AMES, Iowa – A new study by Iowa State University is focusing on the effect an increase of growing cellulosic feedstocks (non-food crop residue left on idle cropland) used for ethanol production could have on land use and water quality – specifically nitrogen loss – in the Mississippi Atchafalaya River Basin in south-central Louisiana.

Kelsie Ferin, who recently received her Ph.D. in agronomy from Iowa State, conducted a modeling study based on the current Renewable Fuel Standard (RFS2) mandate, which set a goal to include 16 billion gallons of cellulosic ethanol production into gasoline by 2022.

She began working with Andy VanLoocke, Iowa State associate professor of agronomy, on two models: the Agro-IBIS (agroecosystem model) and the THMB (hydrology model).

She said VanLoocke “knew these two models would be a great fit to answer the questions we had about land use change driven by the Renewable Fuel Standard mandate on water quality within the Mississippi River Basin.

“Our project for this was to investigate the potential of bioenergy feedstocks, specifically focusing on miscanthus and switchgrass (perennial grasses capable of reducing nitrogen loss from soil and water when incorporated into the current landscape) on reducing nitrogen loss in the Mississippi River Basin,” she said.

She said she started researching this topic with a project funded through the Iowa Nutrient Reduction Center and the U.S. Department of Housing and Urban Development. 

“That project looked at the potential of miscanthus on the unprofitable cropland in the Raccoon River Basin (high-impact watershed in Iowa) under current and future climate conditions to investigate how much a reduction in nitrogen loss we could achieve,” she said.

“Knowing that the Renewable Fuel Standard was set to expire in 2022, and the full potential was never reached (the 16 billion gallons of cellulosic ethanol), we conducted our study to see how big of an impact the full mandate would have if it were achieved, and if we could create scenarios to obtain a reduction in nitrogen loss, while reaching the goals of the Renewable Fuel Standard mandate,” she added.

However, VanLoocke said, this benefit is greater when these grasses are replacing active cropland (i.e., corn and soybean production area) rather than on idle cropland.

“Based on current markets, growing them on the active corn and soybean acres wouldn’t turn a profit based on the economic model,” he said. “If we did plant the perennial grasses on active cropland, we would improve the water quality in our scenarios. It just didn’t make enough money to do so.”

Their research was recently published in the peer-reviewed journal, Environmental Science and Technology.

“The fundamental question is if we grew particular crops in the Mississippi River Basin, would we change the amount of nitrogen that we lose in the Gulf of Mexico?” VanLoocke said.

Three scenarios were tested and analyzed for nitrogen loss: 1) A baseline, which reflects ethanol production of 7.5 billion gallons of 100 percent corn grain-based ethanol produced prior to the renewable fuel standard; 2) A mid-production scenario, producing 15 billion gallons of corn grain ethanol; and 3) A high production example, producing 16 billion gallons of cellulosic ethanol using corn stover (the stalk, leaves, husks and tassels left in the field after harvesting the grain with a combine), miscanthus and switchgrass.

“The amount of ethanol production went from 7.5 billion gallons of corn grain ethanol in the baseline, to 15 billion gallons of corn grain ethanol in the scenarios,” Ferin said. “Our modeling simulations resulted in the 15 billion-gallons corn grain ethanol scenario having 8 percent greater nitrogen loss relative to the baseline. For the full corn grain and cellulosic ethanol scenario, it was between 16-17 percent more nitrogen loss.”

Ferin, who recently started a post-doctoral research position with the University of Wisconsin-Madison under Chris Kucharik, co-creator of the agroecosystem model, said a sensitivity study was also conducted where 100 percent of the cellulosic ethanol was produced with miscanthus and switchgrass, without corn stover.

In this case, she said the economic model determined 68 percent would be planted on active cropland, resulting in a 10 percent decrease in nitrogen loss relative to the corn grain and cellulosic ethanol production scenario.

“There’s no mandate that says 100 percent (of cellulosic ethanol) will 

come from miscanthus or switchgrass,” she said. “We just wanted to assess how big of an impact they could have on our current landscape.”

She said the other two scenarios were the 15 billion gallons of corn grain ethanol, and then the 15 billion gallons of corn grain, plus 16 billion gallons of cellulosic ethanol. 

She said the cellulosic portion includes corn stover, miscanthus and switchgrass, which were determined from the current Renewable Fuels Standard mandate.

“These scenarios helped our research by allowing us to understand how the current landscape and intense focus on corn production impacts nitrogen loss (and therefore can fuel the Gulf of Mexico Hypoxic Zone), and how bioenergy grasses like miscanthus and switchgrass have economic/ethanol potential, while reducing nitrogen loss,” she said.

“After 2022, when (the current mandate) expires, we hope our study will aid in decision making for a new Renewable Fuel Standard mandate if one were to be implemented, which will hopefully include an incentive for growing grasses like miscanthus and switchgrass on the landscape,” she added.

Environmentally speaking, she said it is better to plant miscanthus and switchgrass on active cropland. Economically speaking, she said the research showed it is more profitable to use the active cropland for corn and soybeans.

Ferin and VanLoocke’s research was supported by the new U.S. Department of Energy Center for Advanced Bioenergy and Bioproducts Innovation, which focuses on increasing the value of bioenergy crops with a ‘plants as factories’ approach.

Ferin and VanLoocke said if the new center is successful, crops like miscanthus and switchgrass containing valuable oils, fatty acids and other bioproducts in their stems could be extracted and sold separately from the lower-value cellulosic biomass.

Ferin and VanLoocke said there is potential to grow more cellulosic feedstocks if they can be utilized for products other than ethanol.

“There needs to be other innovations around cellulosic feedstocks to get over the economic hump,” VanLoocke said. “The future of cellulosic ethanol depends on innovations, like finding more value within the crops that we are growing so we can market to multiple markets, and be more diverse.”