Sampling procedure in a willow plantation for chemical elements important for biomass combustion quality

Willow (Salix spp.) is expected to contribute significantly to the woody bioenergy system in the future, so more information on how to sample the quality of the willow biomass is needed. The objectives of this study were to investigate the spatial variation of elements within shoots of a willow clone 'Tordis', and to reveal the relationship between sampling position, shoot diameters, and distribution of elements. Five Tordis willow shoots were cut into 10-50 cm sections from base to top. The ash content and concentration of twelve elements (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Si, and Zn) in each section were determined. The results showed large spatial variation in the distribution of most elements along the length of the willow shoots. Concentrations of elements in 2-year old shoots of the willow clone Tordis were fairly stable within the range of 100-285 cm above ground and resembled the mean concentration of the whole stem (from 86% to 108%, except for Mg, Na, Al and Fe). For practical reasons it is recommended to sample 10 cm sections at the breast height (125-135 cm) to minimise labour costs.