Reducing Greenhouse and Ammonia Emissions from Manure Systems


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Purpose             

Dairy manure systems produce greenhouse gas and ammonia emissions that contribute to climate change. There are many potential practices and management strategies that can reduce these emissions which can conserve nutrients and reduce environmental impacts. This work assesses different processing strategies, additives, and manure storage covers to reduce emissions from dairy manure systems.

What did we do? 

We completed three laboratory/field trials to assess emissions from manure systems. The first trial was to assess the greenhouse gas and ammonia emissions during storage and land application of manure that was processed with solid separation and digestion in combination with solid separation. A second trial assessed emissions and manure characteristics from storage with various commercial additives. The third study assessed ammonia emissions from digested manure storages with various biomass covers including raw wood, steam treated wood, and biochar produced from wood and corn cobs.

What have we learned? 

The results from the study indicate that separation and digestion result in significant reductions in greenhouse gas emissions. However, as expected, ammonia emissions following digestion are increased due to increased nitrogen mineralization. Results also indicate that separation alone had a similar impact to greenhouse gas emissions, but did not further reduce emissions following digestion. Commercially available products that are designed to be added to manure storages had little to no impact on emissions or manure characteristics for the conditions present in this study. Lastly, biochar was capable of reducing ammonia emissions significantly when applied as a cover. Although the biochar was capable of sorbing ammonical nitrogen, the results indicate that the physical barrier on the manure surface was the primary driver for the reduction in ammonia emissions.

Future Plans    

Following the outcomes of this work, information is being added to a dairy manure life cycle assessment to determine larger system wide impacts from changes in management practices or the inclusion of a processing system. In addition, work is being conducted to look at potential benefits that may be gained over a number of impact factors when manure management systems are optimized with other waste management systems from the municipal sector.

Corresponding author, title, and affiliation        

Rebecca Larson, Assistant Professor, University of Wisconsin-Madison

Corresponding author email    

rebecca.larson@wisc.edu

Other authors   

M.A. Holly, Agricutural Engineer at USDA ARS, J.M. Powell, Soil Scientist at USDA ARS, H. Aguirre-Villegas, Assistant Scientist at University of Wisconsin-Madison

Additional information 

Holly, M.A., R.A. Larson, M. Powell, M. Ruark, and H. Aguirre-Villegas. 2017. Evaluating greenhouse gas and ammonia emissions from digested and separated manure through storage and land application. Agriculture, Ecosystems & Environment, 239:410-419. http://www.sciencedirect.com/science/article/pii/S0959652616321953

Holly, M.A. and R.A. Larson. 2017. Effects of Manure Storage Additives on Manure Composition and Greenhouse Gas and Ammonia Emissions. Transactions of the ASABE, Accepted in Print.

Holly, M.A. and R.A. Larson. 2017. Evaluation of Biochar, Activated Biochar, and Steam Treated Wood as Dairy Manure Storage Covers for Ammonia Mitigation. In Review.

Acknowledgements       

This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2013-68002-20525. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

Nitrous Oxide Emissions in Snow-covered Agricultural Soils – manure-induced fluxes


Why Study Nitrous Oxide Emissions and Manure Application?*

It is now accepted that soil nitrous oxide (N2O) emissions occur under freezing conditions (Sommerfeld et al., 1993; Pelster et al., 2012), and that overwinter N2O emissions may represent a substantial portion of the total annual emissions from agricultural soils in northern countries (Maljanen et al., 2007; Wagner-Riddle et al., 2007; Virkajärvi et al., 2010). However, the temporal dynamics during winter are poorly documented, and the question whether manure application in the fall may increase winter N2O emissions is under debate. In addition, the possible influence of soil texture in regulating N2O emissions during winter has been overlooked. Our objective was to compare N2O emissions above the snow cover on sandy and clayey soils with and without pig slurry applied in the fall.

What did we do?

The study was carried out for three consecutive winter periods (2010-2013) on a sandy loam and a silty clay soil. Soil N2O concentration and emission were monitored weekly from November to May using soil probes and static chambers, respectively. The static chambers were made of 20-cm diameter white PVC pipe. The chamber base (15 cm height) was permanently inserted to 10 cm depth. Pig slurry was applied within half of the chamber bases (5 per soil type), whereas the other half remained unamended (Control treatment). The manure was immediately incorporated into the top 5 cm of soil using hand tools; soil in control chambers was similarly disturbed. Additional sections of PVC pipe (10 cm height) were secured on the top of each chamber base as the snowpack developed, and were removed stepwise in the spring during snowmelt. The chamber base was therefore emerging above the snow cover at time of chamber deployment. On each sampling date, the accumul ation of N2O within the chamber headspace was monitored at 6-min intervals during 18-min deployments. Soil air was also collected weekly through soil probes installed at 7.5 cm depth. Air samples were withdrawn with a syringe and transferred to pre-evacuated vials. Gas samples in vials were analyzed for N2O within 48 h using a gas chromatograph.

