C4 Grasses: The Future of Bioenergy

C4 Grasses: The Future of Bioenergy

In the quest for sustainable energy solutions, non-woody biomass such as perennial C4 or warm-season grasses has gained significant attention. These grasses are not only resilient and highly productive but also efficient in utilizing water and nutrients, making them ideal candidates for pellet production.

Several studies have analyzed perennial C4 grasses for solid biofuel production, highlighting their potential to drive a global bioenergy industry. This article delves into the need for new pellet sources, the characteristics of C4 grass crops, and why they are the best choice for producing pellets sustainably at scale.

Table of Contents

1. Why We Need C4 Grass Fuel Pellets
2. Promising Perennial C4 Grasses for Pellet Production
   • Napier Grass (Pennisetum purpureum)
   • Switchgrass (Panicum virgatum)
   • Miscanthus (Miscanthus x giganteus)
3. Why C4 Grasses are the Best Crops for Pellet Production
4. Conclusion

Why We Need C4 Grass Fuel Pellets

The demand for pellets has significantly increased in recent years, driven by the global shift towards renewable energy to replace fossil fuels. In 2022, global demand for wood pellets reached 46.2 million tonnes, exceeding production output. The EU accounts for slightly more than half of global pellet consumption, while in Asia, demand for pellets for electricity generation increased by nearly 40% year on year.

This increased demand emphasizes the urgent need to ramp up production. The expansion in the use of biofuels could develop from the agricultural sector through the expanded use of crop residues and dedicated energy crops as fuel sources.

In this scenario, C4 grass emerges as the best option because of its high yield and ability to diversify the feedstock for sustainable pellet production at scale.

Among the abundant species of C4 grass, three stand out with attributes that make them excellent feedstock for bioenergy applications: Napier Grass, Switchgrass, and Miscanthus.

Promising Perennial C4 Grasses for Pellet Production

Napier Grass (Pennisetum purpureum)

‍Napier grass is a highly productive crop known for its vigorous tillering, large leaf area, high photosynthetic rate, and tall canopy (Ito and Inaga, 1988; Matsuda et al., 1991). This grass can thrive in a wide range of soil and climatic conditions, from low-fertility acid soils to slightly alkaline soils (Hanna et al., 2016).

Studies show that Napier grass produces a high yield of biomass, approximately 100 barrels of oil equivalent per hectare (boe/ha), and can be harvested every quarter, up to four times a year (Nimmanterdwong et al., 2017; Mohammed et al., 2015).

It grows easily in tropical conditions and can reach heights between 4 to 7.5 meters, with an extensive root system that can penetrate up to 4.5 meters. This makes it highly drought-tolerant and gives it a long lifespan of up to 7 years (Cook et al., 2005; Primavera, Rollon & Samson, 2012).

Napier grass also maintains a high photosynthetic rate and can efficiently utilize radiation over extended periods (Ito & Inaga 1988). It is one of the best alternatives for biomass conversion to solid fuel for industrial purposes due to its high heating value, averaging 16 MJ/kg (Treedet et al., 2020).

Switchgrass (Panicum virgatum)

‍Switchgrass, a native tall grass from the prairies (Samson et al., 2005), has been identified as a promising species for pellet production. As a warm-season C4 grass, it is capable of generating large quantities of biomass, even in resource-limited environments (Escobar et al., 2017). Due to its high adaptability to different soils and climates, switchgrass can potentially be grown in both cold and warm regions, even under semiarid conditions (Escobar et al., 2017).

With a biomass yield potential of 10 to 20 oven-dried tonnes (ODT) per hectare per year (Samson et al., 2005), switchgrass can be harvested once annually, typically in late summer or early fall. The best growing conditions for switchgrass include full sunlight and moderate to high rainfall, which help maximize its growth and biomass production.

Switchgrass can grow to heights of 1.5 to 2.5 meters, supported by a deep and extensive root system that enhances its drought tolerance and soil stabilization properties (Matin et al., 2023). This deep rooting system allows the plant to access water and nutrients from deeper soil layers, contributing to organic matter accumulation in the soil and thus to carbon sequestration (Liebig et al., 2005; Ma, Wood & Bransby, 2000; Giannoulis et al., 2026).

