Recently Bred Willow (Salix spp.) Biomass Crops Show Stable Yield Trends Over Three Rotations at Two Sites
Yields of willow biomass crops have large impacts on production, economic, energy, and environmental assessments of these systems. Studies that report data for three or more rotations show various yield quantities and patterns, and few of these studies investigate North American cultivars. This study reports yield data from 18 willow cultivars over three rotations at two research sites (Belleville and Tully) in New York State, USA. Mean yields of the top five cultivars after three rotations were 12.5 Mg ha−1 year−1 (Belleville) and 10.8 Mg ha−1 year−1 (Tully). Seven cultivars had statistically higher yields at Belleville than at Tully. Repeated measures modeling indicated that site by cultivar by time interaction was present, with 13 out of 36 site-cultivar combinations showing quadratic yield trends over time, three showing linear trends, and 20 showing no trend. The large proportion of site-cultivar combinations with consistent yields indicates stability in biomass production over time. Spearman rank correlation coefficients analyzing cultivar rank after one and three rotations were 0.91 (Belleville) and 0.83 (Tully), though the highest yielding cultivars varied by site. Planting a suite of five cultivars evaluated for high yield after the first rotation led to 1.6–1.7 % losses in potential yield compared to the highest producing suite evaluated after three rotations at the same site. However, planting a suite of cultivars evaluated for high yield after the first rotation at a different site led to 10.7–13.6 % losses in potential yield with considerable economic consequences.