Title: Nitrous Oxide Emissions in Snow-covered Agricultural Soils – manure-induced fluxes

Authors and affiliations:

Martin H. Chantigny, Philippe Rochette & Denis A. Angers, Agriculture and Agri-Food Canada, Québec;

Claudia Goyer, Agriculture and Agri-Food Canada, Fredericton, Canada

Table 1. Range of cumulative N2O-N emission, magnitude of emissions, and emission factors measured for three consecutive winter periods.

 

Sandy loam

 

Silty clay

Cumulative emission

(kg N2O-N/ha)

 

0.1 to 2.0

 

 

0.6 to 1.6

Magnitude of emissions

(% of total annual emission)

32 to 67

 

10 to 27

Emission factor

(% N applied)

0.3 to 3.0

 

0.9 to 2.4

What have we learned?

Nitrous oxide was produced in soils and emitted in all years, with a low in late fall (Nov.-Dec.) and significant increases when snow depth exceeded 20 cm (late Dec. – early Jan.) and during spring thaw (late March – early April). Ice formation on and within the soil occurred during freeze-thaw events. This phenomenon generally blocked the emission of N2O but did not prevent its production in the soil. Therefore ice formation resulted in a marked decline in N2O emissions with concurrent increase in soil N2O concentration. The temporal dynamics of N2O emissions was variable among years, and the significance of manure-induced N2O emissions was mainly explained by early winter frost penetration, which was dependent on snow accumulation in late fall. As opposed to N2O emissions measured during the growing season, sandy soils tended to emit as much N2O as clayey soils during the non-growing season. Consequently, the cumulative N2O-N emi ssions in the non-growing season (November-April) accounted for 10 to 25% of total annual emissions in clayey soils, and from 20 to 70% in sandy soils (Table 1). Soils amended with pig slurry in the fall emitted more N2O than soils without, with emissions factors up to 3%, higher than the default IPCC coefficient (1%).

References

Maljanen M., Kohonen, A.R., Virkajärvi P., Martikainen P.J. 2007. Fluxes and production of N2O, CO2 and CH4 in boreal agricultural soil during winter as affected by snow cover. Tellus, Series B: Chem. Phys. Meteor. 59, 853-859.

Pelster, D.E., Chantigny, M.H., Rochette, P., Angers, D.A., Laganière, J., Zebarth, B., Goyer, C. 2012. Crop residue incorporation alters soil nitrous oxide emissions during freeze-thaw cycles. Can. J. Soil Sci. 93:415-425.

Sommerfeld, R.A., Mosier, A.R., Musselman, R.C. 1993. CO2, CH4, and N2O flux through a Wyoming snowpack and implications for global budgets. Nature 361:140-142.

Virkajärvi P., Maljanen M., Saarijarvi K., Haapala J., Martikainen P.J. 2010. N2O emissions from boreal grass and grass-clover pasture soils. Agric. Ecosyst. Environ. 137, 59-67.

Wagner-Riddle, C., Furon, A., McLaughlin, N. L., Lee, I., Barbeau, J., Jayasundara, S., Parkin, G., von Bertoldi, B., Warland, J. 2007. Intensive measurement of nitrous oxide emissions from a corn-soybean-wheat rotation under two contrasting management systems over 5 years. Global Change Biol. 13:1722-1736.

Future Plans

Now that we evidenced the significance of N2O emissions from soils during the winter period, we are initiating field work to determine best practices for fall application of manure (e.g. early vs. late fall application; use of additives to delay nitrification of manure ammonia) that will mitigate losses and help efficiently transferring applied N to crop in the next spring.