With a lifespan of up to 10 years (Fike et al., 2006), switchgrass is a sustainable and long-term feedstock option for pellet production. Its high photosynthetic rate and efficient nutrient use further contribute to its potential as a reliable and efficient bioenergy source.

Miscanthus (Miscanthus x giganteus)

Researchers have identified Miscanthus as a versatile perennial grass suitable for bioenergy feedstock (Arnoult & Brancourt-Hulmel, 2015). This rhizomatous perennial C4 grass, native to East Asia, was introduced to Europe in the early 20th century (Greef & Deuter, 1993). Currently, it ranks among the main perennial biomass crops grown in Europe (Don et al., 2012). Miscanthus thrives in temperate climates and adapts to various soil types, including marginal soils (Coffin et al., 2015), though it prefers well-drained, fertile soils (Winkler, 2020).

Miscanthus demonstrates remarkable yield potential, producing between 10 to 20 oven-dried tonnes (ODT) per hectare per year (Samson et al., 2005). Farmers typically harvest it once annually, in late winter or early spring, when it turns brown. A ‘brown’ harvest after winter provides lignified Miscanthus biomass with low moisture and nutrient content (Winkler, 2020).

Miscanthus can reach heights of up to 4 meters. Its deep and extensive root system enhances its drought tolerance and allows it to access nutrients from deeper soil layers. This root system can penetrate up to 3 meters (Christensen et al., 2015), contributing to the plant's longevity and resilience, with a lifespan of up to 20 years (Witzel & Finger, 2016).

Miscanthus boasts a high photosynthetic rate, which drives its rapid growth and high yield, making it a reliable and efficient feedstock for bioenergy pellets.

Why C4 Grasses are the Best Crops for Pellet Production

High Yield: One of the most significant advantages of perennial C4 grasses is their high biomass yield. In temperate zones, Switchgrass and Miscanthus can produce biomass yields of 10 to 20 oven-dried tonnes (ODT) per hectare per year. In tropical areas, Napier grass produces 25 to 35 ODT per hectare per year (Samson, et al., 2005). This high yield provides more raw material for bioenergy production, making these crops a more efficient bioenergy source.

Efficient Photosynthesis: C4 grasses use the C4 photosynthetic pathway, which is more efficient than the C3 pathway used by most other plants. This efficiency is due to the ability of C4 plants to minimize photorespiration, a wasteful process that occurs in C3 plants, especially under high light and temperature conditions. As a result, C4 grasses can maintain higher rates of photosynthesis, leading to greater biomass production (Mullet, 2017).

Water and Nutrient Use Efficiency: Perennial C4 grasses exhibit remarkable water  and nutrient use efficiency (Mullet, 2017). They possess deep root systems that allow them to access water and nutrients from deeper soil layers, making them more drought-resistant compared to many other crops. Additionally, their efficient photosynthetic mechanism enables them to utilize nutrients more effectively, reducing the need for fertilizers.

Carbon Sequestration: These grasses also play a vital role in carbon sequestration. Their deep root systems not only help in stabilizing soil but also in storing carbon underground (Bresciano et al., 2018). This characteristic is particularly beneficial in mitigating climate change, as it reduces the amount of carbon dioxide in the atmosphere.

Efficient Use of Marginal Farmlands: Growing warm-season grasses is the most efficient strategy to utilize marginal farmlands that are not suitable for food crops in most temperate and tropical climates. Previous studies of warm-season grasses indicate that C4 grasses have significant impacts on restoring soil organic matter levels on degraded soils (Liebig et al., 2005).

Optimal Energy Balance: Perennial C4 grasses offer an excellent energy balance. They provide a high energy output relative to the energy input required for their cultivation and processing (Samson, et al., 2005).

Versatility in Energy Applications: These C4 grass fuel pellets serve a wide range of energy applications, including residential heating and large-scale electricity generation. They are an excellent choice for both domestic and industrial energy needs.

Conclusion

Perennial C4 grasses, with their high yield, efficient photosynthesis, and superior water and nutrient use, hold significant promise for developing a global bioenergy industry. Their environmental benefits, combined with advancements in biomass quality and combustion technologies, make them the best choice for producing pellets. As the world moves towards sustainable energy solutions, these grasses play a crucial role in meeting global energy needs while protecting the environment.

