Simulation of Nitrous Oxide Emissions from Dairy Farms to Assess Greenhouse Gas Reduction Strategies

Farming practices can have a large impact on the net emission of greenhouse gases, including carbon dioxide (CO2), methane, and nitrous oxide (N2O). The primary sources of N2O 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 N2O and other greenhouse gas emissions. A module was added to simulate N2O emissions from croplands using relationships from the previously established DAYCENT model, and relationships were incorporated to predict emissions from slurry storage and free-stall barn floors. The new module was found to predict N2O 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 N2O emissions. Simulations illustrated the impact of management practices on a representative farm in central Pennsylvania. Reducing the use of inorganic fertilizer by accounting for manure nitrogen (N) reduced N2O emission from the farm by 6% and reduced the net farm emission of all greenhouse gases in CO2-equivalent units by 1%. Adding a mulch cover crop to corn land reduced N2O emission by 34% with a 7% reduction of all greenhouse gases. Use of a top-loaded manure storage tank prevented formation of a surface crust, which eliminated storage N2O emission with little effect on net farm emission of all greenhouse gases. This extended whole-farm model provides a tool for evaluating proposed N2O reduction strategies along with their effects on other greenhouse gas emissions, other N and phosphorus losses, and farm profitability.