Authors

Martin H. Chantigny, Soil Scientist, Agriculture and Agri-Food Canada, Quebec martin.chantigny@agr.gc.ca

Philippe Rochette, Denis A. Angers, Agriculture and Agri-Food Canada, Québec;

Additional information

Scientific papers and reports can be accessed through my webpage:  www.agr.gc.ca/fra/science-et-innovation/centres-de-recherche/quebec/centre-de-recherche-et-de-developpement-sur-les-sols-et-les-grandes-cultures/personnel-et-expertise-scientifiques/chantigny-martin-phd/?id=1181933396583

Acknowledgements

This project was financially supported by the Sustainable AGriculture Environmental Systems (SAGES) Initiative of Agriculture and Agri-Food Canada

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

Life Cycle Greenhouse Gas Emissions of Dairy and Bioenergy Systems

 

Why Study Greenhouse Gas Emissions from Dairy Systems?

Animal agriculture presents multiple challenges for sustainability and the dairy sector alone contributes 30% of agricultural greenhouse gas (GHG) emissions. Bioenergy systems have been implemented to reduce GHG emissions and contribute to energy independence goals, but the production of bioenergy must be done with caution to avoid the generation of additional emissions during feedstock production and harvesting. This research used life cycle assessment (LCA) techniques to evaluate the integration of dairy and bio-energy systems to address global warming. The first place for integration is the dairy feed preparation level, where potential co-products of the biofuel industry (e.g. dry distillers grains with solubles and soybean meal) can be included in the dairy ration. A lifecycle approach should be considered to evaluate changes in GHG emissions related to the production of these added dairy feeds. This is important because the embedded emissions and energy resources related to upstream processes (e.g. manufacturing of seeds, fertilizers, pesticides, and fuels) and downstream processes (e.g. transportation and harvesting) can result in added greenhouse gases. The second point where dairy and bioenergy systems can be integrated happens at the waste management level, where manure is digested in an anaerobic digestion (AD) system to produce renewable energy. Different cow feeding scenarios, management practices, and anaerobic digestion pathways are modeled to identify practices that minimize GHG emissions at the dairy farm.

Figure 1. Cradle-to-farm gate boundaries

Figure 1. Cradle-to-farm gate boundaries

What did we do?

The effect of integrating bioenergy and dairy systems on GHG emissions was evaluated. First, a reference milk-producing system representative of Wisconsin (WI) was modeled using a partial LCA approach from cradle-to-farm gate. To integrate bioenergy products to the modeled farm, the boundaries of the system were defined and included corn and soybean production for ethanol and biodiesel, respectively. This was necessary in the analysis since co-products dry distillers grains with solubles (DDGS) and soybean meal (SBM) are part of the dairy diet in numerous farms of WI. In addition, the production of biogas through anaerobic digestion (AD) from the collected manure was evaluated as a second opportunity to integrate bioenergy systems with dairy systems. Given that this integrated system is multi-functional (producing milk, meat, ethanol, biodiesel and biogas); the GHG emissions were assigned to milk by system expansion, a method recommended by the International Organization for Standardization (ISO) to assign the environmental impacts of multi-functional systems among co-products. This method can be applied when a co-product clearly replaces the production of an external product (in our paper ethanol replaces gasoline and biodiesel replaces fossil diesel). Results indicate that GHG emissions for the reference system are 1.02 kg CO2-eq per kg of milk (corrected for fat and protein (FPCM). When analyzing the integration of ethanol and biodiesel (and after applying system expansion) GHG emissions are reduced to 0.86 kg CO2-eq per kg of FPCM in a diet that maximizes DDGS. The installation of a digester further reduced GHG emissions to 0.63 kg CO2-eq/kg FPCM, highlighting the importance of this system to achieve both energy and climate change goals.

Given the important role that AD systems have to reduce greenhouse gases, we explored different AD scenarios based on manure management practices, co-digestion strategies, and energy conversion processes in order to achieve further emission reductions. AD is the main focus of this part of the study; therefore, a new functional unit was defined as 1 GJ of produced electricity. A base-case pathway was compared against seven alternative AD pathways. In the base-case, manure is collected with a skid steer, digested in a plug-flow digester, biogas is used for electricity production without heat recovery, and digestate is separated in a screw press and land-applied by surface broadcast. The alternative AD pathways are defined in Table 1.

Table 1. Summary of the eight AD pathways analyzed

Table 1

For the base-case, GHG emissions are 243.3 kg CO2-eq/GJ of produced energy. Results show that the AD pathway has a substantial influence on the estimates of environmental impacts and GHG emissions range from 178 to 267 kg CO2-eq/G J of produced energy (Figure 2).

Figure 2. Contribution to greenhouse gas (GHG) emissions from each unit-process and AD pathway

Figure 2.

