Switchgrass has gripped the soils of the American Midwest for millions of years, but soon, this earthbound prairie grass may take to the skies. New research from the University of Illinois Urbana-Champaign has identified economic and environmental factors that position switchgrass as a promising candidate for sustainable aviation fuel (SAF). With global efforts intensifying to reduce aviation emissions, the potential role of switchgrass could prove transformational.
The Sustainable Aviation Fuel Grand Challenge, launched in 2021, aims to scale SAF production to 35 billion gallons annually by 2050, halving greenhouse gas emissions from aviation. Switchgrass, forecasted to contribute up to 230 million dry tons per year, stands among several purpose-grown bioenergy feedstocks that could help meet this ambitious target. Not only does this perennial species produce abundant biomass, but it can also be harvested annually for a decade or longer without replanting. It demands far less nitrogen fertiliser than traditional crops such as maise and delivers vital ecosystem services, making it a desirable option for sustainable agriculture.
Scientists have long recognised the bioenergy potential of switchgrass. Yet, much of the existing research relied on older, less productive cultivars and smaller experimental plots or did not fully account for necessary fertiliser inputs. Addressing these gaps, researchers at the University of Illinois conducted two new studies in which modern, high-yielding “energy” cultivars were grown at field scale across the Midwest. The research sought to identify the most profitable cultivars for different regions while simultaneously comparing their environmental impacts to those of maise, a traditional bioenergy crop.
D.K. Lee, senior author of both studies and professor in the Department of Crop Sciences within the College of Agricultural, Consumer and Environmental Sciences, explained the rationale behind the work. “All the data that helps us estimate switchgrass suitability for SAF comes from small plot research or older forage-type switchgrass cultivars. We wanted to test high-yielding switchgrass cultivars on a larger scale to provide a more accurate picture of the benefits these new cultivars provide,” Lee stated. Under the leadership of postdoctoral researcher Muhammad Umer Arshad, the team planted three newer energy-type cultivars — Independence, Liberty, and Carthage — alongside two forage types — Shawnee and Sunburst — on marginal lands in Illinois, Iowa, Nebraska, and South Dakota. They tested two fertiliser rates, 28 and 56 kilograms of nitrogen per hectare, significantly lower than the 200 kilograms typically used for maise.
The results, after five years, were compelling. Independence and Liberty cultivars consistently outperformed the forage types in profitability across all locations, although the optimal nitrogen rate varied by site. “In most cases, 56 kilograms per hectare achieved higher yields, but in some sites, 28 kilograms performed better in terms of profit,” Arshad noted. Moreover, the most profitable cultivar differed depending on hardiness zones: Independence excelled in zone 6a, Liberty in zone 5b, and Carthage in zone 4b. These findings suggest that farmers could successfully convert marginal lands into profitable bioenergy production sites within two years with strategic cultivar selection.
Beyond profitability, switchgrass also offers significant environmental benefits. In a companion study led by postdoctoral fellow Nictor Namoi, researchers assessed ecosystem services such as soil greenhouse gas emissions and nitrate leaching from switchgrass fields, comparing them directly with no-till maise fields. Results demonstrated that switchgrass dramatically reduced environmental impacts: nitrous oxide emissions and nitrate leaching were significantly lower, with nitrate leaching decreasing by 80% by the third year. Switchgrass’s reduced nitrogen fertiliser requirements explain this improvement, highlighting the environmental advantage of cultivating purpose-grown energy crops on marginal lands.
While carbon dioxide emissions from switchgrass fields were more than 50% higher than those from maise after the second year, the researchers attribute this to switchgrass’s significantly greater belowground biomass, leading to increased root respiration. However, this apparent drawback may herald long-term carbon sequestration benefits. “When we measure the total biomass of switchgrass, there’s about 10 megagrams of carbon belowground. That’s huge,” Lee emphasised. The extensive root systems of switchgrass support carbon storage and enhance soil health and resilience over time.
Although the current demand for bioenergy feedstocks remains modest, mainly due to low commodity and oil prices, the researchers are optimistic about the future. As global markets shift and renewable energy policies strengthen, switchgrass is well-positioned to enter commercial SAF production. “Our research ensures that we can feed productive cultivars into the SAF production system once the economy and the technology are ready to transition,” Namoi said. With its profitability, environmental services, and adaptability to marginal lands, switchgrass may soon find itself not just rooted in Midwestern soils but soaring through the skies.
More information: Nictor Namoi et al, Field-scale evaluation of ecosystem service benefits of bioenergy switchgrass, Journal of Environmental Quality. DOI: 10.1002/jeq2.70025
Journal information: Journal of Environmental Quality Provided by University of Illinois College of Agricultural, Consumer and Environmental Sciences