Modeling greenhouse gas emissions from dairy farms

Authors: Rotz, Clarence - Al

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2017
Publication Date: 7/1/2018
Citation: Rotz, C.A. 2018. Modeling greenhouse gas emissions from dairy farms. Journal of Dairy Science. 101(7):6675-6690. https://doi.org/10.3168/jds.2017-13272.
DOI: https://doi.org/10.3168/jds.2017-13272

Interpretive Summary: Dairy farms are a major contributor to the total greenhouse gas emissions over the life cycle of milk and other dairy products. Much effort has been given to measuring emissions from important sources on dairy farms, but monitoring and simultaneously quantifying all emissions from a given farm or production system is essentially impossible and prohibitively expensive. Mathematical modeling provides another option, and models of various scales have been developed and used to estimate or predict greenhouse gas emissions from the various sources on farms. Comprehensive whole farm models provide essential tools for integrating the effects and interactions of all sources on the farm to provide the overall net emission. To look beyond the farm, life cycle assessment provides an environmental accounting tool for evaluating emissions over the full life cycle of the milk and dairy products produced. Models provide important tools for quantifying emissions, identifying opportunities for reduction and evaluating mitigation strategies.

Technical Abstract: Dairy farms have been identified as an important source of greenhouse gas emissions. Within the farm, important emissions include enteric methane (CH4) from the animals, CH4 and nitrous oxide (N2O) from manure in housing facilities, during long-term storage and during field application, and N2O from nitrification and denitrification processes in the soil used to produce feed crops and pasture. Models using a wide range in level of detail have been developed to represent or predict these emissions. They include constant emission factors, variable process-related emission factors, empirical or statistical models, mechanistic process simulations and life cycle assessment. To fully represent farm emissions, models representing the various emission sources must be integrated to capture the combined effects and interactions of all important components. Farm models have been developed using relationships across the full scale of detail from constant emission factors to detailed mechanistic simulations. Simpler models based upon emission factors and empirical relationships tend to provide better tools for decision support; whereas, more complex farm simulations provide better tools for research and education. To look beyond the farm boundaries, life cycle assessment provides an environmental accounting tool for quantifying and evaluating emissions over the full cycle from producing the resources used on the farm through processing, distribution, consumption and waste handling of the milk and dairy products produced. Models are useful for improving our understanding of farm processes and their interacting effects on greenhouse gas emissions. Through better understanding, they assist in the development and evaluation of mitigation strategies for reducing emissions and improving overall sustainability of dairy farms.