What have we learned?

The dairy industry will continue to dominate agricultural activities in WI for the foreseeable future and the emerging bioenergy industry will need to be integrated into existing agricultural systems. System models like this one have potential to help farmers and policy makers identify synergies between dairy production and renewable energy development. GHG emissions of a reference dairy system representative of WI are compared to a system that integrates dairy and bioenergy production. Diet scenarios that maximize DDGS content are the most effective in reducing GHG emissions. Reductions in GHG emissions come mainly from the credits of avoided emissions and primary energy from displaced fossil fuels after system expansion. GHG emissions are further reduced when implementing AD to process the manure generated in the farm.

The second part of the study focused on improving the sustainability of AD systems by evaluating different manure management practices, co-digestion strategies, and energy conversion processes. GHG emissions can be reduced 31% by management practices alone, 24% if heat from the electricity generation process is recovered, and 4% by co-digesting manure with corn stover. Replacing sand with digested solids for cow bedding contributes to reduce GHG emissions as it avoids the manufacturing of this resource. Co-digesting corn stover with manure is an effective strategy to reduce GHG emissions as this feedstock requires only harvesting as opposed to switchgrass that needs to be added to the already existing crop mix requiring additional planting as well as harvesting. Finally, results show the major improvement in GHG emissions when heating the digester with recovered heat from the generator, highlighting the potential of this pathway to reduce environmental impacts without adding major technical or economic challenges to the farmer.

Future Plans

There is potential to expand the current analysis by using the survey data collected as part of this study. For example, it would be interesting to compare management practices coming from small and large dairy farm operations.

We still need to develop our knowledge on the sustainability impacts of co-digesting manure with other waste streams, such as cheese whey and whey permeate. These pathways can provide useful information to dairy processing plants about alternative uses of whey as an energy source with and without protein separation, which could be a decisive factor when making investment decisions.

It will be important to quantify other environmental services of AD systems, such as water quality preservation and odor reduction.

Authors

Aguirre-Villegas Horacio Andres. Postdoctoral Research Associate. Department of Biological Systems Engineering, University of Wisconsin-Madison aguirreville@wisc.edu

Larson Rebecca. Assistant Professor. Department of Biological Systems Engineering, University of Wisconsin-Madison. Reinemann Douglas J. Chair and Professor. Department of Biological Systems Engineering, University of Wisconsin-Madison

Primary author: Horacio Aguirre-Villegas, aguirreville@wisc.edu, 217-898-0345

Acknowledgements      

This study is part of the Green Cheese Project, funded by Wisconsin Focus on Energy, Environmental and Economic Research and Development Program and the National Institute of Food and Agriculture, United States Department of Agriculture, under ID number WIS01604

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

Measuring Greenhouse Gas and Nitrogen Gaseous Losses When Comparing Bulking Agents Used to Compost Separated Hog Solids

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Why Study Composting Separated Manure Solids?

This research is evaluating management options for conventional hog producing facilities in regions of Manitoba that will have insufficient land base for sustainably applying raw slurry manure when manure application regulations switch from nitrogen based to phosphorus based rates. Producers are being encouraged to use solid-liquid separation, such as centrifugation, to remove the phosphorus rich solid fraction so that it can be transported and applied further away where there is a phosphorus deficiency. However, the resulting separated hog solids (SHS) product is still odorous and prone to nitrogen losses through ammonia volatilization. Therefore, it has been suggested that composting the SHS before it is applied is a beneficial management practice that would allow producers to capitalize on agricultural and environmental benefits such as reduced odours, stabilization of minerals, application of a homogeneous product, and acts as a multi-beneficial soil conditioner. However, the low starting C:N of 15:1 and small particle size of SHS make it a unique and challenging product to compost in windrows, a common form of large production on-farm composting. The SHS must be combined with a bulking agent that allows adequate nutrient balance for decomposition as well as a porous structure. Therefore, this project is comparing wood shavings (WS) and wheat straw (WHT) as bulking agents to evaluate which is the better management practice based upon minimizing greenhouse gas emissions and additional nitrogen gas losses as well as overall quality of the mature compost. 

LI-8100a automated flux chamber

What Did We Do?

Starting in October 17, 2012 we created two windrows containing SHS, one with wood shavings as a bulking agent and one with wheat straw. The materials were mixed in a feed mixer to produce a homogeneous mixture with the initial starting parameters shown in Table 1. The windrows were turned once a week for the first four weeks with a Backus windrow turner.

