Conservative amounts of corn residue can be removed annually for cellulosic ethanol production without affecting future grain yields, updated research data shows.

The ongoing study, by Iowa State University and USDA researchers near Emmetsburg, IA, is funded by Poet, which plans to build a cellulosic ethanol plant there.

The company reports that Iowa State has analyzed data from the third year of the study on how soil health is affected when crop residue is removed. Poet’s planned 25-million-gallon-per-year plant, Project Liberty, will use corncobs, leaves, husks and some stalk to produce renewable fuel.

The newest data confirms previous assertions that removing about 1 dry ton per acre (about 25% of the above-ground crop residue) will not cause significant nutrient loss. In fact, corn yields continued to show no yield loss or moderate increases in fields with that rate of biomass removal.

"Based on this study, we conclude that 1½-2 tons/acre of corn stover can safely be harvested" from fields similar to those used in the study, according to the research summary prepared by Douglas Karlen, USDA-ARS soil scientist, and Stuart Birrell, Iowa State ag engineer. Appropriate removal rates will vary depending on how productive the soil is in a specific area, they add.

Poet is committed to a conservative approach to biomass harvesting, says Jim Sturdevant, Project Liberty director.

"We're contracting for fewer tons per acre to ensure good soil management even in years when yields are lower,” says Sturdevant. “Also, our farmers have moved away from traditional methods of stover removal: of chopping, raking, baling and leaving the field black."

Farmers harvesting for Poet typically turn off the choppers on their combines and leave windrows behind during grain harvest. They don’t rake the biomass before balers gather it. Last fall, 85 farmers harvested 56,000 tons of biomass and are almost finished delivering it to Project Liberty's 22-acre stackyard. They’re also developing conservation plans with help from the Natural Resources Conservation Service.

Once operational, the plant will use approximately 300,000 tons of biomass annually, Sturdevant reports. Construction is planned to begin later this year.

Karlen and Birrell will continue their work this year. They stress that farmers should "know your land," and say routine soil testing and plant analysis are good practices for monitoring nutrients.

Based on the three years of data, they recommend that farmers apply about 15 lbs additional potassium per acre to fields where biomass harvesting has occurred at a rate similar to what Poet contracts. No significant increase for nitrogen or phosphorus replacement compared to grain-only harvest is needed.

Biomass removal caused no grain yield losses and often moderate yield improvements over the control plots. One theory is that removing a small amount of cover helps the soil warm earlier in spring, causing earlier corn plant emergence.

"We'll continue to monitor the soil through our on-going partnership with Iowa State and USDA, and we'll share that data with farmers," says Sturdevant. "We've learned a lot from the first three years of data and from the feedback from farmers. Results have been positive, but we're trying to be conservative as we keep learning."

The research summary is available at Poet’s Web site.