Enhancing the Sustainability of Integrated Biofuel Feedstock Production Systems

Patrick D. Keyser pkeyser@utk.edu   

Stuart A. Weiss sweiss@live.uvi.edu


Fundamental to producing a sustainable bioenergy feedstock is determining organic-Nitrogen (N) sources and levels over a range of soils that will aid in the development of carbon-neutral energy technologies. One likely replacement of synthetic N is incorporation of legumes into biofuel production systems. This model is potentially viable but largely untested and producer acceptance should be high given the traditional use of legumes in forage-agricultural systems. An additional inorganic-N alternative that we will explore is biochar, the by-product of switchgrass and other lignocellulosic biomass pyrolysis. Biochar has been shown to increase carbon sequestration and nutrient retention in soils, thereby decreasing inputs (Mullen et al., 2010). Two of the most promising technologies which farmers could adopt to support sustainable soil fertility for feedstock production are inter-cropped legume (Snapp et al., 1998) and biochar systems (Anex et al., 2007) ; however, in order for this to be put into practice, a protocol for the most economically and nutrient efficient system is needed.

Furthermore, impacts of global climate change will require innovations to existing production systems.  Our goal is to develop an economically and ecologically sustainable cellulosic energy production model to replace inorganic-N on marginal agricultural land, on a range of projected future climatic and soil conditions, which is essential to future viable bio-based economies.

Comparisons of guinea grass and switchgrass systems will be made of biochar versus two leguminous intercrops: sunn hemp (Crotalaria juncea) and pigeon pea (Cajanus cajan)


  • Compare biochar rates versus three leguminous inter-crop spp. against inorganic Nitrogen
  • Establish a recommended harvest date for maximum nutrient translocation to perennating plant parts
  • Analyze the economic feasibility of the two systems based on our native grass economic decision tool.


  • When evaluating these systems for its potential to improve soil fertility, it is necessary to investigate the current soil-nutrient profile; therefore, preliminary soil nutrient levels will be quantitated.
  • Switchgrass variety (cv. Alamo) and guinea grass, a naturalized panicum species, will be established separately in 5 x 10 m plots at the onset of the rainy season (mid-July).
  • Plant tissue analysis will include N-source based on: plant total C, total N, total minerals (P, K, Ca, Mg, Na, S, Fe, Mn, Zn, and Cu), potential ethanol yield, ash content, yield response, plant moisture content, and soil-nutrient flux.

Anticipated Outcomes and Benefits

Our research will determine the investment potential of the proposed systems by monitoring management costs, it will also provide much needed field data on switchgrass response to inorganic-N alternatives and promote the assimilation of the most economically and agriculturally productive feedstock system to respective area farmers.

In addition, results will help establish a harvest recommendation date that will maximize nutrient retention by obtaining a feedstock with low mineral concentrations in biomass post-senescence due to remobilization, thus producing a high quality feedstock for conversion processes.

Lastly, this research will contribute to the understanding of N-mineralization promotion from the two organic-N sources as they relate to sustainable bioenergy production based on soil-biochemical processes and plant-nutrient retention.


USDA-Southeastern Sun Grant


Patrick D. Keyser, PI

Director, Center for Native Grasslands Management

Department of Forestry, Fisheries & Wildlife, University of Tennessee


Fred L. Allen

Professor & Coordinator, Agronomic Crop Variety Testing

Department of Plant Sciences, University of Tennessee


Stuart Weiss

Acting Agronomy Program Leader

University of the Virgin Islands-Agricultural Experiment Station


Amanda J. Ashworth

Research Associate

Center for Native Grasslands Management


Elizabeth Doxon

Research Associate

Center for Native Grasslands Management


University of the Virgin Islands
Agricultural Experiment Station
RR 1 Box 10,000
Kingshill, VI 00850
Telephone: (340) 692-4020 Fax: (340) 692-4035