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Ethanol from stover

Corn stover could provide as much as 20% of the feedstocks needed for ethanol production by 2030. But is corn stover sustainable? Will growers be able to remove corn stover without harming productivity and soil and water quality?

These are questions being tackled by researchers at Iowa State University (ISU) and USDA's National Soil Tilth Laboratory. They are in the first year of a three-year study that focuses on ground-cover species, hybrids that tolerate ground cover and how to manage ground cover.

Ground-cover species

Ken Moore, ISU agronomist, is evaluating 36 species of ground covers. The challenge is to find species that do not compete with corn during corn's critical growth stages, but that provide enough cover through fall and winter to minimize loss of soil nutrients and to protect soil from erosion by wind and water.

The ideal cover crop would go dormant in the summer so as not to compete with corn, but then grow during the cool season. In addition, its root system ideally would not compete with corn roots in drought conditions.

Moore says that perennial ryegrasses look promising. They are summer dormant and also are associated with fungal endophytes. Endophytes live symbiotically within perennial ryegrasses and fescues and produce toxins that confer insect and disease resistance to the grass. They also could help suppress weeds, Moore says.

Another ground cover showing early promise is sideoats grama, a warm season grass that does not have much growth activity until mid to late summer, says Scott Flynn, an ISU agronomy graduate student. Corn may already be in the eight-leaf collar stage by the time sideoats grama begins growing. But the grass continues to grow well under the corn canopy, Flynn says. He adds, however, that the sideoats grama may not persist the following season.

Competitive genetics

In the second experiment, Kendall Lamkey, ISU agronomist, is evaluating the genetic characteristics of 50 corn hybrids grown using three different treatments: a control with no cover crop, a treatment with sweet clover, and a treatment with Kentucky bluegrass. All 50 hybrids are open pedigree hybrids with the glyphosate-tolerance trait.

At harvest, Lamkey observed a notable difference between the control corn and corn that was intercropped with sweet clover. Corn planted with sweet clover was 1 ft. to 1½ ft. shorter.

Over the next two years, Lamkey will evaluate the stages in the corn life cycle that are important to determining yield in the presence of ground covers. He also will evaluate the grain weight as well as the weight of the above-ground biomass, which are roughly equal.

Carbon balancing

Jeremy Singer, agronomist, USDA National Soil Tilth Laboratory, established the third experiment using four ground-cover treatments in fall 2006, which will remain in continuous corn. The ground covers were white clover, Kentucky bluegrass, creeping red fescue and a mix of white clover and creeping red fescue. The mixture could provide a good balance of carbon and nitrogen inputs with less competition between plants, Singer says.

Singer also is evaluating management systems within the ground-cover species. They include:

  • Control with no cover crop;

  • Cover crop using a pre- and post-corn emergence 10-in. glyphosate herbicide band;

  • Cover crop using a pre- and post-corn emergence 10-in. glyphosate herbicide band with fall strip tillage;

  • Cover crop with spring broadcast paraquat (nonselective, non-translocated herbicide) burndown and 10-in. post glyphosate band; and

  • Cover crop with spring broadcast paraquat burndown and 10-in. post-glyphosate band with fall strip tillage.

The glyphosate will kill the cover crop where it was banded in the spring, but the cover crop will recover during the summer and in the fall when it is needed to protect the soil.

“The real question we hope to answer is how much carbon the cover crops can add to the soil to offset the carbon that will be harvested in the stover,” Singer says. Putting this carbon back in the soil is essential to maintain soil organic matter, which is critical to soil productivity.

“What we hope to find at the end of the three years are the best combinations of corn genetics, ground covers and management so we can move this research closer to being commercially viable,” Singer says.

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