Miscanthus × giganteus, known as giant miscanthus or elephant grass, is a tall, perennial grass originally from Asia. It is considered a sterile hybrid that has been bred to not produce viable seeds. Instead, rhizomes are planted to establish the crop, which is commonly used for biofuels and feedstocks. The rhizome is a modified underground stem mass that puts out shoots and roots that support new growth each year. This perennial crop takes two to three years to reach maturity, but established stands can exceed 12 feet tall and have a very thick canopy (Pyter et al. 2007) (Figure 1).

Giant miscanthus has shown potential for high dry-matter yields compared to other biomass crops, which could in turn lead to more efficient land use. In one comparison study, switchgrass (Panicum virgatum) yielded 10.3 megagrams per hectare (Mg/ha) of biomass on average, while giant miscanthus yielded 22.4 Mg/ha (Heaton et al. 2004). In addition, giant miscanthus production has been associated with many environmental benefits, including protecting water quality, removing nutrient loads, stabilizing soil, and improving soil health (Bhardwaj et al. 2011; Hussain et al. 2019).

Many of the possible practical and environmental benefits that are associated with production of giant miscanthus may be attractive to stakeholders who are interested in alternative land use options, particularly in areas considered to be marginal for crop productivity.

Even with its value as a biofuel and potential for cellulosic yield, in most farming operations, a perennial crop like giant miscanthus may not provide the flexibility and high yields that annual crops provide. The inability to change crops from year to year may be a concern for some producers. However, marginal lands, areas that generate low to no profit from traditional row crops, appear to be an ideal landscape for giant miscanthus. In such settings, production of giant miscanthus can constitute an environmentally beneficial land use change.

Examples of marginal lands include areas with poor drainage, high water tables, steep slopes, and nonproductive soils, as well as zones within fields where crop yields are regularly low. Unlike acreage enrolled in conservation programs, in which the government provides financial incentives to landowners to take land out of production completely and convert it to forests, riparian buffers, or wetlands, land managed for giant miscanthus can generate a profit. Giant miscanthus can be harvested and the material sold or used on the farm, depending on the type of operation. Giant miscanthus, which can produce high-yielding biomass feedstocks, could be well suited for livestock fodder in North Carolina and across the United States.

Figure 1. Miscanthus x giganteus plot in eastern North Carolina.

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Figure 1. Miscanthus x giganteus plot in eastern North Carolina.

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Production of giant miscanthus has many positive environmental benefits. For example, compared to many row crops, relatively low levels of nutrients and chemicals are required to maintain a healthy stand. If miscanthus is being grown on land that once supported commodity crop production, the decrease in fertilizer and herbicides required would reduce costs and provide benefits to the local surface water and groundwater supply. Nutrient content in agricultural runoff and drainage is a major problem in North Carolina and throughout the United States. Multiple studies have shown the effectiveness of giant miscanthus at mitigating these negative environmental impacts when compared to traditional row cropping systems. Some of this research is summarized here.

A giant miscanthus crop is very nutrient-efficient because the nutrients in the biomass of the crop are transported back into the rhizome below the surface post-senescence, which occurs before harvesting, so those nutrients will be available after overwintering. Studies have indicated that nitrate loss into the groundwater during giant miscanthus production is negligible or, at the very least, significantly reduced compared to traditional cropping systems (Lesur et al. 2014). A study in Illinois found a 13x decrease in the amount of nitrate lost in a year due to leaching into the groundwater with planted giant miscanthus compared to a traditional corn-soybean rotation, with similar results for other nitrogen forms (McIsaac et al. 2010).

A North Carolina State University study found that with the same amount of nitrogen fertilizer input, the biomass yield of giant miscanthus can be as much as four times greater than bermudagrass (Wang et al. 2018). The study further determined that more nitrogen is translocated into the belowground biomass if harvest is pushed to post-senescence compared to a pre- and post-senescence harvest system. Nitrogen removal rates generally decreased as harvest was delayed.

Another possible application of giant miscanthus is in the management of animal waste applied to spray fields. An NC State study compared the nutrient uptake and yields of giant miscanthus and switchgrass to bermudagrass on spray fields located in eastern North Carolina (Wang et al. 2017). Bermudagrass was chosen as the comparison plant due to its known high nutrient uptake and its common use on spray fields. The results of this study indicated that when harvest times are adjusted to limit groundwater leaching, giant miscanthus and switchgrass outperform bermudagrass both in yield and nutrient removal. Spray fields can potentially add large nutrient loads to groundwater and surface water, and the use of biomass crops like giant miscanthus on such land could decrease these loads significantly.

The dense canopy produced by giant miscanthus can decrease the amount of stormwater runoff by intercepting rainfall. The large rhizome masses that expand beneath the soil surface can also help reduce soil erosion (Figure 2). Minimizing soil erosion protects water quality in nearby streams and improves soil quality in a given field. The perennial nature of giant miscanthus means that yearly tilling is not necessary, further limiting soil loss, compared to some other crops, and improving soil stability (Jørgensen 2011).

Another indirect benefit of the efficient use of nutrients by giant miscanthus is a reduction in the amount of greenhouse gases like nitrous oxide (N₂O) and methane entering the atmosphere. Especially when the crop is unfertilized or fertilized at low levels, giant miscanthus produces much lower amounts of these greenhouse gases than traditional crops (Voigt 2015).

