Ecosystem-scale biogeochemical fluxes from three bioenergy crop candidates: How energy sorghum compares to maize and miscanthus

Authors: MOORE, CAITLIN - University Of Western Australia; VON HADEN, ADAM - University Of Illinois; BURNHAM, MARK - University Of Illinois; KANTOLA, ILSA - University Of Illinois; GIBSON, CHRISTY - University Of Illinois; BLAKELY, BETHANY - University Of Illinois; DRACUP, EVAN - University Of Illinois; MASTERS, MICHAEL - University Of Illinois; YANG, WENDY - University Of Illinois; DELUCIA, EVAN - University Of Illinois; Bernacchi, Carl

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2020
Publication Date: 3/1/2021
Citation: Moore, C.E., von Haden, A.C., Burnham, M.B., Kantola, I.B., Gibson, C.D., Blakely, B.J., Dracup, E.C., Masters, M.D., Yang, W.H., DeLucia, E.H., Bernacchi, C.J. 2021. Ecosystem-scale biogeochemical fluxes from three bioenergy crop candidates: How energy sorghum compares to maize and miscanthus. Global Change Biology Bioenergy. 13(3):445-458. https://doi.org/10.1111/gcbb.12788.
DOI: https://doi.org/10.1111/gcbb.12788

Interpretive Summary: The need for energy sources that are more sustainable and less carbon intensive has prompted research into a wide variety of crops to more efficiently product ethanol and other liquid fuels. Corn is currently the most widely grown bioenergy crop, but a perennial grass, miscanthus, has long been studied as a more productive alternative. But because miscanthus is a perennial, it takes longer to reach maturity and costs more money to plant than most annuals. Bioenergy sorghum is increasingly studied as a bioenergy crop because it is easy to plant and has very high productivity. This research addresses a comparison of the growth, water use, and ecosystem photosynthetic rates during the growing season for these three crops. The results show that sorghum behaves similar to corn in many ways, including planting, emergence, and establishment, but behaves more similar to miscanthus in the productivity, photosynthesis and water use. These results are limited to a single growing season, however, they are a critical data set for parameterizing models to extrapolate these crops beyond the field scale.

Technical Abstract: Perennial crops have been the focus of bioenergy research and development for their sustainability benefits associated with high soil carbon (C) and reduced nitrogen (N) requirements. However, perennial crops mature over several years and their sustainability benefits can be negated through land reversion. A photoperiod sensitive energy sorghum (Sorghum bicolor) may provide an annual crop alternative more ecologically sustainable than maize (Zea mays), that can more easily integrate into crop rotations than perennials, such as miscanthus (Miscanthus x giganteus). This study presents an ecosystem-scale comparison of C, N, water and energy fluxes from energy sorghum, maize and miscanthus during a typical growing season in the Midwest United States. Gross primary productivity (GPP) was highest for maize during the peak growing season at 21.83 g C m-2 d-1, followed by energy sorghum (17.04 g C m-2 d-1) and miscanthus (15.57 g C m-2 d-1). Maize also had the highest peak growing season evapotranspiration at 5.39 mm d-1, with energy sorghum and miscanthus at 3.81 mm d-1 and 3.61 mm d-1, respectively. Energy sorghum was the most efficient water user (WUE), while maize and miscanthus were comparatively similar (3.04, 1.75 and 1.89 g C mm-1 H2O, respectively). Maize albedo was lower than energy sorghum and miscanthus (0.19, 0.26, 0.24, respectively), but energy sorghum had a Bowen ratio closer to maize than miscanthus (0.12, 0.13 and 0.21, respectively). Nitrous oxide (N2O) flux was higher from maize and energy sorghum (8.86 and 12.04 kg N ha-1, respectively) compared to miscanthus (0.51 kg N ha-1), indicative of their different agronomic management. These results are an important first look at how energy sorghum compares to maize and miscanthus grown in the Midwest United States. This quantitative assessment is a critical component for calibrating biogeochemical and ecological models used to forecast bioenergy crop growth, productivity and sustainability.