Assessment of Feedstock Quality of Poplars (Populus L.) Using Selected Pellet-Quality Parameters

Wood pellet is an important biomass-based source of cleaner and renewable energy with a growing global demand. Populus spp. (poplars) are fast-growing trees with high productivity potential in the southeastern US. Selected pellet-quality parameters were examined as a proxy for assessing if the feedstock quality of poplar stem wood was affected by stand location (Coastal, Piedmont, Mountains of North Carolina, clone “140”), stand age (five vs. seven years, clone-“140”), clones (“140”, “176”, “230”, “185”, “356”) and stem sections (clone-“356”) by examining sulfur, ash, volatile-matter, fixed-carbon, gross caloric, carbon, hydrogen, and nitrogen contents of moisture-free samples. Location-study samples significantly varied (p≤0.027) in ash (0.6–0.9 wt%), and gross caloric (19.75–19.89 MJ/kg) contents and study clones significantly differed (p≤0.0271) in ash (means: 0.75–0.97 wt%), volatile-matter (means: 80.5–82.7 wt%), fixed-carbon (means: 16.5–18.7 wt%) and hydrogen (means: 4.19–4.78 wt%) contents. The only other significant variations were hydrogen (mean: 4.19–4.67 wt%) content with stand age (p≤0.009) and gross caloric values (19.5–19.9 MJ/kg) among stem sections (p = 0.0003). This study showed that poplars have stem-wood quality suitable for pellet production and most of the studied feedstock samples had ash, nitrogen, sulfur, and caloric (at 10% moisture content) contents that would meet the ENplus pellet-quality standards. Results from this study can be used for facilitating decisions about managing poplar stands for sustainable pellet feedstock production in the southeastern US, including selecting optimum rotation length, pellet-suitable clones, and sites.