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