There's a question floating out there about producing biomass-based biofuels: How much crop residue can you remove from a field and still have left what you need for healthy cropland? While a lot of biomass proponents are hot about using switchgrass and other perennial crops, corn stover is also going to be a great resource, as work by Agco and Vermeer is showing. Iowa State University researchers may have an answer - living cover crops.

Two years into a study looking at methods of combining a living cover crop between corn rows, the researchers have found that corn yields can be maintained. They were testing between-row cover grasses as part of research looking at ways to reduce soil runoff and keep crop nutrients in the soils while residues are removed to produce biofuels.

With U.S. government targets calling for 30% displacement of petroleum consumption with fuels made from biomass by 2030, researchers are studying ways to harvest more stover. Targets will require moving as much as 75% of stover to use as feedstock for biofuel production, but removing that much stover can cause more water runoff, creating a host of issues.

One approach to keeping soil in place would be to plant grasses between corn rows that would stay in the field year round - in effect growing corn in perennial sod. Sounds like a great idea, but farmers won't do it if the practice reduces yield. After two years of researching the idea, researchers say the system allows removal of up to 95% of stover while boosting the amount of carbon kept in the soil, increasing water use efficiency in corn and maintaining corn yield.

One cropping system the team examined in 2009, for example, increased harvest from about 195 bushels per acre using traditional methods to more than 209 bushels per acre with the new system. And they did that while improving the soil and harvesting almost all the stover.

While they're not saying they've uncovered the perfect system (and in the photo below you can see it does look odd), they are encouraged by the results so far. They got these kinds of improved yields in 2008 (a year of record floods) and 2009 (with the coolest July on record). In each of those years, the researchers were able to harvest close to 100% of the stover and maintain yields similar to, or better than, the no-ground-cover control crop. And they increased carbon additions to the field.

This was a thorough test as researchers looked at 36 different ground covers, mostly grasses, different tillage systems including no-till and strip-till and 50 different corn hybrids. In addition they tried a range of chemical treatments. One key they discovered is to find a grassy ground cover that is less active in the spring allowing the corn to absorb needed water and sunlight at the beginning of the growing season with less competition.

The idea of more than one species surviving in a single field isn't a new idea, of course. Researchers point out that traditional prairies contain many different grass species and plants that complemented ech other while competing for water, sun and inputs. Researchers on this project include Ken Moore, professor of agronomy; Jeremy Singer, assistant professor of agronomy and researcher at USDA's National Laboratory for Agriculture and the Environment; and Kendall Lamkey, professor of agronomy and Pioneer Distinguished Chair in maize breeding.

The research plot on the Iowa State University Agronomy Farm shows how different combinations of cover crop and corn net different results. Early research has shown that with some combinations, almost all corn stover can be removed for biofuels while yields remain high and soil improves.