Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2007
Publication Date: 11/6/2007
Citation: Wilhelm, W.W., Johnson, J.M., Karlen, D.L., Lightle, D. 2007. Corn Stover to Sustain Organic Carbon Further Constrains Biomass Supply. Agronomy Journal. 99:1665-1667.
Interpretive Summary: The United States has embarked on an ambitious program to develop technology and infrastructure to economically and sustainably produce ethanol from biomass. Corn stover, the aboveground material left in fields after corn grain harvest, has been identified as a primary feedstock. Stover and other crop biomass or residue is frequently referred to as "trash" or a waste, implying it has minimal value. However, when returned to the land, crop biomass helps to control erosion and replenishes soil organic matter. Organic matter in the soil retains and recycles nutrients and, improves soil structure, aeration, and water exchange characteristics. In addition, it is the energy source for the soil ecosystem. Sustainable biofuel production will require that these functions of organic matter be addressed before crop residue is removed from the land. To date, projected sustainable harvest levels have been calculated by reducing total stover production by amounts needed to keep soil loss within accepted limits (T). No estimate amounts of crop residue needed to prevent loss of soil organic matter have been published. Under all of the conditions considered in this study, stover needed to replenish soil organic matter was greater than that required to control either water or wind erosion. This report emphasizes the need to further evaluate the validity of widely circulated estimates of US cropland capacity to sustainably supply feedstock for the emerging cellulosic ethanol industry. Great urgency exists to gather reliable data to confirm our calculations and to expand these computations to a broader range of cropping systems. In addition, an extensive effort is needed to develop crops and advanced cropping systems that greatly expand biomass production and provide a sustainable supply of cellulosic feedstock without further reducing soil organic matter, thus undermining the productive capacity of our soil resource.
Technical Abstract: Sustainable aboveground crop biomass harvest estimates for cellulosic ethanol production, to date, have been limited by the need for stover or residue to control erosion. Recently, estimates of the amount of crop biomass needed to maintain soil carbon, which is responsible for favorable soil properties, was reported. Biomass needed to maintain soil organic carbon and thus productivity, will be a greater limitation to environmentally sustainable cellulosic feedstock harvest than control of water and wind erosion. An extensive effort is needed to develop advanced cropping systems that greatly expand biomass production to sustainably supply cellulosic feedstock without undermining productivity of our soils. [REAP Publication]