Project explores alternative cropping systems for the bioeconomy

By LAURA MILLER, Newsletter editor

Andy Heggenstaller grew up around dairy farms in Pennsylvania, where an integrated crop/livestock system works well. The crops feed the cows, the cows fertilize the crops, and the system provides multiple economic and environmental benefits for farmers and their communities.

Since coming to Iowa six years ago, he's been hoping to find the functional equivalent of this self-sustaining system for the state's emerging biofuels industry. How can cropping systems work together to provide feedstock biomass, protect the environment and support farmers and rural communities?

"You have to look at cropping systems differently than what we have now; you need to consider a system that produces more than one crop at one time of the year," Heggenstaller explained. "We found that alternative systems could produce significantly more biomass than a lone corn crop. They also leached less nitrogen, so the environmental impacts were reduced."

Heggenstaller is a graduate research assistant on projects managed by Matt Liebman, the Henry A. Wallace Endowed Chair for Sustainable Agriculture and professor of Agronomy, and Rob Anex, associate professor in Agricultural and Biosystems Engineering. The Leopold Center's Ecology Initiative provided special grants to fund part of the research, which also was supported by the ISU Plant Sciences Institute. Andy will complete his PhD in Agronomy and Biorenewable Resources and Technology later this year.

"It's a matter of working with the growth patterns of our crops and climate," he explained. "Triticale, a cereal that is planted in the fall, is well adapted to Iowa and produces a lot of biomass by late spring, so this project was designed to find out how it could be combined with other crops to improve the system."

The project included field plots west of Ames on the ISU Agronomy Research Farm. In 2006 and 2007, the team evaluated productivity and nutrient utilization in a conventional corn production system (sole-crop corn) and three bioenergy double-cropping systems. The alternative systems were fall-seeded triticale (a cross between wheat and rye, planted after soybeans are harvested) followed by one of three summer-adapted crops:

corn,

sorghum-sudangrass or

sunn hemp (a tropical legume that can fix large quantities of atmospheric nitrogen).

In all plots, triticale was harvested for biomass in early June, prior to full maturity. Summer crops, seeded directly following triticale, were harvested for biomass in late fall after a killing frost. Sole-crop corn was harvested at normal maturity, in early October, with dry matter separated into grain and stover. Crop and soil nitrogen were assessed three times each year (mid-April, early June and early October) to determine if opportunities for nitrogen leaching would be reduced in the alternative systems.

Here's what they found:

Triticale-corn and triticale-sorghum cropping systems produced 25 percent more biomass (on a dry matter basis) than a sole-crop corn system.

Gross potential ethanol yield for the triticale/corn system was 15 percent greater than sole-crop corn (one acre could yield an additional 123 gallons of ethanol); of course, the double-crop system also required greater energy inputs.

Due to increased crop nitrogen uptake by the alternative systems, leachable soil nitrogen relative to sole-crop corn was reduced by 34 percent, 78 percent and 25 percent, respectively, in April, June and October.

However, the alternative systems also produced biomass rich in nutrients. For example in the triticale/corn system, harvest of all biomass and grain resulted in the export of 265 pounds of nitrogen per acre (compared to 137 lb/acre for sole-crop corn), 42 pounds of phosphorus per acre (compared to 29 lb/acre for sole-crop corn), and 235 pounds of potassium per acre (compared to 81 lb/acre for sole-crop corn).

The researchers noted that sustained removal of large quantities of this nutrient-rich biomass would necessitate increased fertilizer inputs, or recycling the nutrients contained in the biomass.

“We’re trying to figure out how much of the nutrients in the biomass we can actually recover in the process of converting it into fuel and energy," Heggenstaller explained. "If the biomass is gasified, we get a form of charcoal as a by-product that can be used as a fertilizer but also might help increase soil organic matter."

“In a lot of ways the concept is like the integrated system with dairy cows. The biomass gets converted into a product we need, but the nutrients get cycled back to the land. Whether we are making milk or ethanol, sustainability is ultimately going to be determined by how we put the system together.”