the composting period (13 Dec. 2004 to 28 Sept. 2005).

Construction of the compost windrows began by placing barley straw on the ground in a 2 x 30 m pile to a depth of approximately 38 cm. For the CM treatment, 23 partially frozen carcasses of calves that had died of natural causes were laid on top of the straw. The carcasses were placed side-by-side in a single layer with spines positioned perpendicular to the long axis of the pile. Carcasses were then completely covered with fresh cattle feedlot manure (a mixture of feces, urine, and straw bedding) cleaned from adjacent feedlot pens. The CK treatment was constructed in an identical manner but did not include calf mortalities. For both windrows, one half of the manure cover was loaded with FL, and the other half was loaded with SB. Each half was demarcated into two sections that were treated as replicates for all solid and gas data collection. The chemical properties of the materials used are presented in Table 1 .

Windrow Management
The two halves of the CK and CM compost windrows were turned using the same technology used in their construction at the beginning of the experiment (FL, SB). This was done after the maximum temperature inside each windrow had dropped to approximately 50 to 55°C and the necessary machinery and personnel were available (Day 72, 23 Feb. 2005). During the first windrow turning, windrows were physically divided, resulting in four compost windrows: two CK windrows (one turned by FL and one turned by SB) and two CM windrows (one turned by FL and one turned by SB). A second turning was performed on Day 190 using the same turning techniques as the first turning (maximum temperatures in each windrow were 50–55°C). The composting process was completed on Day 289 when the temperature in the compost windrows dropped below 40°C. After each turning, known weights of fresh manure were added to the surface of the CM windrows to ensure residual carcass materials were not protruding through the windrow surface and to the surface of the CK windrows to maintain similar composting conditions between CK and CM, other than the presence of calf mortalities. The total amounts of manure reported for the CK and CM treatments include the amount used during initial construction of the windrows plus the additions after each turning. The windrows were turned only twice during this composting study because the focus of the project was to develop economical and effective manure management practices using readily available on-farm equipment and because it was necessary that calf mortalities be largely decomposed before the first turning.

Manure and Straw Properties
At establishment (13 Dec. 2004), four straw and eight manure samples were collected from the materials used to build the compost windrows. Just before the first windrow turning (Day 72) and at the end of the experiment (Day 289), 12 manure samples (six depths, two locations) were collected from each replicate. Approximately 20 g of compost material was sampled from the windrow peak and from sites 15, 45, 75, 105, and 130 cm below the peak. Samples were divided into two 10-g portions. The first was used to determine water content (WC), and the second was placed into 100-mL bottles containing 2 M KCl (50 mL) for determination of mineral N (NO₂^–, NO₃^–, and NH₄⁺) content. The WC was determined gravimetrically by drying in an oven at 60°C for 4 to 6 d. The bottles (with KCl solution and compost material) were shaken for 1 h and filtered through KCl-washed filter paper (Whatman No. 42). The mineral N concentrations (NO₂^–, NO₃^–, and NH₄⁺) in the extracts were determined using a Bran+Luebbe AutoAnalyzer III (Bran + Luebbe GmbH, Norderstedt, Germany).

For chemical analysis, a separate set of larger (1 kg) samples was taken from each replicate windrow at the same locations and times as described previously. These samples were placed in plastic bags, brought to the laboratory, oven-dried at 60°C, and coarsely ground (<2 mm). Subsamples were ground further (0.150 mm) for TC and TN determinations in an automated CNS analyzer (Carlo Erba, Milan, Italy). The initial straw samples were analyzed following the same methods used for manure. All results are expressed on a dry weight basis unless otherwise indicated. The C and N contents of cattle carcasses were estimated using values from Berg and Butterfield (1976).

Windrow Temperatures
Temperatures inside the compost windrows were determined weekly during the first 4 wk and every 2 to 4 wk for the remainder of the experimental period. The temperatures at 15, 45, 75, 105, and 130 cm below the window peak were determined using a multi-depth temperature and gas depth sampler (Hao et al., 2001) and a HH-25TC thermocouple Cu-CuNi thermometer (OMEGA Engineering Inc., Laval, Quebec, Canada). All temperature results are based on data collected from four replications except for some values from Days 72 to 147 that were not recorded due to a malfunction of the depth samplers. These results are based on two or three replications.

