Trade‐offs across productivity, GHG intensity, and pollutant loads from second‐generation sorghum bioenergy

Abstract

Greenhouse gas (GHG) intensity is frequently used to assess the mitigation potential of biofuels; however, failure to quantify other environmental impacts may result in unintended consequences, effectively shifting the environmental burden of fuel production rather than reducing it. We modeled production of E 85 , a gasoline/ethanol blend, from forage sorghum (Sorghum bicolor cv. photoperiod LS) grown, processed, and consumed in California's Imperial Valley in order to evaluate the influence of nitrogen (N) management on well-to-wheel (WTW) environmental impacts from cellulosic ethanol. We simulated 25 N management scenarios varying application rate, application method, and N source. Life cycle environmental impacts were characterized using the EPA's criteria for emissions affecting the environment and human health. Our results suggest efficient use of N is an important pathway for minimizing WTW emissions on an energy yield basis. Simulations in which N was injected had the highest nitrogen use efficiency. Even at rates as high as 450 kg N ha À1 , injected N simulations generated a yield response sufficient to outweigh accompanying increases in most N-induced emissions on an energy yield basis. Thus, within the biofuel life cycle, trade-offs across productivity, GHG intensity, and pollutant loads may be possible to avoid at regional to global scales. However, trade-offs were seemingly unavoidable when impacts from E 85 were compared to those of conventional gasoline. The GHG intensity of sorghum-derived E 85 ranged from 29 to 44 g CO 2 eq MJ À1 , roughly 1/3 to 1/2 that of gasoline. Conversely, emissions contributing to local air and water pollution tended to be substantially higher in the E 85 life cycle. These adverse impacts were strongly influenced by N management and could be partially mitigated by efficient application of N fertilizers. Together, our results emphasize the importance of minimizing on-farm emissions in maximizing both the environmental benefits and profitability of biofuels.

Simulating impacts of nitrogen fertilization using DAYCENT to optimize economic returns and environmental services from bioenergy sorghum production

“…Lower optimum rates might be attributed to greater yield responses to N in irrigated systems and under sweet sorghum production compared with photoperiod‐sensitive sorghum. Our analyses for economic and environmental outcomes in response to N fertilization were not thorough, but the results restrained the optimum N rate range that would have not been achieved if only economic or environmental analysis were conducted alone (Amatya, Wight, Mjede, & Hons, 2014; Fertitta‐Roberts et al., 2017). Since biogeochemical models integrate weather, soil, crop, and field management information, a verified model can be used as a tool to provide reference for optimum N rate determination in different locations using the same assessment conducted in this study.…”

“…However, when GHG mitigation from fossil fuel replacement by bioethanol produced from bioenergy sorghum feedstock was considered, global NetGHG emissions became negative at any N rate, implying substantial GHG mitigation potential in bioenergy sorghum systems (Figure 8). Greenhouse gas mitigation from biofuel production outweighed the emissions resulting from N fertilization, even at a N rate of 450 N kg ha −1 , in another study conducted in California's Imperial Valley where the sorghum biomass was responsive to N addition and multiple harvests were conducted in a calendar year (Fertitta‐Roberts, Spatari, Grantz, & Jenerette, 2017). When it comes to net economic profit to N application by accounting for both bioenergy sorghum biomass and N fertilizer prices, the RTN trend line increased as N rate increased and peaked around the rate of 140 N kg ha −1 , then started declining afterwards (Figure 8).…”

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.…”

An optimization framework to identify key management strategies for improving biorefinery performance: a case study of winter barley production

“…The biogeochemical properties of cropland influence soil GHG emissions. Due to the spatially diverse characteristics of soil GHG emissions, selecting appropriate nitrogen fertilizer management specific to soil types can help reduce the contribution of soil GHG emissions to the biofuel's carbon intensity 9,24 . Besides the cultivation parameters, optimizing feedstock transportation, feedstock‐to‐energy conversion technologies, and biorefinery's co‐product use can improve the life cycle performance of the biofuel.…”

“…Due to the spatially diverse characteristics of soil GHG emissions, selecting appropriate nitrogen fertilizer management specific to soil types can help reduce the contribution of soil GHG emissions to the biofuel's carbon intensity. 9,24 Besides the cultivation parameters, optimizing feedstock transportation, feedstock-to-energy conversion technologies, and biorefinery's co-product use can improve the life cycle performance of the biofuel. Several studies have optimized parameters across the feedstock-fuel production chain, which significantly increases or decreases the lifecycle carbon intensity of the biofuel.…”