SIMULATION OF NITROUS OXIDE 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: 7/2/2009
Publication Date: 8/27/2009
Citation: Chianese, D.S., Rotz, C.A., Richard, T.L. 2009. SIMULATION OF NITROUS OXIDE EMISSIONS FROM DAIRY FARMS TO ASSESS GREENHOUSE GAS REDUCTION STRATEGIES. Transactions of the ASABE. 52(4):1325-1335.

Interpretive Summary: Atmospheric concentrations of greenhouse gases, including nitrous oxide (N**2O), are increasing with evidence that this maybe causing long term change in our global climate. Although many mitigation plans currently focus on reducing carbon dioxide (CO**2¬) emissions, N**2O is a much stronger greenhouse gas with a global warming potential about 296 times that of CO**2. Recent reports indicate that agriculture is associated with 78% of the U.S. total N**2O emission. As a result, quantifying and reducing N**2O emissions is necessary to reduce overall emissions of greenhouse gases in agriculture. The majority of N**2O from dairy farms is emitted from soil, followed by manure storages, with relatively small amounts emitted from manure deposited by animals in barns. As steps are taken to evaluate and reduce greenhouse gas emissions from dairy farms, tools are needed to quantify net emissions from the whole farm. Considering the many processes throughout the farm affecting emissions, a comprehensive, farm specific evaluation is needed. Computer simulation provides a cost-effective and efficient method of estimating gaseous emissions from dairy farms and analyzing how management affects these emissions. A dairy farm simulation model was extended to include emissions of N**2O 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. Farm simulations illustrated that use of a top-loaded manure storage tank could eliminate storage N**2O emissions and thus reduce the global warming potential of all greenhouse gas emissions by 7%. Over applying inorganic N fertilizer increased net farm emission of greenhouse gases a small amount; whereas, adding a mulch cover crop to corn land reduced N**2O emission by 50% with a net reduction over all greenhouse gases. This extended whole-farm model provides a tool for evaluating proposed N**2O reduction strategies along with their effects on other greenhouse gas emissions, environmental issues related to nitrogen and phosphorus losses, and farm profitability.

Technical Abstract: Farming practices can have a large impact on the net emission of greenhouse gases including carbon dioxide, methane, and nitrous oxide (N**2O). The primary sources of N**2O from dairy farms are nitrification and denitrification processes in soil, with smaller contributions from manure storage and barn floors. Emissions from all greenhouse gas sources are interrelated, so strategies to reduce emissions from one source can affect emissions from another. Therefore, a comprehensive whole-farm evaluation is needed, which can be cost-effectively achieved through computer simulation. The Integrated Farm System Model (IFSM), a process-based whole-farm model, was extended to simulate sources of N**2O and other greenhouse gas emissions. A module was added to simulate N**2O emissions from croplands using relationships from the previously established DAYCENT model, and relationships were incorporated to predict emissions from slurry storage and barn floors. The new module was found to predict N**2O emissions consistent with reported values from specific experiments and previously estimated whole-farm emissions. The model also predicted sensitivity to soil texture and soil water content similar to experimental data and DAYCENT model predictions, which further verified this most important component of N**2O emissions. Simulations illustrated the impact of management changes on a representative farm in Central Pennsylvania. Use of a top-loaded manure storage tank prevented formation of a surface crust, which eliminated storage N**2O emission and reduced net farm emission of all greenhouse gases in CO**2 equivalent units by 7%. Ignoring available manure N and thus over applying inorganic N fertilizer increased the net farm emission of greenhouse gases by 3%. Adding a mulch cover crop to corn land reduced N**2O emission by 50%, with a 9% reduction over all greenhouse gases. This extended whole-farm model provides a tool for evaluating proposed N**2O reduction strategies along with their effects on other greenhouse gas emissions, environmental issues related to nitrogen and phosphorus losses, and farm profitability.