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Switchgrass cultivation presents some challenges including exacerbating indirect land use change, stand establishment, and logistical challenges

Summary​

Switchgrass faces several challenges as a bioenergy crop despite its high advertised potential. Habitat destruction concerns arise from potential land use changes, including conversion of conservation lands and soil organic carbon benefits may be limited without no-till practices. Commercial cultivation requires nitrogen fertilizer, whose production emits CO₂. Stand establishment is difficult due to weed competition, water stress susceptibility, and a 1 – 2 year maturation period. Genetic concerns exist around trait transfer to between selectively bred and native populations. Storage and handling present logistical challenges due to low bulk density, and por flowability.

Switchgrass is considered the "model" high potential energy crop in the United States, exhibiting traits such as high biomass yield, ability to grow on infertile land, adaptability to US growing conditions, and its ability to store soil organic carbon. However, switchgrass is not without its issues that can limit its success as a "sustainable" energy crop.

Habitat destruction (direct and indirect land use change)​

One of the major concerns with switchgrass is its links to habitat destruction through direct and indirect land use change (ILUC). Although switchgrass has definitively proven that it can be grown on what is considered marginal land with low fertility, financial incentives and the desire to maximize yields will most likely lead to agricultural land being used for switchgrass cultivation to some degree 1 2. If this occurs on a large enough scale that it leads to indirect land use change in areas of pristine nature, many of the environmental benefits of switchgrass biofuels can be erased 3. With regards to direct land use change, conservation plantings such as those found in the United States Conservation Reserve Program (CRP) are likely to be converted to switchgrass cultivation 1. However, it should still be noted that switchgrass can provide wildlife habitat and soil protection benefits in the same way as conservation plantings.

Questionable soil organic carbon benefits​

Switchgrass has the ability to increase soil organic carbon (SOC) due to its extensive root system. However, research has shown that the SOC benefits of switchgrass have low resistance to decomposition back into the atmosphere if exposed to the atmosphere, meaning that unconventional cropping systems such as no-till may be required to maintain the SOC benefits 4. There currently is a gap in the literature relating to the long term effects of switchgrass cultivation and reestablishment that would need to be filled to better quantify the sustainability benefits of switchgrass.

The concerns of releasing stored soil organic carbon are also relevant to conservation land such as Conservation Reserve Program which would need to be converted back into productive land. In general if no-till cultivation is used, soil organic carbon levels tend to remain the same after revegetation 1.

Fertilizer usage​

Although switchgrass can grow in low fertility soils, commercial cultivation primarily requires the use of nitrogen fertilizer in order to produce high yields 1. High yields are generally favorable as they increase crop profitability for farmers and utilize less land, leading to less land use change. Commercial nitrogen fertilizers are generally ammonia (NH₃) based, produced by the Haber-Bosch process, which requires high temperatures and pressures for successful synthesis. Hydrogen (H₂), the other important component in ammonia production, is almost exclusively produced via steam methane reforming (SMR) of natural gas, which releases large amounts of carbon dioxide (CO₂) into the atmosphere 5. These emissions could be reduced if hydrogen is produced through sustainable methods such as electrolysis with clean energy.

Stand establishment​

Although switchgrass is considered a durable and resilient crop once mature, it is generally considered a difficult crop to establish 6. Competition from weeds is a major challenge for initial switchgrass cultivation and a major cause of crop failure, often requiring the application of herbicides 1. Additionally, switchgrass is at its most susceptible to water stress when it is being established, meaning that costly irrigation may be required if rainfall is insufficient 6. Lastly, switchgrass requires 1 – 2 years in order to reach its maximum growth potential, with many test plots requiring at least a year before the first harvest 6. These three challenges introduce a high level of uncertainty and financial risk to farmers who may be dissuaded from investing the time and capital into switchgrass cultivation.

Sterility​

Switchgrass is native to the United States, which dampens fears of switchgrass becoming an invasive pest. However, concerns do exist regarding the sterility of switchgrass cultivars that have been naturally selected to optimize for usage as an energy crop. Switchgrass is an out crossing crop, meaning that it is fertilized with pollen from other switchgrass plants, passing on the genetic material of both plants. If switchgrass monocultures are grown nearby native populations, the selected energy crop traits could be passed onto the native populations 6.

Storage and handling​

It is generally recommended that switchgrass be harvested once per year in order to maximize yields and maintain stand health. This means that for a large-scale lignocellulosic biofuel industry to run all year round, the majority of biomass will need to be stored in some form or another. Baling is the most cost-effective form of switchgrass storage, but due to the low bulk density of switchgrass bales, this can lead to cumbersome and expensive storage where losses are inevitable 6.

A secondary challenge with switchgrass is that its low bulk density makes it a logistical challenge to transport and handle. For a hypothetical large-scale refinery, almost constant round-the-clock truckloads of switchgrass bales would be required to meet the demand of the production line 7. Additionally, feedstocks with low bulk density that are grassy tend to have poor flowability and can easily clog up production lines, adding extra labor costs and inefficiencies 7.

Pelletization, where biomass is compressed into small and dense pellets, has been proposed as a solution to the logistical challenges of switchgrass, which would effectively address storage and handling issues, while allowing biorefineries to operate at further distances from the biomass source. However, pelletization itself is a costly and energy-intensive process, which also introduces its own unique challenges to the ethanol biochemical conversion process.

Sources​

Footnotes​

  1. Downing, M., Eaton, L. M., Graham, R. L., Langholtz, M. H., Perlack, R. D., Turhollow, A. F., ... & Brandt, C. C. (2011). U.S. billion-ton update: Biomass supply for a bioenergy and bioproducts industry (No. ORNL/TM-2011/224). Oak Ridge National Laboratory. ↩ ↩2 ↩3 ↩4 ↩5

  2. Langholtz, M. H. (Lead). (2024). 2023 Billion-Ton report: An assessment of U.S. renewable carbon resources (ORNL/SPR-2024/3103). Oak Ridge National Laboratory. https://doi.org/10.23720/BT2023/2316165 ↩

  3. Searchinger, T., Heimlich, R., Houghton, R. A., Dong, F., Elobeid, A., Fabiosa, J., Tokgoz, S., Hayes, D., & Yu, T. H. (2008). Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change. Science (New York, N.Y.), 319(5867), 1238–1240. https://doi.org/10.1126/science.1151861 ↩

  4. Min, K., Nuccio, E., Slessarev, E., Kan, M., McFarlane, K. J., Oerter, E., Jurusik, A., Sanford, G., Thelen, K. D., Pett-Ridge, J., & Berhe, A. A. (2025). Deep-rooted perennials alter microbial respiration and chemical composition of carbon in density fractions along soil depth profiles. Geoderma, 455, 117202. https://doi.org/10.1016/j.geoderma.2025.117202 ↩

  5. Ghavam, S., Vahdati, M., Wilson, I. A. G., & Styring, P. (2021). Sustainable ammonia production processes. Frontiers in Energy Research, 9, 580808. https://doi.org/10.3389/fenrg.2021.580808 ↩

  6. Wright, L. (2007, August). Historical perspective on how and why switchgrass was selected as a "model" high-potential energy crop (ORNL/TM-2007/109). U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy. https://www.energy.gov/eere/bioenergy/articles/switchgrass-high-potential-energy-crop ↩ ↩2 ↩3 ↩4 ↩5

  7. Hess, J. R., Wright, C. T., & Kenney, K. L. (2007). Cellulosic biomass feedstocks and logistics for ethanol production. Biofuels, Bioproducts and Biorefining, 1(2-3), 181–190. https://doi.org/10.1002/bbb.26 ↩ ↩2