Energy Sorghum May Combine Best of Annual, Perennial Bioenergy Crops

by Julie Wurth (University of Illinois at Urbana-Champaign Institute for Sustainability, Energy, and Environment) ... A study by researchers at the U.S. Department of Energy (DOE) Center for Advanced Bioenergy and Bioproducts Innovation (CABBI) found that energy sorghum (Sorghum bicolor) behaves more like miscanthus in the way it efficiently captures light and uses water to produce abundant biomass. It has higher nitrogen emissions like maize, but researchers believe careful fertilizer management could reduce those levels.

The study, published in Global Change Biology: Bioenergy, offers an important first look at how energy sorghum compares to maize and miscanthus grown in the Midwest, providing critical data for biogeochemical and ecological models used to forecast crop growth, productivity, and sustainability. It was led by former CABBI Postdoctoral Researcher Caitlin Moore and her advisor, Carl Bernacchi, Plant Physiologist with the U.S. Department of Agriculture's Agricultural Research Service and Adjunct Professor of Plant Biology and Crop Sciences at the University of Illinois Urbana-Champaign (UIUC).

Sorghum appears to be a "middle-road crop," with an annual growth cycle but the ability to use much less water than maize to produce "a ton" of biomass, said Moore, now a Research Fellow at the University of Western Australia's School of Agriculture and Environment. "It certainly holds promise as a crop that supports the bioenergy economy."

The researchers conducted ecosystem-scale comparisons of carbon, nitrogen, water, and energy fluxes of Sorghum bicolor with maize and Miscanthus x. giganteus at the UIUC Energy Farm during the 2018 growing season, a near-average year in terms of temperature, rainfall, and soil moisture. The fluxes reflect "the breathing of the ecosystem"—how water, carbon dioxide (CO₂), nitrogen (N), and energy move between plants and the atmosphere, Moore said.

The long-term ecological sustainability of bioenergy crops depends on how well the system "breathes." An ideal crop would use water and light efficiently to maximize the amount of biomass, keep carbon in the soil instead of releasing it into the atmosphere, and require little nitrogen fertilizer, which can leach into water or react with soil to produce nitrous oxide (N2O), a potent greenhouse gas.

Energy sorghum falls somewhere in between. As an annual, it can be easily rotated with other crops like soybeans and maize. It's photoperiod-sensitive, so it produces generous yields of biomass late into the season when grown in regions with long days. And because it is drought-tolerant, energy sorghum can be grown in low-rainfall regions, alleviating the pressure a growing biofuel industry could place on existing land used for food production. READ MORE

Therese Mitros et al, Genome biology of the paleotetraploid perennial biomass crop Miscanthus, Nature Communications (2020). DOI: 10.1038/s41467-020-18923-6

Caitlin E. Moore et al. Ecosystem‐scale biogeochemical fluxes from three bioenergy crop candidates: How energy sorghum compares to maize and miscanthus, GCB Bioenergy (2020). DOI: 10.1111/gcbb.12788