Current Status and Future Directions for the U.S. Department of Energy's Short-Rotation Woody Crop Research

G.A. Tuskan², M.E. Downing³, and L.L. Wright², Biofuels Feedstock Development Program, ²Environmental Sciences and ³Energy Divisions, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6352

ABSTRACT

The U.S. Department of Energy (DOE) initiated the Biofuels Feedstock Development Program (BFDP) at Oak Ridge National Laboratory (ORNL) in 1978. The program's goal is to provide leadership in the development, demonstration and implementation of environmentally acceptable and commercially viable biomass supply systems. Three model short-rotation woody crop (SRWC) species, i.e. Populus spp., Acer saccharinum and Salix spp., have been selected for further development based on their productivity, adaptability, and suitability as biomass feedstocks. Of these three, Populus is the primary candidate for SRWC in the United States. For Populus the prescribed management system involves the use of intensive site preparation of agricultural quality lands, improved clonal plant materials at ca. 2,470 trees/ha, mechanical and chemical weed control for the first 2 years, and rotation length of 6 to 8 years, followed by replanting. Currently, due to the wider spacings and larger tree sizes, traditional, start-stop, one- piece harvesting techniques are being applied to SRWC; this includes the use of feller-bunchers, skidding to a common landing, and on-site chipping. Under the above silvicultural system, harvesting and transportation expenditures account for 50 to 60 percent of the total production costs. The productivity goals for SRWC are 20 to 30 t/ha/yr, with the current average across all sites and clones at ca. 10 t/ha/yr. Productivity rates on large-scale plantings have been documented at 27 t/ha/yr. To increase the average productivity rates, silvicultural enrichments [e.g., spacing variances, fertilization once per rotation (ca. 78.5 kg/ha N), and irrigation], genetic improvement, and molecular genetics techniques are being applied to all model species. This research is being managed under the concept of regional, integrated "Crop Development Centers." There are presently 3 Populus crop development centers.

Historical Background

The Environmental Sciences Division (ESD) at Oak Ridge National Laboratory (ORNL) has provided technical leadership for DOE's Biofuels Feedstock Development Program (BFDP) since DOE began energy crop research in 1978. The BFDP, a mission-oriented program involving research, analysis, and market assessment activities, provides leadership in the development, demonstration, and implementation of environmentally acceptable and commercially viable biomass supply systems capable of meeting a substantial portion of U.S. energy needs.

During the first 15 years of the program's existence, the primary emphasis was on plant breeding and selection, plant physiology, and biotechnology directed toward the development of fast-growing, pest-resistant woody crops. More than 150 woody plant species have been evaluated in 55 previous or current short-rotation woody crops (SRWC) projects representing all major regions of the United States (Figure 1. Geographic depiction of previous and current locations of subcontracted research associated with the U.S. Department of Energy's Biofuels Feedstock Development Program since 1978). Silvicultural and agronomic studies have been used to identify the best methods for achieving the optimum yields from these new crops. Much of the research has been and continues to be performed by cooperators at universities and U.S. Department of Agriculture research facilities. Directed, widely-distributed, competitive solicitations have been used to initiate most new research projects. Regular external technical reviews and BFDP subcontractor's workshops are used to ensure the quality of ongoing projects and to establish linkages among cooperating institutions.

ORNL uses its unique national perspective and technically experienced staff in its Environmental Sciences and Energy Divisions to provide integrated analysis, including resource assessments, and environmental and economic analyses. ORNL technical staff not only provide technical oversight to subcontracted research and development projects, but also serve as facilitators in the creation of consortia or cooperatives between academic and industrial partners. Table 1 lists some of the accomplishments of the BFDP over the past ten years.

Current Status

The BFDP currently manages nine short rotation woody crops (SRWC) subcontracts and three scale-up projects involving SRWC. SRWC systems development is currently limited to hybrid poplars, although a small amount of genetic screening is ongoing with silver maples and hybrid willow. Hybrid poplar crop development centers are located in the Pacific Northwest centered at the University of Washington/Washington State University and in the midwest with the breeding work centered at Iowa State University. A new center in the southeast is scheduled to initiate work in July 1994. Each crop development center (Figure 3. Schematic representation of interrrelationship among the various dissciplines associated with each crop development center) combines a principle breeding program (to insure the continuous development of new clones) with associated levels of basic and applied research on plant physiology, silviculture, insect and disease evaluations, and molecular genetics The BFDP intends to create fully integrated crop development centers consisting of experts in the fields of crop development, economics, environment assessment, mechanization, and agricultural extension. Production systems developed at each center will be transferred to individual producers and industrial cooperators in the various regions of the U.S.

