Modelling the biophysical and economic impact of on-farm greenhouse gas abatement

© 2015 Dr. Natalie Doran-BrowneClimate change has resulted in a number of global challenges, such as the need to reduce greenhouse gas emissions (GHGE) with the simultaneous challenge of feeding a burgeoning world population. Agriculture is responsible for 10-12% of global anthropogenic GHGE. In Australia, 15% of national emissions come from agriculture, which is also the main source of anthropogenic nitrous oxide (N2O) and methane (CH4). Information is needed on various mitigation options and their effect on farm profitability before GHGE can be reduced from the agricultural sector,. Determining agricultural emissions is complicated by a number of factors such as the range of production environments and management practices that characterise agriculture, as well as the methods chosen to calculate farm GHGE. Understanding how farms with different types of production manage under current climate variability is the precursor to examining the potential for mitigation. From an industry perspective it is challenging, especially for livestock farms, to expand the industry while attempting to reduce GHGE. Additionally, unless mitigation options are profitable there is no incentive for farmers to change the management of their farms to reduce emissions. Therefore, the costeffectiveness of mitigation options needs to be analysed against the current profitability of farms. The purpose of this thesis was to compare the GHGE produced by wool, prime lamb, beef, dairy, and grain production in southwest Victoria and to compare the profitability of these farms under different rainfall and market price scenarios. This thesis also sought to demonstrate selected ways that farmers can mitigate GHGE through changes in farm management or improvements in productivity, while assessing the potential of these mitigation options to generate carbon offsets. The importance of methods and metrics when researching farm GHGE was also explored. This research focused on farm enterprises in the high rainfall areas of southwest Victoria. This region was chosen because its fertile soils and climate make it suitable for multiple types of livestock and crop production, enabling the comparison of emissions from these different types of production within the one environment. Computer modelling was used extensively to examine the GHGE, mitigation options, production levels, profitability and economic feasibility of mitigation strategies in this thesis. Farms are complex systems that consist of numerous components such as different soil types, pasture species and livestock. Whole-farm models allow the relationships between components to be analysed and incorporated into a whole system that can be examined across numerous years, including various changes to management or the environment. In this thesis, whole-farm biophysical models were used to represent the livestock enterprises. To calculate emissions that were compliant with Kyoto accounting, the Australian National Inventory methodology was used, which is based on the IPCC methodology but substitutes Australian values and algorithms where they exist and otherwise uses the default IPCC values. This thesis contributed a number of important findings to the body of knowledge that exists on GHGE from agricultural enterprise and clarified key concepts on effective ways of mitigating on-farm GHGE. The enterprise comparison showed that the emissions intensity of grain farms was the lowest (0.04-0.15 t CO2e/t grain), followed by steers (6.3-6.7 t CO2e/t carcase weight), dairy (8.5-9.4 t CO2e/t milk fat plat protein), prime lamb (11.4-12.0 t CO2e/t carcase weight), wool (18.1-18.7 t CO2e/t clean fleece) and cow-calf enterprises (22.4-22.8 t CO2e/t carcase weight). The research demonstrated that the profitability of these enterprises was affected more by changes in rainfall than commodity prices. Dairy enterprises were the more profitable ($/ha), but the profitability of wheat, steer and prime lamb enterprises were least affected by low rainfall scenarios. The self-replacing cow-calf beef systems, canola and dairy enterprises were the most vulnerable to reduced rainfall. This thesis showed that mitigation strategies that focused on emissions intensity have more potential to be implemented by farmers because the improved productivity often leads to increased profitability. Selected mitigation strategies were explored that analysed the lifetime emissions of livestock and also the use of a novel legume on sheep farms that increased productivity and profitability while simultaneously reducing GHGE. The profitability from productivity gains was 4 to 13 times larger than likely offset income at a carbon price of $23/t. Finally, a new metric was developed, t CO2e/unit nutrient density, that compared GHGE from food production using the nutritional value of the food. Further analysis into this metric would be beneficial. Farm emissions using the metric t CO2e/unit nutrient density were compared with emissions intensity, as well as against the protein (t CO2e/t protein) and energy (t CO2e/GJ) content in food. The knowledge gained through this research will help farmers and policy makers to more effectively reduce GHGE. Of key importance is that while carbon offsets in Australia have been generated from a limited number of farms, the uptake by broadacre farmers has been slow because implementation costs of mitigation options generally exceed potential carbon offset income. However, pursuing productivity increases profitability and using an emissions intensity metric to evaluate proposed mitigation strategies is likely to be a more successful approach to reducing agricultural emissions, provided that increased productivity occurs sustainably