Growing Season Harvests of Shrub Willow (Salix spp.) Have Higher Nutrient Removals and Lower Yields Compared to Dormant-Season Harvests

The commercial establishment of shrub willow (Salix spp.) biomass crops with three- or four-year harvest cycles raises concerns about nutrient removal (NR). In addition, leaf-on harvests outside of the typical harvesting window are becoming more prevalent with a changing climate, and require a better understanding of the potential impact of these changes on biomass production and NR. This study examined the time of harvest effects for six harvest dates on the nutrient and biomass removal of four shrub willow cultivars in central New York State. There were significant differences in biomass in the first-rotation harvest; yields ranged between 77 and 85 Mg ha(-1) for the time of harvest treatments during the growing season, and between 93 and 104 Mg ha(-1) after dormancy. Harvest timing had significant effects on N and K removal in the combined wood and foliar biomass. Willow harvested in October removed comparatively higher amounts of N (77.1 kg ha(-1) year(-1)) and P (11.2 kg ha(-1) year(-1)) than other harvests. Potassium removal was greater for plants harvested in June (51.2 kg ha(-1) year(-1)) and August (52.5 kg ha(-1) year(-1)). Harvest timing and cultivar interactions suggest that targeted cultivar selection and deployment could maintain yields and limit excess nutrient losses.