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Agronomy Day 2008

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Tour D

Corn Stover: A Second Crop?

Martin Bohn
Martin Bohn
Associate Professor, Maize Breeding and Genetics
University of Illinois
Department of Crop Sciences
mbohn@illinois.edu
Andrew Hauck
Graduate Research Assistant
University of Illinois
Department of Crop Sciences
ahauck@illinois.edu

The growing demand for food, feed, and fuel in the world is spurring rapid development in a bio-based economy. Concerns about energy security, rising food prices, and climate change have highlighted the importance of second generation bio-fuels produced from biomass feedstock sources, especially “dual purpose crops” yielding substantial grain and vegetative tissue. Corn has excellent potential to be a dual purpose crop, as it is grown over a wide area and a large fraction of the stalk and leaf material, or stover, is readily available. As technologies to convert biomass into products mature, a new market is expected to emerge. Deconstruction of biomass into the component sugars and polymers will allow replacement of energy, chemicals, and products traditionally produced from petroleum with alternatives that facilitate the nation’s security and economy.

Our research at the University of Illinois is focused on the genetics that will make the stover tissues of modern elite hybrids better biomass feedstocks without negative effects. Although we use information gained from investigations of the digestible forage varieties, corn that is improved for use as a biomass feedstock will not be weakened with undesirable traits. The processes used to deconstruct stover will circumvent the need for any significant compromises. We have identified a number of important quality traits that contribute to the economics and, ultimately, the farm gate profitability of using stover as a biomass feedstock. These stover quality traits include ease of collection, density, moisture content, structural sugar content, extractability, and co-product characteristics. We are using a combination of plant breeding, genomics, and molecular biology approaches to evaluate these traits.

Stover quality is initially defined by the ease of collection, storage, and transport. Since only a fraction of the stover will be harvested, it is desirable to improve and collect the portion of stover that requires the least modifications to existing equipment. Due to the bulky nature of biomass, even when compressed, density is important, especially at the quantities a bio-refinery will require. Stover that dries down more completely in the field before harvest is another value trait, as high levels of moisture will reduce the storage life and inflate transportation costs.

Other aspects of stover quality are related to the composition of the cell walls of the stalk tissues, where most of the biomass is concentrated. Unlike the starch sugars of kernels, which are easily degraded with simple enzymes, the structural sugars that give stem and leaf tissues strength and rigidity are much less easily deconstructed. Structural sugars in the form of cellulose and hemi-cellulose each comprise about a third of stover biomass. The remaining third is divided between a strong polymer called lignin, which determines the hardness of the tissues, and other minor components, such as protein and ash. The sugars in cellulose are arranged linearly in tight bundles that function like steel cables, in a concrete-like matrix of hemi-cellulose and lignin. Stover value and product yields can be maximized by increasing the amounts of structural sugars, the ease with which they can be removed, and the amount of desirable by-products.

Energizing Agriculture