On-farm greenhouse gas emissions and water use: case studies in the Queensland beef industry

In response to climate change, research is being undertaken to understand the on-farm greenhouse gas emissions and water use for agricultural systems and investigate options farmers may have for mitigating or offsetting emissions. In the present study, a life cycle assessment framework is used to determine on-farm GHG emissions and water use, and the overall 'cradle-to-farm gate' GHG emissions and water use attributed to beef production. The total on-farm emissions for the two properties were 2984 t CO2-e/year (or 1.93 t CO2-e/livestock unit) for the 634-cow enterprise turning off weaner cattle at Gympie and 5725 t CO2-e/year (or 1.70 t CO2-e/livestock unit) for the 720-cow enterprise turning off finished steers in the Arcadia Valley. The on-farm emissions are largely attributable to enteric methane emissions from the beef herd. The overall 'cradle-to-farm gate' GHG emissions associated with enterprise products were 3145 t CO2-e/year at Gympie and 7253 t CO2-e/year in the Arcadia Valley, with the additional emissions coming from off-farm inputs (fuel for farm vehicles and earth-moving equipment, electricity, supplementary feed, agricultural chemicals, farm services) and additionally, for the Arcadia Valley enterprise, from purchased store steers. The carbon footprint of beef products at the farm gate ranged from 17.5 to 22.9 kg CO2-e/kg liveweight at Gympie, where wearers are the primary product, and from 11.6 to 15.5 kg CO2-e/kg liveweight in the Arcadia Valley, where finished steers are the primary product. Green water use ranged from 7400 to 12 700 L/kg liveweight depending on class of livestock, with on-farm blue water use of 51-96 L/kg liveweight and off-farm blue water use of 0.1-59 L/kg liveweight. The ability to offset on-farm GHG emissions through reforestation varied between the two locations, with predicted biosequestration rates of 19.3-34.7 t CO2-e/ha per year at Gympie (rainfall 1200 mm/year) from eucalypt plantation and 1.5-9.8 t CO2-e/ha per year in the Arcadia Valley (rainfall 600 mm/year) through reforestation from a combination of brigalow regrowth, leucaena and environmental eucalypt plantings. The area that would need to be reforested to offset on-farm emissions (over a 30-year time horizon) would be 86-155 ha at Gympie (7-13% of the holding) and 629-4108 ha in the Arcadia Valley (9-60%). If carbon sequestration could be achieved at the higher end of the rates nominated, a significant proportion of on-farm emissions could be offset by sequestration in timber, with minimal impact on beef production. However, at the lower end of the forest sequestration range, the required level of land-use change would reduce the carrying capacity, and hence beef production, especially at the Arcadia Valley site.