Crop residues, including stems, leaves, and other plant parts left over after grain harvesting, account for a significant source of biomass for bioenergy. Residues from crops like corn, wheat, and sugarcane are all being actively used as biomass sources. With over 90 million acres of corn planted in the US, corn residues or corn stover, as it is commonly called, is the primary residue in use today.
Corn stover is normally harvested after grain harvests are complete and will yield approximately 1.5 dry tons per acre of usable biomass. This amount of stover varies based upon two factors. First, the yield of the corn is directly correlated with the amount of stover available. With high yields of corn grain in the Midwestern US, some approaching 300 bushels per acre, stover can actually be so plentiful that it has to be removed prior to the next planting season. In other areas of the country, where yields are in the 125 bushel per acre range, stover is more limited in availability. Second, the amount of stover removed depends on the soil and slope of a field. One of stover’s traditional benefit is to prevent soil erosion and to allow nutrients to re-enter the soil as the material decays on the ground. More sensitive soils and more sloping ground will require more stover left to prevent problems. Through extensive research, USDA and others have determined that in most cases, up to 50% of the available stover can be removed without impacting soils. All in all, the average availability is 1 to 1.5 dry tons per acre.
Stover is beneficial in that it is not the primary crop on a given acre and can be a problem for some farmers. However, when removing stover, two issues must be addressed. First, nutrients are being removed in the stover and farmers must apply additional nutrients to replace them. Second, and likely more of an issue, is the ash content of stover. Most stover is collected from the ground after a corn grain harvest. Since it comes into contact with the ground, soil and debris are inevitably collected with the stover. Some stover bales have been as high as 20% ash (soil and debris). This high ash content requires removing the soil and debris from the stover during processing, a sometimes difficult and expensive process.
While hurdles exist, Genera Energy expects corn stover to play a significant role in cellulosic biomass. Through innovation and planning, all of the challenging issues can be overcome. Like any feedstock, it will need to fit the particular region and conversion technology in your project. Genera has extensive experience in both collecting and processing stover. Contact us today to see how it fits into your project’s supply chain!
By Sam Jackson, Ph.D., VP Business Development