In one study on highly saturated soils in Pennsylvania, unfertilized giant miscanthus produced 18.5 Mg/ha of dry aboveground biomass, compared with 11.4 Mg/ha produced by switchgrass fertilized at a rate of 50 kilograms of nitrogen per hectare (kg N/ha) (Rau et al. 2019). In addition, the miscanthus field emitted 244 grams per hectare (g/ha) of N2O compared to 1,113 g/ha emitted by fertilized switchgrass and 820 g/ha emitted by unfertilized switchgrass. This study highlights the ability of the crop to produce at a high level while having favorable environmental inputs and outputs.

Figure 2. The rhizome of a miscanthus plant, with two nodes. The nodes are where new shoots and vertical roots originate (Carmenate et al 2019).

Heaton Lab and Iowa State University, with permission

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Figure 2. The rhizome of a miscanthus plant, with two nodes. The nodes are where new shoots and vertical roots originate (Carmenate et al 2019).

Heaton Lab and Iowa State University, with permission

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The United States Department of Agriculture’s Natural Resources Conservation Service (NRCS) provides many resources for planting and managing Miscanthus x giganteus. One helpful publication is Planting and Managing Giant Miscanthus as a Biomass Energy Crop (Technical Note No. 4). This document provides thorough detail about strategies for planting, harvesting (Figure 3), and in-season management of the crop. It further describes criteria and considerations for site selection and also outlines strategies to limit the dispersal of the crop outside the plot. The publication also provides some background on the biology of the plant.

Figure 3. Harvesting of a miscanthus plot in eastern North Carolina.

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Figure 3. Harvesting of a miscanthus plot in eastern North Carolina.

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Bhardwaj, A. K., T. Zenone, P. Jasrotia, G. P. Robertson, J. Chen, and S. K. Hamilton. 2011. “Water and Energy Footprints of Bioenergy Crop Production on Marginal Lands.” GCB-Bioenergy: Bioproducts for a Sustainable Bioeconomy 3 (3): 208–222. ↲

Carmenate, P., D. Clark, and E. Heaton. 2019. “Let's Plant Some Miscanthus!” Integrated Crop Management Blog, Iowa State University Extension and Outreach. ↲

Heaton, E., T. Voigt, and S. P. Long. 2004. “A Quantitative Review Comparing the Yields of Two Candidate C4 Perennial Biomass Crops in Relation to Nitrogen, Temperature, and Water.” Biomass and Bioenergy 27 (1): 21–30. ↲

Hussain, M. Z., A. K. Bhardwaj, B. Basso, G. P. Robertson, and S. K. Hamilton. 2019. “Nitrate Leaching from Continuous Corn, Perennial Grasses, and Poplar in the US Midwest.” Journal of Environmental Quality 48 (6): 1849–55. ↲

Jørgensen, U. 2011. “Benefits Versus Risks of Growing Biofuel Crops: The Case of Miscanthus.” Current Opinion in Environmental Sustainability 3 (1–2): 24–30. ↲

Lesur, C., M. Bazot, F. Bio-Beri, et al. 2014. “Assessing Nitrate Leaching During the Three-First Years of Miscanthus × Giganteus from On-Farm Measurements and Modeling.” GCB-Bioenergy: Bioproducts for a Sustainable Bioeconomy 6 (4): 439–49. ↲

McIsaac, G.F., M. B. David, and C. A. Mitchell. 2010. “Miscanthus and Switchgrass Production in Central Illinois: Impacts on Hydrology and Inorganic Nitrogen Leaching.” Journal of Environmental Quality 39 (5): 1790–99. ↲

Pyter, R., T. B. Voigt, E. A. Heaton, F. G. Dohleman, and S. P. S. Long. 2007. “Giant Miscanthus: Biomass Crop for Illinois.” In Issues in New Crops and New Uses, edited by J. Janick and A. Whipkey. ASHS Press. ↲

Rau, B. M., P. R. Adler, C. J. Dell, D. Saha, and A. R. Kemanian. 2019. “Herbaceous Perennial Biomass Production on Frequently Saturated Marginal Soils: Influence on N2O Emissions and Shallow Groundwater.” Biomass and Bioenergy 122 (March): 90–98. ↲

Voigt, T. B. 2015. “Are the Environmental Benefits of Miscanthus × Giganteus Suggested by Early Studies of this Crop Supported by the Broader and Longer-Term Contemporary Studies?” GCB-Bioenergy: Bioproducts for a Sustainable Bioeconomy 7 (4): 567–69. ↲

Wang, Z., T. J. Smyth, C. R. Crozier, R. J. Gehl, and A. J. Heitman. 2018. “Yield and Nitrogen Removal of Bioenergy Grasses as Influenced by Nitrogen Rate and Harvest Management in the Coastal Plain Region of North Carolina.” BioEnergy Research 11 (1): 44–53. ↲

Wang, Z., T. J. Smyth, C. R. Crozier, R. J. Gehl, and A. J. Heitman. 2017. “Yield and Nutrient Removal by Bioenergy Grasses on Swine Effluent Spray Fields in the Coastal Plain Region of North Carolina.” BioEnergy Research 10 (4): 979–91. ↲