In summary, the future of bioenergy lies in harnessing the potential of perennial C4 grasses, transforming them into a major global fuel source that is both economically viable and environmentally friendly.

Curious about how Jord's C4 grass fuel pellets can transform the bioenergy industry? Visit our page dedicated to pellets to learn more.

Reference

Arnoult, S., & Brancourt-Hulmel, M. (2014). Areview on miscanthus biomass production and composition for bioenergy use:Genotypic and environmental variability and implications for breeding. BioEnergyResearch, 8(2), 502–526. https://doi.org/10.1007/s12155-014-9524-7

Bresciano, D., del Pino, A., Borges, A., Tejera,M., Speranza, P., Astigarraga, L., & Picasso, V. (2018). Perennial c4grasses increase root biomass and carbon in sown temperate pastures. NewZealand Journal of Agricultural Research, 62(3), 332–342. https://doi.org/10.1080/00288233.2018.1504089

Cook, B., Pengelly, C., Brown, D., Donnelly, L.,Eagles, A., Franco, A. (2005). Tropical forages. CS IRO, DPI&F (Qld), CIATand ILRI, Brisbane, Australia. https://www.feedipedia.org/node/1689

Christensen, B. T., Lærke, P. E., Jørgensen, U.,Kandel, T. P., & Thomsen, I. K. (2016). Storage of miscanthus-derivedcarbon in rhizomes, roots, and soil. Canadian Journal of Soil Science, 96(4),354–360. https://doi.org/10.1139/cjss-2015-0135

Coffin, A. W., Strickland, T. C., Anderson, W. F.,Lamb, M. C., Lowrance, R. R., & Smith, C. M. (2016). Potential forproduction of perennial biofuel feedstocks in conservation buffers on theCoastal Plain of Georgia, USA. BioEnergy Research, 9(2), 587–600. https://doi.org/10.1007/s12155-015-9700-4

Don, A., Osborne, B., Hastings, A., Skiba, U.,Carter, M. S., Drewer, J., Flessa, H., Freibauer, A., Hyvönen, N., Jones, M.B., Lanigan, G. J., Mander, Ü., Monti, A., Djomo, S. N., Valentine, J., Walter,K., Zegada‐Lizarazu, W., & Zenone, T. (2011). Land‐Use Change to bioenergyproduction in Europe: Implications for the Greenhouse Gas Balance and soilcarbon. GCB Bioenergy, 4(4), 372–391. https://doi.org/10.1111/j.1757-1707.2011.01116.x

Escobar, N., Ramírez-Sanz, C., Chueca, P., Moltó,E., & Sanjuán, N. (2017). Multiyear life cycle assessment of switchgrass (Panicum virgatum L.) production in the Mediterranean region of Spain: Acomparative case study. Biomass and Bioenergy, 107, 74–85. https://doi.org/10.1016/j.biombioe.2017.09.008

Fike, J. H., Parrish, D. J., Wolf, D. D., Balasko,J. A., Green, J. T., Rasnake, M., & Reynolds, J. H. (2006). Long-term yieldpotential of switchgrass-for-biofuel systems. Biomass and Bioenergy, 30(3),198–206. https://doi.org/10.1016/j.biombioe.2005.10.006

Greef, J.M., Deuter, M. (1993). Syntaxonomy ofMiscanthus x giganteus Greef et Deu Angewandte Botanik 67(3-4): 87-90

Giannoulis, K. D., Karyotis, T.,Sakellariou-Makrantonaki, M., Bastiaans, L., Struik, P. C., & Danalatos, N.G. (2016). Switchgrass biomass partitioning and growth characteristics underdifferent management practices. NJAS: Wageningen Journal of Life Sciences,78(1), 61–67. https://doi.org/10.1016/j.njas.2016.03.011

ITO, K., & INANAGA, S. (1988). Studies on drymatter production of Napiergrass. iv. direct- and after-effects of temperatureon leaf growth and dry matter production. Japanese Journal of Crop Science,57(4), 699–707. https://doi.org/10.1626/jcs.57.699

