|Rotz, Clarence - Al|
Submitted to: Transactions of the ASABE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2009
Publication Date: 8/27/2009
Citation: Chianese, D.S., Rotz, C.A., Richard, T.L. 2009. SIMULATION OF METHANE EMISSIONS FROM DAIRY FARMS TO ASSESS GREENHOUSE GAS REDUCTION STRATEGIES. Transactions of the ASABE. 52(4):1313-1323. Interpretive Summary: The Intergovernmental Panel on Climate Change has reported that it is “extremely likely” that anthropogenic emissions of greenhouse gases are causing a change in the global climate. Although many mitigation plans currently focus on reducing carbon dioxide (CO**2¬) emissions, methane (CH**4) is a stronger greenhouse gas with a global warming potential around 23 times that of CO**2. The claim has been made that globally, livestock emit more CH**4 in CO**2 equivalent units than is emitted through the burning of fossil fuels for transportation. Therefore, quantifying and reducing CH**4 emissions from livestock farms is important for developing sustainable production systems. Multiple processes emit CH**4 from dairy farms including enteric fermentation in animals and microbial processes in manure. Emissions are very difficult and expensive to measure. A more practical approach is to use process-level modeling and computer simulation to estimate farm emissions and analyze how management affects these emissions. A whole-farm simulation model was extended to include emissions of CH**4 and other greenhouse gases to obtain a comprehensive tool for evaluating management effects on farm performance, profitability, and environmental pollutants such as nitrate leaching, ammonia volatilization, and phosphorus runoff loss along with greenhouse gas emissions. Two potential CH**4 reduction strategies were evaluated to illustrate the use of the revised model. Farm simulations showed that increasing forage production and use in animal diets increased CH**4 emission with little impact on the global warming potential over all greenhouse gas emissions from the farm. Using a manure storage cover and burning the captured biogas reduced farm emission of CH**4 by 30% with a 22% reduction in the net farm emission of greenhouse gases. Incorporation of greenhouse gas emissions in the farm model provides a tool for estimating whole-farm emissions of CH**4 and evaluating proposed reduction strategies along with their impact on net greenhouse gas emission and other environmental and economic measures.
Technical Abstract: As a sector, agriculture is reported to be the third greatest contributor to atmospheric methane (CH**4) in the U.S., emitting one-quarter of total emissions. Primary sources of CH**4 emission on dairy farms are the animals and manure storage, with smaller contributions from field-applied manure, feces deposited by grazing animals, and manure on barn floors. The Integrated Farm System Model (IFSM) was expanded to include simulation of CH**4 emissions from all farm sources along with modules predicting other greenhouse gas emissions. The new CH**4 module incorporated models from previously published relationships and experimental data that were consistent with our modeling objectives and the current structure of IFSM. When used to simulate previously reported experiments, the model was found to predict enteric fermentation and slurry manure storage emissions similar to those measured. In simulating a representative 100-cow dairy farm in Pennsylvania, the model predicted a total average annual emission of 20 Mg CH**4. This included annual emissions of 135 kg CH**4 per cow from the Holstein herd and 5.4 kg CH**4 per m**3 of stored manure, which were consistent with previously summarized emission data. To illustrate the use of the expanded whole-farm model, two potential CH**4 reduction strategies were evaluated. Farm simulations showed that increasing the production and use of forage (corn silage) in animal diets increased CH**4 emission by 17% with little impact on the global warming potential of the net farm emission of all greenhouse gases. Using a manure storage cover and burning the captured biogas reduced farm emission of CH**4 by 30% with a 22% reduction in the net farm emission of greenhouse gases. Incorporation of greenhouse gas emission modules in IFSM provides a tool for estimating whole-farm emissions of CH**4 and evaluating proposed reduction strategies along with their impact on net greenhouse gas emission and other environmental and economic measures.