First Rotation Biomass Production and Nutrient Cycling within Short-Rotation Coppice Willow Plantations in Saskatchewan, Canada

Abstract

Although numerous studies have quantified different social, economic, energetic, and environmental benefits associated with short-rotation coppice (SRC) willow plantations, comprehensive assessments of nutrient cycling are rare. The objective of this study was to examine the biomass production and attendant biogeochemical cycling of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg) during the initial 4-year rotation of six willow varieties grown at four locations along a 500 km north-south pedoclimatic gradient within Saskatchewan, Canada. Nutrient budgets consisted of quantifying various nutrient inputs (e.g., atmospheric deposition and soil mineral weathering), outputs (e.g., fine and coarse root biomass, leaf biomass, harvested biomass, leaching, and denitrification), and transfers (e.g., soil organic matter mineralization, canopy exchange, leaf litter decomposition, and fine root turnover) associated with the plant available soil nutrient pool. Total above- and below-ground production during the rotation was approximately 40 Mg ha−1, with calculated soil nutrient budget deficits (i.e., nutrient outputs > inputs + transfers) of 17, 39, 112, 271, and 74 kg ha−1 for N, P, K, Ca, and Mg, respectively, averaged across the varieties and sites, but a soil S surplus of 60 kg ha−1. While soil nutrient budget deficits varied among sites, there were no significant differences (P > 0.05) among willow varieties. Despite the relatively low nutrient-demanding nature of willow and negligible leaching or denitrification losses, nutrient export in harvested biomass over multiple rotations will require soil nutrient amendments to maintain SRC willow productivity, particularly N and P, albeit a fraction of the amount required for annual agronomic crops.