Life cycle assessment of cotton-corn farming systems in the Namoi Valley, Australia

Life Cycle Assessment (LCA) is commonly applied to identify greenhouse gas emissions arising from agricultural production. Greenhouse emissions were determined for the life cycle from “cradle-to-gate ” of different cotton and corn production systems in the Namoi Valley, Australia. Analysis was based on data from three co-operating growers in the lower Namoi Valley and a long term experiment at the Australian Cotton Research Institute (ACRI) at Myall Vale, obtained through farmer interviews using a questionnaire. Analysis was conducted using SimaPro software, drawing background data from international databases. Greenhouse gas emissions averaged 345 kg CO2-e for the production of 1 tonne of cotton lint and seed for both irrigated and dryland cotton and 325 kg CO2-e for the production of 1 tonne of corn. The emissions profile for irrigated cotton grown in rotation included N2O directly from fertilisers (35.3%), production of fertilisers (14%), CO2 emissions from the use of nitrogenous fertilisers (11.6%), N2O emissions indirectly via leaching (7.2%), N2O emissions via volatilisation and indirectly from fertiliser re-deposition (3.8%), CO2 emissions from on-farm combustion (7.8%) and irrigation (9.2%). The emissions were dominated by the production and use of nitrogenous fertilisers, at 72 % for cotton and 65 % for corn. Replacing these fertilisers with biologically fixed N using a legume-based system may reduce these emissions