|Rotz, Clarence - Al|
Submitted to: World Wide Web
Publication Type: Other
Publication Acceptance Date: 8/22/2008
Publication Date: 8/22/2008
Citation: Rotz, C.A., Chianese, D.S. 2008. The Dairy Greenhouse Gas Emission Model: Reference Manual. Version 10. Available: http://www.ars.usda.gov/sp2UserFiles/Place/19020000/DairyGHGReferenceManual.pdf.
Technical Abstract: The Dairy Greenhouse Gas Model (DairyGHG) is a software tool for estimating the greenhouse gas emissions and carbon footprint of dairy production systems. A relatively simple process-based model is used to predict the primary greenhouse gas emissions, which include the net emission of carbon dioxide plus all emissions of methane and nitrous oxide occurring from the production system. Emissions are predicted through a daily simulation of feed use and manure handling. Carbon dioxide emissions include the net annual flux in feed production and daily values from animal respiration and microbial respiration in manure on the barn floor and during manure storage. The emission from fuel combustion in farm engines is included as proportional to the amount of fuel used in the production and feeding of feeds and the handling of manure. Methane emissions include those from enteric fermentation, the barn floor, manure storage, and feces deposited in pasture. Nitrous oxide emissions are that emitted from crop and pasture land during the production of feeds with minor emissions from the manure storage and barn floor. Total greenhouse gas emission is determined as the sum of the net emissions of all three gases where methane and nitrous oxide are converted to carbon dioxide equivalent units. This conversion is done assuming that each unit of methane is equal to 23 units of carbon dioxide and each unit of nitrous oxide is equal to 296 units of carbon dioxide. The carbon footprint of milk production is determined as the net of all greenhouse gases sequestered and emitted in the production system divided by the total milk produced. This net emission is determined through a life cycle assessment of the production system. Emissions include both primary and secondary sources where secondary emissions are those that occur during the manufacture or production of resources used in the production system. These resources include machinery, fuel, electricity, fertilizer, pesticides, and plastic. By totaling the net of all annual sinks and emissions from both primary and secondary sources and dividing by the annual milk produced by the production system, a carbon footprint is determined.