Evaluating options to reduce greenhouse gas emissions from an Australian temperate wheat cropping system

Increases in atmospheric concentrations of greenhouse gases as a result of human activities are thought to be resulting in discernible changes in global climate. Australia, as a signatory to the Climate Change Convention, has agreed to stabilize emissions of these gases at 1990 levels. There is a need to identify options that may reduce emissions from all industry sectors including those emissions arising from agricultural activities such as wheat cropping. The wheat cropping systems of the Wimmera region of Victoria studied here are likely to be significant net emitters of greenhouse gases with average annual emissions equivalent to 1350 to 2150 kg of carbon dioxide per hectare. Choosing stubble retention wheat cropping systems could reduce the average net emissions per hectare by up to 37% depending on the systems used. More importantly though, the stubble retention cropping systems which have lower emissions also tend to have greater yields, and thus may produce up to four times the grain yield per unit emissions than other systems such as conventionally tilled, continuous wheat. This indicates that there is significant potential to adapt wheat cropping systems to reduce greenhouse gas emissions in a cost-effective way. This capability may be enhanced by tactical management decisions that change fertilizer inputs depending on soil moisture levels at sowing or on seasonal forecasts based on factors such as the Southern Oscillation Index. This approach is also likely to have financial and risk management benefits. Loss of soil carbon was the most substantial component of the emissions budget for all cropping systems (63 to 84% of total emissions), followed by nitrous oxide emissions (from 12 to 42%) with methane forming a relatively small component (from 0.003 to 17%). Emissions from fossil fuel combustion (from 0.8 to 8%) and from burning crop stubble (from 0 to 21%) formed relatively small components of the emissions budget. Policy issues are discussed including the removal of barriers to adoption of the more sustainable, low-emission systems identified in this study. (C) 1997 Elsevier Science Ltd.