Chartered Institution of Water and Environmental Management (CIWEM)

The global warming potential of wheat

Nitrous oxide concentrations in the earth’s atmosphere have increased since the industrial revolution. This is of concern as nitrous oxide contributes to global warming and the destruction of the ozone layer. It has 310 times the global warming potential of carbon dioxide and a lifespan of 120 years. Emissions from agricultural soils are considered to account for 70 to 80 percent of the increase.

In a recent paper published CIWEM’s Water and the Environment Journal (WEJ), a life cycle assessment took place on one tonne of wheat transported to port in south-western Australia, including emissions from pre-farm, on-farm and post-farm stages.

A life cycle assessment enables evaluation of environmental impacts for comparative or improvement purposes. This assessment included green house gas emissions from agricultural machinery, fertiliser and pesticide production, diesel use, liming and nitrous oxide emissions from fertiliser applications, grain storage and transportation to port.

Their study found that fertiliser production accounted for a significant portion of the global warming potential (35 percent), followed by on-farm (27 percent) and transportation emissions (12 percent).

As other greenhouse gases can be emitted in agricultural production systems, the authors argue that a holistic approach is needed if the overall impact of agricultural production systems on global greenhouse emissions is to be addressed.

The authors said:

“Semi-arid and arid lands constitute one third of the global land area and are widely used for agricultural production. Understanding of gas emissions from agricultural soils in these regions is necessary if we are to improve our knowledge of terrestrial global emissions.”

“In addition to life cycle assessments, full economic, social and other environmental impacts need to be taken into account in order to assess the sustainability of grain industries. This is particularly important when assessing the use of biodiesel, as it as been found that biodiesel use impacted more on soil and water acidification, eutrophication and radioactive waste, than use of diesel.”

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