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The Center for Native Grasslands Management

Projects: Biofuel

Regional Responses of Grassland Birds and Pollinators to Switchgrass Biofuel Feedstock Production

Improving energy independence through use of sustainable biofuel feedstocks, especially switchgrass, is a strategic goal for the United States. Although progress has been made recently in understanding ecosystem services in switchgrass, impacts on wildlife conservation have remained largely unstudied. This shortcoming is especially critical given that many wildlife species associated with switchgrass, especially grassland birds and pollinators, are imperiled. Because of the potential footprint (>50 million ac), and the fact that wildlife responses are likely to vary by region, it is critical to examine wildlife and pollinator responses at multiple scales across the eastern US and to do so while production paradigms are still being developed. To properly understand how switchgrass production impacts population sustainability, it is essential to have spatially-explicit, empirically-derived fecundity, density, and community measures that can be related to habitat metrics at multiple scales. We will collect these data and develop appropriate models to test the relative influence of switchgrass production strategies on targeted biota. Such data are essential to conducting meaningful assessments of population responses to large-scale biomass production and how land use change, habitat loss, habitat alteration, fragmentation, edge effects, and the impacts of frequency and timing of harvest influence these species. Our broad-based approach will allow for region-specific analyses and, in turn, provide robust and sensitive assessment of trade-offs in production strategies versus wildlife/pollinator sustainability for a suite of imperiled species. We will also be uniquely positioned to develop regionally applicable BMP’s that optimize the long-term sustainability of biomass production systems.

Biofuels Integration

The lack of warm-season forages in Mid-South grasslands may limit economic viability of cattle operations, especially during summer months. Perennial native warm-season grasses (NWSG) could provide substantial economic benefits through increased stocking rates, weight gains, and production of higher value grass-finished animals, an expanding market niche.  An additional opportunity for NWSG is bioenergy feedstock production, which can provide cattle producers a significant opportunity for diversification and improved farm income, as well as harvest flexibility. Overall, the use of warm-season grasses established for biofuel feedstocks as a component of integrated forage systems could increase total forage production and provide substantial economic benefits through increased stocking rates and weight gains of grazing cattle, while substantially enhancing wildlife habitat for at-risk bird species.  However, data as well as a protocol for implementing this strategy for the region are lacking.

Grassland birds are experiencing severe and sustained (>40-years) declines, more so than any other group of birds, making this among the most intractable challenges in contemporary conservation. Extensive establishment of switchgrass (>50 million acres) holds some promise of providing habitat that could reverse these declines. However, current evidence suggests dense, monotypic stands may not provide acceptable habitat. Increased plant and structural diversity provided by associated species mixtures may be a powerful solution to this problem. Invertebrate populations may also provide pest (and associated cost) control benefits to other crop production systems on these landscapes.

Northern bobwhite nest burrowed in a clump of native warm season grasses

Two experiments are underway to establish production parameters for the Mid-South for NWSG as forages, biofuels, and wildlife habitat. In the first experiment, we are testing three harvest stages (vegetative + dormant, boot + dormant, and dormant only) in three species mixtures (switchgrass only, switchgrass/big bluestem/indiangrass, and big bluestem/indiangrass) treatments in a randomized block design at four Tennessee locations. In the second experiment, two of the same three species mixtures and two grazing (intensive early and full-season) treatments are being tested in a randomized block design at three Tennessee locations using steers on 3-ac paddocks. Wildlife habitat is being assessed for all treatment levels in both experiments.

Steer grazing big bluestem/indiangrass at the Highland Rim Research and Education Center

Switchgrass Integrated Management Study

The use of native perennial grasses as bioenergy feedstocks promises to become an important land-use practice in the South.  Fundamental to producing a sustainable supply of forage/ biomass is understanding how yield varies as a function of nutrient management over a range of soils.  Research projects underway will provide a more extensive investigation into a subset of questions pertinent to low input integrated forage/ biofuel production systems.  Identifying sustainable nutrient input levels in long-term agricultural production systems is critical to developing a baseline understanding for nutrient requirements, assessing their environmental fate; and implementing management strategies that maximize agricultural productivity and reduce greenhouse gas production.

 Currently, nutrient management guidelines for switchgrass cv. Alamo include 60 lbs ac-1 of nitrogen after the establishment period and no phosphorus (P) or potassium (K) unless soil test levels are low-medium. In this study, bigluestem, switchgrass and eastern gamagrass will be treated with various nutrient levels of N, P and K (ranging from low to high) under a two-cut system, in order to simulate forage-biofuel production. In efforts to prevent soil-nutrient mining in long-term production systems, nutrient removal data are imperative to formulate recommended application rates for producers.

Switchgrass bale in Loudon County. Courtesy Tina Johnson.

Sustainability of Biofuel Feedstock Production Systems

Studies are currently underway at the Center for Native Grasslands Management to enhance the sustainability, productivity and biodiversity for biofuel production systems.  Inorganic nitrogen (N) is a major input, has pricing linked to petroleum markets, and can degrade surface and groundwater. Incorporation of legumes into switchgrass biofuel production systems is a potentially viable but untested alternative to inorganic-N. Producer acceptance should be high given the traditional use of legumes in agricultural systems and the strong interest in multifunctional systems that integrate forage and biofuel production. However, data are lacking.

Switchgrass is grown as a biofuel feedstock for ethanol production on land considered marginally economical for annual row-crop production.  Legume selection is underway to select successful species for soil-N contributions, which will be compared to switchgrass monoculture stands, as well as convention systems receiving inorganic-N. This has implications for reducing the conventional reliance upon fossil fuel based-N to produce cellulosic feedstocks, which have been promoted as an environmental alternative to fossil fuel-based energy sources. ctive of this research is to develop legume management strategies for switchgrass production systems that are economically and ecologically sustainable for biomass and forage production.

Legumes (clover) inter-seeded into switchgrass stubble at Knoxville, Plant Sciences Unit to supply organic nitrogen.


Experiments (three) are underway to evaluate the feasibility of incorporating legumes into biofuel production systems and their subsequent impacts on quantity and quality of feedstock production, forage production, and biodiversity, particularly grassland birds. A fourth experiment will evaluate wildlife use of newly established switchgrass supporting a 5 million gallon/year pilot biorefinery.

Lastly, an additional biofuel legume integration project is underway in collaboration with the University of the Virgin Islands that aims to test inorganic-N alternatives i.e., inter-cropping legumes and biochar (a byproduct of thermochemical biofuel production). This project includes a site representative of future environmental stochasticity for bioenergy feedstock production, as more frequent and extreme droughts, intense rainfall events, and heat waves are already typical of the sub-tropics. Furthermore, impacts of global climatic variation will require innovations to existing production systems. These projects have the potential to reduce input costs, support other bio-based production systems, reduce carbon footprints, while providing habitat to wildlife.

Sunn hemp grown as a cover crop to supply nitrogen at The University of the Virgin Islands, Agricultural Experiment Station.