Sorghum biomass production in the continental United States and its potential impacts on soil organic carbon and nitrous oxide emissions

Abstract

National scale projections of bioenergy crop yields and their environmental impacts are essential to identify appropriate locations to place bioenergy crops and ensure sustainable land use strategies. In this study, we used the process‐based Daily Century (DAYCENT) model with site‐specific environmental data to simulate sorghum (Sorghum bicolor L. Moench) biomass yield, soil organic carbon (SOC) change, and nitrous oxide emissions across cultivated lands in the continental United States. The simulated rainfed dry biomass productivity ranged from 0.8 to 19.2 Mg ha−1 year−1, with a spatiotemporal average of 9.7‐2.4+2.1 Mg ha−1 year−1, and a coefficient of variation of 35%. The average SOC sequestration and direct nitrous oxide emission rates were simulated as 0.79‐0.45+0.38 Mg CO2e ha−1 year−1 and 0.38‐0.06+0.04 Mg CO2e ha−1 year−1, respectively. Compared to field‐observed biomass yield data at multiple locations, model predictions of biomass productivity showed a root mean square error (RMSE) of 5.6 Mg ha−1 year−1. In comparison to the multi State (n = 21) NASS database, our results showed RMSE of 5.5 Mg ha−1 year−1. Model projections of baseline SOC showed RMSE of 1.9 kg/m2 in comparison to a recently available continental SOC stock dataset. The model‐predicted N2O emissions are close to 1.25% of N input. Our results suggest 10.2 million ha of cultivated lands in the Southern and Lower Midwestern United States will produce >10 Mg ha−1 year−1 with net carbon sequestration under rainfed conditions. Cultivated lands in Upper Midwestern states including Iowa, Minnesota, Montana, Michigan, and North Dakota showed lower sorghum biomass productivity (average: 6.9 Mg ha−1 year−1) with net sequestration (average: 0.13 Mg CO2e ha−1 year−1). Our national‐scale spatially explicit results are critical inputs for robust life cycle assessment of bioenergy production systems and land use‐based climate change mitigation strategies.

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

“…As the energy sorghum system reaches steady state, the C and N fluxes are likely to shift drastically to reflect the perpetual reduction in biomass C and N inputs (Jin et al, 2014; Kent et al, 2020). Recent model‐based work showed the potential for energy sorghum to increase soil organic C through root biomass input in regions of the United States where rainfall, temperature and moisture availability facilitate high growth rates (Gautam et al, 2020). However, this study was based on broad assumptions made regarding agronomic management and the energy sorghum variety used (Gautam et al, 2020), so further observational studies of long‐term ecosystem C and N pools and fluxes are needed to fine‐tune models that assess the long‐term differences between these three bioenergy crop candidates.…”

“…drought, floods and frost) and for assessing inter‐annual biogeochemical differences. Perhaps most uncertain for energy sorghum are its long‐term effects on soil organic C due to the high amount of biomass removed during harvest with little stover return (Dou et al, 2014; Gautam et al, 2020; Mitchell et al, 2016). A detailed understanding of the interaction between crop type, climate and management will be critical for forecasting the long‐term sustainability of these key bioenergy crops that will play an important role in ensuring the United States meets its future cellulosic bioenergy requirements.…”

Production Cost and Carbon Footprint of Biomass-Derived Dimethylcyclooctane as a High Performance Jet Fuel Blendstock

“…For the current state-of-technology scenario, the soil organic carbon (SOC) sequestration potential of biomass sorghum, on average, of -0.46 metric tons of CO2e/ha 20,21 and electricity generated onsite offset 18% and 44% of the total GHG emissions from DMCO production stages, respectively(Fig. 4-a).…”

Supply Cost and Life-Cycle Greenhouse Gas Footprint of Dry and Ensiled Biomass Sorghum for Biofuel Production

“…This net SOC sequestration factor reduces the GHG footprint by an average of 25% (Figure 2b). The SOC sequestration potential of biomass sorghum depends on sitespecific biomass yield, nutrient application, irrigation, soil type, management history, and local climate, which we account for in the uncertainty analysis, 11,58 but warrants further in-depth study.…”