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Title: Integrating biorefinery and farm biogeochemical cycles offsets fossil energy and mitigates soil carbon losses

item Adler, Paul
item Del Grosso, Stephen - Steve

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2014
Publication Date: 5/27/2015
Citation: Adler, P.R., Mitchell, J.G., Pourhashem, G., Spataria, S., Del Grosso, S.J., Parton, W.J. 2015. Integrating biorefinery and farm biogeochemical cycles offsets fossil energy and mitigates soil carbon losses. Ecological Applications. 25(4):1142-1156.

Interpretive Summary: Maintaining soil carbon while removing crop residues as feedstock for production of biofuels is an important objective for allowing their sustainable use. We used a model to evaluate the impact of crop residue harvest and application of a high lignin residue that is co-produced at the biorefinery (separated from the stream of feedstock that produces fuel) on soil carbon and other greenhouse gases. We found that although soil carbon decreased with harvest of crop residues, this negative impact could be largely eliminated by application of the high lignin residue from the biorefinery back onto the land. Not only did this strategy eliminate the negative impacts on soil carbon, but it allowed a greater reduction in greenhouse gas emissions than if it had remained on the soil. This strategy would allow farmers to sell crop residues while maintaining their soil quality and provide policy makers with a strategy for greater greenhouse gas reductions and production of domestic and renewable biofuels.

Technical Abstract: Crop residues are a potential significant source of feedstock for biofuel production in the US. However there are concerns with maintaining the environmental functions of these residues while also serving as a feedstock for biofuel production. Maintaining soil carbon along with the ancillary benefits is considered a greater constraint than maintaining soil erosion loses to an acceptable level. In this paper we used the biogeochemical model DayCent to evaluate the effect of residue removal, 50% for corn stover and 75% for wheat and barley straw in three distinct locations in the US. We evaluated residue removal with and without N replacement, along with application of a high-lignin fermentation byproduct (HLFB), a high lignin residue remaining at the biorefinery after ethanol production. We found that although soil N2O emissions were higher and soil carbon along with mineralized N decreased with removal of crop residues, these later two functions could be mitigated with application of HLFB to the land. Furthermore, with harvest of crop residues and return of HLFB, the offset of GHGs was greater than if residues had remained in the soil and significant quantities of ethanol were produced from a fraction of carbon with short residence time. Therefore by returning the high lignin fraction of crop residue to the land after production of ethanol at the biorefinery, soil carbon levels could be maintained along with the function of mineralized N, and greater greenhouse gas emissions could be offset than if the crop residue was used solely to maintain soil carbon stocks.