|Rotz, Clarence - Al|
Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/2/2009
Publication Date: 3/1/2010
Citation: Rotz, C.A., Montes, F., Chianese, D.S. 2010. The carbon footprint of dairy production systems through partial life cycle assessment. Journal of Dairy Science. 93(3):1266-1282. Interpretive Summary: Atmospheric concentrations of greenhouse gases have steadily increased throughout the twentieth century, and this is thought to be contributing to an increase in the surface temperature of the earth and related changes in global climate. Although there is still much uncertainty in specific numbers, agriculture appears to have a significant role in this international issue. Agriculture is reported as the largest emitter of nitrous oxide and second largest emitter of methane in the U.S. Within agriculture, livestock production is the major contributor. Animals, particularly ruminants such as dairy animals, release greenhouse gases during the digestion of feed with further emissions during the handling of their manure. Greenhouse gases emitted from dairy farms include carbon dioxide, methane and nitrous oxide, with various sources and sinks throughout the farm. Measuring the assimilation and emission of these gases from farms is difficult, relatively inaccurate, and very expensive. Emissions are also very dependent upon farm management, the climate and other factors, so large differences can occur among farms. A tool is needed to quantify farm emissions and the effect of management choices on these emissions. Relationships for predicting all important sources and sinks of the three greenhouse gases on dairy farms were integrated in a comprehensive model that predicts net farm emission in carbon dioxide equivalent units. A carbon footprint was then determined as this net emission per unit of milk produced. Footprints of 0.37 to 0.69 kg CO2e per kg of milk were found for common production practices in Pennsylvania and southern California. This software provides a unique tool for comprehensive assessment of management effects on greenhouse gas emissions in the production of milk on dairy farms.
Technical Abstract: Greenhouse gas (GHG) emissions and their potential impact on the environment has become an important national and international concern. Dairy production, along with all other types of animal agriculture, is a recognized source of GHG emissions, but little information exists on the net emissions from our farms. Component models for predicting all important sources of methane, nitrous oxide, and carbon dioxide emissions from primary and secondary sources in dairy production were integrated in a software tool called the Dairy Greenhouse Gas Model or DairyGHG. This tool calculates the carbon footprint of a dairy production system as the net exchange of all GHGs in CO2 equivalent (CO2e) units per unit of milk produced. Primary emission sources include enteric fermentation, manure handling facilities, cropland used in feed production, and the combustion of fuel in the machinery used to produce feed and handle manure. Secondary emissions are those occurring during the production of resources used on the farm, which can include fuel, electricity, machinery, fertilizer, pesticides, plastic, and purchased replacement animals. A long-term carbon balance is assumed for the production system, which does not account for potential depletion or sequestration of soil carbon. An evaluation of dairy farms of various sizes and production strategies gave carbon footprints of 0.37 to 0.69 kg CO2e per kg of milk, depending upon milk production level and the feeding and manure handling strategies used. This footprint was most sensitive to the amount of methane produced through enteric fermentation, moderately sensitive to the GHG emissions during long-term manure storage, and mildly sensitive to the amount of fuel, electricity and inorganic fertilizer used on the farm. DairyGHG provides a relatively simple tool for evaluating management effects on net GHG emissions and the overall carbon footprint of dairy production systems.