A decision support framework for greenhouse gas accounting on Australian dairy farms. (Abstract)

Abstract

20A A decision support framework for greenhouse gas accounting on Australian dairy farms R.J. Eckard1, R.S. Hegarty2 and G. Thomas3 1 2 3 Institute of Land and Food Resources, The University of Melbourne, Parkville Victoria 3010 NSW Agriculture Beef Industry Centre, University of New England, Armidale NSW 2351 Dairy Research Institute, Ellinbank, Warragul Victoria 3820 roger.hegarty@agric.nsw.gov.au The livestock industries contribute 12% of Australias greenhouse gas (GHG) emissions and the principal emissions associated with livestock are methane from enteric fermentation and nitrous oxide from soils. While emitting relatively little GHG compared to the beef cattle and sheep industries, the dairy industry is expanding rapidly and also has greater opportunity to utilise dietary additives, modify diets and manage fertiliser usage than do the extensive livestock industries. A computer based model was developed for spreadsheet or internet use by which the GHG emissions from dairy farms can be calculated, displayed, and the effects of management changes on emissions evaluated. The model used equations from the NGGIC (1998) as the basis for estimating enteric and effluent methane as well as nitrous oxide from fertiliser, excreta and effluent. These equations required input data on herd numbers, structures and animal weights, together with estimated pasture digestibility and crude protein content. Additional information on the diesel and electricity consumption on the farm, together with nominating the fossil fuel source used for electricity generation was required to complete the calculation of total GHG emissions from the farm. While the model was not designed to fully describe carbon sinks, the option to include tree plantings to sequester atmospheric CO2 was included. An example of the profile of emissions of CO2, N2O and CH4 and their sources in tabular and piechart form are shown in Figure 1. The GHG are from a 275 cow herd grazing 100 ha of improved pasture (75% dry matter digestibility) fertilised annually with 200 kg N/ha. Emissions of CH4 and N2O, tonnes, are expressed as CO2 equivalents; CO2e is (CH4 x 21) and (N2O x 310). Effects of altering the herd, pasture, fertiliser or crop structure on the level and origin of emissions could be observed. The model was tested across 40 farmlets, with emissions ranging from 5441463 g CO2e/L milk, 37 t CO2e/cow/annum and 545 t CO2e/ha/annum. The model provides a valuable tool to quantify the sources of dairy GHG emissions and evaluate the consequences of management choices on enterprise emissions against the criterion used for national greenhouse gas accounting. NGGIC (1998). Workbook for livestock 6.1 with supplements 1998. National Greenhouse Gas Inventory Committee, Canberra, Australia. Outputs Energy CH4 - Enteric CH4 - Effluent N2O N2O N2O N2O Tree Tota - Effluent - N Fertiliser - Soils - Dung & Urine plantings (after 1990) l Emissions t CO2e/farm Summary CO2 88.0 825.7 3.7 0.7 121.7 14. 1 542.8 -204 1393 CH4 N2O t CO2e/farm 88 829 679 Greenhouse Gas Profile CO2 Summary 6% N2O 39% CH4 55% Figure 1 GHG emissions from a 275 cow herd grazing 100 ha of improved pasture expressed as tons of CO2 equivalents (CO2e) per annum. Calculated with model at www.nitrogen.landfood.unimelb.edu.au Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)