Using the OVERSEER nutrient budget model to estimate on-farm greenhouse gas emissions

The OVERSEER nutrient budget model is a farm-scale nutrient reporting and greenhouse gas (GHG) emission accounting tool used extensively throughout New Zealand (NZ) by farmers, farm consultants and fertiliser representatives. The model is increasingly being used as a tool for implementing regional council resource management requirements to limit nitrogen (N) and phosphorus losses to waterways. NZ’s main dairy company, Fonterra, also requires dairy farmers to have a nutrient budget as part of the national Clean Streams Accord. This means that a high proportion of NZ farmers can obtain reports of their on-farm GHG emission profile. The GHG emission model is based on models and algorithms used for the NZ GHG national inventory, modified to include a wide range of on-farm management practices. The model estimates methane, nitrous oxide and carbon dioxide (CO2) emissions, and presents the results as CO2 equivalents. This paper describes the model and the benefits of combining nutrients budgets and GHG emissions into a single model. It also demonstrates the effects of management practices on a range of outputs, including N leaching and GHG emissions.