Gas Collection and Analysis
Greenhouse gas surface fluxes during composting were measured on the same schedule as windrow temperatures using a vented chamber technique (Hutchinson and Mosier, 1981) modified by Hao et al. (2001). Gas samples (11 mL) were collected from the chamber at 0, 5, 10, 20, and 30 min after the chamber was placed on the windrow surface. Each gas sample was extracted with a plastic syringe and injected into a 5.9-mL, pre-evacuated, septum-stoppered vial (Exetainer; Labco Limited, Buckinghamshire, UK). The samples were analyzed for O₂, CO₂, CH₄, and N₂O concentrations using a gas chromatograph (Varian 3800; Varian Instruments, Walnut Creek, CA) equipped with an electron capture detector, a flame ionization detector, and a thermal conductivity detector as well as a micro-GC (Varian 4900) equipped with thermal conductivity and electron capture detectors. The concentration versus time relationships for each chamber were fitted with a second-order polynomial equation for each sampling time (SAS Institute, 1999), and the flux at time 0 was calculated by taking derivatives of the second-order polynomials (Hao et al., 2001). Cumulative emissions were approximated by assuming that daily fluxes represent the average for each period. The total GHG emissions over the composting period were expressed per initial unit surface area (kg C m^–2 and kg N m^–2 of manure) and initial unit dry weight (kg C Mg^–1 and kg N Mg^–1 manure).

Statistical Analysis
Data were analyzed for ANOVA separately before and after the first turning (as a 2 x 2 factorial design with two replications) using Proc MIXED in SAS (SAS Institute, 1999). When there was no treatment effect, means were pooled for comparisons using the Tukey test (p < 0.05). For NH₄⁺–N and NO₃^––N, statistical analysis was performed on log-transformed data because the original data were not normally distributed.

	Results and Discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Summary and Implications REFERENCES

 
The compost windrow construction and turning technologies (FL or SB) tested in this study had no significant effect on any parameter investigated, nor were there any interactions between windrow management technology and mortality treatment. Consequently, only the effect of inclusion of mortalities in the windrow is discussed in detail.

Manure/Compost Properties
For samples taken immediately before the first turning (Day 72), no significant differences in WC; concentrations of TC, TN, NH₄⁺, and NO₂^–; or C/N ratio were observed between CK and CM (Table 2 ). Although calf decomposition released more NH₄⁺, the NH₄⁺ content in CM was not significantly higher than in CK (Table 2). The NO₂^––N contents of 2200 (CK) and 2979 mg kg^–1 (CM) were higher than values previously reported from cattle manure windrow composting in this region (Hao et al., 2001, 2004) but were similar to those reported for cattle mortality composting (Xu et al., 2007). Given that the compost windrow had undergone 72 d of composting with no turning, anaerobic microsites had probably developed inside. This may have slowed the oxidation of NO₂^– to NO₃^–, resulting in the accumulation of NO₂^–. The NO₃^––N content in the CM compost was higher (p < 0.05) than in CK, reflecting greater TN decomposition and conversion of NH₄⁺ to NO₃^–.

View this table: [in this window] [in a new window]   Table 2. Changes in properties of composted material.

Because TN content was determined by combustion, using dried samples, C/N ratios reported for CK and CM may be higher than the actual values in the respective windrows, especially before first turning, when the NH₄⁺ contents were high. At pH 7 to 8, 1 to 10% of total NH₄⁺ in manure is present as NH₃ gas (data not shown). Thus, some of the NH₄⁺ could have been lost during the drying process, which would lead to slightly higher C/N ratios calculated for the compost.

Compost Windrow Temperatures
Although mean daily ambient air temperature was below zero for most of first 40 d of the experiment (Fig. 1), temperatures as high as 67°C were achieved inside the CK windrow (Day 10) and 64°C in the CM windrow (Day 37). The slower rate of temperature increase in CM likely reflects the fact that the carcasses incorporated into the windrow were partially frozen. After reaching peak temperature, the windrow temperature slowly decreased and dropped to 8.4°C in CK but remained as high as 57°C at the bottom of the CM windrow until the first turning on Day 72 (Fig. 2a ). Similar high temperatures have been reported in other cattle mortality composting studies (Looper, 2002; Fonstad et al., 2003; Murphy et al., 2004; VanDevender and Pennington, 2004; Xu et al., 2007). Temperatures exceeding 55°C during composting are sufficient to kill most pathogens studied by Larney et al. (2003), Van Herk et al. (2004), and VanDevender and Pennington (2004).

