WASHINGTON, D.C. – Perennial bioenergy crops such as miscanthus and switchgrass have shown advantages to traditional annual bioenergy crops like corn and soybean rotations. They  assimilate more carbon dioxide, and require fewer nutrients and less water, according to a new study by the U.S. Department of Energy.

“This suggests these perennials are promising bioenergy crops,” said Jennie Rice, senior research scientist at Pacific Northwest National Laboratory, and Bob Vallario, biological and environmental research program manager for the U.S. Department of Energy Office of Science, and co-authors of the study.

Rice and Vallarion projected biofuel production will continue its global expansion. However, to understand the effects of this trend, they said scientists must accurately represent biofuel crops in land surface models.

The study constitutes the first attempt to simulate perennial bioenergy crops in the Community Terrestrial System Model.

“The (model) is an important multisector model,” the researchers said. “With this enhancement, (this model) becomes one of the first land models that can evaluate the complex dynamics of biofuel expansion. The model incorporates energy, water, land and climate dynamics, and it works at local, regional and global scales.”

Using observations from biofuel plants in the Midwest, researchers simulated two biofuel perennial plants, miscanthus and switchgrass.

Researchers implemented miscanthus and switchgrass into the Community Terrestrial System Model, using parameters for photosynthesis, seasonal changes, resource allocation, plant decomposition and carbon cost for nitrogen uptake.

“They simultaneously integrated land management practices,” the study said. “When the researchers validated the simulations against site-level measurements, the results demonstrated that the model was capable of capturing both overall patterns of carbon and energy fluxes, and the plants’ growth from leaf emergence to old age.”

According to the study, the perennials miscanthus and switchgrass tend to be more productive than a maize-soybean rotation, and offer larger net carbon sinks as a result of their longer growing season, larger leaf areas, and above-ground biomass, which is plant or animal material used as fuel to produce electricity or heat.

Compared to annual crops, these perennials crops lead to increased transpiration, lower annual runoff and larger carbon uptake, the study said.

“The model simulations suggest that with higher carbon dioxide assimilation rates and lower demands for nutrients and water, high-yielding perennial crops are promising alternatives to traditional annual crops for bioenergy feedstocks,” the study said.

“This promise includes stabilizing greenhouse gas concentrations,” the study continued. “It also includes the environmental conservation benefits from reducing fertilizer application, which alleviates surface water and groundwater contamination.”

Emily Heaton, University of Illinois at Urbana-Champaign professor of regenerative agriculture, and extension biomass specialist, said, “Perennial biofuel crops are better than annual crops at sustainably storing sunlight in plant biomass (nature’s battery).

“Because perennials only need to be planted once, and because they internally recycle their nutrients each year, it takes less fossil fuel, fertilizer and irrigation to grow them,” she said. “Biofuels are the original fuel. Modern biofuels like ethanol have been around since the automobile was invented, and you can find many stories about Henry Ford’s interest in plant-based fuels while the liquid fuel industry was developing.

“Corn grain ethanol and sugarcane ethanol have been mature, widely-used fuels in the U.S. and Brazil, respectively for decades,” she added.

She said the Community Terrestrial System Model used in the study is a new unified model for research and prediction in climate, weather, water and ecosystems supported by the U.S. National Center for Atmospheric Research.

“I have not personally used it, but my research benefits from the tools and predictions developed by it,” she said. “In my research, we test predictions made by models like (the Community Terrestrial System Model), and provide data on biofuel crops that the modelers can use.

“Said another way, we do experiments in the field to inform the models about perennial crop growth,” she added. “If the model predicts something that doesn’t match what we observe in the field, we do experiments to help understand why.”

She said her research investigates “the role of perennial plants in a regenerative agriculture portfolio. We identify ways to use perennial crops to regenerate and improve our air, soil, and water resources, while also enhancing natural habitat and human communities,” she said.

“Much of my research centers on integrating perennial crops like those in the study (miscanthus and switchgrass) into row-crop land in ways that ensure rural communities prosper, and the natural resource base on which we all depend thrives,” she added.

She said there are also other advantages of bioengineered crops for biofuel and biomass production. “While switching to renewable energy like wind and solar are great for putting less carbon dioxide in the air, only crops actually ‘remove’ carbon dioxide from the atmosphere,” she said. “Basically, they offer one of our greatest chances to work with nature to protect and enhance the foundation of life on this planet,” she added.

Rice and Vallarion said although the local-scale simulations (used in the study) shed light on the potential benefits of using these perennial grasses as bioenergy feedstocks, quantifying the consequences of their plantations at larger scales warrants additional investigation.