Fertilizer use and the environmental cost of a loaf of bread

Photo credit: Karen Sabin Photo credit: Karen Sabin

A new study published in the journal Nature Plants analyzed the environmental impact of the complete supply chain for producing a loaf of bread. The study found that more than half of the total environmental impact occurred during wheat cultivation. Moreover, the use of ammonium nitrate fertilizer on wheat crops was responsible for the majority of the environmental impact, alone accounting for 43% of the total. The large environmental impact of fertilizer use was largely driven by carbon dioxide emissions associated with their manufacturing—a very fossil fuel-intensive process—and the release of the greenhouse gas nitrous oxide when soil microbes break down excess fertilizer in the soil. One solution proposed by the authors to reduce pollution associated with fertilizer use is to shift away from chemical fertilization altogether and instead focus on fertility management techniques commonly used in organic agriculture such as crop rotations. Such rotations include legumes and fostering healthy soil microbial communities that interact with plant roots to promote growth. The authors conclude that because the environmental impact of fertilizer use is not factored in the cost of bread, there is currently no incentive to improve soil fertility management.