Currently, the prescribed silvicultural production system for Populus involves diligent site preparation of agricultural quality lands, use of improved clonal plant materials planted at ca. 2,470 trees/ha, mechanical and chemical weed control for the first 2 years, and a rotation length of 6 to 8 years, followed by replanting (Hansen and others 1984, Hansen 1986). Because of the wider spacings and larger tree sizes, traditional, start-stop, one-piece-harvesting techniques are recommended for SRWC. This includes the use of feller-bunchers, skidding to a common landing, and on-site chipping. Under this scenario, harvesting and transportation expenditures account for 50 to 60 percent of the total estimated production costs. The productivity goals for SRWC are 20 to 30 t/ha/yr, with the current average across all sites and clones at ca. 10 t/ha/yr. Productivity rates on large-scale plantings have been documented at 27 t/ha/yr. To increase the average productivity rates, silvicultural enrichments [e.g., spacing variance, fertilization once per rotation (ca. 78.5 kg/ha N), and possibly irrigation]; genetic improvement; and molecular genetics techniques are being tested and applied to all model species.

Future Directions

One of the challenges for the BFDP is to provide the new plant materials, technologies, and information needed to support the initiation of commercial biomass energy ventures, plus expand the basic R&D needed to meet the challenges posed by large-scale commercialization in the future. Major initiatives are being proposed by DOE's Biomass Power Program, the Biofuels Program and by a program to produce chemicals from biomass. The five-year plan of the Biomass Power Program suggests a production of 100,000 MW of biomass energy by 2030, the use of 14.6 million ha of land (Figure 3. Estimates of the total and regional land potentially available to biomass energy crops within the continental United States), and the generation of $3.4 billion in private investments (U.S. DOE 1993). The Biofuels Program goal is to supply 10 percent of the nations liquid transportation fuels from cellulosic biomass by 2020 and half in the long term (U.S. DOE 1994). While the first biofuels will be produced from wastes and residues, as much as 8.1 million ha of land in energy crop production will be needed to meet short term goals and more than 81 million ha will be need for the long term goals. It is reasonable to assume that short rotation woody crops would be the energy crop of choice on at least 30 million ha of that land.

The scale of these goals and the large percentage of the total cost that mechanization contributes to the per ton cost of the feedstock suggests that additional efforts should be made to improve the efficiency of all aspects of mechanization associated with SRWC production. Mechanization of SRWC cuts across all aspects of the production system, including site preparation, plantation establishment, routine maintenance, harvesting, processing, and shipping. If 30 million ha of land is managed for short rotation woody crop production, then 3.8 million ha will be harvested annually, 3.9 million ha will require site preparation, and 7.6 million ha will require mechanical and chemical weed control and maintenance. Harvesting and processing alone requires 6,000 operating units annually, each containing a feller/buncher, two skidders, and a chipper, functioning simultaneously at a value of $560,000 per unit. This appears to represent a large business opportunity for agricultural and forestry equipment manufacturers.

The rate at which demand develops for short-rotation woody crops as an energy feedstock will occur slowly; however, the success of the early trials will determine the rate at which demand will increase. By the year 2000, it is likely that only a few demonstration biomass power facilities will be in place. The Biopower initiative suggests that about 243,000 ha of land may be required by the year 2000 of which less than 1/3 is likely to be woody crops. In addition, the pulp and paper industry may add 40,000 to 81,000 ha of short rotation woody crops during the next 6 years. While the immediate market demand for highly efficient SRWC mechanization is small, the importance of demonstrating that such equipment can contribute to reducing feedstock production cost is extremely important. To be economically competitive with petroleum-based transportation fuels, biomass feedstocks will have to be produced at a cost of $33 to $44 per dry t. This is a tremendous challenge that the U.S. can not meet unless considerably more resources are put into research, development, demonstration, and technology transfer on energy crop supply systems. If the 2015 and 2030 Biopower and Biofuels goals are to be met, an investment in technology development and demonstration will need to be made by both government and private sources within the next 10 years.

Optimizing mechanization, harvesting, and handling may best be achieved through the formation of a cooperative consisting of equipment manufactures, potential equipment users and crop researchers who can describe the qualities of the systems needed. It would be desirable, however, for the harvest and handling cooperatives to be vertically and horizontally integrated within and across each energy crop centers which emphasizes the development of SRWC silvicultural systems. Each reduction in the proportional cost of producing SRWC achieved through the development of improved systems for SRWC mechanization will result in a proportional increase in SRWC profitability.

ACKNOWLEDGEMENTS

Manuscript preparation was sponsored by the Biofuels System Division, U.S. Department of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.

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File posted on March 5, 1996; Date Modified: February 21, 1999