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bioweb.sungrant.org » Technical » Biomass Resources » Agricultural Resources » New Crops » Short Rotation Woody Crops » Willow

Willow	Printer Friendly

Development of shrub willow (Salix spp.) as a bioenergy crop began in the mid 1980s. Most of the research focuses on developing willow for production in the Northeastern and Mid-Atlantic U.S. and Southern Quebec and Ontario, but research is also underway for the Midwestern U.S. and Canadian prairie provinces.    The sites for willow production are generally prepared in the summer or fall. Site preparation depends on field history and soil type, but generally involves mowing and an application of herbicide, followed by plowing and disking before winter. A final cultivation is conducted the next spring just before planting.   Fall site preparation increases the potential for soil erosion on some sites, and alternative site preparation methods that include the use of cover crops and strip tillage methods have been developed. Good results have been obtained with the use of a winter rye (Secale cereale L.) cover crop. Willows stands are planted at a density of about 6,200 plants/ac (15,300 plants/hectare) in a double row system of 5 feet (1.5  m) between double rows, 2.5 feet (0.75 m) between the rows, and 2 feet (0.60 m) between plants within rows. Mixtures of 4 to 6 different varieties planted in blocks within a field are recommended. Planting is done with a specialized 4 or 6 row planter that uses 4 to 7 foot (1.5 to 2 m) long unrooted, dormant whips, which it cuts into 8 inch (20 cm) long sections and inserts about 7.5 in. (19 cm) into the ground. Immediately following planting, a pre-emergent herbicide is applied.   If needed, specially designed cultivators can be used to mechanically control weeds until canopy closure the following year, when weed control should no longer be needed. At the end of the first growing season (after leaf fall and before spring buds appear, typically November to early March), the shrubs are cut back (coppiced) using a sickle bar mower. Coppicing promotes the development of multiple sprouts from a single root system. Nitrogen fertilizer is applied during the second season and after each harvest. Rates of application depend on local soil conditions, but are generally about 100 lbs N/ac (88 kg N/ha). Potassium and phosphorus may be applied if soil tests indicate they are needed. The first harvest of willows occurs in the 4th year after planting (three years after coppicing), and every 3rd to 4th year thereafter depending on site conditions and management.   It is anticipated that willow can be harvested 6 to 7 times before replanting is needed. Harvesting is conducted during the dormant season using modified forage harvesters which cut and chip (< 2 inches) the willow stems in a single pass (such as New Holland and Claas harvesters with specially designed willow cutting heads). The planting equipment and willow cutting head were developed in Sweden and England and are not currently manufactured in the U.S., but some U.S. manufacturers are exploring the possibility of producing them.   Between 1998 and 2000, over 500 acres of willow were established in New York and smaller trials have been established in nine states and five Canadian provinces. The New York trials involve 14 landowners with field sizes ranging from 5 to 100 acres (2 to 40 ha), with smaller fields being planted in close proximity to one another so that no harvesting site is less than 25 acres (10 ha). First rotation yields of the best clones ranged from 3.7 to 5.1 dry tons/ac/year (8.4 to 11.6 dry metric tons/ha/year). Second rotation yields of the best clones have increased by 18 to 62%, depending on site. Yields of 12 dry tons/ac/year (72 dry metric tons/ha/year) have been achieved on fertilized, irrigated stands grown for three years. First rotation yields of the most consistent clones averaged 7.4 dry metric tons/ha/year (3.3 dry tons/ac/year) when produced under commercial scale conditions.   A shrub willow breeding and selection program was initiated at the State University of New York, Syracuse in the mid 1990s, which currently has over 700 accessions. Several new and higher yielding varieties have been developed and are being tested. Several are commercially available.

References
Abrahamson, L.P.; Volk, T.A.; Kopp, R.F.; White, E.H.; and Ballard, J.L. (2002). Willow biomass producer’s handbook. College of Environmental Science and Forestry. State University of New York, Syracuse, NY. Volk, T.A.; Abrahamson, L.P.; Nowak, C.A.; Smart, L.B.; Tharakan, P.J.; and White, E.H. (2006). The development of short-rotation willow in the northeastern United States for bioenergy and bioproducts, agroforestry and phytoremediation, Biomass and Bioenergy 30, 715-727. Volk, T.A.; Abrahamson, L.P.; White, E.H.; Neuhauser, E.; Gray, E.; Demeter, C.; Lindsey, C.; Jarnefeld, J.; Aneshansley, D.J.; Pellerin, R.; and Edick, S. (2000). Developing a willow biomass crop enterprise for bioenergy and bioproducts in the United States. In Proceedings of Bioenergy 2000: Moving Technology into the Marketplace. Buffalo, NY: October 15-19. Volk, T.A.; Kiernan, B.D.; Abrahamson, L.P.; and White, E.H. (2002, March). Wood biomass as an alternative farm product. (2001 annual report). College of Environmental Science and Forestry. State University of New York, Syracuse, NY.