First Rotation Yields From Willow Plantations Across an Environmental Gradient in Saskatchewan.

Saskatchewan has over two million ha of marginal agricultural land that could be used for biomass crops; however, the types of biomass crops that could be grown and provide adequate yields are unknown. Therefore, the objective of this study was to determine the first rotation willow yields along an environmental gradient across Saskatchewan. Six willow clones (Allegany, Canastota, Fish Creek, Sherburne, SX61 and SX64) were obtained from SUNY-ESF and planted in 2007 at four sites: Estevan, Saskatoon, Birch Hills and Prince Albert, and an additional 24 clones at the Saskatoon site. This north-south gradient of approximately 500 km covers a range of soil and climatic conditions from the SE corner of the province to the central part of the province, just south of the boreal forest. Soils and environmental data were collected from each site and biomass yields were estimated from measured diameters (30 cm aboveground) of each stem and an allometric relationship between diameter and biomass. Clones were coppiced after the first year and the first rotation was harvested 3 years later. First rotation biomass yields (oven dry) for all six clones ranged from 15.1 to 21.0 Mg ha^-1 across the four sites being highest in Estevan and lowest in Saskatoon. The highest yielding clones varied at each of the four sites. Allometric relationships compared well with the measured biomass yields.  Estevan had higher rainfall, air and soil temperatures accounting for the better growth; however, the much lower yields at Saskatoon are a result of very heavy clay soils with moisture limitations. The measured yields for the SV1 clone in Saskatoon were similar with our modeled simulations using the 3PG model. The use of willow as a bioenergy source appears promising but an increase in second rotation yields will be needed to sustain a biomass industry.