Response to AP Story on Corn Stover

Background: On Monday, April 21st, the Associated Press published a story on a new study in Nature Climate Change by researchers at the University of Nebraska-Lincoln. The AP reporter working on the article was Dina Capiello, who wrote the damaging piece on corn ethanol last November. The Nature paper makes the claim that ethanol from corn stover may be worse than gasoline in terms of overall GHG impacts; they argue this is due to soil organic carbon (SOC) losses. The authors, including Adam Liska, suggest SOC losses have been grossly underestimated or absent from previous lifecycle studies on corn stover.

• Whether stover is harvested or left in the field to decompose, the end result is about the same – much of the organic matter leaves the field and does not get incorporated into soil organic carbon (SOC) and soil organic matter (SOM).
  
• Tillage  mixes soil, moisture and oxygen to decompose the stover – essentially to burn it up through oxidation and release it as CO2.  Only a small percent of the above ground corn stover actually converts to organic matter.
  
• There are a large number of factors affecting soil organic carbon status of soils and stover removal is just one of them.  Other factors include rotation, weather, soil type, tillage, cover crops, manure application and fertilization.
  
• Residue in a no-till system decays and decomposes on the surface, albeit slower than when tilled under.  However, the main advantage of no-till is erosion control.
  
• Much of the soil organic carbon and soil organic matter in the soil actually results from the roots.  Stover harvest has no impact on root organic matter and therefore has little impact on SOC. 
  
• Even if all of the carbon in stover is removed, that is all recycled carbon acquired from the atmosphere during the previous growing season.  It is not new carbon being added to the atmosphere. Gasoline is 100% ancient carbon that represents additional carbon being added to the atmosphere. 

Conclusion: Partial stover removal can be done sustainably in terms of soil organic carbon, but should be accompanied by a change in tillage and other management practices.  Cover crops or manure application can also be used to replace the organic matter removed through stover removal.  With both stover removal and tillage, the result is the same. A large portion of the  carbon and organic matter from the stover is removed from the field. 

By converting stover to ethanol, at least we get one use out of the carbon before it goes back to the atmosphere.  RUSLE2 is a widely recognized program that can calculate the effect of various management practices on soil organic carbon through its Soil Conditioning Index.

What the authors of this paper seem to assume is that stover ends up as soil organic carbon if it isn’t harvested, when in reality, most of it ends up as carbon dioxide.

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