Hanna, W. W., Chaparro, C. J., Mathews, B. W.,Burns, J. C., Sollenberger, L. E., & Carpenter, J. R. (2016). Perennial pennisetums.Agronomy Monographs, 503–535. https://doi.org/10.2134/agronmonogr45.c14

Liebig, M. A., Johnson, H. A., Hanson, J. D., &Frank, A. B. (2005). Soil carbon under switchgrass stands and cultivatedcropland. Biomass and Bioenergy, 28(4), 347–354. https://doi.org/10.1016/j.biombioe.2004.11.004

Ma, Z., Wood, C. W., & Bransby, D. I. (2000).Carbon Dynamics subsequent to establishment of switchgrass. Biomass andBioenergy, 18(2), 93–104. https://doi.org/10.1016/s0961-9534(99)00077-x

Matin, B., Leto, J., Antonović, A., Brandić, I.,Jurišić, V., Matin, A., Krička, T., Grubor, M., Kontek, M., & Bilandžija,N. (2023). Energetic properties and biomass productivity of switchgrass(Panicum virgatum L.) under agroecological conditions in northwestern Croatia. Agronomy,13(4), 1161. https://doi.org/10.3390/agronomy13041161

Matsuda Y., Kubota F., Agata W., Ito K. (1991).Analytical study on high productivity in napier grass (Pennisetum purpureumSCHUMACH.) 1. Comparison of the characteristics of dry matter productionbetween napier grass and corn plants. J. Japan. Grassl. Sci. 37 (1),150–156. Available at: https://www.semanticscholar.org/paper/Analytical-Study-on-High-Productivity-in-Napier-%3A-Yoshinobu-%E7%BE%A9%E4%BF%A1/de428b223e3feeb4d987f03c8ab3d8d2b5ffa1ee

Mohammed, I., Abakr, Y., Kazi, F., Yusup, S.,Alshareef, I., & Chin, S. (2015). Comprehensive characterization of Napiergrass as  a feedstock for thermochemical conversion. Energies, 8(5),3403–3417. https://doi.org/10.3390/en8053403

Mullet, J. E. (2017). High-biomass c 4grasses—filling the yield gap. Plant Science, 261, 10–17. https://doi.org/10.1016/j.plantsci.2017.05.003

Nimmanterdwong, P., Chalermsinsuwan, B., Østergård,H., & Piumsomboon, P. (2017). Environmental performance assessment ofnapier grass for bioenergy production. Journal of Cleaner Production, 165,645–655. https://doi.org/10.1016/j.jclepro.2017.07.126

Samson, R., Mani, S., Boddey, R., Sokhansanj, S.,Quesada, D., Urquiaga, S., Reis, V., & Ho Lem, C. (2005). The potential ofC4perennial grasses for developing a global bioheat industry. CriticalReviews in Plant Sciences, 24(5–6), 461–495. https://doi.org/10.1080/07352680500316508

Primavera, J. H., Rollon, R. N., & Samson, M.S. (2011). The pressing challenges of mangrove rehabilitation. Treatise onEstuarine and Coastal Science, 217–244. https://doi.org/10.1016/b978-0-12-374711-2.01010-x

Treedet, W., Suntivarakorn, R., Mufandi, I.,Singbua, P. (2020). Bio-Oil Production from Napier Grass Using a PyrolysisProcess: Comparison of Energy Conversion and Production Cost between Bio-Oiland Other Biofuels. Int. Energy Journal, 20, 155−168.

Winkler, B., Mangold, A., von Cossel, M.,Clifton-Brown, J., Pogrzeba, M., Lewandowski, I., Iqbal, Y., & Kiesel, A.(2020). Implementing miscanthus into farming systems: A review of AgronomicPractices, capital and labour demand. Renewable and Sustainable EnergyReviews, 132, 110053. https://doi.org/10.1016/j.rser.2020.110053

Witzel, C.-P., & Finger, R. (2016). Economicevaluation of Miscanthus Production – A Review. Renewable and SustainableEnergy Reviews, 53, 681–696. https://doi.org/10.1016/j.rser.2015.08.063