SIMULATION OF CARBON DIOXIDE EMISSIONS FROM DAIRY FARMS TO ASSESS GREENHOUSE GAS REDUCTION STRATEGIES

Authors: CHIANESE, DAWN - ENVIRON INTNL CORP; Rotz, Clarence - Al; RICHARD, TOM - PENN STATE UNIV

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2009
Publication Date: 8/27/2009
Citation: Chianese, D.S., Rotz, C.A., Richard, T.L. 2009. SIMULATION OF CARBON DIOXIDE EMISSIONS FROM DAIRY FARMS TO ASSESS GREENHOUSE GAS REDUCTION STRATEGIES. Transactions of the ASABE. 52(4):1301-1312.

Interpretive Summary: Greenhouse gas concentrations are increasing in our atmosphere and their potential effect on global climate change has become an important national and international issue. Carbon dioxide (CO**2) accounts for 84% of total U.S. anthropogenic greenhouse gas emissions. The majority of these emissions are due to the combustion of fossil fuel with additional contributions from land use change, oil and gas production, industrial processing, and waste combustion. Agriculture is not explicitly included as a significant contributor, but agriculture has important roles associated with the potential release and sequestering of CO**2 in soil through changes in cultural practices and land use. Although not important global sources, multiple processes on farms emit or sequester CO**2. Dairy farm emissions are primarily from animal respiration, followed by losses from manure storage and barn floors with crop production normally serving as a sink. Computer simulation provides a cost-effective and efficient method of estimating gaseous emissions from farms and analyzing how management affects these emissions. A whole-farm simulation model was extended to include the carbon cycle 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. Farm simulations illustrated that changes in cropping practices affected emissions from all farm sources with a primary effect on the sequestering of CO**2 in feed production. Use of more alfalfa in place of corn production caused a small increase in net farm greenhouse gas emission while replacing grassland with corn production reduced the net emission. Changing from Holstein to Jersey animals affected most emission sources with a 20% increase in net greenhouse gas emission per unit of milk produced. Incorporation of the carbon cycle and greenhouse gas emissions with farm simulation provides a tool for estimating whole-farm net emission of CO**2 and evaluating proposed reduction strategies along with their effect on net greenhouse gas emission and other environmental and economic impacts.

Technical Abstract: Farming practices can have a large impact on the soil carbon cycle and the resulting net emission of greenhouse gases including carbon dioxide (CO**2), methane and nitrous oxide. Primary sources of CO**2 emission on dairy farms are soil, plant, and animal respiration with smaller contributions from microbial respiration in manure. Strategies designed to reduce emissions from one source can cause an increase in emissions from another source. Therefore, a comprehensive whole-farm evaluation is needed, which can be cost-effectively met through computer simulation. The Integrated Farm System Model (IFSM), a process-based whole-farm model, was extended to simulate the carbon cycle. Relationships were added to predict photosynthetic fixation, soil and plant respiration, animal respiration, and emissions from manure storage and barn floors. The new module was verified to predict the mass of carbon present in soil pools at the end of annual simulations and to predict CO**2 emissions within expected emission ranges for both specific sources and overall farm emissions. A farm level carbon balance was used to further verify that predicted emissions were reasonable across a variety of production strategies. Farm simulations illustrated that changes in cropping practices affected emissions from all farm sources with a primary effect on the sequestering of CO**2 in feed production. For a representative farm in Central Pennsylvania, use of more alfalfa in place of corn production caused a 6% increase in net farm greenhouse gas emissions in CO**2 equivalent units while replacing grassland with corn production reduced net emissions by 16%. Changing from a Holstein herd to Jersey animals with animal numbers increased to produce the same amount of milk affected most emission sources with a net impact of increasing greenhouse gas emissions by 20%. Incorporation of greenhouse gas emission modules in IFSM provides a tool for evaluating the overall farm-level environmental and economic impacts of management scenarios used to reduce emissions.