Date of this Version
Published in Nature Climate Change 4 (May 2014), pp. 398–401; doi: 10.1038/NCLIMATE2187 http://www.nature.com/natureclimatechange
Removal of corn residue for biofuels can decrease soil organic carbon(SOC) and increase CO2 emissions because residue C in biofuels is oxidized to CO2 at a faster rate than when added to soil. Net CO2 emissions from residue removal are not adequately characterized in biofuel life cycle assessment (LCA). Here we used a model to estimate CO2 emissions from corn residue removal across the US Corn Belt at 580 million geospatial cells. To test the SOC model, we compared estimated daily CO2 emissions from corn residue and soil with CO2 emissions measured using eddy covariance, with 12% average error over nine years. The model estimated residue removal of 6 Mg per ha–1 yr–1 over five to ten years could decrease regional net SOC by an average of 0.47–0.66 Mg C ha–1 yr–1. These emissions add an average of 50–70 g CO2 per megajoule of biofuel (range 30–90) and are insensitive to the fraction of residue removed. Unless lost C is replaced, life cycle emissions will probably exceed the US legislative mandate of 60% reduction in greenhouse gas (GHG) emissions compared with gasoline.
Supplementary information is attached below as an additional (pdf) file.