An analysis of the environmental impact of the steps involved in producing a loaf of bread, from growing the wheat to its delivery to the consumer, is presented in a paper published online this week in Nature Plants. The study reveals that over half of the environmental impact of this production process comes from cultivating the wheat used to make the bread loaf, with over 40% attributable to the use of ammonium nitrate fertiliser alone.

Peter Horton and colleagues used a life cycle assessment approach for a single wholegrain loaf of bread, weighing a total of 800 g and produced within the UK, looking at all aspects of its manufacture. They were able to obtain direct data for almost all stages by collaborating with a commercial bread and flour producer and a large agronomy services provider. They then assessed six categories of environmental effects, including global warming potential, pollution of freshwater, and production of toxins dangerous to human health. They found that the global warming potential from the whole supply chain was 0.589 kg CO2 equivalent per loaf of bread. By all measures, the authors show that cultivation accounted for at least half of the harmful effects and, within that, the use of nitrate fertilizer was the biggest single component.

The authors note that delivering high yields of high protein bread wheat without using unsustainable amounts of fertiliser will be a grand challenge for the twenty-first century. However, as the environmental impact of fertiliser use is not costed within the system, there are currently no effective incentives to use it sustainably.