Abstract
The pressing need to mitigate climate change and find alternative uses for marginal agricultural land have stimulated the establishment of short rotation woody crops (SRWC), like shrub willow, in both North America and Europe. There is limited research on the dynamics of nutrient removal over several rotations in these systems and little is known about the long-term impacts of repeated whole-plant harvesting on soil nutrient concentrations. This study compared nutrient removals among 18 cultivars of willow harvested across three three-year rotations at two sites and changes in the soil nutrient concentrations. Nutrient removal was statistically different among rotations for all studied elements in the following order 2011 ≤ 2017 < 2014. For example, K removal was 7 kg ha<sup>-1</sup> year<sup>-1</sup> in 2011, 14 kg ha<sup>-1</sup> year<sup>-1</sup> in 2017, and 20 kg ha<sup>-1</sup> year<sup>-1</sup> in 2014 at the Belleville site. Additionally, significant effects of site (for N and Ca) and cultivar (all elements) were observed. A significant decrease in soil concentrations among years was observed for total N (1,986 g kg<sup>-1</sup> in 2008 and 1,633 g kg<sup>-1</sup> in 2017) and P (6.9 g kg<sup>-1</sup> in 2008 and 3.4 g kg<sup>-1</sup> in 2017) at one site (Belleville) while a significant increase was observed for K (44 g kg<sup>-1</sup> in 2008 and 57 g kg<sup>-1</sup> in 2017) at the other site (Tully). These results show that shrub willow crops are not negatively impacting extractable nutrient reserves and are capable of recycling nutrients effectively over a 10-year period. Adequate nutrient management guidelines for commercial willow sites should be site specific, consider the selection of cultivars deployed given the high variation in nutrient removal among cultivars, and the soil nutritional status.