Woody Perennial Biomass
Hybrid Willow, Hybrid Poplar, and Alder
Left: Hybrid poplar. Right: Hybrid willow.
Woody perennial biomass crops are an important component of a comprehensive agricultural strategy that provides high quality feedstock for bioindustrial applications. Woody biomass is a prime feedstock for generating steam to produce heat and electricity or in the production of biofuels and other high-value bio-based products. These crops include fast growing short cycle plants (typically 3-5 years) that can be continued over multiple cycles and plants that through association with soil microbes are capable of adding nitrogen to the soil. Moreover, woody biomass crops are adaptable to a wide range of soil and climate conditions allowing them to be planted in areas where annual crops do not grow well. The perennial nature of woody biomass crops also offers significant environmental and ecological benefits. This offers Minnesota farming systems the potential to improve economic vitality in rural communities while achieving broader public goals of clean water, reduced soil erosion and carbon sequestration. In order to take advantage of that potential, research is needed which will allow us to ensure a consistent, productive, and high-quality supply of biomass at a reasonable price across a range of soils in a way that offers needed environmental/ecosystem services.
Woody perennials can and have been used for: 1) provision of feedstock for energy and high-value bioproducts; 2) riparian buffers which protect our surface waters and stabilize stream banks by preventing erosion; 3) windbreaks that protect croplands from erosion and lower heating costs and energy use on farms and homesteads; 4) remediation of contaminated sites or as a filter for solid or liquid wastes; and 5) adding nitrogen to the soil to render it more agriculturally productive.
Left: Hybrid willow in riparian buffer. Center: Windbreak including woody biomass species. Right: Hybrid poplar on phytoremdiation site.
When it is possible to combine bio-fuel production with high value, bio-based products the entire production system becomes more profitable and robust. In addition, woody biomass production reduces climate-changing atmospheric carbon in two ways: 1) renewable biomass fuels substitute for fossil fuels, and 2) unharversted roots and residues contribute to sequestered soil carbon.
These multiple benefits will be most readily obtained from an integrated biomass production system based on perennial crops planted in strategic areas of the landscape close to local and regional processing centers. Research is needed to develop reliable highly productive germplasm to support a comprehensive eco-industrial system that 1) integrates perennial crop production, processing and conversion technologies to create diverse high-value products, and 2) supports the use of low-value residuals for energy production in concert with other renewable energy sources.
Hybrid poplars have been subject to much production research and genetic improvement over the past several decades. However, most of the genetic improvement work has targeted paper/timber production in northern Minnesota. Recently, there has been an effort to expand the genetic improvement program to include southern Minnesota with a focus on the production of biomass to support bioindustrial sectors. U of M agronomists and foresters (NRRI group) are collaborating on several field trials to evaluate new genetic lines of poplar in southern Minnesota.
Hybrid poplar accessions under evaluation
Hybrid willow is just now being established in Minnesota as a raw product for the bioenergy sector. Most of the genetic work for willow in the U.S. is being done at SUNY in Syracuse, NY. Genotype performance is often location specific; thus the U of M is collaborating with SUNY Syracuse to conduct trials across Minnesota to evaluate genetic performance of willow clones from New York. Efforts are currently underway to begin introducing native willow genetics into highly productive hybrid clones to enhance their long term resilience. U of M researchers and Extension are also working to develop production strategies that fit with the soils and climate of Minnesota, reduce establishment costs, and improve harvest efficiency to increase overall profitability.
Multi-species biomass production: hybrid willow and grass
Native and introduced alders are also being evaluated for biomass production. A trial of thirteen alder species in five diverse, non-agricultural sites in Minnesota revealed three of the species to exceed 90% survival at all five sites. On a low-nitrogen site with coarse sandy soils, these three alder species demonstrated biomass production that exceeded that of all other materials in the trial, including commercially available poplar and willow selections. Future alder research will focus on these three species.
Our group is also exploring ways that perennial bioenergy crops can support biological control services to surrounding food crops. For example, we are conducting field research to evaluate perennial woody and herbaceous crops as habitat for beneficial organisms to keep soybean aphid, a devastating soybean pest, in check. Finally, U of M Extension has established a program to educate farmers and other land managers about the benefits of woody biomass crops and how to grow and manage these crops for various end uses.
In order for woody perennial biomass crops to become economically sustainable, we need to be able to provide industry with custom-grown feedstock that meets very specific requirements set by a given end use, such as lower lignin content to improve conversion efficiency, or longer fiber length for composite materials. By providing a custom-grown product, farmers and industrial partners will both benefit. In addition, for less well known woody crops such as alder, efficient cropping systems will need to be developed that take into account nitrogen budgets altered by the species nitrogen fixing capacity. Research needs to be conducted regarding the potential to us alder as a nurse crop with other woody species on low fertility sites. Other uses for woody crops such as extracting natural plant chemicals and increasing carbon storage should also be considered.
Support is needed to conduct research that considers woody crops as: 1) a feedstock for multiple and highly valued products and 2) a potential solution for sensitive environmental and ecological issues. A site-specific approach to biomass crop placement is paramount. We hope to develop knowledge-based decision tools that can be used by farmers and other land managers to design cropping systems that meet market demands for food, fiber, and biomass, address critical environment issues (water quality, soil stabilization, carbon sequestration, nitrogen budgets and wildlife habitat), and optimize profitability (multiple high value profit centers). We believe that industry will provide even greater efficiencies by creating small regional processing centers that take advantage of unique feedstock characteristic inherent in a given region thereby increasing efficiency and diversifying industry presence across the state.
Key to the success of these efforts will be a robust program of woody germplasm development and improvement to guarantee highly productive planting material adapted to diverse Minnesota conditions with the specific characteristics that the industry will require.
The emerging bioeconomy presents new opportunities for farmers to improve economic return and reduce risk through integration of a wide range of bioenergy crops into the farming enterprise. The economic prospects for woody perennial systems are improving with the growth of new bioproducts and bioenergy industries. Several businesses have supplemented their current energy needs with renewable sources of energy such as Rahr Malting in Shakopee, Chippewa Valley Ethanol Company, and the Virginia and Hibbing Public Utilities in Northern Minnesota that burn biomass to meet local energy demand. There is a need to ensure that these new initiatives to develop renewable energy options have sufficient woody feedstocks available at a reasonable cost to be able to meet the State’s Renewable Energy Mandate.
Left: Hybrid poplar plantation. Right: Harvested hybrid willow.
Dean Current, Director, Center for Integrated Natural Resources and Agricultural Management
Andrew David, Associate Professor, Department of Forest Resources
Stan Hokanson, Professor, Department of Horticultural Sciences
Gregg Johnson, Associate Professor, Department of Agronomy and Plant Genetics
Ulrike Tschirner, Professor, Department of Bioproducts and Biosystems Engineering