Leaf Litter Decomposition and Nutrient-Release Characteristics of Several Willow Varieties Within Short-Rotation Coppice Plantations in Saskatchewan, Canada

Quantifying short-rotation coppice (SRC) willow leaf litter dynamics will improve our understanding of carbon (C) sequestration and nutrient cycling potentials within these biomass energy plantations and provide valuable data for model validation. The objective of this study was to quantify the decomposition rate constants (k Bᵢₒₘₐₛₛ) and decomposition limit values (LVBᵢₒₘₐₛₛ), along with associated release rates (k Nᵤₜᵣᵢₑₙₜ) and release limits (LVNᵤₜᵣᵢₑₙₜ) of nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca), and magnesium (Mg) of leaf litter from several native and exotic willow varieties during an initial 4-year rotation at four sites within Saskatchewan, Canada. The k Bᵢₒₘₐₛₛ, LVBᵢₒₘₐₛₛ, k Nᵤₜᵣᵢₑₙₜ, and LVNᵤₜᵣᵢₑₙₜ values varied among the willow varieties, sites, and nutrients, with average values of 1.7 year⁻¹, 79 %, 0.9 year⁻¹, and 83 %, respectively. Tissue N had the smallest k Nᵤₜᵣᵢₑₙₜ and LVNᵤₜᵣᵢₑₙₜ values, whereas tissue K and Mg had the largest k Nᵤₜᵣᵢₑₙₜ and LVNᵤₜᵣᵢₑₙₜ values, respectively. The leaf litter production varied among willow varieties and sites with an average biomass accumulation of 7.4 Mg ha⁻¹ after the 4-year rotation and associated C sequestration rate of 0.2 Mg C ha⁻¹ year⁻¹. The average contribution of nutrients released from leaf litter decomposition during the 4-year rotation to the plant available soil nutrient pool across varieties and sites was 22, 4, 47, 10, 112, and 18 kg ha⁻¹ of N, P, K, S, Ca, and Mg, respectively. Principal component analysis identified numerous key relationships between the measured soil, plant tissue, climate, and microclimate variables and observed willow leaf litter decomposition and nutrient-release characteristics. Our findings support the contention that SRC willow leaf litter is capable of enhancing both soil organic C levels and supplementing soil nutrient availability over time.