Evaluation of biomass production potential and heating value of hybrid poplar genotypes in a short-rotation culture in Italy

Abstract

Ensuring increased and sustainable biomass production is critical for European countries. Short-rotation coppice (SRC) plantations on agricultural lands have a great potential to increase biomass supply for biofuels, bioenergy, and bioproducts. In Italy, SRC is based on the use of fast growing species, high planting density, and short harvesting cycles. In this study, the performance of new genotypes to be used in SRC plantations for biomass production was evaluated after three biennial rotations. At the trial plantation in Mira (Northern Italy), six different poplar (Populus) genotypes, belonging to different interspecific hybrids were studied. This plantation provided the opportunity to study the relationships between survival, biomass production and other growth parameters over multiple rotations and for a wide genotypic range. Biomass production differed significantly among rotations starting from 16Mgha−1year−1 in the first, peaking at 20Mgha−1year−1 in the second, and decreasing to 17Mgha−1year−1 in the third rotation. At the end of each rotation, significant differences among genotypes were observed in number of shoots per stool and per ha, stem diameter, tree height, and biomass production. Mean survival rates became significantly different from the other rotations only in the third rotation during which survival rate ranged from 95% for (P.×generosa)×P. nigra ‘Monviso’ to 75% for (P.×generosa)×P. nigra ‘AF6’, but non-significant difference was observed among genotypes. Skewness and inequality of shoot size distributions were genotype-dependent and increased with rotations. Highest biomass production was found for genotypes P.×canadensis ‘83.148.041’, ‘Monviso’ and (P.×generosa)×P. trichocarpa ‘AF8’ with mean annual dry mass production of 21.7, 19.5 and 19.3Mgha−1year−1, respectively. Genotype×rotation interactions were significant on shoot size, diameter and number, but not on survival and biomass production highlighting that genotypes behaved differently over rotations. Moisture and ash content, wood specific gravity, and higher heating value were determined at the end of the third biennial rotation, and significant differences among genotypes were found. This study is critical for investigating the behavior of novel poplar genotypes with potential for commercial biomass production over multiple coppice rotations.