Gas emissions were measured with the use of the highly innovative technology of the LI-8100a automated chamber system (LICOR BioSciences) and Fourier Transform Infrared spectroscopy (FTIR) multi-gas analyzer (Gasmet DX4015). By combining these two instruments it has the advantage of nearly continuous unattended data collection and simultaneous measurement of greenhouse gases (carbon dioxide, methane, nitrous oxide) and additional nitrogen gases (ammonia, nitrous dioxide, and nitrogen monoxide). There were four automated chambers on each windrow; a flux measurement was taken every half hour, alternating between the two windrows. Flux emissions were calculated using linear regression analysis.

Table 1. Initial starting parameters for the two windrows

Initial In-process Compost

Starting C:N

Starting Moisture %

Starting Bulk Density (kg/m3)

Starting pH

WHT + SHS

32.5

63.70

170.5

6.86

WS + SHS

35.5

60.45

350

6.5

The temperature, % oxygen, and moisture content of the windrows were recorded to identify when the compost needed to be turned and to track the composting process and relate it to the gases emitted.

Backhus compost windrow turner

What Have We Learned?

In September 2011 we conducted a trial that used straw as a bulking agent but found the contact between the separated hog solids and straw was poor due to the difference in particle size allowing for large pore spaces and the waxy texture of straw. The porous structure made it difficult to maintain moisture in the compost windrow and when water was added some of the separated hog solids actually “washed off”.  In the winter, the windrow wasn’t big enough or it was too porous that it did not insulate well so self heating stopped and the pile froze in January. These problems slowed the decomposition process and resulted in compost with straw pieces still visible.

For this trial we decided to try using wood shavings as an alternative bulking agent, because wood shavings have a smaller particle size which we predicted would result in better contact with the separated hog solids and a less porous structure allowing better insulation against the weather (water loss in the summer, heat loss in the winter). Additionally, it is expected that wood shavings are also beneficial in reducing ammonia losses.

However, during this trial we experienced much wetter and cooler conditions compared to the year before, so we did not have to add water to the windrows. This was beneficial for the windrow with straw because the moisture content did not decline resulting in a steady rate of decomposition during the first month of composting noted by continuous CO2 emissions. Eventually the moisture content became too high creating anaerobic conditions and the production of CH4 after the second and fourth turnings. NO2 emissions were also detected during the same time as CH4, indicating some aerobic respiration occurring. After CO2 emissions reduced there was a small amount of N2O and NO measured.

The windrow with wood shavings took a little longer to start producing CO2 because it became anaerobic from the start. CH4 was produced much early and at higher emission rates compared to the windrow with the straw as a bulking agent. N2O, NO, and NO2 were emitted at the same time as CH4, indicating there were anaerobic and aerobic pockets throughout the windrow. N2O emissions continued after CO2 emissions declined.

Composting in the winter

After the windrows had been in the active stage of composting for three months, the temperature within the windrows gradually declined and both windrows froze up in early January.

We are currently in the process of calculating the ammonia flux determinations. Due to the nature of ammonia it is prone to absorbtion reactions on the surface of the LI-8100a and FTIR systems’ tubing. The surface reactions cause a time delay for the FTIR to analyze the concentration compared to the other gases. Thus, this gas requires a different time interval to calculate the flux.

Future Plans

A common problem with using chamber measurements on compost windrows is underestimation of gas emissions from chambers placed on the top of the windrow when high winds blow through the windrow horizontally, reducing the “chimney effect”. Having the ability to collect gas emission data at such a high frequency using the LI-8100a automated chamber and FTIR system allows us to identify when gases emissions may be underestimated due to wind. The next step is to determine if we can correlate the wind speed and direction with under estimation of gas losses.  

Authors

Jolene Rutter, MSc. Candidate, University of Manitoba, Jolene_rutter@hotmail.com

Mario Tenuta, Canada Research Chair in Applied Soil Ecology, University of Manitoba

Matt Gervais, Soil Ecology Field Technician, University of Manitoba

Acknowledgements

Western Economic Diversification Canada, Manitoba Pork Council, Manitoba Horticultural Productivity Enhancement Centre, Manitoba Rural Adaptation Council, NSERC, National Center for Livestock and the Environment, University of Manitoba Soil Ecology Laboratory, Glenlea Research Farm, Prairie Agricultural Machinery Institute, Compo-stages, Puratone

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

Greenhouse Gas Emissions from a Typical Cow-Calf Operation in Florida, USA

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Purpose

The purpose of this study was to investigate greenhouse gas (GHG) emission sources in a typical cow-calf operation in Florida and to calculate its total carbon footprint. The most important greenhouse gas source found was enteric fermentation, hence further investigation of this factor is being developed with field trials.

