Managing Perennial Cover Crops for Sustainable Corn Stover Biomass Production.

Plant residues remaining in the field after grain crops have been harvested represent the largest potential stock of readily available biomass in the United States. Corn stover is by far the most abundant crop residue with about 75 million available dry tons produced each year.  However, corn crop residues are generally returned to the soil for conservation. Residues left in the field reduce soil erosion by wind and water and increase soil carbon when incorporated into the soil. Removal of most of the above ground plant material for grain and biomass will likely have negative environmental consequences unless alternative cropping systems that protect the soil from erosion and sequester soil carbon can be developed and implemented.  The goal of this research was to develop corn production systems that use perennial groundcovers to allow removal of crop residue with minimal negative effects on soil and water quality.  This project addressed three primary research objectives: 1) identify groundcover species that are compatible with corn grown for grain and biomass, 2) determine genetic characteristics of corn that enhance its potential to germinate and compete with perennial groundcover; and 3) develop management systems that minimize competition between corn and the groundcover.  These objectives were addressed in three experiments.  Overall, this research demonstrated that it is possible to grow corn with perennial groundcover without taking a yield penalty.  Doing so, however, required chemical suppression of the groundcover and yields were further sustained by strip tillage.  Groundcovers varied in their competitiveness with corn, but none of those evaluated in this study could be used without some form of suppression.  Long term there does appear to be potential for selecting and improving groundcover species so that less suppression is required.  Finally, there were genetic differences among corn hybrids in their ability to tolerate the presence of a perennial groundcover.  Therefore, it should be possible to development hybrids that are specifically bred for growth in association with a perennial groundcover.  This work established the feasibility of using perennial groundcover to compensate for the environmental effects of removing of corn stover as a biofuel feedstock.  However, significant development work remains to be done to develop robust management practices that will ensure corn growers of competitive grain yields.  This will require significant investment in the co development of groundcover varieties and corn hybrids along with advanced tillage and other management practices.