View larger version (66K): [in this window] [in a new window]   Fig. 2. Compost windrow temperatures recorded by indwelling multi-depth probes during 289 d of composting of (a) barley straw and manure (control compost, CK) or (b) barley straw, manure, and calf mortalities (mortality compost, CM). Arrows indicate windrow turning dates.

Surface Fluxes of CO₂, CH₄, and N₂O
For the CK treatment, most CO₂ emissions occurred during the first 50 d, whereas very low CH₄ and N₂O emissions were observed throughout the rest of the composting period. Greater (p < 0.05) CO₂, CH₄, and N₂O surface fluxes occurred in CM than CK during the first 72 d of composting, but little difference between treatments was observed after the first turning event (Fig. 3 ). Similar to CK, there was minimal CO₂, CH₄, and N₂O emission from CM after the first turning. The greater CO₂, CH₄, and N₂O emission rates from CM than from CK are consistent with the higher TC and TN contents in the CM treatment as a result of the presence of calf mortalities. The high rate of CO₂ emissions during the first 70 d of composting indicates that most of the decomposition of calf mortalities occurred during this period.

View larger version (10K): [in this window] [in a new window]   Fig. 3. Flux of greenhouse gases CO2, CH4, and N2O at the surface of compost windrows constructed from barley straw and manure (control compost, CK) or from barley straw, manure, and calf mortalities (mortality compost, CM) during 289 d of composting. Bars indicate SEs, and arrows indicate windrow turning dates.

Including carcasses in the composting windrow increased (p < 0.05) cumulative CO₂, CH₄, and N₂O emissions compared with composting manure alone (Table 3 ). At Day 289, emission rates of CO₂, CH₄, and N₂O (per unit windrow surface area) were 3, 26, and 5 times higher, respectively, from CM than from CK. Emission rates of CO₂ (75.2 g d^–1 m^–2) and CH₄ (2.540 g d^–1 m^–2) from CM from this study were higher than were reported for the composting of adult cattle mortalities (53.6 g d^–1 m^–2 for CO₂ and 2.204 g d^–1 m^–2 for CH₄) (Xu et al., 2007). The reason(s) for the higher emission rates with calf than with adult mortalities are not clear but may reflect a shorter experimental period (289 d in this study vs. 310 d in Xu et al. [2007]) and differences in the compost windrow mortality-to-manure ratio of 1 to 18 in this study vs. 1 to 9 in Xu et al. (2007). Possible differences in readily degradable C in manure (which was not measured) between the two experiments could also contribute to this disparity. It is very difficult to obtain manure with identical properties across different experiments.

	Summary and Implications

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Summary and Implications REFERENCES

 
The emissions of CO₂, CH₄, and N₂O increased (p < 0.05) when calf mortalities were added to manure during windrow composting. Typically, cattle feedlots in the study area have an average calf mortality rate of 2.5% (AAFRD, 2002), and each feedlot steer produces approximately 2.5 Mg fresh or 1 Mg dry manure (moisture content at 60%) per year. Based on results by Xu et al. (2007) on compost manure calf mortality, the actual increases in GHG emission that would arise from including even 100% of calf mortalities in manure compost would be small. Composting may represent an economical alternative to rendering while avoiding the hazards and odors associated with using natural exposure as a means of disposal. The resulting product could potentially be used as a fertilizer and would have a higher available N content than compost produced from manure alone.

	ACKNOWLEDGMENTS

 
This project was funded by the Agriculture and Agri-Food Canada's Environmental Technology Assessment for Agriculture (ETAA) Program. Technical assistance was provided by G. Travis, B. Hill, P. Caffyn, A. Olson, G. Wallins, and H. Zahiroddini. The authors also acknowledge P. Morrison of Roseburn Ranches, High River, AB for granting access to the research site, supplying all materials, and constructing and maintaining compost windrows. The AAFC Lethbridge Research Centre Contribution No. is 387-07017.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and Methods Results and Discussion Summary and Implications REFERENCES

 
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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Xu, S. Articles by Wang, J. Search for Related Content PubMed PubMed Citation Articles by Xu, S. Articles by Wang, J. Agricola Articles by Xu, S. Articles by Wang, J. Related Collections Nutrient Management Animal Waste Other Waste Management