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

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 × 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 day−1, followed by energy sorghum (17.04 g C m−2 day−1) and miscanthus (15.57 g C m−2 day−1). Maize also had the highest peak growing season evapotranspiration at 5.39 mm day−1, with energy sorghum and miscanthus at 3.81 and 3.61 mm day−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 and 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 with 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.

An assessment of the potential for biomass sorghum to be produced as a dedicated bioenergy crop in Iowa, USA

“…These values are higher than prior measured values of 5.1-5.6 for sorghum grown in central Iowa using similar methodology (Roby et al, 2017). However, peak LAI values exceeding 8 m 2 m -2 have been measured in Illinois (Moore et al, 2020) and Texas (Olson et al, 2012). To our knowledge, these crop did not suffer from lodging.…”

“…In a fertilizer rate trial at sites in Illinois (lower latitudes than Ames), peak yields ranged from 20.4-35.1 Mg ha -1 , with highest yields at the southernmost site (Maughan et al, 2012). Moore et al, 2020 measured an average peak biomass sorghum aboveground dry matter yield of 23.0 Mg ha -1 near Urbana, IL in 2018. Peak LAI in both seasons at SABR exceeded 8 m 2 m -2 across methods of measurement.…”

Modeling perennial bioenergy crops in the E3SM land model

“…Energy Farm located in the Midwest region of the United States. The mean annual precipitation at the UIUC Energy Farm is 1009 mm and the mean annual temperature is 10.9 • C with large seasonal variation ranging from monthly minimum below -5 • C in winter to monthly maximum above 25 • C in summer (Moore et al, 2021). The soil at the UIUC Energy Farm is deep and poorly drained silty clay loam.…”

“…Earth System Models (ESMs) that are used for climate projections should have adequate representation of crops due to the impact of agriculture on regional and global climate. However, most ESMs represent crops as generic-grass that fails to capture the various phenological phases of crops and differences across various crop species (Levis, 2010;McDermid et al, 2017;Moore et al, 2021). This simplistic representation of crops underestimates gross primary productivity and latent heat flux from agricultural-dominated regions (Lombardozzi et al, 2020).…”

Mobilizing sorghum genetic diversity: Biochemical and histological‐assisted design of a stem ideotype for biomethane production

“…The relevance of sorghum as a feedstock to support bioenergy production has been underlined at the economic and environmental levels in the United States (Cai et al, 2013; Fertitta‐Roberts et al, 2017; Fulton‐Smith and Cotrufo, 2019; Gautam et al, 2020; Moore et al, 2021; Oikawa et al, 2015), China (Liu et al, 2015), Latin America (Almeida et al, 2019; Rezende & Richardson, 2017), Africa (Vries et al, 2012), and Europe (Jankowski et al, 2020; Shu et al, 2020; Szambelan et al, 2018; Vlachos et al, 2015). Jointly with its use in starch and soluble sugar‐based first‐generation ethanol production (Szambelan et al, 2018), sorghum vegetative parts or even whole plants can also be used in second‐generation ligno‐cellulosic‐based ethanol (Almeida et al, 2019; Mitchell et al, 2016; Rooney et al, 2007) or anaerobic digestion (Barbanti et al, 2014; Pasteris et al, 2021; Shoemaker & Bransby, 2010; Thomas et al, 2017), taking advantage of their structural carbohydrates reservoir.…”