Why Study the Carbon Footprint of Cow-Calf Systems?

We estimated the carbon footprint of the cow-calf operation held in Buck Island Ranch, with data from 1998 to 2008. This production system has around 3000 cows and 250 bulls, has low fertilizer and lime inputs and feeding is pasture and hay based with some use of molasses and urea. Natural mating is used and calves are kept in the farm until 7 months old.  The Intergovernmental Panel on Climate Change (IPCC, 2006) methodology was used along with emission factors from USDA (EPA, 2009) to estimate emissions at different levels of complexity (Tier 1 being the least complex and Tier 3 the most), according to data availability, and transformed in carbon dioxide equivalent (CO2eq). A field trial to measure ruminal methane emissions was held at the North Florida Research and Education Center in Marianna, Florida, from June 26th to September 18th. The experiment treatments consisted of three stocking rates (1.2, 2.4 and 3.6 AU/ha, where one animal unit is 360) with four replicates each. The ruminal methane emissions were measured three times using the sulfur hexafluoride (SF6) tracer technique (Johnson et al., 1994). Experimental weight gain and average initial weight of each experimental unit were used to estimate emissions with the IPCC’s Tier 3 methodology.

Table 1. Sources of greenhouse gases in units of carbon dioxide equivalent (CO2eq). Data retrieved from Buck Island Ranch from 1998 to 2008.

Figure 2. Animal with SF6 sample collection apparatus. Marianna, Florida, August 2012.

What Have We Learned?

Results of the carbon footprint calculation are shown in Table 1. We can observe that enteric fermentation is responsible for almost 60% of total emissions in this production system, varying with feed quality, age of animal (since calves under 7 months age are not considered to produce any methane), and number of animals in the farm. It was also found that this model is most sensitive to variations in weight gain. The second most important source of GHG is manure with more than 23 of emissions. The yearly variation in emissions is a result of the use of nitrogen fertilization and lime or burning of the pasture. On average 477,936 kg of live weight are produced every year in the ranch, resulting in an average of 24.6 kg CO2eq/kg live weight that leaves the farm. Results from the field trials were compared with default values from IPCC’s Tier 1 methodology and USDA, and to IPCC’s Tier 3. We can see that on Period 2 the weight gain on the 2.4 AU/ha treatment was greater than on the 3.6 AU/ha (Figure 1). Since the model used is highly sensitive to weight gain, the prediction resulted in higher methane emissions from the 2.4 AU/ha treatment. The field measurements (Figure 2), however, showed more emissions in the 3.6 AU/ha treatment showing that other factors besides weight gain might play an important role on enteric fermentation methane emissions.

Future Plans

Our future plans include the use of field data to perform a prediction analysis with the model under study. Also, we plan to do in vitro gas production technique (IVGPT) to simulate ruminal fermentation and have a better understanding of emissions.

Authors

Marta Moura Kohmann, M.S. student, Agricultural and Biological Engineering Department, University of Florida. mkohmann@ufl.edu

Clyde W. Fraisse, PhD., Associate Professor, Agricultural and Biological Engineering Department, University of Florida.

Hilary Swain, PhD., Executive Director, Archbold Biological Station.

Martin Ruiz-Moreno, PhD, Post-doctoral, Animal Science Department, University of Florida

Lynn E. Sollenberger, PhD., Professor and Associate Chair, Agronomy Department, University of Florida

Nicolas DiLorenzo, PhD., Animal Science Department, University of Florida

Francine Messias Ciríaco, M.S. student, Animals Science Department, University of Florida

Darren D. Henry, M.S. student, Animals Science Department, University of Florida

Additional Information

The Carbon Footprint for Florida Beef Cattle Production Systems: A Case Study with Buck Island Ranch. Available in

<http://www.archbold-station.org/statiohttps://www.archbold-station.org/documents/agro/Kohmann,etal.-2011-FlaCattleman-carbonfootprint.pdfn/documents/publicationspdf/Kohmann,etal.-2011-FlaCattleman-carbonfootprint.pdf>

Acknowledgements

The author would like to thank Faculty and Staff at the North Florida Research and Education Center for the assistance during the field trial.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.